A scheme for realizing loss-induced enhancement of optical nonlinearity in a non-Hermitian cavity quantum electrodynamics system is proposed and investigated. It is shown that the system can experience an exceptional point (EP)-based phase transition process by varying the additional loss induced on the system, which leads to nontrivial phenomena with interesting counterintuitive features. We demonstrate that the Kerr nonlinearity in the system can be counterintuitively monotonically enhanced by increasing the additional loss, meanwhile, a high on-resonance linear transmission rate of the system can be maintained. Furthermore, we also demonstrate that the loss-induced nonlinearity enhancement is beneficial for realizing broadband and robust optical frequency comb. These results indicate that the additional loss can be utilized as an alternative degree of freedom to control the nonlinear dynamics of the system based on the EP-related features, which may be used in a variety of nonlinearity-based applications ranging from information processing to precision measurement.
Parity-time (
PT) symmetric systems, which rely on the balanced gain-loss condition and render the Hamiltonian non-Hermitian, have provided a new platform to engineer effective light-matter interactions in recent years. Here we explore the high-order sideband features of the output fields obtained from a
PT-symmetric optical system consisting of a passive nonlinear cavity coupled to an active linear cavity. By employing a perturbation technique, we derive analytic formulas used to determine the nonlinear transmission coefficient of optical second-order sideband in this structure. Using experimentally achievable parameters, it is clearly shown that the efficiency of the second-order sideband generation can be greatly enhanced in the
PT-symmetric dimer, extremely in the vicinity of the transition point from unbroken- to broken-
PT regimes. Moreover, we further analyzed the influences of the system parameters, including the photon-tunneling rate between two cavities, Kerr nonlinearity strength, and optical detuning, on the second-order sideband generation. Subsequently we investigate the higher-order sideband output spectrum by numerical simulations, where the sideband amplitude also is largely enhanced in the
PT-symmetric arrangement, compared with the passive-passive double-cavity system. Our obtained results provide a new avenue for acquiring optical high-order sidebands and operating light, which may inspire further applications in chip-scale optical communications and optical frequency combs.
Nonreciprocal light propagation plays an important role in modern optical systems, from photonic networks to integrated photonics. We propose a nonreciprocal system based on a resonance-frequency-tunable cavity and intensity-adaptive feedback control. Because the feedback-induced Kerr nonlinearity in the cavity is dependent on the incident direction of light, the system exhibits nonreciprocal transmission with a transmission contrast of 0.99 and an insertion loss of 1.5 dB. By utilizing intensity-adaptive feedback control, the operating intensity range of the nonreciprocal system is broadened to 20 dB, which relaxes the limitation of the operating intensity range for nonlinear nonreciprocal systems. Our protocol paves the way to realize high-performance nonreciprocal propagation in optical systems and can also be extended to microwave systems.
Abstract We propose and analyze an effective scheme to enhance Kerr nonlinearity with a single quantum dot (QD) coupled to a gain cavity. Under the weak-excitation approximation, we derive the analytic formulas used to determine the coefficient of the nonlinear transmission by employing the perturbation technique. Using experimentally achievable parameters, we identify the conditions under which a QD gain cavity coupled system allows us to modify the linear transmission of the input probe field and enhance the Kerr nonlinearity beyond what is achievable in a QD loss cavity system. It is found that enhanced optical Kerr nonlinearity with high linear transmission rate and suppressed nonlinear absorption can be achievable even in the case of weak coupling between QD and gain cavity. The present results illustrate the potential to utilize gain cavity for enhancing optical Kerr nonlinearities and controlling the transmission of light, as well as guide the design of optical devices.
Nonlinear phenomena underpin a broad array of technologies, from electronic frequency mixers and harmonic generation to parametric amplification and optical frequency doubling. Conventional schemes for generating microwave frequency combs are constrained by intrinsic material or junction properties that require high driving powers. Here, we overcome these limitations via phase-transition physics. We show that a hybrid quantum system—composed of a solid-state spin ensemble and a nonlinear oscillator—exhibits a distinct bistable phase transition point (BP) where system response becomes both highly enhanced and nonlinear. The nonlinearity around the BP is higher order than other phase transitions, such as exceptional points, critically producing high-order frequency response which enhances nonlinear processes. Approaching the BP, we demonstrate a frequency comb with a record number of teeth at unprecedentedly low driving powers, surpassing previous results using magnonic systems and traditional diode-based approaches. These findings highlight the potential of hybrid quantum systems in advancing high-performance frequency manipulation.
Recent demonstrations of cavity quantum electrodynamics (QED) with a single quantum emitter coupled to an optical microcavity have shown the great potential of this system for engineering the light-matter interaction and developing a wide range of robust quantum devices. Here, we study the creation and all-optical control of optical frequency combs (OFCs) in photon emission from a single-quantum-emitter-microcavity QED system driven with a biharmonic pump light in the presence of a classical control light. We find that, when the strengths and phases of the applied control light are appropriately tuned, enhanced OFC generation can occur by using the parameters of currently existing QED systems. The interference between the biharmonic pump light, which is used to drive the cavity mode, and the light scattered by the two-level emitter into the cavity mode due to the second control light are responsible for the enhancement or suppression of OFCs. We further analyze in detail the influences of the other system parameters including the emitter-cavity coupling strength, the incident pump power, and all kinds of relative frequency detunings on all-optical generation of OFCs. In addition to numerical simulations demonstrating this controlled OFC effect, a complete physical explanation of the underlying mechanism is presented. The presented mechanism can be employed for tailoring and controlling OFCs in a cavity QED architecture.
The field of cavity quantum electrodynamics (QED) has seen a recent resurgence of interest in few- and many-body physics owing to the realization that the breaking of symmetries and the presence of disorder can give rise to entirely new phenomena. Here we demonstrate a few-emitter cavity QED system capable of realizing new Hamiltonians in quantum optics based on breaking of symmetries and the realization of an in situ Kerr nonlinearity. Our experiment relies on a high-finesse silicon carbide whispering gallery mode resonator hosting an ensemble of silicon vacancy color centers. The simultaneous presence of spectral and spatial disorder of the mesoscopic atom system gives rise to emergent chirality, and the optical nonlinearity of the silicon carbide host crystal enables the observation of atom-photon correlations induced by a four-photon nonlinear process. This work demonstrates the potential for solid state defect systems to realize emerging proposals and to study fundamental physics in quantum electrodynamics.