SuperFluctuations 2019

Fluctuations and Highly Non Linear Phenomena in Superfluids and Superconductors

University of Padova, Italy

September 2–4, 2019

Jointly organized by: University of Camerino and University of Padova, Italy

Scientific and Organizing Committee

Luca Dell'Anna and Luca Salasnich, University of Padova, Italy

Andrea Perali, University of Camerino, Italy and International MultiSuper Network

Local Organizers

Alberto Cappellaro, Andrea Tononi, and Paola Zenere, University of Padova

SuperFluctuations 2019

Fluctuations and Highly Non Linear Phenomena inSuperfluids and Superconductors

University of Padova, Italy

First day: Archivio Antico del Palazzo "Bo"Second and third day: Aula magna "Rostagni", Dipartimento di Fisica e Astronomia

"Galileo Galilei"

September 2–4, 2019

Jointly organized by: University of Camerino and University of Padova, Italy

Main Topics

Fluctuations and BCS-BEC crossover phenomena in multicomponent and lowdimensional systems.

Quantum Technologies and Novel Phenomena with Bose and Fermi Mixtures.Highly nonlinear phenomena: Josephson and Andreev effects, topological defects,

skyrmions and solitons, vortex states.Novel quantum phenomena in multicomponent / multigap superconductors and

superfluids.Innovative numerical methods: Machine Learning and its applications.

Scientific and Organizing Committee

Luca Dell'Anna and Luca Salasnich, University of Padova, Italy

Andrea Perali, University of Camerino, Italy and International MultiSuper Network

Local Organizers

Alberto Cappellaro, Andrea Tononi, and Paola Zenere, University of Padova, Italy

Financial Support

Financial support from the Dipartimento di Fisica e Astronomia ‘GalileoGalilei’, University of Padova, Italy

and from the School of Pharmacy, University of Camerino, Italy.

Sponsor

Leiden Cryogenics, The Netherlands. https://leiden-cryogenics.com/

MDPI Condensed Matter Award

The open journal Condensed Matter (MDPI) offers an award to the bestoral or poster contribution presented by a young scientist.

Conference Proceedings of SuperFluctuations 2019 will be published by Condensed Matter. Submission within the 31-st December 2019.

https://www.mdpi.com/journal/condensedmatter/special_issues/SuperFluctuations_2019

Web site of the conference: http://www.multisuper.org/superfluctuations-201 9

SUPERFLUCTUATIONS 2019Conference Programme – 2-4 September 2019

Monday – Sept. 2 [Archivio Antico – Main University Building “Palazzo Bo”]

12:30 Registration and welcome reception

14:00 - 14:30 Opening and Introduction

14:30 – 15:00 Antonio Bianconi, RICMASS, Rome, Italy.Topological multigap superconductivity in quantum complex matter showing quantum criticality near Lifshitz transitions.

15:00 – 15:30 Massimo Capone, SISSA, Trieste, Italy.Superconductivity in bad metals: Hund’s driven correlations and boson-mediated pairing.

15:30 – 16:00 Pieralberto Marchetti, University of Padova, Italy.Charge carriers with ½ exclusion statistics in the high Tc cuprates.

16:00 – 16:30 Michele Pini, University of Camerino and University of Florence, Italy.Pair correlations in the normal phase of an attractive Fermi gas.

16:30 – 17:00 COFFEE BREAK

17:00 – 17:30 Simone Montangero, University of Padova, Italy.Quantum technologies on Rydberg atoms.

17:30 – 18:00 Serghei Klimin, TQC, University of Antwerp, Belgium.Collective excitations in one- and two-band superfluid Fermi gases.

18:00 – 18:30 Alessio Recati, University of Trento and INO-CNR BEC Center, Italy.Coherently Coupled Bose gases: from sine-Gordon soliton to Goldstone mode breaking.

19:30 SOCIAL SPRITZ AT CAFFE’ PEDROCCHI

Tuesday – Sept. 3 [Aula Rostagni – Department of Physics and Astronomy “GalileoGalilei”]

09:00 – 09:30 Maria Luisa Chiofalo, University of Pisa, Italy.Universality and Fluctuations in the BCS-BEC Crossover for quantum gases with narrow-to-broad Fano-Feshbach resonances.

09:30 – 10:00 Hiroyuki Tajima, RIKEN Nishina Center, Wako, Saitama, Japan.BCS-BEC crossover and pairing fluctuations in a two-band superluid/superconductor.

10:00 – 10:30 Sara Conti, University of Antwerp, Belgium and University of Camerino, Italy.Multicomponent electron-hole superfluidity in coupled layer systems. 10:30 – 11:00 COFFEE BREAK

11:00 – 11:30 Alessandro De Martino, Department of Mathematics, City, University of London, United Kingdom.Superconductivity from piezoelectric interactions in Weyl semimetals.

11:30 – 12:00 Roberto Raimondi, University of Roma Tre, Italy.Nonlinear sigma-model approach to the coupled spin-charge dynamics in the presence of Rashba spin-orbit coupling.

12:00 – 12:30 Carlos A. R. Sá de Melo, Georgia Institute of Technology, Atlanta, USA.Unconventional color superfluidity without quarks: Ultra-cold fermions in the presenceof color orbit and color-flip fields.

12:30 – 13:00 Giacomo Bighin, IST - Institute for Science and Technology, Klosterneuburg, Austria.Far-from-equilibrium dynamics of molecules in 4He nanodroplets: a quasiparticle perspective.

13:00 – 15:00 LUNCH 15:00 – 15:30 Franco Dalfovo, University of Trento, Italy. Quench Dynamics and sound waves of an Ultracold 2D Bose Gas.

15:30 – 16:00 Alessia Burchianti, CNR-INO, Florence, Italy.Observation of two-species quantum droplets in a Bose-Bose mixture.

16:00 – 16:30 Roberta Citro, University of Salerno, Italy.Meissner to vortex phase transition of spin-orbit coupled bosons in low dimensions.

16:30 – 17:00 COFFEE BREAK

17:00 – 17:30 Boris Malomed, University of Tel Aviv, Israel (Skype talk).Gap solitons in binary condensates.

17:30 – 18:00 Yuriy Yerin, University of Camerino, Italy.Coexistence of giant Cooper pairs and bosonic condensate and anomalous behavior of energy gaps in the BCS-BEC crossover in a two-band superfluid Fermi gas.

18:00 – 18:15 Miki Ota, CNR-INO BEC Center and University of Trento, Italy.

Beyond mean-field theory for binary mixtures of Bose-Einstein condensates at finite

temperature.

18:15 – 19:15 POSTER SESSION and SPONSOR EXHIBITION

Sponsors: Condensed Matter (MDPI), Leiden Cryogenics

20:00 SOCIAL DINNER AT RISTORANTE ZAIRO

Wednesday – Sept. 4 [Aula Rostagni – Department of Physics and Astronomy “G. Galilei”]

09:00 – 09:30 Giuseppe Carleo, Simons Foundation, New York, USA. Neural-Network quantum states.

09:30 – 10:00 Sebastiano Pilati, University of Camerino, Italy.Machine learning ground-state energies and many-body wave functions.

10:00 – 10:30 Vittorio Penna, Politecnico di Torino, Italy.Formation of supermixed states in ultracold boson mixtures loaded in ring lattices.

10:30 – 11:00 COFFEE BREAK

11:00 – 11:30 Patrizia Vignolo, Institut de Physique de Nice, France.Scaling properties of the Tan's contact: from two to infinity.

11:30 – 12:00 Tomasz Sowinski, Institute of Physics, Polish Academy of Sciences, Warsaw, Poland.Inter-component correlations in one-dimensional mass-imbalanced ultra-cold few-fermion mixtures.

12:00 – 12:30 Stefano Lupi, “Sapienza” Università di Roma, Italy.Sound and Light in 3D Graphene.

12:30 – 13:00 Antun Balaz, Institute of Physics, Belgrade, Serbia.Stability of quantum degenerate Fermi gases of tilted polar molecules.

13:00 – 15:00 LUNCH 15:00 – 15:30 Tommaso Macrì, Universidade Federal do Rio Grande do Norte, Natal, Brazil.Superfluids and quasicrystals with nonlocal interactions.

15:30 – 16:00 Bruno Julia-Diaz, University of Barcelona, Spain.Entanglement entropy in low-energy non-relativistic field theory descriptions.

16:00 – 16:30 Alberto Parola, Università dell'Insubria, Italy.Analogue Hawking radiation in BECs.

16:30 – 17:00 Sandro Wimberger, University of Parma, ItalyAccelerating adiabatic state transfer with high-frequency drivings. 17:00 – 17:30 Andrea Trombettoni, SISSA, Italy.

Integrable Floquet Hamiltonian for a Periodically Tilted 1D Gas. 17:30 – 17:45 CLOSING AND ANNOUNCEMENT OF THE RECIPIENT OF THE MDPI CONDENSED MATTER AWARD

POSTER SESSION

Alberto Cappellaro, University of Padova, Italy.

Collisionless dynamics in two-dimensional Bose gases.

Marco Faccioli, University of Padova, Italy. Gaussian quantum fluctuations in the superfluid–Mott-insulator phase transition.

Koichiro Furutani, Keio University, Japan.

Strong-coupling Effects on Transport Properties of an Ultracold Fermi Gas.

Alberto Gallemi, INO-CNR BEC Center, INFN, and Dip. di Fisica, Univ. Trento, Italy.

Collisions between Self-Bound Quantum Droplets.

Benjamin McNaughton, University of Antwerp, Belgium and Univ. of Camerino, Italy.

Tuning and Control of Vortex Configurations in Superconducting Nanostripes.

Francesco Minardi, LENS, Florence, Italy.

Effective expression of the Lee-Huang-Yang energy functional for heteronuclear

mixtures.

Miki Ota, CNR-INO BEC Center and University of Trento, Italy.

Beyond mean-field theory for binary mixtures of Bose-Einstein condensates at finite

temperature.

Santo Roccuzzo, CNR-INO and University of Trento, Italy.

Supersolid symmetry breaking from compressional oscillations in a dipolar quantum

gas.

Donato Romito, CNR-BEC, Trento, Italy and University of Southampton, United

Kingdom.

Linear response study of collisionless drag in quantum fluids.

Bilal Tanatar, Bilkent University, Ankara, Turkey.

Ground-state properties and strong correlation effects in Rydberg-dressed Bose gases.

Antonio Tiene, Universidad Autonoma de Madrid, Spain.

Imbalanced electron-hole-photon systems in two-dimensional structures.

Andrea Tononi, University of Padova, Italy.

Quantum solitons in one-dimensional spin-orbit coupled Bose-Bose mixtures.

Wout Van Alphen, University of Antwerp, Belgium. Solitons in superfluid Fermi gases.

Senne Van Loon, University of Antwerp, Belgium.

The fermionic branch of a superfluid Fermi gas and its coupling to the collective mode.

Stability of quantum degenerate Fermi gases of tilted polar molecules

V. Veljić1, A. Pelster2, and Antun Balaž1

1Scientific Computing Laboratory, Center for the Study of Complex Systems,Institute of Physics Belgrade, University of Belgrade, Serbia

2Physics Department and Research Center OPTIMAS, TU Kaiserslautern, Germany

A recent breakthrough experiment with ultracold polar molecules of KRb [1]demonstrates that an almost a decade-long pursuit to realize a strongly interactingregime of dipolar Fermi gases at quantum degeneracy is close to completion. This opensup prospects of exploring not only the strong dipolar Fermi gases, but also a variety ofmany-body phenomena arising in that regime. Here we derive a mean-field variationalapproach [2] based on the Wigner function for the description of ground-state propertiesof such systems [3, 4]. We show that the stability of dipolar fermions in a generalharmonic trap is universal as it only depends on the trap aspect ratios and the dipoles'orientation. We calculate the species-independent stability diagram and the deformationof the Fermi surface (FS) for polarized molecules, whose electric dipoles are orientedalong a preferential direction. Compared to atomic magnetic species, the stability of amolecular electric system turns out to strongly depend on its geometry and the FSdeformation significantly increases.

