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Science Advances

All-optical reversible single-photon isolation at room temperature

Ming‐Xin Dong, Keyu Xia, Weihang Zhang, Yichen Yu, Ying-Hao Ye, Enze Li, Lei Zeng, Dong-Sheng Ding, Bao-Sen Shi, Guang‐Can Guo, Franco Nori

Published Mar 19, 2021• 90 citations
Publisher

Abstract

Nonreciprocal devices operating at the single-photon level are fundamental elements for quantum technologies. Because magneto-optical nonreciprocal devices are incompatible for magnetic-sensitive or on-chip quantum information processing, all-optical nonreciprocal isolation is highly desired, but its realization at the quantum level is yet to be accomplished at room temperature. Here, we propose and experimentally demonstrate two regimes, using electromagnetically induced transparency (EIT) or a Raman transition, for all-optical isolation with warm atoms. We achieve an isolation of 22.52 ± 0.10 dB and an insertion loss of about 1.95 dB for a genuine single photon, with bandwidth up to hundreds of megahertz. The Raman regime realized in the same experimental setup enables us to achieve high isolation and low insertion loss for coherent optical fields with reversed isolation direction. These realizations of single-photon isolation and coherent light isolation at room temperature are promising for simpler reconfiguration of high-speed classical and quantum information processing.

DOI
10.1126/sciadv.abe8924

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Nonreciprocal devices operating at the single-photon level are fundamental elements for quantum technologies. Because magneto-optical nonreciprocal devices are incompatible for magnetic-sensitive or on-chip quantum information processing, all-optical nonreciprocal isolation is highly desired, but its realization at the quantum level is yet to be accomplished at room temperature. Here, we propose and experimentally demonstrate two regimes, using electromagnetically induced transparency (EIT) or a Raman transition, for all-optical isolation with warm atoms. We achieve an isolation of 22.52 ± 0.10 dB and an insertion loss of about 1.95 dB for a genuine single photon, with bandwidth up to hundreds of megahertz. The Raman regime realized in the same experimental setup enables us to achieve high isolation and low insertion loss for coherent optical fields with reversed isolation direction. These realizations of single-photon isolation and coherent light isolation at room temperature are promising for simpler reconfiguration of high-speed classical and quantum information processing.
Abstract Nonreciprocal devices, such as isolators, are of great importance for optical communication and optical information processing. To bypass the limitation of a strong magnetic field imposed by the traditional Faraday magneto-optic effect, many alternative mechanisms have been proposed to demonstrate magnetic-free nonreciprocity. However, limited by the drive-induced noise, the noiseless isolator capable of working in the quantum regime has yet to be realized in the experiment. Here, we show a noiseless all-optical isolator with genuine single photons in hot atoms. We experimentally study this mechanism using an open V-type level scheme and demonstrate a low insertion loss of 0.6 dB and high isolation of 30.3 dB with bandwidth up to hundreds of megahertz. Furthermore, the nonreciprocal direction can be truly reversed only by tuning the frequency of the pump laser with the same setup. Our scheme relies on widely used optical technology and is thus universal and robust.
On-chip single-photon nonreciprocal devices with high isolation and low insertion loss become a key element in quantum information processing. Based on electromagnetically induced transparency in chiral quantum systems, a single-photon isolator and a single-photon circulator are obtained without requiring unbalanced coupling. These devices have high isolation and low insertion loss. Moreover, their bandwidths are significantly broadened with the assistance of electromagnetically induced transparency.
Breaking optical reciprocity enables new regimes of light--matter interaction with broad implications for fundamental physics and emerging quantum technologies. Although various approaches have been explored to achieve optical nonreciprocity, realizing it at the single-photon level has remained a major challenge. Here, we demonstrate nonmagnetic optical nonreciprocity -- including both isolation and circulation -- in the quantum regime, enabled by efficient and noiseless all-optical frequency conversion on an integrated III-V photonic chip. Our device preserves the quantum coherence and entanglement of the input photons while delivering exceptional performance parameters, including a high extinction ratio of 34 dB, low insertion loss of 0.8 dB, broad bandwidth of 44 GHz, high operational fidelity of 97%, and widely tunable operation wavelength. This realization of quantum optical nonreciprocity in a scalable photonic platform opens a pathway toward directional quantum communication and noise-resilient quantum networks.
Breaking electromagnetic reciprocity enables directional control of light and is essential for both classical and quantum photonic systems. However, realizing integrated optical nonreciprocity that simultaneously combines low loss, broad bandwidth, and compatibility with quantum states of light remains a major challenge. Here, we demonstrate optical nonreciprocity based on quantum frequency conversion in an integrated [Formula: see text] nonlinear waveguide. Operating from classical power levels down to the single-photon level, the device preserves quantum coherence and entanglement of the input photons. We achieve an isolation of 34 decibels with a low on-chip insertion loss of 0.8 decibels and a broad isolation bandwidth, together with a four-port circulator exhibiting an operational fidelity of up to 0.97. Our results establish parametric frequency conversion as a scalable and quantum-compatible route toward integrated nonreciprocal photonic devices for applications in quantum communication and noise-resilient photonic networks.
Nonreciprocal optical devices are essential for laser protection, modern optical communication and quantum information processing by enforcing one-way light propagation. The conventional Faraday magneto-optical nonreciprocal devices rely on a strong magnetic field, which is provided by a permanent magnet. As a result, the isolation direction of such devices is fixed and severely restricts their applications in quantum networks. In this work, we experimentally demonstrate the simultaneous one-way transmission and unidirectional reflection by using a magneto-optical Fabry–Pérot cavity and a magnetic field strength of 50 mT. An optical isolator and a three-port quasi-circulator are realized based on this nonreciprocal cavity system. The isolator achieves an isolation ratio of up to 22 dB and an averaged insertion loss down to 0.97 dB. The quasi-circulator is realized with a fidelity exceeding 99% and an overall survival probability of 89.9%, corresponding to an insertion loss of ∼0.46 dB. The magnetic field is provided by an electromagnetic coil, thereby allowing for reversing the light circulating path. The reversible quasi-circulator paves the way for building reconfigurable quantum networks.
A scheme for magnetic-free optical nonreciprocity in an ensemble of four-level cold atoms is proposed by exploiting the directional four-wave mixing effect. Using experimentally achievable parameters, the nonreciprocal optical responses of the system can be observed and the conversion on nonreciprocal transmission and nonreciprocal phase shift can be implemented. These nonreciprocal phenomena originate from the directional phase matching, which breaks the time-reversal symmetry and dynamic reciprocity of the cold atomic system. Moreover, by embedding the cold atoms into a Mach-Zehnder interferometer and choosing proper parameters, a two-port optical isolator with an isolation ratio of 79.70 dB and an insertion loss of 0.35 dB and a four-port optical circulator with a fidelity of 0.9985 and a photon survival probability of 0.9278 can be realized, which shows the high performance of isolation and circulation. The proposal may enable a new class of optically controllable cavity-free nonreciprocal devices in optical signal processing at the low light level.