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arXiv:2110.05016 · Physical Review Letters

Quantum Squeezing Induced Optical Nonreciprocity

Lei Tang, Jiang-Shan Tang, Mingyuan Chen, Franco Nori, Min Xiao, Keyu Xia

Published Feb 23, 2022• 191 citations
arXivHTMLPDF

Abstract

We propose an all-optical approach to achieve optical nonreciprocity on a chip by quantum squeezing one of two coupled resonator modes. By parametric pumping a χ^{(2)}-nonlinear resonator unidirectionally with a classical coherent field, we squeeze the resonator mode in a selective direction due to the phase-matching condition, and induce a chiral photon interaction between two resonators. Based on this chiral interresonator coupling, we achieve an all-optical diode and a three-port quasicirculator. By applying a second squeezed-vacuum field to the squeezed resonator mode, our nonreciprocal device also works for single-photon pulses. We obtain an isolation ratio of >40 dB for the diode and fidelity of >98% for the quasicirculator, and insertion loss of <1 dB for both. We also show that nonreciprocal transmission of strong light can be switched on and off by a relative weak pump light. This achievement implies a nonreciprocal optical transistor. Our protocol opens up a new route to achieve integrable all-optical nonreciprocal devices permitting chip-compatible optical isolation and nonreciporcal quantum information processing.

DOI
10.1103/physrevlett.128.083604

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We propose an all-optical approach to achieve optical nonreciprocity on a chip by quantum squeezing one of two coupled resonator modes. By parametric pumping a χ^{(2)}-nonlinear resonator unidirectionally with a classical coherent field, we squeeze the resonator mode in a selective direction due to the phase-matching condition, and induce a chiral photon interaction between two resonators. Based on this chiral interresonator coupling, we achieve an all-optical diode and a three-port quasicirculator. By applying a second squeezed-vacuum field to the squeezed resonator mode, our nonreciprocal device also works for single-photon pulses. We obtain an isolation ratio of >40 dB for the diode and fidelity of >98% for the quasicirculator, and insertion loss of <1 dB for both. We also show that nonreciprocal transmission of strong light can be switched on and off by a relative weak pump light. This achievement implies a nonreciprocal optical transistor. Our protocol opens up a new route to achieve integrable all-optical nonreciprocal devices permitting chip-compatible optical isolation and nonreciporcal quantum information processing.
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.
Abstract Optical circulators are key components for integrated photonic information processing and quantum networks, yet realizing compact and magnet-free closed-loop circulation remains challenging. We propose an on-chip four-port optical circulator consisting of three evanescently coupled microring resonators, with directional quantum squeezing introduced into the central nonlinear resonator. The squeezing selectively enhances the effective inter-resonator coupling and renormalizes the resonance frequency for one propagation direction, while leaving the counterpropagating channel unaffected. This directional asymmetry breaks optical reciprocity and enables closed-loop circulation along 1 → 2 → 3 → 4 → 1. At the optimal operating point, the circulator achieves a fidelity of approximately 0.99 and an average insertion loss of about 0.22 dB. In addition, pump-induced quantum noise can be suppressed by injecting a phase-matched broadband squeezed-vacuum field, allowing low-noise operation from the classical to the single-photon regime. The proposed scheme provides a compact, magnet-free, and chip-compatible route to closed-loop optical circulation, with potential applications in integrated optical routing and quantum photonic networks.
Nonreciprocal optical devices play a pivotal role in modern optical systems and advanced quantum technologies. Nonreciprocal devices based on optical nonlinearity have garnered significant attention due to their compatibility with on-chip photonics fabrication techniques. However, when the opposite-propagating continuous waves are incident to such nonlinear nonreciprocal devices simultaneously, achieving dynamic nonreciprocity has remained a formidable challenge. In addition, the devices relying on nonlinear resonators suffer from limited bandwidths. In this paper, we theoretically propose a method for achieving an on-chip isolator and quasicirculator by employing a nonlinear Mach-Zehnder interferometer. Harnessing the chirality between self- and cross-Kerr nonlinearities in the nonlinear arm of the interferometer, our device achieves remarkable dynamic nonreciprocity. We obtain an isolation contrast of $\ensuremath{\geqslant}0.9$ for the optical isolator and fidelity of $\ensuremath{\geqslant}0.97$ for the optical quasicirculator, and a broad bandwidth of 20nm20\phantom{\rule{3.33333pt}{0ex}}\text{nm}20nm for both. Our protocol paves a way to realize a broadband on-chip nonlinear nonreciprocal device.
We propose a theoretical method to realize nonreciprocal light transmission in an optomechanical device assisted by directional quantum squeezing. Specifically, we consider the device consisting of an optomechanical resonator and a nonlinear optical resonator with directional pumping. We find that optical squeezing occurs along the pump direction when the nonlinear resonator is directionally pumped, enabling nonreciprocal light transmission as well as nonreciprocal group delay (slow light) or advancement (fast light). Furthermore, we find that the efficiency of the second-order sidebands can be enhanced in one direction compared with the opposite direction. Our work provides a promising design for the application of directionally squeezed optomechanical devices in nonreciprocal optical communication and signal processing.
Optical nonreciprocity is important in photonic information processing to route the optical signal or prevent the reverse flow of noise. By adopting the strong nonlinearity associated with a few atoms in a strongly coupled cavity QED system and an asymmetric cavity configuration, we experimentally demonstrate the nonreciprocal transmission between two counterpropagating light fields with extremely low power. The transmission of 18% is achieved for the forward light field, and the maximum blocking ratio for the reverse light is 30 dB. Though the transmission of the forward light can be maximized by optimizing the impedance matching of the cavity, it is ultimately limited by the inherent loss of the scheme. This nonreciprocity can even occur on a few-photon level due to the high optical nonlinearity of the system. The working power can be flexibly tuned by changing the effective number of atoms strongly coupled to the cavity. The idea and result can be applied to optical chips as optical diodes by using fiber-based cavity QED systems. Our work opens up new perspectives for realizing optical nonreciprocity on a few-photon level based on the nonlinearities of atoms strongly coupled to an optical cavity.
Nanophotonic components allow the control of the flow of light in integrated optical environments. Thereby, the light’s strong confinement leads to an inherent link between its local polarization and propagation direction which fundamentally alters the physics of light-matter interaction and gives rise to phenomena such as directional emission and direction-dependent coupling strengths [1]. I will present the underlying principles of this chiral light-matter interaction and its consequences for integrated applications [1]. In particular, I will show how we employ this effect to control the direction of spontaneous emission [2] and to realize low-loss nonreciprocal transmission at the single-photon level through a silica nanofiber [3]. We use two different approaches where either an ensemble of spin-polarized atoms is weakly coupled to a nanofiber or a single atom is strongly coupled to the nanofiber via a whispering-gallery-mode resonator. The resulting optical isolators show a strong imbalance between the transmissions in forward and reverse direction and, at the same time, a forward transmissions exceeding 70%. We extended this system to a 4-port device, where a single atom routes photons nonreciprocally from one fiber port to the next. This realizes a quantum optical circulator [4] which can even be prepared in a superposition of its operational modes. The demonstrated systems exemplify a new class of (quantum) nanophotonic devices that are ideally suited for photonic quantum information processing and quantum simulation. [1] Nature 541, 473, (2017). [2] Science 346, 67 (2014). [3] Phys. Rev. X 5, 041036 (2015). [4] Science 354, 1577 (2016).