Nonreciprocal Coupling Research Articles

Dissipation engineering of nonreciprocal quantum dot circuits: An input-output approach

Nonreciprocal effects in nanoelectronic devices offer unique possibilities for manipulating electron transport and engineering quantum electronic circuits for information processing purposes. However, a lack of rigorous theoretical tools is hindering this development. Here, we provide a general input-output description of nonreciprocal transport in solid-state quantum dot architectures, based on quantum optomechanical analogs. In particular, we break reciprocity between coherently-coupled quantum dots by dissipation-engineering in which these (so-called) primary dots are mutually coupled to auxiliary, damped quantum dots. We illustrate the general framework in two representative multiterminal noninteracting models, which can be used as building blocks for larger circuits. Importantly, the identified optimal conditions for nonreciprocal behavior hold even in the presence of additional dissipative effects that result from local electron-phonon couplings. Besides the analysis of the scattering matrix, we show that a nonreciprocal coupling induces unidirectional electron flow in the resonant transport regime. Altogether, our analysis provides the formalism and working principles towards the realization of nonreciprocal nanoelectronic devices.

Photon blockade in a double-cavity optomechanical system with nonreciprocal coupling

Photon blockade is an effective way to generate single photon, which is of great significance in quantum state preparation and quantum information processing. Here we investigate the statistical properties of photons in a double-cavity optomechanical system with nonreciprocal coupling, and explore the photon blockade in the weak and strong coupling regions respectively. To achieve the strong photon blockade, we give the optimal parameter relations under different blockade mechanisms. Moreover, we find that the photon blockades under their respective mechanisms exhibit completely different behaviors with the change of nonreciprocal coupling, and the perfect photon blockade can be achieved without an excessively large optomechanical coupling, i.e., the optomechanical coupling is much smaller than the mechanical frequency, which breaks the traditional cognition. Our proposal provides a feasible and flexible platform for the realization of single-photon source.

Unraveling non-Hermitian pumping: Emergent spectral singularities and anomalous responses

Within the expanding field of non-Hermitian physics, non-Hermitian pumping has emerged as a key phenomenon, epitomized through the skin effect via extensive boundary mode accumulation modifying the conventional Bloch picture. Beyond redefining bulk-boundary correspondences, we show that non-Hermitian pumping induces an unprecedented type of spectral topology: it admits a classification in terms of graph topology, which is distinct from conventional topological classifications of the eigenstate or energy Riemann surface. Each topological class is characterized by a conformally invariant configuration of spectral branching singularities, with gap-preserving transitions giving rise to emergent band geometry and Berry curvature discontinuities physically manifested as anomalous response kinks. By placing all Hermitian and non-Hermitian lattice Hamiltonians on equal footing, our comprehensive framework also enables the first analytic construction of topological phase diagrams in the presence of multiple non-reciprocal coupling scales, as prototypically demonstrated for the extended non-Hermitian Chern and Kitaev models. Based on general algebraic geometry properties of the energy dispersion, our framework can be directly generalized to multiple bands, dimensions, and even interacting systems. Overall, it reveals the conspiracy of band representations, spectral topology, and complex geometry as it unfolds in directly measurable quantities.

Nonreciprocal Transport Based on Cavity Floquet Modes in Optomechanics

Directional transport is obtained in various multimode systems by driving multiple, nonreciprocally interfering interactions between individual bosonic modes. However, systems sustaining the required number of modes become physically complex. In our microwave-optomechanical experiment, we show how to configure nonreciprocal transport between frequency components of a single superconducting cavity coupled to two drumhead oscillators. The frequency components are promoted to Floquet modes and generate the missing dimension to realize an isolator and a directional amplifier. A second cavity left free by this arrangement is used to cool the mechanical oscillators and bring the transduction noise close to the quantum limit. We furthermore uncover a new type of instability specific to nonreciprocal coupling. Our approach is generic and can greatly simplify quantum signal processing and the design of topological lattices from low-dimensional systems.

Robust Interface-State Laser in Non-Hermitian Microresonator Arrays

We propose a scheme to achieve the analogous interface-state laser by dint of the interface between the two intermediate-resonator-coupled non-Hermitian resonator chains. We find that, after introducing the couplings between the two resonator chains and the intermediate resonator at the interface, the photons of the system mainly gather into the three resonators near the intermediate resonator. The phenomenon of the photon gathering towards the certain resonators is expected to construct the photon storage and even the laser generator. We reveal that the phenomenon is induced via the joint effect between the isolated intermediate resonator and two kinds of non-Hermitian skin effects. In particular, we investigate the interface-state laser in a topologically trivial non-Hermitian resonator array in detail. We find that the pulsed interface-state laser can be achieved accompanying with the intermittent proliferation of the photons at the intermediate resonator when an arbitrary resonator is excited. Also, we reveal that the pulsed interface-state laser in the topologically trivial non-Hermitian resonator array is immune to the on-site defects in some cases, whose mechanism is mainly induced by the nonreciprocal couplings instead of the protection of topology. Our scheme provides a promising and excellent platform to investigate interface-state laser in the microresonator array.

