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

Transcription

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

2 Squeezed Light and Quantum Imaging with Four-Wave Mixing in Hot Atoms Alberto Marino Ulrich Vogl Jeremy Clark (U Maryland) Quentin Glorieux Neil Corzo Trejo (CINVESTAV, Mexico) Ryan Glasser PDL 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 Technology Gaithersburg, MD also with the Joint Quantum Institute (NIST/U Maryland) $ JQI NSF-PFC, DARPA, AFOSR $

3 something for (almost) everyone squeezed light from 4WM in Rb vapor 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!

4 history 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.

5 Goals 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.

6 Producing correlated atoms from correlated photons dress the atoms in the BEC with the downward-going frequency of a Raman transition BEC drive the upward-going transition with correlated photon beams k 1 k 2 k laser twin beams of atoms out k 1 k i k laser 2hk 0hk Raman transition hk hk 2/2hk hk k 2 P. Lett, J. Mod Opt. 51, 1817 (2004)

7 Single-mode squeezing

8 Two-mode squeezing: phase-insensitive amplifier p 1 x 1 Coupled Gain correlations p 2 x 2 two vacuum modes two noisy, but entangled, vacuum modes

9 Squeezing quadratures

10 squeezing from 4WM in hot Rb vapor 85 Rb in a double- Λ scheme ~120 C cell temp. ~1 GHz detuned ~400 mw pump ~100 µw probe - narrowband - no cavity

11 strong intensity-difference squeezing measured 1 MHz detection frequency RBW 30 khz VBW 300 Hz pump detuning 800 MHz Raman detuning 4 MHz

12 noise squeezed light implies, in some form, reduced fluctuations this is usually compared to shot noise N particles/second => noise ~ N 1/2 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 source world record (using an OPO): -9.7 db (11%) twin beam; db for single-mode quadrature squeezing We have -3 db of single-mode squeezing previous best with 4WM in atoms: -2.2 db LIGO will use -6 db of squeezing in phase II

13 intensity-difference squeezing at low frequencies better than 8 db noise suppression if backgrounds subtracted!

14 no cavity means fewer constraints on modes! image correlations

15 image correlations in space amplified probe (spatially filtered + ) pump relic generated conjugate (spatially filtered) expect that correlations are reflected radially through the pump note that images do not constitute multiple spatial mode 4.7 db intensity difference squeezing between images at 1 MHz

16 demonstrating entanglement scan LO phase alignment and bright beam entanglement + or - probe pump conjugate pzt mirror phase stable local oscillators at +/- 3GHz from the pump pzt mirror

17 demonstrating entanglement vacuum squeezing unsqueezed vacuum + and - probe conjugate pumps pzt mirror 50/50 BS signal pump LO pump pzt mirror scan LO phase

18 twin beam vacuum quadrature entanglement measurements at 0.5 MHz

19 entangled images measurements at 0.5 MHz V. Boyer, A.M. Marino, R.C. Pooser, and P.D. Lett, Science 321, 544 (2008).

20 seeded, bright modes cone of vacuum-squeezed modes (allowed by phase matching)

21 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 case no feedback loops or mode cleanup cavities!

22 no cavity, so freedom for complex and multiple spatial modes! Images

23 ω - phase-sensitive amplifier the 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! phase-insensitive ω 0 ω + given the phase of 3 input beams the 4th phase is free to adjust for gain φ + = 2φ 0 - φ - gain: 0 = 2φ 0 - φ - - φ + ω 0 phase-sensitive ω no free + parameter s ω -

24 phase-sensitive amplifier set-up ti:sapph laser Phase lock each pump beam to the probe. Double-pass 1.5 GHz AOM -3 GHz +3 GHz Double-pass semiconductor tapered amp optics ~1 mw ~ 500 mw probe Rb cell pzt for phase lock

25 problems - tapered amps noisy; astigmatic output beams; feedback adds laser noise - detuning needs to be large to avoid other 4WM 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)

26 competing 4WM processes pump 1 pump 2 extra conjugate probe extra 4WM can be suppressed by putting pump1 mid-way between the absorptions (more power needed)

27 Experimental Setup - PSA 5P 1/2 Probe Pumps 5S 1/2 3GHz Probe 3GHz Experimental Parameters Double Lambda Scheme in Pump ~200mW each 85 Rb Probe ~ 0.1mW Cell ~12mm Gain ~ 2 Angle ~ 0.5 Orthogonal Linear Pol. The probe gets amplified or deamplified depending on its phase.cell Temperature 86 C

28 single mode quadrature squeezing PSA (phase-sensitive amplifier) seeded direct detection squeezing calculated from probe gain vacuum seeded homodyne detection lower cell temp ~90 C than for phaseinsensitive case

29 Vacuum Squeezing Squeezing trace at 1 MHz (zero span, RBW: 30 KHz, VBW: 100 Hz) for the vacuum squeezed state, normalized to the shot noise. One-photon detuning 0.8 GHz. Two-photondetuning4MHz.

30 Vacuum Squeezing vs Pump Power Squeezing [db] Squeezing at 1 MHz (zero span, RBW: 30 KHz, VBW: 100 Hz) for the vacuum squeezedstate, normalizedto the shot noise. One-photondetuning0.8 GHz.

31 Vacuum Squeezing Bandwidth

32 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-photon detuning4mhz. Pump1 = 225 mw. Pump 155mW.

33 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 = 225 mw. Pump 155mW.

34 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 = 225 mw. Pump 155mW.

35 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 = 225 mw. Pump 155mW.

36 phase-sensitive amplifier To avoid other phase-insensitive 4WM processes the detuning is much different than with the phaseinsensitive 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.

37 multi-spatial mode single-mode quadrature squeezing attenuating beam (modes) by blocking in different manners

38 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 Summary

39 group photo Quentin Glorieux Zhifan Zhou Ulrich Vogl Alberto Marino Ryan Glasser Jeremy Clark Neil Corzo Trejo