Squeezed Light and Quantum Imaging with Four-Wave Mixing in

Hot Atoms

Alberto Marino Ulrich VoglJeremy Clark (U Maryland) Quentin GlorieuxNeil Corzo Trejo (CINVESTAV, Mexico) Ryan GlasserPDL Zhifan Zhou (ECNU)

Andrew Lance (Quintessence Labs)Raphael Pooser (Oak Ridge)Kevin Jones (Williams College)Vincent Boyer (Birmingham)Atomic Physics Division

National Institute of Standards and TechnologyGaithersburg, MD

also with the Joint Quantum Institute (NIST/U Maryland)

$ JQI NSF-PFC, DARPA, AFOSR $

Squeezed Light and Quantum Imaging with Four-Wave Mixing in Hot Atoms

something for (almost) everyone

• squeezed light– bright beams– vacuum

• slow light• continuous-variable entanglement• images (multiple-spatial-mode)• narrowband at Rb color (atom optics)• relatively simple experiments!

really cool! if only this were 20 years ago!

squeezed light from 4WM in Rb vapor

First observations of squeezed light in 1985 (Slusher, et al.) were based on degenerate 4WM in atomic vapors.

Most experimental reports of squeezing by 4WM in atomic vapors were published more than 10 years ago... mostly based on 2-level systems; these ended with several attempts in cold atom samples.

Most recent squeezed-light results use OPO’s and OPA’s with χ(2) materials in a cavity; strong squeezing achieved.

4WM in fibers generates correlated photons and ~7 dB of squeezing.

Lots of theoretical examinations...... but none that actually predicted squeezing under our conditions.

history

We are trying to perform quantum optics and “quantum atom optics” experiments:

create non-classical photon beams that can, in turn, be used to produce non-classical atom beams.

also try to do “real” quantum optics and image processing experiments with non-classical light amplifiers.

Goals

Raman transition 0hk

2hk

klaserki

hk

k1

k2

hk

hk √2/2hk

k1

“dress” the atomsin the BEC with the“downward-going” frequency of a Ramantransition

drive the “upward-going”transition with correlated photon beams

k2

twin beams of atoms out

klaserBEC

Producing correlated atomsfrom correlated photons

P. Lett, J. Mod Opt. 51, 1817 (2004)

Single-mode squeezing

p1

x1

p2

x2

CoupledGain

correlations

two vacuummodes

two noisy, but entangled,vacuum modes

Two-mode squeezing:phase-insensitive amplifier

Squeezing quadratures

squeezing from 4WM in hot Rb vapor

85Rb in a double-Λ scheme ~120 C cell temp.~1 GHz detuned ~400 mW pump~100 µW probe- narrowband- no cavity

strong intensity-differencesqueezing measured

1 MHz detection frequencyRBW 30 kHzVBW 300 Hzpump detuning800 MHzRaman detuning 4 MHz

noise“squeezed light” implies, in some form, reduced

fluctuationsthis is usually compared to “shot noise”

N particles/second => noise ~ N1/2

state of the art; (linear and log)3 dB = factor of 2; 10% noise = -10 dB

Two-Mode: We have -8.8 dB (13% of “shot noise”)“project” lossless squeezing level of -11 dB at sourceworld record (using an OPO): -9.7 dB (11%) twin beam;

-11.5 dB for single-mode quadrature squeezingWe have -3 dB of single-mode squeezingprevious best with 4WM in atoms: -2.2 dB

LIGO will use -6 dB of squeezing in phase II

intensity-difference squeezing at low frequencies

better than8 dB noise suppressionif backgroundssubtracted!

image correlations

no cavitymeans fewerconstraintson modes!

image correlations in space

pump relic

amplified probe(spatially filtered + )

generated conjugate(spatially filtered)

expect that correlations are “reflected” radially through the pump

note that “images” do not constitute multiple spatial mode4.7 dB intensity difference squeezing between images at 1 MHz

phase stable local oscillators at +/- 3GHz from the pump

demonstrating entanglement

pump

probe

conjugate

pztmirror

pztmirror

+ or -

scan LO phase

alignment andbright beam entanglement

demonstrating entanglement

pumps

probe

conjugate

LO pump

pztmirror

pztmirror

+ and -

scan LO phase

signal pump50/50BS

vacuumsqueezing

unsqueezedvacuum

measurements at 0.5 MHz

“twin beam” vacuum quadrature entanglement

entangled images

measurements at 0.5 MHz

• V. Boyer, A.M. Marino, R.C. Pooser, and P.D. Lett, Science 321, 544 (2008).

cone of vacuum-squeezed modes(allowed by phase matching)

seeded, bright modes

entangled “images”arbitrarily-shaped local oscillators can be used

(we used a “T”-shaped beam)squeezing in both quadratures;

(equivalent results in all quadratures)

Gaussian bright-beam (-3.5 dB) or vacuum (-4.3 dB); T-shaped vacuum (-3.7 dB)implies EPR-levels of CV-entanglement could

be measured in each caseno feedback loops or mode cleanup cavities!

Imagesno cavity, sofreedom for complex and multiple spatial modes!

phase-sensitive amplifierthe phase of the injected beam, with respect to those of the pumps, will determine whether the beam will be amplified or de-amplified

One can design an amplifier for given field quadratures -useful for signal processing!