References

[1] L. De Marco, et al., Science 363, 853 (2019).[2] V. Veljić, A. Pelster, and A. Balaž, Phys. Rev. Research, accepted (2019).[3] V. Veljić, et al., New J. Phys. 20, 093016 (2018).[4] V. Veljić, A. Balaž, and A. Pelster, Phys. Rev. A 95, 053635 (2017).

Topological multigap superconductivity in quantum complex matter showingquantum criticality near Lifshitz transitions

Antonio Bianconi1,2

1 Rome International Centre for Material Science Superstripes, RICMASS, via deiSabelli 119A, 00185 Rome, Italy

2 National Research Nuclear University MEPhI, 115409 Moscow, RussiaEmail: antonio.bianconi@ricmass.eu

We report novel experimental results showing the universal complex spatial correlateddisorder in high temperature superconductors obtained by scanning micro X-raydiffraction and scanning micro XANES, using advanced focused coherent synchrotronradiation. Quantum complex matter like cuprates (La2CuO4+y, Hg1201, Bi2212),diborides (Al1-xMgB2, Sc1-xMgB2), iron chalcogenides and bismuthates (BaBixPb1-x). Wesee a universal fractal spatial segregation of inhomogeneous charge density wave order,spin density wave order and dopants segregated puddles, where superconducting orderspan filamentary networks at the interfaces between different puddles mapped to ahyperbolic space. All experimental results are interpreted as manifestation of systemsdriven by strain and doping into a regime of quantum criticality near electronictopological transitions or Lifshitz transitions with appearing hot spots of interactingparticles in particular locations of the Fermi surfaces. Using the numerical solution ofjoint solution of Bogoulibov equations and the density equation for multigapsuperconductors the Bianconi-Perali-Valletta (BPV) theory has been able to predictnon-BCS superconductivity driven by the Majorana exchange interaction betweencondensates (not considered in the conventional BCS theory) in a variety of systenspredicting room temperature superconductivity by tuning the chemical potential near aLifshitz transition by strain or pressure. The idea was first developed in 1993-1998 [1-3]applied to quasi 1D incommensurate lattice modulation of Bi2212 cuprate forming asuperlattice of weakly interacting quasi 1D quantum stripes and in organics [4]. Wehave predicted first the “Feshbach resonance” at the Lifshitz transion with a BCScondensate gap resonating with a BEC appearing condensate giving a dip of the criticaltemperature; and the Fano “shape resonance” with the new appearing superconductinggap at the BCS-BEC crossover where the critical temperature shows a “dome” reachingroom temperature at its maximum in cuprates, diborides [5,6] and in iron basedsuperconductors [7]. The theory of quantum criticality [8,9] near the Lifshitz transitionpredicts the arrested phase separation or nematic phase, observed by local probes [10-11] with filamentary interface pathways mapped into a hyperbolic space with mixedBose and Fermi statistics [12-15]. Finally we show that the 260 K superconductivity inLaH10 [16] occurs by using pressure to tune the Fermi level at a Lifshitz transition as inH3S [17,18].

References

1. A. Bianconi, US Patent 6,265,019 (2001) priority date Dec 7, 1993.2. A. Perali, A. Bianconi, A. Lanzara, N.L. Saini, Solid State Comm. 100, 181 (1996)

3. A. Valletta, et al. Z. Phys. B: Condens. Matter, 104, 707 (1997) 4. M.V. Mazziotti, et al. EPL (Europhysics Letters) 118, 37003 (2017)

doi:10.1209/0295-5075/118/37003 5. A. Bianconi, Journal of Superconductivity 18, 625 (2005) doi:10.1007/s10948-005-

0047-5 6. D. Innocenti et al., Phys. Rev. B 82, 184528 (2010) 7. A. Bianconi, Nature Physics 9, 536-537 (2013) doi:10.1038/nphys2738. 8. K. I. Kugel, et al., Phys. Rev. B 78, 165124 (2008) 9. A. Bianconi et al., Supercond. Sci. Technol., 28, 024005 (2015) 10. G. Campi et al., Nature 525, 359 (2015) doi:10.1038/nature1498711. G. Campi, A. Bianconi, J. of Superconductivity and Novel Magnetism 29, 627

(2016). 12. G. Bianconi, Journal of Statistical Mechanics: Theory and Experiment, 2012(07),

P07021. (2012).13. G. Bianconi, C. Rahmede Scientific Reports 7, 41974 (2017) 14. G. Bianconi, Phys. Rev. E 66, 056123 (2002) 15. M.Y. Kagan, A. Bianconi Condensed Matter 4, 51. (2019).16. M. Somayazulu, M. Ahart, A.K. Mishra, et al., Physical Review Letters, 122, 027001. (2019).17. A. Bianconi, T. Jarlborg EPL (Europhysics Letters) 112 , 37001 (2015)18. T. Jarlborg, A. Bianconi, Scientific Reports 6, 24816 (2016)

Far-from-equilibrium dynamics of molecules in 4He nanodroplets:a quasiparticle perspective

G. Bighin1, I.N. Cherepanov1, R. Schmidt2, M. Lemeshko1

1IST Austria (Institute of Science and Technology Austria)2Max Planck Institute of Quantum Optics

Angular momentum plays a central role in a plethora of quantum processes, fromnuclear collisions to decoherence in quantum dots to ultrafast magnetic switching. Herewe consider a single molecule embedded in a superfluid Helium nanodroplet as aprototype of a fully controllable many-body system in which to reveal angularmomentum dynamics: an ultrashort, high-intensity laser pulse can induce molecular axisalignment, creating extreme out-of-equilibrium conditions, while imaging of molecularfragments after Coulomb explosion allows to obtain time-resolved measurements ofmolecular alignment [1].

The rotational dynamics of a molecule in superfluid Helium cannot be simplyunderstood in terms of interference of rotational molecular states due to the stronginteractions with many-body environment: we show that this scenario can be describedin terms of the angulon quasiparticle [2,3] – a quantum rotor dressed by a field of many-body excitations – with a very good agreement with experimental data [4] for severalmolecular species and across a wide range of laser fluences. The dynamical theory wedevelop contributes to advancing the understanding of angular momentum dynamics ina many-body environment, with applications ranging from ultracold molecules tocondensed matter.

References

1. D. Pentlehner et al., Phys. Rev. Lett. 110, 093002 (2013).2. R. Schmidt and M. Lemeshko, Phys. Rev. Lett. 114, 203001 (2015).3. M. Lemeshko, Phys. Rev. Lett. 118, 095301 (2015).4 I.N. Cherepanov, G. Bighin, L. Christiansen, A.V. Jørgensen, R. Schmidt, H.Stapelfeldt, M. Lemeshko, arXiv:1906.12238.

Figure 1. Molecular alignment of an I2 molecule in superfluid Helium as a function of time: theory (red) vs. experiment (black).

Observation of two-species quantum droplets in a Bose-Bose mixture

A. Burchianti1,2, C. D’Errico1,2, M. Prevedelli3, L. Salasnich1,4, F. Ancilotto4,5, M. Modugno6,7, F. Minardi1,2,3, and C. Fort1,2

1Istituto Nazionale di Ottica, CNR-INO, Sesto Fiorentino, Italy2LENS and Dipartimento di Fisica e Astronomia, Università di Firenze, Sesto

Fiorentino, Italy3Dipartimento di Fisica e Astronomia, Università di Bologna, Bologna, Italy

4Dipartimento di Fisica e Astronomia 'Galileo Galilei' and CNISM, Università diPadova, Padova, Italy

5CNR-IOM Democritos, Trieste, Italy6Depto. de Fisíca Teriórica e Hist. de la Ciencia, Universidad del Pais Vasco

UPV/EHU, Bilbao, Spain7IKERBASQUE, Basque Foundation for Science, Bilbao, Spain

We report on the experimental realization of quantum droplets in a heteronuclearbosonic mixture of 41K and 87Rb [1]. By exploiting the tunability of the interspeciesscattering length, we drive the dual-species condensate into the attractive regime.Beyond the mean-field threshold for collapse, in the strongly attractive limit, we findthat, without any external potential, the mixture remains localized for several tens ofmilliseconds, consistently with the formation of long-lived droplet states. We study thedynamics of such states in an optical waveguide under the effect of a species-dependentmagnetic force, confirming their bound nature. Both in free space and in the opticalwaveguide, by increasing the strength of the attractive interaction, we observe thetransition from freely expanding clouds to localized states. The experimental results arewell reproduced by numerical simulations in the whole range of explored interactions.Our findings extend the realm of ultracold gases where quantum droplets can form.Further, the expected long lifetime of 41K-87Rb droplets opens new perspectives for thestudy of these quantum states and their superfluid properties.

References

[1] C. D’Errico, A. Burchianti, M. Prevedelli, L. Salasnich, F. Ancilotto, M. Modugno,F. Minardi and C. Fort, “Observation of Quantum Droplets in a Heteronuclear BosonicMixture”, submitted (2019).

Superconductivity in bad metals: Hund’s driven correlations and boson-mediatedpairing

L. Fanfarillo1, A. Valli2,1, M. Capone1

1International School for Advanced Studies (SISSA) and CNR-IOM Democritos, ViaBonomea 265, 34136 Trieste, Italy

2Institute for Solid State Physics, Vienna University of Technology, 1040 Vienna, Austria

The phenomenology of iron-based superconductors shows that the normal state is a badmetal characterized by orbital-selective correlations associated with the Hund’sexchange coupling [1,2,3], suggesting an important role of the electron-electroninteractions sharing similarities with the cuprates.On the other hand theories based on the exchange of bosons (spin fluctuations are themost popular candidate) describe correctly a variety of phenomena [4] pointing towardsa more standard mechanism.

In other to overcome this dychotomy we study how a multiorbital superconductingpairing driven by a generic weak-copuling boson exchange is affected by the presenceof correlations. As a first step we include the electron-electron correlations induced bythe combined effect of the Hubbard repulsion and the Hund's coupling computed withinDynamical Mean-Field Theory at the single-particle level.

We find that superconductivity survives in a Hund's metal much more than in anordinary correlated metal with the same degree of correlations. We also find anenhancement of the orbital-selective character of the superconducting gaps. Wesuccessfully disentangle the specific role of Hund's driven correlation in the pairingmechanism providing a new building block towards the understanding ofmulticomponent strongly correlated superconductivity [5].

References

[1] L. de’ Medici, G. Giovannetti and M. Capone, Phys. Rev. Lett. [2] P. O. Sprau et al., Science 357, 75 (2017); A. Kostin et al. Nature Materials 17 869 (2018).[3] M. Capone, Nature Materials 17 855 (2018).[4] R. M. Fernandes1 and A. V. Chubukov, Rep. Prog. Phys. 80, 014503 (2017).[5] L. Fanfarillo, A. Valli and M. Capone, in preparation.

Collisionless dynamics in two-dimensional Bose gases

A. Cappellaro1, F. Toigo1 and L. Salasnich1,2

1 Dipartimento di Fisica e Astronomia “Galileo Galilei,” Università di Padova, Padova, Italy

2 CNR, Istituto Nazionale di Ottica (INO), Sesto Fiorentino, Italy.

We study the dynamics of dilute and ultracold bosonic gases in a quasi-two-dimensional(quasi-2D) configuration and in the collisionless regime [1].