Subradiance dynamics in a singly excited chirally coupled atomic chain

We theoretically investigate the subradiance dynamics in a nonreciprocal chiral-coupled atomic chain, in which infinite-range dipole-dipole interaction emerges in the dissipation. We find that super- and subradiance are both present in the dissipation process following single photon excitation, and the decay dynamics shows burst emissions from uniform initial excitations, which reflects the influence of atomic ordering on the propagation of light-induced atom-atom correlations. By tuning the nonreciprocal couplings in the chiral-coupled atomic system, we show that the subradiance dynamics can be greatly modified. We further study the effect of atomic local disorder, and find occurrence of plateaus on the decay curve dependent on the defect locations, as well as persistent localized excitations induced by disorders. We also discuss the effect of imperfections of systems on the subradiance dynamics. Our results show rich opportunities in the chiral-coupled system toward photon storage and routing.

Dissipation-Induced Instabilities of a Spinor Bose-Einstein Condensate Inside an Optical Cavity.

We investigate the dynamics of a spinor Bose-Einstein condensate inside an optical cavity, driven transversely by a laser with a controllable polarization angle. We focus on a two-component Dicke model with complex light-matter couplings, in the presence of photon losses. We calculate the steady-state phase diagram and find dynamical instabilities in the form of limit cycles, heralded by the presence of exceptional points and level attraction. We show that the instabilities are induced by dissipative processes that generate nonreciprocal couplings between the two collective spins. Our predictions can be readily tested in state-of-the-art experiments and open up the study of nonreciprocal many-body dynamics out of equilibrium.

Nonreciprocal control and cooling of phonon modes in an optomechanical system.

Mechanical resonators are important components of devices that range from gravitational wave detectors to cellular telephones. They serve as high-performance transducers, sensors and filters by offering low dissipation, tunable coupling to diverse physical systems, and compatibility with a wide range of frequencies, materials and fabrication processes. Systems of mechanical resonators typically obey reciprocity, which ensures that the phonon transmission coefficient between any two resonators is independent of the direction of transmission1,2. Reciprocity must be broken to realize devices (such as isolators and circulators) that provide one-way propagation of acoustic energy between resonators. Such devices are crucial for protecting active elements, mitigating noise and operating full-duplex transceivers. Until now, nonreciprocal phononic devices3-11 have not simultaneously combined the features necessary for robust operation: strong nonreciprocity, in situ tunability, compact integration and continuous operation. Furthermore, they have been applied only to coherent signals (rather than fluctuations or noise), and have been realized exclusively in travelling-wave systems (rather than resonators). Here we describe a scheme that uses the standard cavity-optomechanical interaction to produce robust nonreciprocal coupling between phononic resonators. This scheme provides about 30 decibels of isolation in continuous operation and can be tuned in situ simply via the phases of the drive tones applied to the cavity. In addition, by directly monitoring the dynamics of the resonators we show that this nonreciprocity can control thermal fluctuations, and that this control represents a way to cool phononic resonators.

A compact low-loss one-way transmission structure based on nonreciprocal coupling

Based on Magnetic Plasmon States and the coupling effect, a compact low-loss one-way transmission structure is proposed. The structure is composed of a two-way transmission line channel and a one-way ferrite loop channel. The length of the structure has an inverse relationship with working frequency. By applying a static bias magnetic field, One-Way Edge States of ferrite on the surface of the loop are excited, which results in the unidirectional coupling between the two channels. Excellent forward transmission efficiency can be achieved due to the cutoff of the forward coupling. On the other hand, the good coupling of the reversed transmission ensures good isolation between the two ports of the two-way channel. To validate the design, a prototype has been fabricated and measured. Both the simulation and experiment results verify the low-loss one-way transmission property.

Synthetic phonons enable nonreciprocal coupling to arbitrary resonator networks.