ω+

ω-

ω0

given the phase of 3 “input” beams the 4th phase is free to adjust for gain

ω-

ω0

ω+

φ+ = 2φ0 - φ- 0 = 2φ0 - φ- - φ+

phase-insensitive phase-sensitiveno free parameters

gain:

phase-sensitive amplifier set-up

ti:sapph laser

Double-passsemiconductortapered amp

Double-pass 1.5 GHz AOM

~1 mW

~ 500 mW Rb celloptics

pzt for phase lock

Phase lock each pump beam to the probe.

-3 GHz +3 GHz

probe

problems- tapered amps noisy; astigmatic output beams; feedback adds laser noise

- detuning needs to be large to avoid other 4WM- 500 mW is marginal power- non-co-linear geometry helps separate the beams

but makes the (distorted) wavefronts not match(getting a fixed phase for amplification is hard)

phase relation varies across probe beam (phase fronts are distorted)

competing 4WM processes

pump 1 pump 2

“probe”“extra conjugate”

extra 4WM can be suppressed by putting “pump1”mid-way between the absorptions (more power needed)

Experimental Setup - PSA

Double Lambda Scheme in85Rb

Experimental Parameters

Pump ~200mW eachProbe ~ 0.1mWCell ~12mm Gain ~ 2Angle ~ 0.5°Orthogonal Linear Pol.Cell Temperature 86 CThe probe gets amplified or deamplified depending on its phase .

PumpsProbe

5S1/2

5P1/2

3GHz 3GHzProbe

“single mode” quadrature squeezingPSA (phase-sensitive amplifier)

homodyne detection

direct detection

squeezing calculatedfrom probe gain

lower cell temp ~90 Cthan for phase-insensitive case

seeded

“vacuum seeded”

Vacuum Squeezing

Squeezing trace at 1 MHz (zero span, RBW: 30 KHz, VBW: 100 Hz) for thevacuum squeezed state, normalized to the shot noise. One-photon detuning0.8 GHz. Two-photon detuning 4MHz.

Vacuum Squeezing vs Pump PowerSq

ueez

ing [

dB]

Squeezing at 1 MHz (zero span, RBW: 30 KHz, VBW: 100 Hz) for the vacuumsqueezed state, normalized to the shot noise. One-photon detuning 0.8 GHz.

Vacuum Squeezing Bandwidth

Vacuum Squeezing Bandwidth

Squeezing trace (RBW: 10 KHz, VBW: 100 Hz) for the vacuum squeezed state,normalized to the shot noise. One-photon detuning 0.8 GHz. Two-photondetuning4MHz. Pump1 = 225 mW. Pump 155mW.

Vacuum Squeezing Bandwidth

Squeezing trace (RBW: 10 KHz, VBW: 100 Hz) for the vacuum squeezed state,normalized to the shot noise. One-photon detuning 0.8 GHz. Pump1 = 225mW. Pump 155mW.

Vacuum Squeezing Bandwidth

Squeezing trace (RBW: 10 KHz, VBW: 100 Hz) for the vacuum squeezed state,normalized to the shot noise. One-photon detuning 0.8 GHz. Pump1 = 225mW. Pump 155mW.

Vacuum Squeezing Bandwidth

Squeezing trace (RBW: 10 KHz, VBW: 100 Hz) for the vacuum squeezed state,normalized to the shot noise. One-photon detuning 0.8 GHz. Pump1 = 225mW. Pump 155mW.

phase-sensitive amplifierTo avoid other phase-insensitive 4WM processes the detuning is much different than with the phase-insensitive version of the 4WM amplifier.

These processes can be suppressed, however, not completely. This leads to excess noise and limits the gain at which the PSA can be operated.

It still operates with multiple spatial modes, but the symmetry of the spatial modes will be an issue to some (unknown) extent.

multi-spatial mode “single-mode quadrature squeezing”

attenuatingbeam (modes)by blockingin differentmanners

Summary• 4WM should add to

our ability to perform quantum imaging and amplifier experiments

• narrowband source should allow us to use this to interface with Rb atom quantum memories

group photo

Ulrich Vogl Ryan GlasserJeremy Clark

Quentin GlorieuxZhifan Zhou

Neil Corzo TrejoAlberto Marino

Slide Number 1Slide Number 2something for (almost) everyonehistoryGoalsProducing correlated atoms�from correlated photons�Slide Number 7Slide Number 8Slide Number 9squeezing from 4WM in hot Rb vaporstrong intensity-difference�squeezing measured noiseintensity-difference squeezing at low frequenciesimage correlationsimage correlations in spacedemonstrating entanglementdemonstrating entanglement“twin beam” vacuum quadrature entanglemententangled imagesSlide Number 20entangled “images”Imagesphase-sensitive amplifierphase-sensitive amplifier set-upproblemscompeting 4WM processesExperimental Setup - PSA“single mode” quadrature squeezing�PSA (phase-sensitive amplifier)�Vacuum SqueezingSlide Number 30Slide Number 31Slide Number 32Slide Number 33Slide Number 34Slide Number 35phase-sensitive amplifierSlide Number 37SummarySlide Number 39