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arXiv:2608.29515

Demonstration of traveling-wave interactions between spontaneous photon emissions and atoms in a chiral F-P cavity

Jiajin Lu, Minjie Wang, Haole Jiao, Xiang Chen, Hongze Zhang, Shujing Li, Hai Wang

quant-phSubmitted Aug 30, 2026• Announced Sep 1, 2026• 0 citations
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Abstract

The enhancement of atom-photon interactions with F-P cavities provides a suitable platform for studying quantum optics and atomic physics. However, the emission fields in linear F-P cavities are in the standing-wave mode, which leads to non-uniform atom-photon coupling and a short storage lifetime of cavity-enhanced spin-wave quantum storages. This study experimentally demonstrates traveling-wave atom-light interactions in an F-P cavity that can preserve light helicity. First, a bias magnetic field is applied along the z-axis to define the quantization axis, which lifts the Zeeman degeneracy and breaks the time reversal symmetry. Next, non-classically correlated pairs of Stokes photons and spin waves are produced based on the Duan-Lukin-Cirac-Zoller scheme. The Stokes photons initially emitted from a single circularly polarized atomic transition have left-and right-hand circular polarizations when propagating along the +z (forward) and -z (backward) directions, which are preserved in the chiral cavity within the atom-photon interaction region. Thus, when the forward and backward Stokes fields resonate with the cavity, they may interact with the atoms in a traveling-wave manner. This is confirmed by measuring the time-dependent retrieval efficiencies of spin waves correlated with the forward and backward Stokes fields. This work paves the way for demonstrating traveling-wave atom-photon interactions in F-P cavities.

AI Summary

Fabry–Pérot cavities enhance atom–photon coupling, but their standing-wave fields produce spatially nonuniform coupling and can limit the lifetime of cavity-enhanced spin-wave memories. This paper asks whether spontaneous emission from an atomic ensemble can instead interact with atoms in a traveling-wave manner inside a linear, helicity-preserving cavity. The experiment uses a bias magnetic field along the cavity’s $z$ axis to define the atomic quantization axis, lift Zeeman degeneracy, and break time-reversal symmetry. A Duan–Lukin–Cirac–Zoller protocol generates nonclassically correlated Stokes photons and collective atomic spin waves. For emission on a single circularly polarized atomic transition, the forward- and backward-propagating Stokes fields have opposite helicities. The chiral cavity preserves these polarizations within the atom–light interaction region, allowing the two resonant propagation directions to couple to the atoms in a traveling-wave manner rather than as a conventional standing-wave mode. The reported experimental evidence consists of time-dependent retrieval-efficiency measurements for spin waves correlated with the forward and backward Stokes fields. The abstract states that these measurements confirm traveling-wave interactions. It provides no numerical retrieval efficiencies, storage lifetimes, correlation values, or comparison with a conventional cavity, so the magnitude of any memory-performance improvement cannot be assessed from the available material. The full text is unavailable, and the abstract states no further experimental limitations.

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Written by gpt-6.1-sol from the abstract only. Automated: it can be wrong.