Inducing nonreciprocal wave propagation is a fundamental challenge across a wide range of physical systems in electromagnetics, optics, and acoustics. Recent efforts to create nonreciprocal devices have departed from established magneto-optic methods and instead exploited momentum-based techniques such as coherent spatiotemporal modulation of resonators and waveguides. However, to date, the nonreciprocal frequency responses that these devices can achieve have been limited, mainly to either broadband or Lorentzian-shaped transfer functions. We show that nonreciprocal coupling between waveguides and resonator networks enables the creation of devices with customizable nonreciprocal frequency responses. We create nonreciprocal coupling through the action of synthetic phonons, which emulate propagating phonons and can scatter light between guided and resonant modes that differ in both frequency and momentum. We implement nonreciprocal coupling in microstrip circuits and experimentally demonstrate both elementary nonreciprocal functions such as isolation and gyration, as well as reconfigurable, higher-order nonreciprocal filters. Our results suggest nonreciprocal coupling as a platform for a broad class of customizable nonreciprocal systems, adaptable to all wave phenomena.

Optimization of figure of merit in magnetoplasmonic waveguides with Fe/Au multilayer for optical isolator based on nonreciprocal coupling on Si waveguides

We report on magnetoplasmonic Si waveguides with a ferromagnetic Fe/conductive metal Au multilayer for realizing a sizable magnetooptic effect with a low propagation loss for integrated optical isolators. By combining the ferromagnetic metal Fe with a highly conductive Au layer, the largest nonreciprocal differences in effective index were estimated for propagation lengths of 1–20 µm. Mode analysis with and without a Au layer clarified that the insertion of a Au layer on an Fe layer improves the optical confinement in the Fe layer with reduced propagation loss and is effective in enlarging the magnetooptic effect for the same propagation length. On the basis of the optimized Fe/Au multilayer structure, we designed waveguide optical isolators based on nonreciprocal coupling by the finite difference time domain (FDTD) method. We estimated an optical isolation of 10.8 dB with a forward insertion loss of 13.4 dB in a 34-µm-long nonreciprocal directional coupler.

Minimal Models for Nonreciprocal Amplification Using Biharmonic Drives

We present a generic system of three harmonic modes coupled parametrically with a time-varying coupling modulated by a combination of two pump harmonics, and show how this system provides the minimal platform to realize nonreciprocal couplings that can lead to gainless photon circulation, and phase-preserving or phase-sensitive directional amplification. Explicit frequency-dependent calculations within this minimal paradigm highlight the separation of amplification and directionality bandwidths, universal in such schemes. We also study the influence of counter-rotating interactions that can adversely affect directionality and associated bandwidth; we find that these effects can be mitigated by suitably designing the properties of the auxiliary mode that plays the role of an engineered reservoir to the amplification mode space.

Tunable photon statistics in a non-Hermitian system

In the present study, the antibunching effect is considered in a parity time (PT)-symmetric system, using the recently proposed non-Hermitian model for resonant cavities. The model consists of a cavity coupled to an optomechanical system by a chiral mirror, with both cavities being driven coherently. The nonreciprocal coupling strength between the two cavities leads to the generation of the non-Hermitian but PT-symmetric model. The optimal conditions of strong antibunching are calculated in this system, and then the antibunching effect is considered using the two-photon correlation function and the Wigner function. The results showed that this model presented the best control over the strong antibunching effect by tuning the nonreciprocal coupling strength between the cavities, the strength ratio between the two fields, and nonlinearity strength—an outcome inaccessible by the Hermitian system.

Asymmetric diffraction from two-component optical gratings made of passive and lossy materials.

Diffraction with asymmetric enhancement and suppression, and alternating contrast for symmetric diffraction orders is demonstrated from planar two-component optical gratings made of passive/lossy materials. Simulations agree well with the experimental diffraction pattern of the fabricated sample. Our fabrication approach uses simple, standard planar micro/nano lithography employing one photoresist and one dye. No 3D profiling is needed. The phenomena is due to the left-right asymmetric material distribution in the periodic grating, which gives rise to non-reciprocal light coupling for diffraction to the positive and negative orders.

Mode conversion in magneto photonic crystal fibre

The first concept of an integrated isolator was based on nonreciprocal TE–TM mode conversion, the nonreciprocal coupling between these modes is caused by the Faraday rotation if the magnetization is aligned along the z–axis, parallel to mode propagation.We propose to study this magneto-optical phenomenon, by the simulation of magneto photonic crystal fibre (MPCF), it consists of a periodic triangular lattice of air-holes filled with magnetic fluid which consists of magnetic nanoparticles into a BIG (Bismuth Iron Garnet) fibre. We simulated the influence of gyrotropy and the wavelength, and calculated Faraday rotation and modal birefringence. In this fibre the light is guided by internal total reflection, like classical fibres. However it was shown that they could function on a mode conversion much stronger than conventional fibres.