We adopt the 2D Landau-Vlasov equation to describe a three-dimensional gas undervery strong harmonic confinement along one direction [2]. We use this effective equa-tion to investigate the speed of sound in quasi-2D bosonic gases, i.e., the sound propa-gation around a Bose-Einstein distribution in collisionless 2D gases. We derive coupledalgebraic equations for the real and imaginary parts of the sound velocity, which arethen solved also taking into account the equation of state of the 2D bosonic system.

Above the Berezinskii-Kosterlitz-Thouless critical temperature we find that there israpid growth of the imaginary component of the sound velocity, which implies a strongLandau damping. Quite remarkably, our theoretical results are in good agreement with

very recent experimental data obtained with a uniform 2D Bose gas of 87

Rb atoms [3,4].

References

[1] A. Cappellaro, F. Toigo an L. Salasnich, Phys. Rev. A 98, 043605 (2018).[2] F. Baldovin, A. Cappellaro, E. Orlandini and L. Salasnich, J. Stat. Mech. 063303 (2016).[3] J. L. Ville, R. Saint-Jalm, É. Le Cerf, M. Aidelsburger, S. Nascimbène, J. Dalibard, and J. Beugnon, Phys. Rev. Lett. 121, 145301 (2018).[4] M. Ota, F. Larcher, F. Dalfovo, L. Pitaevskii, N. Proukakis and S. Stringari, Phys. Rev. Lett. 121, 145302 (2018).

Neural-Network quantum states

Giuseppe Carleo

Simons Foundation, New York, USA

Machine-learning-based approaches, routinely adopted in cutting-edge industrialapplications, are being increasingly adopted to study fundamental problems in science[1].Recently, their effectiveness has been demonstrated also for many-body physics. In thisseminar I will present applications to the quantum realm.First, I will discuss how a systematic machine learning of the many-body wave-functioncan be realized. This goal has been achieved in [2], introducing a variationalrepresentation of quantum states based on artificial neural networks. This representationcan be used to study both ground-state and unitary dynamics, with controlled accuracy.I will discuss several applications in diverse domains, including Quantum StateTomography of highly-entangled states [3], frustrated spin systems [4], and as analternative to the standard path integral [5].

References

[1] Carleo, Cirac, Cranmer et al., arXiv:1903.10563 (2019)

[2] Carleo, and Troyer — Science 355, 602 (2017).

[3] Torlai, Mazzola, Carrasquilla, Troyer, Melko, and Carleo — Nature Physics 14, 447(2018).

[4] Choo, Neupert, and Carleo — arXiv:1903.06713 (2019).

[5] Carleo, Nomura, and Imada — Nature Communications 9, 5322 (2018).

Universality and Fluctuations in the BCS-BEC Crossover for quantum gases withnarrow-to-broad Fano-Feshbach resonances

Pietro Maria Bonetti1, Davide Giambastiani2, Silvia Musolino3, Michele Barsanti4 and

Maria Luisa Chiofalo5

1Max Planck Intitute-Stuttgart2Department of Physics "Enrico Fermi", University of Pisa, Italy

3Department of Applied Physics, Coherence and Quantum Technology, TU Eindhoven,The Netherlands

4Department of Civil and Industrial Engineering and INFN, University of Pisa, Italy

5Department of Physics "Enrico Fermi" and INFN, University of Pisa, Italy

We consider the evergreen and still surprising problem of the evolution of superfluidityin a quantum gas of interacting fermionic particles crossing over from a Bose-EinsteinCondensation (BEC) of composite bosons to a Bardeen-Cooper-Schrieffer (BCS)superfluidity of Cooper pairs. We review how the concepts of BCS-BEC crossover and universality have become aparadigm to understand more complex systems, such as high-Tc superconductors, andhow their systematic probe against different microscopic models under controllableconditions, is now possible in the combined experimental and theoretical quantum-gasesplatforms. We thus probe universality in two microscopic Fermi-gases systems, with (i)effective-range effects [1], and (ii) spin-orbit coupling [2]. Finally, we focus on the fluctuations and derive a self-consistent unifying strong-coupling theory, that embodies the limiting Fano-Feshbach four-body problem, includesamplitude and phase fluctuations beyond mean-field, and accounts for variableresonance widths and interaction strengths [3]. The theory bridges the treatment of theextreme narrow towards broad resonance regimes in the superfluid and normal phases,providing a so-far missing theoretical framework to address experiments that arebecoming available.

References

[1] S. Musolino and M. L. Chiofalo, Correlation Length and Universality in the BCS-BEC Crossover for Energy-Dependent Resonance Superfluidity, The Eur. Phys. J.-SPECIAL TOPICS 226, 2793 (2017).[2] D. Giambastiani, M. Barsanti, and M. L. Chiofalo, Interaction-Range Effects andUniversality in the BCS-BEC Crossover of Spin-Orbit Coupled Fermi Gases, Eur. Phys.Lett. 123, 66001 (2018).[3] P. M. Bonetti and M. L. Chiofalo, Local-Field Theory of the BCS-BEC Crossover, inthe course of submission.

Meissner to vortex phase transition of spin-orbit coupled bosons in low dimensions

R. Citro

Dipartimento di Fisica “E.R. Caianiello,” Università degli Studi di Salerno and UnitàSpin-CNR,

Via Giovanni Paolo II, 132, I-84084 Fisciano (Sa), Italy

We consider a model of interacting spin-orbit coupled bosons in one dimension. Using amapping to a boson-ladder, we show that a Meissner to a Vortex phase (M-V) transitiontakes place as a function of the spin-orbit coupling with a considerable enlargement ofthe Meisser phase for hard-core intraspecies interaction. We show that M-V phasetransition is replaced by a charge density wave phase at finite interspecies interaction. Adisorder point is also found after which a melting of the vortex phase takes place. Therich phase diagram is traced out by the study of the spin current, the momentumdistribution and the correlation functions. The relevance of our study in understandingthe effect of interactions in quantum computation with coupled Josephson junctions orin cold atoms setups with artificial gauge fields is also addressed.

Figure: Phase diagram as a function of the spin-orbit interaction and interspeciesinteraction from Ref. [3].

References

1. M. Di Dio et al. Phys. Rev. B 93, 220507(R) (2015). 2. E. Orignac et al. New Journal of Physics 18, 055017 (2016).3. E. Orignac, R. Citro, M. Di Dio, S. De Palo Phys. Rev. B 96, 014518 (2017).4. R. Citro, S. De Palo, M. Di Dio, E.Orignac, Phys. Rev. B 97, 174523 (2018).

Multicomponent electron-hole superfluidity in coupled layer systems.

Sara Conti1,2, David Neilson1,2, Andrea Perali1, Francois M. Peeters2

1University of Camerino, Camerino, Italy, 2University of Antwerp, Antwerp, Belgium

Email: sara.conti@unicam.it We investigate high-Tc multicomponent electron-hole superfluidity in coupled layersystems, focusing on two very different systems [1,2]. One system consist of twoparallel bilayer graphene sheets (DBG), the other system is a bilayer heterostructure of

transition metal dichalcogenides MoSe2 and WSe2 (TMD).

While superfluidity is multicomponent in both systems, its origins are fundamentallydifferent. In the DBG, superfluidity is multicomponent because of the small tunablebandgap between the conduction and valence bands [3], while in TMD it ismulticomponent because of the splitting of the bands caused by the strong spin-orbitcoupling.

We investigate the superfluid BEC-BCS crossover as a function of the carrier densities,using a comprehensive mean-field multicomponent model. We determine themomentum dependent multicomponent superfluid gaps, the corresponding condensatefractions, and the chemical potential. The pairing interaction is Coulomb long-rangedand self-consistently screened interaction [4].

We demonstrate the superfluidity in both these systems is dominated by two band-dependent condensates, but that the condensates in the two systems are strikinglydifferent. Interestingly, the multicomponent nature of the superfluidity can be switchedon and off, in the case of DBG by tuning the bandgap, and in the case of TMD by tuningthe density and switching the doping. We determine optimal ranges of densities formaximising the Tc of the superfluidity.

References

[1] A. Perali, D. Neilson, and A. R. Hamilton, Phys. Rev. Lett. 110, 146803 (2013).[2] M. M. Fogler, L. V. Butov, and K. S. Novoselov, Nature Comm. 5, 4555 (2014).[3] S. Conti, A. Perali, F. M. Peeters, and D. Neilson, Phys. Rev. Lett. 119, 257002 (2017).[4] S. Conti, A. Perali, F. M. Peeters, and D. Neilson, Phys. Rev. B 99, 144517 (2019).

Quench Dynamics and sound waves of an Ultracold 2D Bose Gas

Franco Dalfovo

CNR-INO BEC Center and Dipartimento di Fisica, Università di Trento

In this talk, I present some recent results obtained with the Stochastic Gross-Pitaevskiiequation applied to a two-dimensional uniform Bose gas at finite temperature. I willfirst discuss the propagation of sound below and above the Berezinskii-Kosterlitz-Thouless (BKT) transition, showing the occurrence of a collisionless sound wave evenabove the critical temperature, in agreement with linear response theory within therandom phase approximation and with experimental observations. Then I will discussthe dynamics of the gas after an instantaneous quench of an initially ultracold thermalatomic gas across the BKT phase transition, showing that the system undergoes phaseordering kinetics and fulfills dynamical scaling hypothesis at late-time dynamics.

References

[1] Collisionless sound in a uniform two-dimensional Bose gas, M. Ota, F. Larcher, F.Dalfovo, L. Pitaevskii, N.P. Proukakis, S. Stringari, arXiv:1804.04032, Phys. Rev. Lett.121, 145302 (2018);

[2] Quench Dynamics of an Ultracold 2D Bose Gas, P. Comaron, F. Larcher, F. Dalfovo,N.P. Proukakis, arXix:1905.0526.

Superconductivity from piezoelectric interactions in Weyl semimetals

R.G. Pereira1,2, F. Buccheri2, A. De Martino 3, R. Egger2

1 International Institute of Physics and Departamento de Física Teórica e Experimental,Universidade Federal do Rio Grande do Norte, BR

2 Institut für Theoretische Physik, Heinrich-Heine-Universität Düsseldorf, DE3 Department of Mathematics, City, University of London, UK

In this talk I will present a low-energy theory of piezoelectric electron-phononinteractions in undoped Weyl semimetals, taking into account also Coulomb interactions[1]. Piezoelectric interactions generate a long-range attractive potential between Weylfermions. Using the renormalization group approach and a mean-field analysis, I willshow that superconducting phases with either conventional s-wave singlet pairing ornodal-line triplet pairing could be realized for sufficiently strong piezoelectric coupling.

References

[1] R.G. Pereira, F. Buccheri, A. De Martino, and R. Egger, Phys. Rev. B 100, 035106(2019).

Gaussian quantum fluctuations in the superfluid–Mott-insulator phase transition

M. Faccioli

Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università di Padova, ViaMarzolo 8, 35131 Padova, Italy

L. Salasnich

Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università di Padova, ViaMarzolo 8, 35131 Padova, Italy

Istituto Nazionale di Ottica (INO) del Consiglio Nazionale delle Ricerche (CNR), ViaNello Carrara 1, 50019 Sesto Fiorentino, Italy

Recent advances in cooling techniques make possible the experimental study ofquantum phase transitions, which are transitions near absolute zero temperatureaccessed by varying a control parameter. A paradigmatic example is the superfluid-Motttransition of interacting bosons on a periodic lattice. From the relativistic Ginzburg-Landau action of this superfluid-Mott transition we derive the elementary excitations ofthe bosonic system, which contain in the superfluid phase a gapped Higgs mode and agapless Goldstone mode. We show that this energy spectrum is in good agreement withthe available experimental data and we use it to extract, with the help of dimensionalregularization, meaningful analytical formulas for the beyond-mean-field equation ofstate in two and three spatial dimensions. We find that, while the mean-field equation ofstate always gives a second-order quantum phase transition, the inclusion of Gaussianquantum fluctuations can induce a first-order quantum phase transition. This predictionis a strong benchmark for future experiments on quantum phase transitions.