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19 pages,2 figures

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The enhancement of atom-photon interactions with F-P cavities provides a suitable platform for studying quantum optics and atomic physics. However, the emission fields in linear F-P cavities are in the standing-wave mode, which leads to non-uniform atom-photon coupling and a short storage lifetime of cavity-enhanced spin-wave quantum storages. This study experimentally demonstrates traveling-wave atom-light interactions in an F-P cavity that can preserve light helicity. First, a bias magnetic field is applied along the z-axis to define the quantization axis, which lifts the Zeeman degeneracy and breaks the time reversal symmetry. Next, non-classically correlated pairs of Stokes photons and spin waves are produced based on the Duan-Lukin-Cirac-Zoller scheme. The Stokes photons initially emitted from a single circularly polarized atomic transition have left-and right-hand circular polarizations when propagating along the +z (forward) and -z (backward) directions, which are preserved in the chiral cavity within the atom-photon interaction region. Thus, when the forward and backward Stokes fields resonate with the cavity, they may interact with the atoms in a traveling-wave manner. This is confirmed by measuring the time-dependent retrieval efficiencies of spin waves correlated with the forward and backward Stokes fields. This work paves the way for demonstrating traveling-wave atom-photon interactions in F-P cavities.
Fabry–Pérot cavities enhance atom–photon coupling, but their standing-wave fields produce spatially nonuniform coupling and can limit the lifetime of cavity-enhanced spin-wave memories. This paper asks whether spontaneous emission from an atomic ensemble can instead interact with atoms in a traveling-wave manner inside a linear, helicity-preserving cavity.
The experiment uses a bias magnetic field along the cavity’s zzz axis to define the atomic quantization axis, lift Zeeman degeneracy, and break time-reversal symmetry. A Duan–Lukin–Cirac–Zoller protocol generates nonclassically correlated Stokes photons and collective atomic spin waves. For emission on a single circularly polarized atomic transition, the forward- and backward-propagating Stokes fields have opposite helicities. The chiral cavity preserves these polarizations within the atom–light interaction region, allowing the two resonant propagation directions to couple to the atoms in a traveling-wave manner rather than as a conventional standing-wave mode.
The reported experimental evidence consists of time-dependent retrieval-efficiency measurements for spin waves correlated with the forward and backward Stokes fields. The abstract states that these measurements confirm traveling-wave interactions. It provides no numerical retrieval efficiencies, storage lifetimes, correlation values, or comparison with a conventional cavity, so the magnitude of any memory-performance improvement cannot be assessed from the available material. The full text is unavailable, and the abstract states no further experimental limitations.
The non-reciprocal (unidirectional) atom-photon couplings are crucial for modern photonics ranging from chiral quantum networks to cold-atom many-body physics. In the presented experiment, we demonstrated unidirectional Raman emission of Stokes photons from 87Rb atoms in a ring cavity. A bias magnetic field B0 is applied along z-direction on the atoms to define the quantum axis, which breaks the time inverse symmetry. By transversely applying write laser pulses to drive a π-transition of the atoms, we generate spontaneous Raman emissions of Stokes photons from a chiral (σ+) transition. The emissions are coupled into the clock-wise (z-direction) and counter-clock-wise (-z-direction) modes of a running-wave cavity, respectively. According to the mirror (parity) symmetry of the atom-light coupling, we demonstrated that spins (polarizations) of the Stokes fields are correlated with their propagation directions along z and -z -axis. The Stokes emissions constrained to the spin-momentum correlation are found to be violation of Kirchhoff's law of thermal radiation. Based on the correlation, we demonstrated that the Stokes emissions propagate along the clock-wise or counter-clock-wise via polarization dissipation. The directional factor is up to 1500:1.
In this study, we demonstrated unidirectional Raman emission from cold 87 Rb atoms with a ring cavity. A bias magnetic field B 0 is applied along the z direction to define the quantization axis. By transversely applying pumping laser pulses on a π-transition of the atoms, we generate spontaneous Raman emissions of Stokes photons from an individual circularly polarized ( σ + ) transition. The emissions are coupled into the running-wave cavity where two quarter-wave plates are inserted. We observed that the Stokes field is right-hand-circularly (left-hand-circularly) polarized when propagating along the z (–z) direction. The measured polarization extinction of the Stokes field escaped from the ring cavity is beyond 1400:1. A polarization interferometer is inserted in the cavity and the two orthogonal polarization modes are spatially split when propagating in the interferometer. By blocking one arm of the interferometer, we demonstrated a chiral cavity system with the atoms in the presence of the magnetic field. On this basis, we demonstrated unidirectional Raman emissions of Stokes photons in the ring cavity. The unidirectional factor reaches ∼99.8%.
