Nonreciprocity and Quantum Correlations of Light Transport in Hot Atoms via Reservoir Engineering

Xingda Lu, Wanxia Cao, Wei Yi, Heng Shen, and Yanhong Xiao

Phys. Rev. Lett. 126, 223603 – Published 4 June 2021

Abstract

The breaking of reciprocity is a topic of great interest in fundamental physics and optical information processing applications. We demonstrate nonreciprocal light transport in a quantum system of hot atoms by engineering the dissipative atomic reservoir. Our scheme is based on the phase-sensitive light transport in a multichannel photon-atom interaction configuration, where the phase of collective atomic excitations is tunable through external driving fields. Remarkably, we observe interchannel quantum correlations that originate from interactions with the judiciously engineered reservoir. The nonreciprocal transport in a quantum optical atomic system constitutes a new paradigm for atom-based nonreciprocal optics and offers opportunities for quantum simulations with coupled optical channels.

Received 4 January 2021
Accepted 28 April 2021

DOI:https://doi.org/10.1103/PhysRevLett.126.223603

Physics Subject Headings (PhySH)

Atom optics Atomic, optical & lattice clocks Light-matter interaction Quantum optics

Atomic ensemble

Homodyne & heterodyne detection

Atomic, Molecular & Optical

Authors & Affiliations

Xingda Lu¹, Wanxia Cao¹, Wei Yi^2,3, Heng Shen ^4,5,6,*, and Yanhong Xiao ^7,5,1,†

¹Department of Physics, State Key Laboratory of Surface Physics and Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Fudan University, Shanghai 200433, China
²CAS Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei 230026, China
³CAS Center For Excellence in Quantum Information and Quantum Physics, Hefei 230026, China
⁴State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China
⁵Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
⁶Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
⁷State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China

^*heng.shen@physics.ox.ac.uk
^†yxiao@fudan.edu.cn

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Vol. 126, Iss. 22 — 4 June 2021

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Images

Figure 1
Schematics for a dissipatively coupled three-channel system. (a) Experiment schematics. Three spatially separated optical channels (Ch0, Ch1, and Ch2 with diameter 6 mm) propagate in a warm paraffin-coated ${}^{87}{Rb}$ vapor cell under EIT interaction. The interchannel couplings are mediated by the mixing of atomic spin of the ground states through atomic motion. A solenoid gives precise control over the longitudinal magnetic field. Output beams from the cell are recollimated and detected by the photon detectors or polarization homodyne detection setup. The noise power of the amplified subtracted photocurrents is recorded with a spectrum analyzer. BS, beam splitter; $D_{0}$ , $D_{1}$ , and $D_{2}$ , photodetectors. Cross section: photo of the optical beams taken from this experiment. (b) The $Λ$ three-level scheme in three channels. The ground states are Zeeman sublevels of $| F = 2 ⟩$ , and the excited state is $| F = 1 ⟩$ of the ${}^{87}{Rb}$ D1 line. $Ω_{c}^{(i)}$ , $Ω_{p}^{(i)}$ , $i = 0$ , 1, 2 are Rabi frequencies of the control and probe beams, respectively. The Zeeman splitting is induced by a common longitudinal magnetic field $δ_{B}$ , serving as either the Larmor frequency in the noise spectra measurement or the two-photon detuning in the EIT measurement (denoted as $δ_{B}$ in Fig. 3). In the measurements of quantum fluctuation, all three weak probes are removed, as shown in (b2) (Ch1 and Ch2 are not shown). $\hat{b}$ , annihilation operator of the coherent vacuum.
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Figure 2
Phase-sensitive light transport for the beam splitter composed of Ch1 and Ch2. Output probe intensities of Ch1 and Ch2 as functions of varying local phase $θ_{0}$ in Ch0 when (a) the weak probe input in Ch2 is off and (b) all three input probes are on. The input laser powers in all channels are $500 μ W$ for the control and $50 μ W$ for the probe, respectively, corresponding to Rabi frequencies $Ω_{c} \sim 1.4 \times 1 0^{7} Hz$ and $Ω_{p} \sim 4.4 \times 1 0^{6} Hz$ . The local phase of Ch1 is set to be $θ_{1} = ψ_{c}^{(1)} - ψ_{p}^{(1)} = 0$ and, for Ch2, $θ_{2} = π$ (if the probe is on). The cell temperature is 60 °C.
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Figure 3
Spin wave interference induced nonreciprocity in optical transport. (a) Schematics of the nonreciprocal transport. (b) Transport spectrum. The two-photon detuning $δ_{B}$ is proportional to the applied common magnetic field. Red curve $T_{12}$ is the transported power from Ch1 to Ch2 when injecting the weak probe in Ch1. Black curve $T_{21}$ is the transported power from Ch2 to Ch1 when injecting the weak probe in Ch2. The local phase of all three channels is set to be $θ_{0} = 0$ , $θ_{1} = 0$ , and $θ_{2} = π$ . The input power of the probe in each channel is $50 μ W$ . The input power of the control in each channel is $500 μ W$ . The cell temperature is 60 °C.
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Figure 4
Quantum correlations exist between any two channels. The experiment noise spectra of $Var ({\hat{X}}_{i})$ , $Var ([({\hat{X}}_{i} \mp {\hat{X}}_{j}) / \sqrt{2}])$ ( $i$ , $j = 0$ , 1, 2 and $i \neq j$ ) are shown. They are identical to $Var ({\hat{P}}_{i})$ , $Var [({\hat{P}}_{i} \pm {\hat{P}}_{j}) / \sqrt{2}]$ , respectively (not shown). The shot noise level is set at 0 dB, observed when only one channel is on. The bias magnetic field is applied to shift the homodyne measurement from dc to the Larmor frequency( $\sim 352 kHz$ ). The input control power is $280 μ W$ in both Ch1 and Ch2 and $500 μ W$ in Ch0. The cell temperature is 60 °C.
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