Reference

M. Faccioli, L. Salasnich Phys. Rev. A 99, 023614 (2019).

Figures:

Strong-coupling Effects on Transport Properties of an Ultracold Fermi Gas

Koichiro Furutani, Daichi Kagamihara, and Yoji Ohashi

Department of Physics, Keio University,3-14-1, Hiyoshi, Yokohama, 223-8522, Japan

Recently, a two-terminal setup has experimentally been realized in cold Fermi gasphysics. In the conventional electronic mesoscopic system, various phenomenaoriginating from the strong confinement, such as the quantization of conductance, haveextensively discussed. In the recent two-terminal setup experiment in an ultracoldFermi gas, however, a remarkable deviation of the conductance from the ordinaryquantized behavior has been observed in the unitary regime [1]. As possible origin ofthis anomaly, the importance of strong pairing fluctuations in reservoirs hastheoretically been pointed out [2, 3].In our presentation, we present a strong-coupling theory for the quantum conductance

in the normal state of an ultracold Fermi gas, over the entire BCS-BEC crossoverregion. Including strong pairing fluctuations within the framework of a T-matrixapproximation, we show that, while pairing fluctuations suppress the quasi-particleconductance, they remarkably enhance the fluctuation-pair conductance near thesuperfluid phase transition temperature in the unitary regime. In the strong-couplingBEC regime, however, the latter contribution is suppressed. We also show that thecalculated conductance given by the sum of the two contributions agrees well with therecent experiment on a 6Li Fermi gas [1]. Since transport properties have recentlyattracted marked attention in cold Fermi gas physics, our results would be useful for theunderstanding of strong-coupling corrections to quantum transport phenomena.

References

[1] S. Krinner, M. Lebrat, D. Husmann, C. Grenier, J-P Brantut, and T. Esslinger, Proc. Natl. Acad. Sci. 113, 8144 (2016).

[2] S. Uchino and M. Ueda, Phys. Rev. Lett. 118, 105303 (2017).

[3] B. Liu, H. Zhai, and S. Zhang, Phys. Rev. A 95, 013623 (2017).

Collisions between Self-Bound Quantum Droplets

Giovanni Ferioli1,2, Giulia Semeghini1,2, Leonardo Masi1,2, Giovanni Giusti1, GiovanniModugno1,2, Massimo Inguscio1,2, Albert Gallemí3,4, Alessio Recati3,4,

and Marco Fattori1,2

1LENS and Dip. di Fisica e Astronomia,Università di Firenze, Sesto Fiorentino, Italy2CNR Istituto Nazionale Ottica, 50019 Sesto Fiorentino, Italy

3INO-CNR BEC Center and Dip. di Fisica, Università di Trento, 38123 Povo, Italy4Trento Institute for Fundamental Physics and Applications, INFN, 38123, Trento, Italy

We report on the study of binary collisions between quantum droplets formed by anattractive mixture of ultracold atoms [1]. We distinguish two main outcomes of thecollision, i.e., merging and separation, depending on the velocity of the colliding pair.The critical velocity that discriminates between the two cases displays a differentdependence on the atom number for small and large droplets. By comparing ourexperimental results with numerical simulations, we show that the nonmonotonicbehavior of the dependence of the critical velocity on the atom number is due to thecrossover from a compressible to an incompressible regime [2], where the collisionaldynamics is governed by different energy scales, i.e., the droplet binding energy and thesurface tension. These results also provide the first evidence of the liquid-like nature ofquantum droplets in the limit of large atom number, where their behavior closelyresembles that of classical liquid droplets.

FIG 1: Examples of two collision measurements resulting in merging (a) and separation(d) of the droplets. In (b) and (e) we report the corresponding evolution of the distance dbetween the droplets and in (c) and (f) of the total atom number N.

References:

[1] G. Semeghini, et al., Phys. Rev. Lett., 120, 235301 (2018).

[2] G. Ferioli, et al., Phys. Rev. Lett. 122, 090401 (2019).

Magnetic phase transition in a mixture of two interacting superfluid Bose gases atfinite temperature

Stefano Giorgini

Università di Trento, Italy

The miscibility condition for a binary mixture of two interacting Bose-Einsteincondensates is shown to be deeply affected by interaction driven thermal fluctuations.These give rise to a first order phase transition to a demixed phase with full spatialseparation of the two condensates, even if the mixture is miscible at zero temperature.Explicit predictions for the isothermal compressibility, the spin susceptibility, and thephase transition temperature TMare obtained in the framework of Popov theory, whichproperly includes beyond mean-field quantum and thermal fluctuations in both the spinand density channels. For a mixture of two sodium condensates occupying the hyperfinestates |F = 1, mF = 1 and |F = 1, mF = −1 respectively, TM is predicted to occur at⟩ ⟩about 0.7 times the usual BEC critical temperature.

Entanglement entropy in low-energy non-relativistic field theory descriptions

Ivan Morera, Artur Polls, Bruno Julia Diaz

Departament de Física Quàntica i Astrofísica and Institute of Cosmos Sciences, University of Barcelona

We provide the leading contribution to the quantum entanglement in a system describedby a general Lagrangian containing first- and second-order time derivatives. This can beseen as an interpolation between a non-relativistic and a relativistic system where onlyfirst- or second order time derivatives appear, respectively. The presence of both termsinduces an area law for the entanglement entropy growth in the system together with afinite correlation length. Our analytic predictions for the entanglement entropy andcorrelation length are successfully compared to previous numerical results in twosample systems: the Mott insulator to superfluid transition [2] and the ground state offerrimagnetic materials. In the latter we compare to previous results [3] and also withDMRG calculations.

References

[1] I. Morera, A. Polls and B. Juliá-Díaz, arXiv: 1907.01204 (2019).

[2] I. Frérot and T. Roscilde, Phys. Rev. Lett. 116, 190401 (2016).

[3] S. K. Pati, S. Ramasesha, and D. Sen, Phys. Rev. B 55, 8894 (1997).

Collective excitations in one- and two-band superfluid Fermi gases

S. N. Klimin1, H. Kurkjian1 and J. Tempere1, 2

1 Theorie van Kwantumsystemen en Complexe Systemen (TQC),Universiteit Antwerpen, Universiteitsplein 1, Antwerpen, Belgium

2 Lyman Laboratory of Physics, Harvard University,Cambridge, Massachusetts 02138, USA

Recently, the two-band superfluidity has found an experimental realization through theso-called orbital Feshbach resonance (OFR) [1, 2]. This has stimulated intensetheoretical studies of multiband condensed Fermi gases.

The present work is devoted to collective excitations in a one- and two-band Fermi gaswith s-wave pairing in the BCS-BEC crossover at nonzero temperatures, beingparticularly focused on phononic and Leggett modes. The treatment is performed usingthe Gaussian pair fluctuation effective action for a two-band system [3]. The spectra ofcollective excitations are determined in a non-perturbative way through complex polesof the fluctuation propagator, similarly to Ref. [4].

For phononic modes, our calculations reveal two branches [5]. At temperatures close tothe transition temperature, this results in a double peak structure in the responsefunction of the phase of the pair field, well resolved in the BCS regime.

The spectra of Leggett modes are investigated [6] as functions of the couplingparameters, temperature, and the detuning factor, which characterizes the band offsetbetween the two bands. In the BEC regime, when pair-breaking collective excitationsabsent, the Leggett mode passes the pair-breaking continuum edge acquiring a finitedamping, but does not dissolve. At the BCS side, the Leggett modes avoid crossing withthe pair-breaking continuum. We show that the frequently used low-energy expansion ofthe effective action fails for Leggett collective excitations. Strong coupling regimes arefavorable for the experimental observation of Leggett modes.

References

[1] R. Zhang et al., Phys. Rev. Lett. 115, 135301 (2015).[2] G. Pagano et al., Phys. Rev. Lett. 115, 265301 (2015).[3] S. N. Klimin, J. Tempere, G. Lombardi, and J. T. Devreese, Eur. Phys. Journal B 88,

122 (2015).[4] H. Kurkjian, S. N. Klimin, J. Tempere, and Y. Castin, Phys. Rev. Lett. 122, 093403

(2019).[5] S. N. Klimin, J. Tempere, and H. Kurkjian, arXiv:1811.07796 (2019).[6] S. N. Klimin, J. Tempere, and H. Kurkjian (to be published).

Sound and Light in 3D Graphene

F. De Nicola1, C. Marcelli2 and S. Lupi3

1 Istituto Italiano di Tecnologia, Graphene Labs Via Morego, 30, 16163 Genova, Italy;2INFN-LNF, via E. Fermi 40, 00044 Frascati, Italy;

3INFN and Department of Physics, University of Rome La Sapienza, P.le A. Moro 2,00185, Rome, Italy;

Sound generation has been explored for millennia for communications, enjoyment, andcultural reasons. In the contemporary society, sound generation and recording are evenmore important and efficient small-scale loudspeakers or contactless communicationdevices represent a cutting-edge technology for daily life.In this talk, the generation of sound and ultrasound up to 20 MHz through a photo-thermo acoustic mechanism in graphene 3D sponge structure will be discussed [1,2].The unique combination of mechanical, optical, and thermodynamic properties of 3Dsponges allow an unprecedented high efficiency conversion independent of lightwavelength from terahertz to ultraviolet. As a first application of this effect, aphotothermal based graphene sponge loudspeaker is demonstrated, providing a fulldigital operation for frequencies from acoustic to ultrasound. The present results suggesta new pathway for light generation and control of sound and ultrasound signalspotentially usable in a variety of new technological applications from high-fidelityloudspeaker and radiation detectors to medical devices.

References

[1] F. Giorgianni et al, Advanced Functional Materials 28, 1702652 (2018);

[2] F. De Nicola et al, Nature Scientific Report, accepted 2019;

Superfluids and quasicrystals with nonlocal interactions

Tommaso Macrì

Universidade Federal do Rio Grande do Norte, Natal, Brazil

In recent years, propelled by the progress in the field of quantum simulations withultracold atoms, there has been an increasing interest of the condensed mattercommunity in what is generally called quasicrystal lattices, long-range ordered but non-periodic structures. Besides retaining intrinsic relevant questions that range from thestability of tiled structures at zero temperature to their relation to fractal lattices,quasicrystals have also shown to support quantum phases of matter such assuperconductors and Bose-Einstein condensates. Nonetheless, in spite of importantworks that address the emergence of quasicrystalline order in classical systems, a deeperunderstanding of the role of quantum fluctuations in these structures still lacks. Here wepresent our proposal to realize quasi-crystalline states in ultra cold setups with non-localinteractions that can be tuned with polar molecules and Rydberg atoms.

