Jerzy ZachorowskiM. Smoluchowski Institute of Physics,

Jagiellonian University

Nonlinear Spectroscopy of Cold Atoms, Nonlinear Spectroscopy of Cold Atoms, Preparations for the BECPreparations for the BEC

ExperimentsExperiments

The GroupThe Group

Tomasz BrzozowskiMaria MączyńskaJerzy ZachorowskiMichał ZawadaWojciech Gawlik IF UJ

Magneto-Optical TrapMagneto-Optical Trap I

I

85RbN 108

T 100 K

Spectroscopy of Cold AtomsSpectroscopy of Cold Atoms

-40 -20 0 20

-50 -40 -30 -20 -10 0 10 20

I = 22.4 · I 0

Detuning from the 3 - 4 resonance [MHz]

trap - probe [MHz]-2 -1 0 1 2 -2 -1 0 21

Laser systemLaser system

Master laser

Laseramplifier

Probelaser

Rb

Trap beamLaser

monitoring

Probe beam

PD

Frequency stabilization

AOM

AOMAOM

AOM

OIOI OI

Central StructureCentral Structure

• Raman transitions between light-shifted Zeeman sublevels

• Raman transitions between vibrational levels in the optical lattice

Zeeman sublevelsZeeman sublevels

-4 -3 -2 -1 0 1 2 3 4

1-2

0-10-1

a

b

c

d

p L - [MHz]

abso

rptio

n si

gnal

[arb

. uni

ts]

23,

13,03,

0-1

1-2

-13,

-23,

Vibrational levelsVibrational levels•Electric field in the trap: 6 beams of different polarizations.

•Relative phases not fixed, but relatively stable.

•Interference: intensity and/or polarization modulation.

•Additional optical forces (dipole forces).

•Atoms cooled and localized in the lattice nodes.

•Atomic movement quantized: vibrational energy levels.

RemarksRemarks

New experiments: trap modulation

Difference absorption-wave mixing

p L - [MHz]

abso

rptio

n si

gnal

[arb

. uni

ts]

FWM

sig

nal [

arb.

uni

ts]

-2 -1 0 1 2 3

Ultra-narrow central resonance

-2 -2-1 -1 0 0 1 1 2 2

abso

rptio

n [a

.u.]

four

-wav

e m

ixin

g [a

.u.]

probe-pump beam detuning [MHz]

Bose-Einstein Bose-Einstein CondensationCondensation

de Broglie wavelength:TmkB

dB

22

density n, distance n1/3,

condensation when: )(3/1 Tn dB

Ketterle, PRL 77,416 (1996)

Lower temperaturesLower temperatures• Spontaneous emission: temperatures limited to 10 – 1K

• „Dark traps”: optical dipole or magnetic forces

• Cooling by evaporation

100 nK100 K300 K

MOT MT

Three steps to BECThree steps to BEC1. Magneto-Optical Trap:Magneto-Optical Trap:

temperature 10 mK, density 1010 cm-3

limit – interaction with light.

2. Magnetic Trap:Magnetic Trap:trap in field minimum - only „low-field-seeking” stateslosses at B = 0.

3. Evaporation cooling:Evaporation cooling:forced evaporation of hot atoms, thermalisation by collisions.

400 nK

200 nK

50 nK

1995 - E. Cornell & C. Wieman Rb87

Evidence:Evidence:• narrow peak in velocity distribution• peak’s amplitude when T• cloud shape same as that of the potential well

Over 30 laboratories produce BEC87Rb, 23Na, 7Li, ↑H , He*, ...  

Experiments with BECExperiments with BEC•Matter-wave optics: condensate interference, atom laser•Nonlinear atom optics•Superfluidity, vortices•Ultra-low density condensed-matter: Mott insulatorCold fermions

NowNow

Matter-wave OpticsMatter-wave Optics – Atom Optics– Atom Optics coherent waves interference

MIT

”atom laser”

MPQ

NIST

a) b)

c)

Nonlinear atom-opticsNonlinear atom-optics kin = kout

in = out

a) light waves

(material medium nonlinearity)

b)   matter waves (always nonlinear)

BECBEC

1999 NIST (W. Phillips)1999 NIST (W. Phillips)

& Marek Trippenbach (UW)& Marek Trippenbach (UW)

Superfluidity, VorticesSuperfluidity, Vortices

MIT

LENS, Florence

Ultra-low density Ultra-low density condensed-mattercondensed-matter

Mott transition

MPQ – Garching

6000 87Rb atoms loading time 8 scooling time 2,1 scurrent 2A

Micro-BEC Micro-BEC

Garching

Micro-BEC 2 Micro-BEC 2

Tubingen87RbNumber of atoms in BEC: 106

Condensation at T=1KCooling time 27s

Cold fermions Cold fermions Do not thermalize (Pauli exclusion)Sympathetic coolinge.g. fermion 40K & boson 87Rb, fermion 6Li & boson 7Li

2001 R. Hulet (Rice)

Li7 Li6

1999 D. Jin (JILA) 40K

Our way towards BEC Our way towards BEC

MOT

MT

Magneto-optical trappingMagneto-optical trapping T 30 K, N 108

Transfer to mTransfer to magnetic trapagnetic trap by radiation pressure, by radiation pressure, recapture in a MOTrecapture in a MOT separated vacuum regions

differential pumping (10-8 mbar 10-11

mbar)

Magnetic trapping:Magnetic trapping: forced evaporation of hottest atoms,

thermalization by collisions T 100 nK, N 105 - 106

Element 87Rb

Transfer of atoms Transfer of atoms • repetitive pushing by resonant light beam, recapture

in lower MOTcollection speed: 108–1010 s-1

loading of lower MOT: 107–109 s-1

• constant pushing by narrow light beam (Dalibard) flux: ~108 s-1

• magnetic transfer directly into magnetic trap (Hänsch)30% efficiency, complicated.

Magnetic traps Magnetic traps

QUIC = Quadrupole + Joffe configuration: B ≠ 0 at trap center

Dalibard Hänsch

September 2002September 2002

• Laser system prepared• Upper MOT ready & operating• Next steps: transfer & recapture

magnetic trapping