We propose a scheme of heralded storages of single photons via spontaneous Raman scattering (SRS) enhanced by a chiral standing-wave cavity, which creates a non-classically correlated pair of a spin wave and a Stokes photon (heralded photon) when a single-photon “write” pulse is applied to an atomic ensemble. In this scheme, to decrease the power of the write pulse for SRS, the write laser and the Stokes fields are aligned to propagate near-collinearly through the atoms. The short storage lifetime remains a challenge in standing-wave cavity-enhanced SRS. To prolong the storage lifetime, we achieve a long-wavelength spin-wave memory by removing the backward-scattering Stokes field from the cavity, which is realized by using non-reciprocal couplings between the Stokes fields and the atoms. In the experiment, the memory lifetime is demonstrated up to ∼100 μs, which is beyond the limitation (∼350 ns) of the storage in the atomic ensembles coupled to standing-wave cavities. We achieve a spin-wave memory for the write pulse containing a mean photon number of ∼4. The quantum correlation of the Stokes-spin-wave pairs is beyond 2, which gives strong evidence of non-classical behavior.
Abstract In the presented experiment, we demonstrated unidirectional Raman emission from 87Rb atoms in a ring cavity. A bias magnetic field B0 is applied along z-direction to define the quantum axis. By transversely applying write laser pulses to drive a π-transition of the atoms, we generate spontaneous Raman emissions of Stokes photons from a chiral (σ+) transition. The emissions are coupled into the clock-wise (z-direction) and counter-clock-wise modes (-z-direction) of a running-wave cavity, respectively. We reveal spin-momentum correlation in the Stokes emissions. The Stokes emissions constrained to the spin-momentum correlation are found to be a violation of the Kirchhoff’s law of thermal radiation. Thus, we demonstrated that the Stokes emissions can propagate along the clock-wise or counter-clock-wise mode via polarization dissipation based on the spin-momentum correlation. The directional factor is up to 1500:1.
Practical realization of quantum repeaters requires quantum memories with high retrieval efficiency, multi-mode storage capacities, and long lifetimes. Here, we report a high-retrieval-efficiency and temporally multiplexed atom-photon entanglement source. A train of 12 write pulses in time is applied to a cold atomic ensemble along different directions, which generates temporally multiplexed pairs of Stokes photons and spin waves via Duan-Lukin-Cirac-Zoller processes. The two arms of a polarization interferometer are used to encode photonic qubits of 12 Stokes temporal modes. The multiplexed spin-wave qubits, each of which is entangled with one Stokes qubit, are stored in a "clock" coherence. A ring cavity that resonates simultaneously with the two arms of the interferometer is used to enhance retrieval from the spin-wave qubits, with the intrinsic retrieval efficiency reaching 70.4%. The multiplexed source gives rise to a ∼12.1-fold increase in atom-photon entanglement-generation probability compared to the single-mode source. The measured Bell parameter for the multiplexed atom-photon entanglement is 2.21(2), along with a memory lifetime of up to ∼125 µs.
Polarization, an intrinsic ingredient of photon, plays a critical role in its interaction with matter. A general polarization state can be an appropriate superposition of two basic polarization states, say, the vertical and horizontal linear state. Here we study spontaneous emission of a V-type three-level atom(with two upper states close in energy level)strongly coupled with a single-mode damped optical cavity. By defining a general polarization state of atom as a specific superposition of the two upper quantum states, we can prepare atoms with linear polarization at arbitrary direction, left and right circular polarization, and left and right elliptical polarization, similar to photons. We find that the spontaneous emission of light from these polarized three-level atoms shows very different profiles of side and axis spectra. This means that the polarization state of three-level atoms can become an active ingredient to manipulate its interaction with light and control the quantum interference effect. Exploitation of the coherent superposition and interference of quantum states inpolarized atoms would allow one to deeply explore new frontiers of light–matter interaction.