Gap solitons in binary condensates

Zhiwei Fan1, Zhaopin Chen1, Yongyao Li1,2 and Boris A. Malomed 1

1Department of Physical Electronics, School of Electrical Engineering,Faculty of Engineering, Tel Aviv University, Tel Aviv 69978, Israel

2School of Physics and Optoelectronic Engineering, Foshan University, Foshan528000, China

It was recently found that, under the action of the spin-orbit coupling (SOC) andZeeman splitting (ZS), binary BEC with intrinsic cubic nonlinearity supports families ofgap solitons, provided that the kinetic energy is negligible in comparison with the SOCand ZS terms [1,2]. We demonstrate that this setting may be extended for BEC with twocomponents representing different atomic states, resonantly coupled by the microwave(MW) radiation, while the Poisson's equation accounts for the feedback of the wavefunction onto the MW radiation. The MW-mediated interaction induces an effectivenonlinear trapping potential, which strongly affects the concept of the linear spectrum inthis system. Thus, families of skew-symmetric and asymmetric solitons are found (seethe figure), which are chiefly stable. The shape of the solitons features exact or brokenskew symmetry. In addition to fundamental solitons (whose shape may or may notinclude a node), a family of dipole solitons is constructed too, which are even morestable than their fundamental counterparts. The stability area is also identified formoving solitons. Colliding solitons merge into a single one.

References

[1] Y. Li, Y. Liu, Z. Fan, W. Pang, S. Fu, and B. A. Malomed, Two-dimensional dipolar gap solitons in free space with spin-orbit coupling, Phys. Rev. A 95, 063613 (2017).

[2] H. Sakaguchi and B. A. Malomed, Flipping-shuttle oscillations of bright one- and two-dimensional solitons in spin-orbitcoupled Bose-Einstein condensates with Rabi mixing, Phys. Rev. A 96, 043620 (2017).

Charge carriers with ½ exclusion statistics in the high Tc cuprates

P. A. Marchetti

Dipartimento di Fisica e Astronomia, Università di Padova, INFN, Padova, I-35131

The exclusion statistics was introduced by Haldane to generalize the Pauli exclusionprinciple. A particle with exclusion statistics 1/2 can have an occupation number at afixed momentum twice that of a free fermion, so that the “volume" of its Fermi surfaceis half of that of a Fermi gas with the same density.We show that, as it occurs for the t-J model in one dimension, one can attributeconsistently an exclusion statistics with parameter 1/2 to spinless charge carriers of thetwo-dimensional t-J model, which can be considered as a model for the CuO planes ofhigh Tc cuprates. With this statistics at high dopings we recover a "large" Fermi surfaceof holes, which describe Zhang-Rice singlets in the cuprates. The volume enclosed isclose to that of the tight binding approximation, in spite of the spinless character of thecharge carriers. Furthermore, the composite nature of the hole, made of charge and spincarriers only weakly bounded, can provide a natural explanation of many unusualexperimental features of the hole-doped cuprates.

References

[1] P. A. Marchetti, in Topological Phase Transitions and New Developments (World Scientific, Singapore, 2018); arXiv: 1806.00280

[2] P. A. Marchetti, F. Ye, Z. B. Su, L.Yu, Phys. Rev B 100, 035103 (2019)

Tuning and Control of Vortex Configurations in Superconducting Nanostripes

B. McNaughton1,3, A. Perali2, N. Pinto1, M. V. Milosevic3,1, M. Fretto4, N. De Leo4

1School of Science and Technology, Physics Division, University of Camerino, Italy,2School of Pharmacy, Physics Unit, University of Camerino, Italy,

3Department of Physics, University of Antwerp, Belgium, 4Istituto Nazionale di Ricerca Metrologica (INRiM), Strada delle Cacce, 91, Torino,

10135, Italy

There is a plethora of superconducting applications at the nanoscale, includingcomputational electronics such as superconducting logic gates, which use fluxquantization associated with vortices nucleation to transfer information [1]. We studynumerically thin superconducting nanostripes [2] and related vortex configurationsusing the stationary Ginzburg-Landau formalism, with finite difference method [3,4].Simulations are performed over a unit cell, with superconducting-insulator boundariesin y-direction, and periodic boundaries along the length of the stripe. We investigate thetransitions to new vortex rows, focusing on transitions to first and second row. Wepredict the magnetic field at which a new vortex configuration occurs for nanostripes ofdifferent width. Changing the unit cell length affects the value of the magnetic field atwhich a given transition occurs. The generation of the second row depends on thevortex density in the unit cell. At lengths longer than 25ξ(T) (ξ(T) is the temperaturedependent coherence length) we observe a near constant magnetic field at which thezigzag second-row configuration occurs. As the length of the stripe increases, thenumber of vortices increases, but the field as a function of the unit cell length remainsnearly constant. We are working to predict the above discussed physics for the case ofniobium nanostripes [5] realized at the INRiM using Electron Beam Lithography [6] andexperimentally characterised at the Unicam SuperNano Laboratory. Further numericalstudies will be carried out using a time-dependent Ginzburg-Landau formalism, whichallows for a dynamic characterisation of the superconducting nanostripes and relatedgeometries for circuit applications.

References

[1] Likharev, K.K., 1993. Rapid single-flux-quantum logic. In The New Superconducting Electronics (pp. 423-452). Springer, Dordrecht.

[2] Perali, A., Bianconi, A., Lanzara, A. and Saini, N.L., 1996. The gap amplification at a shape resonance in a superlattice of quantum stripes: A mechanism for high Tc. Solid State Communications, 100(3), pp.181-186.

[3] Milošević, M.V. and Geurts, R., 2010. The Ginzburg–Landau theory in application. Physica C: Superconductivity, 470(19), pp.791-795.

[4] Berdiyorov, G.R., Milošević, M.V. and Peeters, F.M., 2006. Vortex configurations and critical parameters in superconducting thin films containing antidot arrays: Nonlinear Ginzburg-Landau theory. Physical Review B, 74(17), p.174512.

[5] Pinto, N., Rezvani, S.J., Perali, A., Flammia, L., Milošević, M.V., Fretto, M., Cassiago, C. and De Leo, N., 2018. Dimensional crossover and incipient quantum size effects in superconducting niobium nanofilms. Scientific Reports, 8(1), p.4710.

[6] Fretto, M., Enrico, E., De Leo, N., Boarino, L., Rocci, R. and Lacquaniti, V., 2013. Nano SNIS junctions fabricated by 3D FIB sculpting for application to digital electronics. IEEE Transactions on Applied Superconductivity, 23(3), pp.1101104-1101104.

Effective expression of the Lee-Huang-Yang energy functional for heteronuclearmixtures

F. Minardi1,2,3, F. Ancilotto4,5, A. Burchianti1,2, C. D’Errico1,2, C. Fort1,2, M. Modugno6,7

1 Istituto Nazionale di Ottica, CNR-INO, 50019 Sesto Fiorentino, Italy2 LENS and Dipartimento di Fisica e Astronomia, Università di Firenze, 50019 Sesto

Fiorentino, Italy3 Dipartimento di Fisica e Astronomia, Università di Bologna, 40127 Bologna, Italy4 Dipartimento di Fisica e Astronomia `Galileo Galilei' and CNISM, Università di

Padova, 35131 Padova, Italy5 CNR-IOM Democritos, 265–34136 Trieste, Italy6 Depto. de Fisìca Teòrica e Hist. de la Ciencia, Universidad del Pais Vasco

UPV/EHU, 48080 Bilbao, Spain7 IKERBASQUE, Basque Foundation for Science, 48013 Bilbao, Spain

We show that the Lee-Huang-Yang (LHY) energy functional for a heteronuclear Bosemixture can be accurately approximated by an expression that has the same functionalform as in the homonuclear case. It is characterized by two exponents, which can betreated as fitting parameters. We demonstrate that the values of these parameters whichpreserve the invariance under permutation of the two atomic species are exactly those ofthe homonuclear case. Deviations from the actual expression of LHY energy functionalare discussed quantitatively.

Quantum technologies on Rydberg atoms

Simone Montangero

University of Padova, Italy

Rydberg atoms represents a versatile platform to test quantum technologies protocols.Hereafter, we present some recent developments on the Rydberg atoms quantumsimulators: in particular we present a novel implementation of lattice gauge theories tostudy string breaking phenomena. Finally, we report the recent experimentaldemonstration of a 20 atoms GHZ state, the largest Schroedinger cat state everprepared, obtained by means of many-body optimal control.

Beyond mean-field theory for binary mixtures of Bose-Einstein condensates atfinite temperature

Miki Ota, Stefano Giorgini, and Sandro Stringari

INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Trento,Italy

We study the thermodynamic properties of a binary mixture of two interacting Bose-Einstein condensates, by developing a beyond mean-field Popov theory. Our approachis based on a perturbative treatment of the grand canonical potential to second order inthe interaction coupling constant, and properly includes beyond mean-field quantumand thermal fluctuations in both the spin and density channels. In particular, we includethe effects of two-component anomalous densities, which are shown to drasticallymodify the magnetic properties of the system (see Fig. 1), eventually leading to theemergence of a new phase-separated state [1].

FIG. 1. Spin susceptibility of binary mixtures of weakly interacting Bose gases. Theblue solid line is the result of Hartree-Fock theory, which predicts a divergent behaviorof the susceptibility at intermediate temperature. The red dashed line is the prediction ofPopov theory, which includes the effects of anomalous densities.

References

[1] M. Ota, S. Giorgini, and S. Stringari, Phys. Rev. Lett. 123, 075301 (2019).

Analogue Hawking radiation in BECs

Manuele Tettamanti2,3, Sergio L. Cacciatori1,3 and Alberto Parola1

1 Dipartimento di Scienza e Alta Tecnologia, Università dell'Insubria, Como, Italy2 Dipartimento di Fisica "G. Occhialini", Università di Milano Bicocca, Milano, Italy

3 Istituto Nazionale di Fisica Nucleare

A sonic transition in a flowing fluid defines a boundary that sound waves cannot cross.The apparent analogy with a black-hole horizon suggests that fluidics experiments canbe designed for the study of wave propagation in curved space-times (Unruh 1981) andfor the realization of one of the most intriguing and not yet detected phenomenapredicted in the gravitational framework: The spontaneous emission of quanta from ablack-hole horizon (Hawking 1974). Recent experiments performed in Bose-Einsteincondensates claimed the first observation of (analogue) Hawking phonons in thelaboratory (Steinhauer 2019). Here we present an exactly solvable model of hard core bosons in one dimensiondisplaying many of the expected features of the Hawking effect in a suitably designedGedankenexperiment (Tettamanti et al. 2019). The zero temperature dynamics of theBose fluid impinging onto an external potential is exactly tracked up to the reach of astationary state, which indeed displays the signatures of the presence of a thermalradiation at an effective "Hawking temperature". The analysis of the model, however,identifies several conditions which must be met in order to preserve the gravitationalanalogy. In most experimental set-ups these conditions are violated and the emerging"Hawking-like radiation" is not thermal, showing that the analogue Hawking effect canindeed be detected in Bose condensates but its realization requires suitably designedexperiments.

References

Hawking S.W. Nature 248, 30 (1974).Steinhauer J. Nature 569, 688 (2019).Tettamanti M., Cacciatori S.L. and Parola A. Phys. Rev. D 99, 045014 (2019).Unruh W.G. Phys. Rev. Lett. 46, 1351 (1981).

Formation of supermixed states in ultracold boson mixtures loaded in ring latticesVittorio Penna, Andrea Richaud

Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino

We study the formation of supermixed solitonlike states in bosonic binary mixturesloaded in ring lattices. We highlight the presenceof a common pathway which, irrespective of the lattice sites, when the interspeciesattraction is varied, leads the system from a mixed and delocalized phase to asupermixed and localized one, passing through an intermediate phase where thesupermixed soliton progressively emerges. The mixing-supermixing phase diagram,exhibiting two characteristic critical lines, is reconstructed by determining the degreesof mixing, the localization and quantum correlation of the two species. These propertiesare quantified by means of suitable indicators commonly used in statisticalthermodynamics and quantum information theory. Our analysis is developed bothwithin a semiclassical approach capable of capturing the essential features of the two-step mixing-demixing transition and with a fully quantum approach.