Magnetically-Controlled Logic Gates of Graphene Plasmons Based on Non-Reciprocal Coupling

In this paper, we propose magnetically-controlled logic gates of graphene plasmons based on non-reciprocal coupling within the multilayer graphene waveguide structure. The magnetooptical effect of semiconductor substrate leads to the difference in modal indices of graphene plasmons in opposite directions and non-reciprocal coupling, which is investigated by both coupled mode theory (CMT) and finite elements methods (FEM). Such a mechanism enables the design of magnetically- controlled not logic gate, whose output logic can be inversed by reversing the plasmons propagation directions. Furthermore, according to the Boolean algebra, we design two functional logic gates performing as or ( and ) logic gates for one direction of input plasmons, while nand ( nor ) logic gates for the reversed input direction. Minimum extinction ratios as 13.6 or 17.5 dB can be obtained for or ( nand ) or and ( nor ) logic gate. The proposed magnetically-controlled logic gates may provide new inspiration to non-reciprocal graphene plasmons devices.

Reducing Phase Noise in Multi-Phase Oscillators

This paper investigates phase noise mechanism in arrays of resonant LC oscillators. Such arrays represent today a promising solution for the generation of multi-phase signals needed in several advanced applications. The analysis presented in this paper relies on consolidated phase-domain macromodels as well as on the original concept of noise transfer function illustrated herein. The proposed analysis sheds new light on noise generation in oscillator arrays and is able to explain certain noise degradation effects observed in nonreciprocal coupling networks. Phase-domain simulation together with noise transfer function concept provide a very efficient computational tool for rapid calculations of phase response and output noise. Thanks to this efficient tool and to the gained qualitative understanding, we are able to propose a chain array configuration enhanced by the injection of a clean, low-noise signal. In this paper, it is shown how the injected chain array can provide the prescribed phase separation while significantly reducing output phase noise.

Nonreciprocal TE–TM Mode Conversion Based on Photonic Crystal Fiber of Air Holes Filled With Magnetic Fluid Into a Terbium Gallium Garnet Fiber

The nonreciprocal optical effect of Faraday rotation (FR) is widely exploited in optical isolators to suppress back-reflections to protect optical sources and other devices from injection noise, or in optical circulators to route counter-propagating signals in a single physical channel to different ports [1]. The first concept of an integrated isolator was based on nonreciprocal TE-TM mode conversion. However, most proposals of the waveguide type isolators are based on nonreciprocal TE-TM mode conversion [2], the nonreciprocal coupling between these modes is caused by the FR if the magnetization is aligned along the z-axis, parallel to mode propagation. FR effect can be used for magnet sensors, because the Verdet constant of silica fibre is small (∼1.1 rad/(T.m) at 1064 nm) [3]. In this work, we propose to study the nonreciprocal TE-TM mode conversion phenomenon, by the simulation of magneto photonic crystal fibre (MPCF). It consists of a periodic triangular lattice of air-holes filled with magnetic fluids (Fe 3 O 4 ) into a Terbium Gallium Garnet (TGG) fibre which is a kind of synthetic garnet with chemical composition Tb 3 Ga 5 O 12 . This garnet was chosen as a Faraday rotator material which has excellent transparency properties and is very resistant to laser damage. TGG has also a high Verdet constant which results in the FR effect. We simulated the influence of gyrotropy and the wavelength, and calculated the FR and modal birefringence. In this MPCF fibre, the light is guided by internal total reflection, like classical fibres. However, it was shown that they could function on a mode conversion much stronger than conventional fibres.

Graphene plasmons isolator based on non-reciprocal coupling.

In this paper we propose a graphene plasmons isolator based on non-reciprocal coupling within double graphene layer waveguide structure on a magneto-optical substrate. The difference in modal indices of graphene plasmons in opposite directions enables non-reciprocal coupling, which is theoretically investigated via coupled mode theory (CMT) and shows good agreement with numerical finite elements methods (FEM). The non-reciprocal coupling endows such system functionalities as magnetically controlled "plasmons circulator" or "plasmons isolator". For the latter case, systematical investigations of the insertion losses and isolation ratios with respect to the structural parameters, material properties, environmental parameters, fabrication errors as well as dielectric damping are presented. Theoretical investigation has shown an isolation ratio as 42 dB. The proposed plasmons circulator and isolator may serve as potential building blocks in graphene plasmons circuits.

Optical isolator based on nonreciprocal coupling of two Tamm plasmon polaritons

In this paper, we have studied the one-dimensional photonic crystal (PC) including a magneto-optical metal defect using the developed transfer matrix method for magnetic materials. Around the two interfaces between metal and one-dimensional PC, two nonsymmetric Tamm magneto-plasmon polaritons may be excited and coupled. The coupled states take on a clear nonreciprocal behavior and result in nonreciprocal transmission. The results are demonstrated through electromagnetic field distribution simulations based on finite element software. It provides a useful reference to realize optical isolator design.