References

PRA 100, 013609 (2019), Pathway toward the formation of supermixed states inultracold boson mixtures loaded in ring lattices. Some experimental aspects arediscussed in Sci. Rep. 9 (2019) 6908.

Machine learning ground-state energies and many-body wave functions

S. Pilati1, N. Saraceni1, S. Cantori1, E. M. Inack2, G. E. Santoro3, L. Dell’Anna4, and P. Pieri1

1School of Science and Technology, Physics Division, Università di Camerino, 62032 Camerino (MC), Italy

2Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5, Canada3SISSA - International School for Advanced Studies, 34136 Trieste, Italy

4Dipartimento di Fisica e Astronomia “Galileo Galilei,” Università di Padova, 35131 Padova

In the first part of this talk, I will present supervised machine-learning studies of thelow-lying energy levels of disordered quantum systems. The models we addressdescribe cold-atoms in speckle disorder, and also 1D quantum Ising glasses. Our resultsshow that a sufficiently deep feed-forward neural network (NN) can be trained toaccurately predict low-lying energy levels. Considering the long-term prospect of usingcold-atoms quantum simulator to train neural networks to solve computationallyintractable problems, we consider the effect of random noise in the training data, findingthat the NN model is remarkably resilient. Furthermore, we explore the use ofconvolutional NN to build scalable models and to accelerate the training process viatransfer learning.In the second part, I will discuss how generative stochastic NN, specifically, restrictedand unrestricted Boltzmann machines, can be used as variational ansatzes for theground-state many-body wave functions. In particular, we show how to employ them toboost the efficiency of projective quantum Monte Carlo (QMC) simulations, and how toautomatically train them within the projective QMC simulation itself.

References

S. Pilati, E. M. Inack, P. Pieri, arXiv: arXiv:1907.00907 (2019).

S. Pilati, P. Pieri, Scientific Reports 9, 5613 (2019).

E. M. Inack, G. Santoro, L. Dell’Anna, S. Pilati, Physical Review B 98, 235145 (2018).

Pair correlations in the normal phase of an attractive Fermi gas

M. Pini1, P. Pieri1,2 and G. C. Strinati1,2,3

1School of Science and Technology, Physics Division, Università di Camerino, 62032Camerino (MC), Italy

2INFN, Sezione di Perugia, 06123 Perugia (PG), Italy3CNR-INO, Istituto Nazionale di Ottica, Sede di Firenze, 50125 (Fi), Italy

The self-consistent t-matrix approach has been used with success to describe thethermodynamic properties of an attractive Fermi gas throughout the BCS-BECcrossover [1,2,3]. In this talk, I will show its application to the study of pair correlationsin the normal phase of the Fermi gas, where a local order persists even if the long-rangeorder of the superfluid phase is lost. A direct evidence of this local order can beextracted from the opposite-spin correlation function, that is computed as a function ofcoupling and temperature. We also develop a scheme to calculate the number ofpreformed pairs across the crossover within the same diagrammatic structure. Excellentagreement is found with recent experimental data for the same quantity [4].

References

[1] R. Haussmann, Phys. Rev. B 49, 12975 (1994).

[2] R. Haussmann, W. Zwerger, Phys. Rev. A 78, 063602 (2008).

[3] M. Pini, P. Pieri, G. Calvanese Strinati, Physical Review B 99, 094502 (2019).

[4] T. Paintner et al., Physical Review A 99, 053617 (2019).

Nonlinear sigma-model approach to the coupled spin-charge dynamics in thepresence of Rashba spin-orbit coupling

Roberto Raimondi1, Ilya Tokatly2, and Alessandro Veneri1,3

1Dipartimento di Matematica e Fisica, Università Roma Tre, Via della Vasca Navale 84,00146 Roma Italy

2European Theoretical Spectroscopy Facility (ETSF) Dpto. Fisica de Materiales, U. delPais Vasco, Centro Joxe Mari Corta, Avenida de Tolosa, 72, E-20018 Donostia-San

Sebastian, Spain3Department of Physics, University of York, Heslington, York, YO10 5DD, UK

Spin-charge coupled dynamics is the subject of fundamental and applied research for itsrelevance in spintronics. In this context the understanding of the interplay betweendisorder and spin-orbit coupling (SOC) plays a key role. The nonlinear sigma modelfor disordered electron systems is a powerful effective field theory for transportphenomena in diffusive conductors and superconductors. At the tree level the nonlinearsigma model is equivalent to the Eilenberger and Usadel equations for thequasiclassical Keldysh Green function. The latter, which were originally developed forsuperconductors, have been extended in order to include SOC. Here we derive the nonlinear sigma model with Rashba SOC for the disordered two-dimensional electron gas (2DEG). By starting from a functional integral representationof the partition function for disordered fermions in the presence of Rashba SOC, weintroduce the Q matrix (in Keldysh and spin space) field to decouple the effectivefermion-fermion interaction introduced by the disorder average. After integrating outthe fermion degrees of freedom, we get the effective action for the Q field. The saddle-point approximation reproduces the self-consistent Born approximation, in the presenceof Rashba SOC. By restricting to the manifold QQ=1, we derive the nonlinear sigmamodel for diffusive spin and charge density modes. The Rashba SOC appears as a SU(2)gauge field coupled to the Q field. Nonuniform and time-dependent saddle-pointsolutions for the Q field obey the Usadel equation in the presence of Rashba SOC andrecover the drift-diffusion equation previously derived in the context of the Eilenbergerequation.

Coherently Coupled Bose gases: from sine-Gordon soliton to Goldstone modebreaking

Alessio Recati

University of Trento and INO-CNR BEC Center, Italy.

The physics of coherently coupled Bose gases – a Bose mixtures with an inter-conversion term – is very different with respect to the case of the more standard Bose-Bose mixtures: the ground states, the excitations and the topological defects are stronglyaffected by the explicit breaking of the U(1) symmetry related to the relative particlenumber conservation. In particular, after reviewing the basic phenomenology of thesystem, I will discuss: (i) the generation and the fate of the relative phase sine-Gordondomain wall and its decay into half-quantum vortices [1,2,3] and (ii) the breaking of theGoldstone mode of the only left U(1) symmetry at the ferromagnetic critical point [4].

References

[1] D. T. Son and M. A. Stephanov, Phys. Rev. A 65, 063621(2002).

[2] M. Eto and M. Nitta, Phys. Rev. A 97, 023613 (2018).

[3] M. Tylutki, L. P. Pitaevskii, AR, S. Stringari, Phys. Rev. A 93, 043623 (2016); A. Gallemí, L. P. Pitaevskii, S. Stringari, AR, arXiv:1906.06237.

[4] AR and F. Piazza, Phys. Rev B 99, 064505 (2019) .

Supersolid symmetry breaking from compressional oscillations in a dipolar

quantum gas

L. Tanzi1,3, S. M. Roccuzzo2, E. Lucioni1,3, F. Fama`1, A. Fioretti1, C. Gabbanini1, G. Modugno1,3, A. Recati2, S. Stringari2

1CNR-INO, Sede Secondaria di Pisa, 56124 Pisa, Italy 2CNR-INO BEC Center and Dipartimento di Fisica, Università di Trento, 28123 Povo,

Italy 3LENS and Dipartimento di Fisica e Astronomia, Università di Firenze, 50019 Sesto

Fiorentino, Italy

The existence of a paradoxical supersolid phase of matter, possessing the apparentlyincompatible properties of crystalline order and superfluidity, was predicted 50 yearsago. Solid helium was the natural candidate, but there supersolidity has not beenobserved yet, despite numerous attempts. Ultracold quantum gases have recently shownthe appearance of the periodic order typical of a crystal, due to various types ofcontrollable interactions. A crucial feature of a D-dimensional supersolid is theoccurrence of up to D+1 gapless excitations reflecting the Goldstone modes associatedwith the spontaneous breaking of two continuous symmetries: the breaking of phaseinvariance, corresponding to the locking of the phase of the atomic wave functions atthe origin of superfluid phenomena, and the breaking of translational invariance due tothe lattice structure of the system. The occurrence of such modes has been the object ofintense theoretical investigations, but their experimental observation is still missing.Here we demonstrate the supersolid symmetry breaking through the appearance of twodistinct compressional oscillation modes in a harmonically trapped dipolar Bose-Einstein condensate, reflecting the gapless Goldstone excitations of the homogeneoussystem. We observe that the two modes have different natures, with the higherfrequency mode associated with an oscillation of the periodicity of the emergent latticeand the lower one characterizing the superfluid oscillations. Our work paves the way toexplore the two quantum phase transitions between the superfluid, supersolid and solid-like configurations that can be accessed by tuning a single interaction parameter.

References

[1] Andreev, A. F. & Lifshitz, I. M. Quantum theory of defects in crystals. Sov. Phys.JETP 29, 1107–1113 (1969).

[2] Leggett, A.J. Can a solid be “superfluid”? Phys. Rev. Lett. 25, 1543-1546 (1970) [3] Tanzi, L., Lucioni, E., Famà, F., Catani, J., Fioretti, A., Gabbanini, C., Bisset, R. N.,Santos, L. & Modugno, G. Observation of a dipolar quantum gas with metastablesupersolid properties. Phys. Rev. Lett. 122, 130405 (2019).

[4] Böttcher, F., Schmidt, J.-N., Wenzel, M., Hertkorn, J., Guo, M., Langen, T., & Pfau,T. Transient supersolid properties in an array of dipolar quantum droplets. Phys. Rev. X9, 011051 (2019)

[5] Chomaz, L., Petter, D., Ilzhöfer, P., Natale, G., Trautmann, A., Politi, C., Durastante,G., van Bijnen, R. M. W., Patscheider, A., Sohmen, M., Mark, M. J., & Ferlaino, F.Long-lived and transient supersolid behaviors in dipolar quantum gases. Phys. Rev. X 9,021012 (2019).

[6] L. Tanzi, S.M.Roccuzzo, E. Lucioni, F.Fama`, A.Fioretti, C.Gabbanini, G.Modugno,A.Recati, S.Stringari. Supersolid symmetry breaking from compressional oscillations ina dipolar quantum gas arXiv:1906.02791.

Linear response study of collisionless drag in quantum fluids

D. Romito1, A. Recati2, M. Rizzi3, D. Contessi4

1University of Southampton, United Kingdom and INO-CNR BEC, Trento, Italy2University of Trento and INO-CNR BEC, Trento, Italy

3University of Mainz, Germany 4University of Trento, Italy

The Andreev-Bashkin drag is an effect predicted in the 70s which states that twosuperfluids will drag each other without dissipation whenever we set in motion either ofthe two. This drag is more generally pertinent to mixtures of quantum fluids and,distinctly from other “classical” drag mechanisms, is present even at zero temperatureas it is brought about by quantum fluctuations. Such effect is thought to play a role inthe hydrodynamics of neutron stars but has never been observed directly. Experimentswith cold atoms, thanks to their great level of control and tunability they allow, couldopen the way to its first observation, although calculations predict the drag to be verysmall in the typical cold-atoms setting³.We introduce a microscopic description of the drag in terms of current-current responsefunctions which allows to predict the magnitude of the drag in different settings in asystematic way. Moreover the formalism of linear response theory allows to predict thefrequency shifts of elementary and collective excitations of a trapped mixture by meansof sum rules. We calculate the frequency of elementary excitations, spin dipoleexcitations and scissor modes in a weakly interacting Bose gas and show how the shiftsinduced by the collisionless drag are typically smaller than other beyond mean fieldcorrections.We also show how the approximate analytical calculations agree with ab-initionumerical calculations made for a one dimensional lattice. The study of a onedimensional lattice by means of numerical methods allows the study of regimes wherethe effect is more sizeable.

References [1] A. F. Andreev and E. P. Bashkin, “Three-velocity hydrodynamics of superfluidsolutions,” Sov. Phys.-JETP 42, 164–167 (1975).

[2] J. Nespolo, G. E. Astrakharchik, and A. Recati, “Andreev–bashkin effect insuperfluid cold gases mixtures,” New Journal of Physics 19, 125005 (2017).

[3] D. V. Fil and S. I. Shevchenko Phys. Rev. A 72, 013616 (2005).

Unconventional color superfluidity without quarks:Ultra-cold fermions in the presence of color-orbit and color-flip fields

Carlos A. R. Sá de Melo

Georgia Institute of TechnologyAtlanta, GA 30332 - USA

We describe how color superfluidity is modified in the presence of color-flip and color-orbit fields in the context of ultracold atoms and discuss connections between thisproblem and that of color superconductivity in quantum chromodynamics. We study thecase of s-wave contact interactions between different colors and we identify severalsuperfluid phases, with five being nodal and one being fully gapped. When our systemis described in a mixed-color basis, the superfluid order parameter tensor ischaracterized by six independent components with explicit momentum dependenceinduced by color-orbit coupling. The nodal superfluid phases are topological in natureand the low-temperature phase diagram of color-flip field versus interaction parameterexhibits a pentacritical point, where all five nodal color superfluid phases converge.These results are in sharp contrast to the case of zero color-flip and color-orbit fields,where the system has perfect U(3) symmetry and possesses a superfluid phase that ischaracterized by fully gapped quasiparticle excitations with a single complex orderparameter with no momentum dependence and by inert unpaired fermions representinga nonsuperfluid component. In the latter case, just a crossover between a Bardeen-Cooper-Schrieffer and a Bose-Einstein-condensation superfluid occurs. Furthermore, weanalyze the order parameter tensor in a total pseudospin basis, investigate its momentumdependence in the singlet, triplet, and quintuplet sectors, and compare the results withthe simpler case of spin-1/2 fermions in the presence of spin-flip and spin-orbit fields,where only singlet and triplet channels arise. Finally, we analyze in detail spectroscopicproperties of color superfluids in the presence of color-flip and color-orbit fields, suchas the quasiparticle excitation spectrum, momentum distribution, and density of states tohelp characterize all the encountered topological quantum phases, which can be realizedin fermionic isotopes of lithium, potassium, and ytterbium atoms with three internalstates trapped.

References

[1] D. M. Kurkcuoglu and C. A. R. Sá de Melo, “Color superfluidity of neutral ultracoldfermions in the presence of color-flip and color-orbit fields”, Phys. Rev. A. 97, 023632(2018)[2] D. M. Kurkcuoglu and C. A. R. Sá de Melo, “Creating spin-one fermions in the presence of artificial spin–orbit fields: emergent spinor physics and spectroscopic properties”, J. Low Temp. Phys. 191, 174 (2018). [3] D. M. Kurkcuoglu and C. A. R. Sá de Melo, “Quantum phases of interacting three-component fermions under the influence of spin-orbit coupling and Zeeman fields”,arXiv:1612.02365v1 (2016).

BCS-BEC crossover and pairing fluctuations in a two-bandsuperluid/superconductor

Hiroyuki Tajima1, Yuriy Yerin2, Andrea Perali3, and Pierbiagio Pieri2,4

1 Quantum Hadron Physics Laboratory, RIKEN Nishina Center, Wako, Saitama, 351-0198, Japan

2 School of Science and Technology, Physics Division, Università di Camerino, 62032Camerino (MC), Italy

3 School of Pharmacy, Physics Unit, Università di Camerino, 62032 Camerino (MC),Italy

4 INFN, Sezione di Perugia, 06123 Perugia (PG) Italy

We discuss the BCS-BEC crossover andpairing fluctuation effects in a two-bandFermi system where the shallow and deepbands are coupled [1]. Such a system isrelevant for FeSe superconductors which areexpected to be in the BCS-BEC crossoverregime [2]. By tuning the intraband coupling in theshallow band, we show that the critical temperatureof this system is largely enhanced by the two-bandnature (see Fig.1), compared to the single-band case.For different values of the interband couplingwe observe a progressive transfer of particlesfrom thedeep band to the shallow one, whilefor the case of decoupled bands a full transfer ofparticles between bands is realized in the BEC limit.Furthermore, we calculate the single-particle density ofstates in both bands. We show the shirinking of thepseudogap region in the crossover regime with weakinterband coupling and band-dependent pseudogap effects induced by strong interbandpairing fluctuations.

References

[1] H. Tajima, Y. Yerin, A. Perali, and P. Pieri, Phys. Rev. B 99, 180503(R) (2019).

[2] T. Hanaguri, S. Kasahara, J. Böker, I. Eremin, T. Shibauchi, and Y. Matsuda, Phys. Rev. Lett. 122, 077001 (2019).

Fig. 1 Critical temperature Tc as functions of the intraband coupling in the hot band. The red (blue) points represent particles in the hot (cold) band.

Ground-state properties and strong correlation effects in Rydberg-dressed Bosegases

I. Seydi1, S. H. Abedinpour1, , R. Zillich2, R. Asgari3, and B. Tanatar4

1Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS),Zanjan 45137-66731, Iran

2Institute for Theoretical Physics, Johannes Kepler University, Altenbergerstrasse 69,4040 Linz, Austria

3School of Physics, Institute for Research in Fundamental Sciences (IPM), Tehran19395-5531, Iran

4(Presenting author) Department of Physics, Bilkent University, Bilkent, 06800 Ankara,Turkey

We investigate the ground-state properties and excitations of Rydberg-dressed bosons inboth three and two dimensions, using the hypernetted-chain Euler-Lagrangeapproximation, which accounts for correlations and thus goes beyond the mean fieldapproximation. The short-range behavior of the pair distribution function signals theinstability of the homogeneous system towards the formation of droplet crystals atstrong couplings and large soft-core radius. This tendency to spatial density modulationcoexists with off-diagonal long-range order. The contribution of the correlation energyto the ground-state energy is significant at large coupling strengths and intermediatevalues of the soft-core radius while for a larger soft-core radius the ground-state energyis dominated by the mean-field (Hartree) energy. We have also performed path integralMonte Carlo simulations to verify the performance of our hypernetted-chain Euler-Lagrange results in three dimensions. In the homogeneous phase, the two approachesare in very good agreement. Moreover, Monte Carlo simulations predict a first-orderquantum phase transition from a homogeneous superfluid phase to the quantum dropletphase with face-centered cubic symmetry for Rydberg-dressed bosons in threedimensions.

Imbalanced electron-hole-photon systems in two-dimensional structures

A. Tiene 1 , J. Levinsen 2,3 , M. M. Parish 2,3 , J. Keeling 4 and F. M. Marchetti 1

1Departamento de Física Teórica de la Materia Condensada & Condensed MatterPhysics Center (IFIMAC), Universidad Autónoma

de Madrid, Madrid 28049, Spain2School of Physics and Astronomy, Monash University, Victoria 3800, Australia

3ARC Centre of Excellence in Future Low-Energy Electronics Technologies, MonashUniversity, Victoria 3800, Australia

4SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, KY169SS, United Kingdom

Recent technological progress has led to precise and efficient manipulation of electronicand optical properties of semiconductor solid-state devices. Noticeable examplesinclude GaAs heterostructures, while, recently, transition metal dichalcogenide (TMDC)monolayers have emerged as ideal materials for optoelectronic devices. Crucially, bothstructures have been recently embedded into planar optical cavities, allowing to studythe interplay between strong light-matter coupling and electronic doping. This opens theprospect to generate and control novel strongly correlated phases between exciton-polaritons and 2D electron systems [1]. Here, we study the extremely imbalanced limitof one minority particle (e.g., one electron) in a Fermi sea of majority particles (e.g.,holes) in doped single quantum wells or bilayers, strongly coupled to a cavity mode (seeleft panel of Fig. 1). In particular, we focus the attention on the many-body polaritonicbound state with a finite center of mass momentum which represents the extremelyimbalanced limit of the Fulde-Ferrell-Larkin-Ovchinikiv (FFLO) condensed phase atfinite imbalance [2,3]. This state is the result of the competition between Coulombinteraction, the Pauli blocking of the majority specie Fermi sea, and the strong couplingto light. We find that this phase is favoured by long-range unscreened interactions, asmall minority particle mass and a finite bilayer distance. The strong coupling to lightreduced the parameter region where FFLO occurs yet leaving a sizeable region toobserve it in experiments, where an easy detection can occur via far field spectroscopy.

Fig. 1. Left panel: Schematic representation of the studied system configuration. Right panel: Phase diagram of the photon exciton detuning versus majority particledensity for a GaAs heterostructure with either a single quantum well or a bilayergeometry.

References

[1] M. Sidler, P. Back, O. Cotlet, A. Srivastava, T. Fink, M. Kroner, E. Demler, and A.Imamoglu, Nature Physics 13, 255 EP (2016).

[2] M. M. Parish, F. M. Marchetti, and P. B. Littlewood, EPL (Europhysics Letters) 95,27007 (2011).

[3] O. Cotlet, D. S. Wild, M. D. Lukin, and A. Imamoglu, arXiv e-prints ,arXiv:1812.10494 (2018).

Inter-component correlations in one-dimensional mass-imbalanced ultra-cold few-fermion mixtures

Daniel Pęcak and Tomasz Sowiński

Institute of Physics of the Polish Academy of SciencesAleja Lotników 32/46, 02-668 Warsaw, Poland

With recent experiments on several particles confined in one-dimensional optical traps(fermions as well as bosons), quantum engineering has entered a completely new, so farunexplored, area of strongly correlated quantum systems. In these extremelysophisticated experiments, it is possible to control the total number of particles, theirmutual interactions, and the shape of external potential with very high accuracies. Apartfrom a few exceptions, it has commonly been assumed that particles of different kindshave the same mass and the main impact on properties of the system comes from animbalance of the number of particles.

In my talk, I will discuss the ground-state properties of two-component mixtures of afew fermions of different masses. I will show that in the regime of strong repulsions,independently on the number of particles, a mass difference between fermionic speciesinduces a specific spatial separation in one of the component. Depending on the shapeof the external confinement, spatial separation is present in heavier or in the lightercomponent. Consequently, the ground-state of the system undergoes a specific transitionbetween different orderings when the confinement is changed adiabatically.

In the case of attractive interactions, the mass imbalance also strongly influences theproperties of the system. Namely, when the mass ratio is large enough, the many- bodyground state of the system changes its structure and it can be viewed as an almostperfect product of the non-interacting ground state of the heavier component and somewell-defined state of the lighter particles. In a consequence, inter-componentcorrelations are strongly suppressed and they are almost insensitive to the strength ofattractive mutual interactions.

References

[1] D. Pęcak and T. Sowiński: Inter-component correlations in attractive one-dimensional mass-imbalanced few-body mixtures, Phys. Rev. A 99, 043612 (2019).

Quantum solitons in one-dimensional spin-orbit coupled Bose-Bose mixtures

A. To noni1, Y. Wang1,2,3, L. Salasnich1,4

1Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università di Padova, ViaMarzolo 8, 35131 Padova, Italy

2School of Physics and Electronic Engineering, Shanxi University, Taiyuan 030006,China

3Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi030006, China

4Istituto Nazionale di Ottica (INO) del Consiglio Nazionale delle Ricerche (CNR), ViaNello Carrara 1, 50019 Sesto Fiorentino, Italy

Fig. 1: graphical abstract (unpublished).

Recent experimental and theoretical results emphasize the fundamental role of beyondmean field effects in the stabilization of Bose-Bose mixtures with attractive interspeciesinteraction [1]. In a strictly one-dimensional configuration, we show that a self-boundsolitonic structure - fully stabilized by quantum fluctuations – exists [2]. We study thephase diagram of the transition between a single-peak and a striped soliton, obtainedfrom the interplay of spin-orbit and Rabi couplings. The observation of this self-boundstate is within the current experimental capabilities and the transition between thesephases can be directly probed by measuring the breathing mode frequency.

References

[1] D. S. Petrov, Quantum Mechanical Stabilization of a Collapsing Bose-Bose Mixture, Phys. Rev. Lett. 115, 155302 (2015).[2] A. Tononi, Y. Wang, L. Salasnich, Quantum solitons in spin-orbit coupled Bose-Bose mixtures, Physical Review A 99, 063618 (2019).

Integrable Floquet Hamiltonian for a Periodically Tilted 1D Gas

Andrea Trombettoni

CNR and SISSA, Trieste, Italy

After a brief introduction on 1D ultracold gases, I discuss how to implement anintegrable Floquet Hamiltonian for a periodically tilted 1D Bose gas. In general, anintegrable model subjected to a periodic driving gives rise to a non-integrable FloquetHamiltonian. Here we show that the Floquet Hamiltonian of the integrable Lieb--Liniger model in presence of a linear potential with a periodic time—dependent strengthis instead integrable and its quasi-energies can be determined using the Bethe ansatzapproach. We discuss various aspects of the dynamics of the system at stroboscopictimes and we also propose a possible experimental realization of the periodically driventilting in terms of a shaken rotated ring potential. Finally, comments about applicationsto the field of atomtronics will be presented.

Solitons in superfluid Fermi gases

W. Van Alphen1, G. Lombardi1, H. Takeuchi2, S. Klimin1,3, J. Tempere1,4

1 TQC, Universiteit Antwerpen, Universiteitsplein 1, B-2610 Antwerpen, Belgium2 Department of Physics and NITEP, Osaka City University, Osaka 558-8585, Japan

3Department of Theoretical Physics, State Univ. of Moldova, 2009 Chisinau, Moldova4 Lyman Laboratory of Physics, Harvard University, Cambridge, MA 02138, USA

Solitons are solitary matter waves which retain their shape while propagating at aconstant velocity. They emerge in a wide variety of physical systems, includingsuperfluid Fermi gases, where solitons often manifest themselves as localized dips inthe background density, called dark solitons [1-3]. In recent work, we have studied theproperties and dynamics of dark solitons in superfluid Fermi gases by means of arecently developed effective field theory [4] that is capable of describing fermionicsuperfluids across the BEC-BCS crossover regime in a wide temperature domain. Dark solitons in quantum gases are subject to an instability mechanism called the snakeinstability, which makes the soliton decay into vortex structures when the radial widthof the atom cloud is too large [5,6]. We have studied the effect of various conditions and parameters on the stability of thesoliton [7]. Numerical simulations reveal a transition in the dynamics of the solitondecay when the interactions are tuned from the BEC- to the BCS-regime [8]. We havealso simulated the evolution of two counter-propagating solitons to study the propertiesof dark soliton collisions in superfluid Fermi gases in different conditions oftemperature and imbalance [9].

References

[1] M. Antezza, F. Dalfovo, L. P. Pitaevskii, and S. Stringari, Phys. Rev. A 76, 043610 (2007).[2] R. G. Scott, F. Dalfovo, L. P. Pitaevskii, and S. Stringari, Phys. Rev. Lett. 106, 185301 (2011).[3] R. Liao and J. Brand, Phys. Rev. A 83, 041604 (2011).[4] S. N. Klimin, J. Tempere, G. Lombardi, and J. T. Devreese, Eur. Phys. J. B 88, 122 (2015).[5] S. Donadello, S. Serafini, M. Tylutki, L. P. Pitaevskii, F. Dalfovo, G. Lamporesi, andG. Ferrari, Phys. Rev. Lett. 113, 065302 (2014).[6] M. J. H. Ku, B. Mukherjee, T. Yefsah, and M. W. Zwierlein, Phys. Rev. Lett. 116, 045304 (2016).[7] G. Lombardi, W. Van Alphen, S. N. Klimin, and J. Tempere, Phys. Rev. A 96, 033609 (2017).[8] W. Van Alphen, H. Takeuchi, and J. Tempere, arXiv:1901.10751 (2019).[9] W. Van Alphen, G. Lombardi, S. N. Klimin, and J. Tempere, New J. Phys. 20, 053052 (2018).

The fermionic branch of a superfluid Fermi gas and its coupling to the collective mode

Senne Van Loon, Hadrien Kurkjian, Jacques Tempere

TQC, Universiteit Antwerpen, Universiteitsplein 1, B-2610 Antwerpen, België

The notion of quasiparticles is an essential tool for the study of interacting many-bodysystems. In superfluid Fermi gases, two types of elementary excitations can beidentified: the fermionic branch of broken pairs and the bosonic collective mode,describing the collective motion of the pairs. These can be observed in systems ofultracold fermionic atoms, where, due to Fesbach resonances, a whole range ofsuperfluid systems can be studied, which has led to a substantial interest in superfluidFermi gases both theoretically and experimentally. However, the correction of thefermionic quasiparticle branch has been mainly overlooked .It is generally known that the fermionic quasiparticles are only well-defined near theFermi level, and obtain a finite lifetime elsewhere. By introducing a coupling betweenthe fermionic quasiparticles and the collective mode, we can calculate the damping rateof the excitations associated with the emission of a boson. As this is the only resonantprocess at low energies, we can use this coupling to compute corrections to thequasiparticle dispersion beyond mean field theory in the entire BCS to BEC crossover.

References

N. Lerch, L. Bartosch, and P. Kopietz, Absence of fermionic quasiparticles in thesuperfluid state of the attractive fermi gas, Phys. Rev. Lett. 100, 050403 (2008).

R. Haussmann, M. Punk, and W. Zwerger, Spectral functions and rf response ofultracold fermionic atoms, Physical Review A 80, 063612 (2009).

Scaling properties of the Tan's contact: from two to infinity

P. Vignolo1, F. Hébert1, M. Albert1, F. Sant’Ana1,2, A. Minguzzi3, C. Miniatura1,4, M. Rizzi5, V. Rousseau6 , P. Capuzzi7

1 Université Côte d’Azur, CNRS, Institut de Physique de Nice, 1361 route des Lucioles,06560 Valbonne, France

2 São Carlos Institute of Physics, University of São Paulo, 13566-590, São Carlos, SP,Brazil

3 Univ. Grenoble-Alpes, CNRS, LPMMC, F-38000 Grenoble, France4MajuLab, CNRS-UCA-SU-NUS-NTU International Joint Research Unit, Singapore

5Johannes Gutenberg-Universität, Institut für Physik, Staudingerweg 7, 55099 Mainz,Germany

65933 Laurel St, New Orleans, LA70115, USA7Departamento de Fisica, Universidad de Buenos Aires, Argentina

The Tan's contact of a quantum system tell us how particles can approach each othertaking into account of the presence of all the other particles in the system.Thus it depends on the number of pairs and quantum correlations, that, on their side,depend on the number of particles, interaction strength, and temperature.Here we show that, in the strong-interacting regime, the pair and correlations effects areembedded in the contact at the unitary limit (Tonks limit) [1,2].Thus the contact rescaled by the contact at the Tonks limit is an universal function oftwo parameters, the rescaled interaction strength and temperature [3,4].This claim, that has been proved for a harmonically trapped Lieb-Liniger gas, is validfor any number of particles, from two to infinity, and any temperature, from zero toinfinity [2]. The general case of one-dimensional fermionic and/or bosonic mixtures isunder investigation [5].

References

[1] M. Rizzi, C. Miniatura, A. Minguzzi, and P. Vignolo, Phys. Rev. A 98, 043607 (2018).

[2] F. Hébért, F. Sant'Ana, V. Rousseau, M. Albert, and P. Vignolo, in preparation.

[3] W. Xu and M. Rigol, Phys. Rev. A 92, 063623 (2015).

[4] H. Yao, D. Clément, A. Minguzzi, P. Vignolo, and L. Sanchez-Palencia, Phys. Rev. Lett. 121, 220402 (2018).

[5] P. Capuzzi and P. Vignolo, in preparation.

Accelerating adiabatic state transfer with high-frequency drivings

Sandro Wimberger

Dipartimento di Scienze Matematiche, Fisiche e Informatiche, Università di Parma

E-mail: sandromarcel.wimberger@unipr.it

Quantum adiabatic driving is one of the pillars of time-dependent quantum control.However, the limitations imposed by the coherence times are typically in sharp contrastwith the necessity of slow evolutions imposed by the adiabatic theorem. A method willbe presented for accelerating adiabatic state transfer for few-level systems. This worksby introducing suitably tailored fast oscillations in the intrinsic parameters of theoriginal Hamiltonian: the oscillations mediate an effective Hamiltonian dynamicallycompensating for undesired transitions. It will be shown how the protocol can beexploited for producing entanglement between two qubits, e.g., in a circuit QED setting.

References

[1] F. Petiziol, B. Dive, F. Mintert, S. Wimberger, Phys. Rev. A 98, 043436 (2018).

[2] F. Petiziol, B. Dive, S. Carretta, R. Mannella, F. Mintert, S. Wimberger, Phys. Rev. A99, 042315 (2019).

[3] F. Petiziol, S. Wimberger, Condens. Mat. 4 (1), 34 (2019).

Coexistence of giant Cooper pairs and bosonic condensate in the BCS-BEC

crossover in a two-band superfluid Fermi gas

Yuriy Yerin,1 Hiroyuki Tajima,2 Pierbiagio Pieri,1,3 and Andrea Perali4

1School of Science and Technology, Physics Division, Universita di Camerino, 62032Camerino (MC), Italy

2Quantum Hadron Physics Laboratory, RIKEN Nishina Center, Wako, Saitama, 351-0198, Japan

3INFN, Sezione di Perugia, 06123 Perugia (PG), Italy4School of Pharmacy, Physics Unit, Universita di Camerino, Italy

Reference: Y. Yerin et al. Arxiv: 1907.13344

We investigate Bardeen-Cooper-Schrieffer (BCS) –Bose-Einstein condensation (BEC) crossover in a two-band superfluid Fermi gas with an energy shiftbetween the bands (fig. 1).

When the intraband coupling in the cold (first) band isfixed as weak we find that in the case of vanishing

interband interaction and in the strong-coupling limit of the hot (second) band thesystem undergoes a transition to a single-component configuration with the fullsuppression of the first energy gap and with the full redistribution of particles betweenbands.In the case of weak interband coupling the systemshows a significant amplification of theintrapair correlation length of the condensate in thefirst band in the strong-coupling regime which clearlyindicates the coexistence of giant Cooper pairs and abosonic condensate even for nonzero temperatures(fig. 2). This can lead to a non- monotonic temperaturedependence of the second energy gap with a peak.

Here predicted coexistence of the giantCooper pairs and bosonic molecules canbe verified by means of the visualizationof vortex cores in the two-componentBEC condensates as well as in someiron-based superconductors.

Fig. 2: Evolution of the intrapaircorrelation length of the condensate in thefirst band of a superfluid two-band Fermigas with vanishing interband interaction andfor different coupling strengths in the firstband at T=0.

Fig. 1: The band structure ofthe two-band superfluid Fermigas under consideration (kz = 0projection). Eg is the energyshift between the 1st (i=1) andthe 2nd (i=2) band. EFi

corresponds to the Fermienergy of i-band in the absenceof interactions.