Cavity Coupling Research Articles

Phase-Difference-Dependent Surface Plasmon Polariton Waveguide Coupling in a Symmetrical Dual-Channel Metal-Insulator-Metal Structure

This work reports a phase difference modulated coupling of two surface plasmon polariton (SPP) sources in a symmetrical two-channel metal-insulator-metal (MIM) waveguide device. In the device, two sources with different initial phases interact indirectly through the function of a rectangular cavity. With the phase difference varying, we have achieved tunable SPP coupling followed by continuously adjustable filtering property and Fano resonance. Further results show that the tunable SPP coupling in the resonance cavity can be well described by the electromagnetic wave interference theory. Moreover, we have also demonstrated the excellent performance of this phase-difference-dependent MIM waveguide in refractive-index sensing and have achieved considerable sensitivity as high as 818.8 nm/RIU. This research has great significance for tunable filtering and signal compensation in MIM waveguide-based photonic chips and also provides a device with high potential in refractive-index sensing.

Modeling and Vibro-acoustic Characterization of Elastic Plate-Irregular Hexahedral Acoustic Cavity Coupling Systems

Modeling and Vibro-acoustic Characterization of Elastic Plate-Irregular Hexahedral Acoustic Cavity Coupling Systems

PT symmetric single-mode line-defect photonic crystal lasers with asymmetric loss design.

The exploration of parity-time (PT) symmetry in micro-/nano-cavity lasers has recently gained immense research interest. The PT symmetric phase transition to single-mode lasing has been achieved by arranging the spatial distribution of optical gain and loss in single or coupled cavity systems. In terms of photonic crystal (PhC) lasers, a non-uniform pumping scheme is usually employed to enter the PT symmetry-breaking phase in a longitudinal PT symmetric system. Instead, we use a uniform pumping scheme to enable the PT symmetric transition to the desired single lasing mode in line-defect PhC cavities based on a simple design with asymmetric optical loss. The flexible control of gain-loss contrast is realized by removing a few rows of air holes in PhCs. We obtain single-mode lasing with a side mode suppression ratio (SMSR) of around 30 dB without affecting the threshold pump power and linewidth. The output power of the desired mode is six times higher than that in multimode lasing. This simple approach enables single-mode PhC lasers without sacrificing the output power, threshold pump power, and linewidth of a multimode cavity design.

Hybrid states of a cavity-photon–vortex coupled system in a superconductive cavity

As the Abrikosov vortex lattice has recently been found in van der Waals heterostructures constructed by a two-dimensional (2D) ferromagnet and a superconductor, we propose the realization of cavity-photon–vortex coupling in a superconductive cavity to construct a new hybrid quantum system in this paper. We study the corresponding hybrid states therein, including the exceptional lines (ELs) in the parameter space. Considering that the parameters of our system are adjustable by external magnetic field and temperature, our system and the ELs are much easier to be realized in experiments. Furthermore, the numerical results show that the corresponding hybrid states can be switched by tuning the source of AC, which makes this hybrid system more advantageous to realize hybrid quantum computing in the future. Moreover, for practical use in detecting hybrid states and the vortex dynamics, the transmission amplitude of an external transverse electric wave through the cavity is also studied.

Effective non-adiabatic holonomic quantum computation of cavity modes via invariant-based reverse engineering.

In this paper, we propose a protocol to realize non-adiabatic holonomic quantum computation (NHQC) of cavity modes via invariant-based reverse engineering. Coupling cavity modes with an auxiliary atom trapped in a cavity, we derive effective Hamiltonians with the help of laser pulses. Based on the derived Hamiltonians, invariant-based reverse engineering is used to find proper evolution paths for NHQC. Moreover,the systematic-error-sensitivity nullified optimal control method is considered in the parameter selections, making the protocol insensitive to the influence of systematic errors of pulses. We also estimate the imperfections induced by random noise and decoherence. Numerical results show that the protocol holds robustness against these imperfections. Therefore, the protocol may provide useful perspectives to quantum computation with optical qubits in cavity quantum electrodynamics systems. This article is part of the theme issue 'Shortcuts to adiabaticity: theoretical, experimental and interdisciplinary perspectives'.

Compact Wide-Beam Circularly Polarized End-Fire Antenna Combining Ground Radiation Mode and Vertically Polarized Mode

A compact wide-beam endfire antenna with ground radiation mode and vertically polarized mode for circular polarization (CP) is presented in this article. The antenna is constructed based on a configuration of coupled-mode patch antenna (CMPA), which consists of two coupling cavities with a shorting wall, and can generate vertically polarized modes. The CP is realized through a pair of orthogonally polarized modes of horizontal and vertical polarizations. Meanwhile, rendering them acquires an equal amplitude and a 90° phase difference. The horizontally polarized radiation mode is realized through inserting a crossed ground slot. Offset probe feed is used to excite all the radiation modes and introduce an additional phase shift for the CP. A set of offset ground slots (OGSs) are then applied to perturb the electromagnetic coupling of the modes and adjust the phase and magnitude of the radiating electric fields (E-fields). Several effects are synthesized, which results in a wide-beam circularly polarized (CP) endfire radiation. Aiming to improve the radiation performances, a cavity-backed planar reflector was applied in the experiment. Simulated and measured results are detailed and analyzed, which demonstrate that the measured 3 dB axial ratio (AR < 3 dB) bandwidth (ARBW) ranges from 3.385 to 3.428 GHz (1.2%), and the peak gain can be up to 3.4 dBi if the planar reflector is added. The measured half-power beamwidth (HPBW) and 3 dB ARBW can be up to 88°/114° and 53°/112° at 3.4 GHz, respectively. The antenna size (excluding the reflector) is maintained at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.49\lambda _{0}\times 0.25\lambda _{0}\times 0.017\lambda _{0}$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> is the wavelength in free space, performing a compact configuration.

Plasmon–exciton coupling in a dimer cavity revisited: effect of excitonic dipole orientation

We revisit plasmon–exciton coupling of a single emitter in a dimer cavity, featuring the analysis of how the excitonic dipole orientation influences the coupling behaviour from both the spectral and temporal aspects. Results demonstrate that the dipolar mode could be suppressed to vanish while the magnitude of the pseudomode could only be suppressed to half of the maximum value. The temporal analysis gives further evidence of this effect on the dipolar mode and pseudomode. The analysis might have potential significance on the experimental community as the excitonic dipole orientation could be precisely measured and has a rather important impact on the experiments.

Polariton enhanced free charge carrier generation in donor-acceptor cavity systems by a second-hybridization mechanism.

Cavity quantum electrodynamics has been studied as a potential approach to modify free charge carrier generation in donor-acceptor heterojunctions because of the delocalization and controllable energy level properties of hybridized light-matter states known as polaritons. However, in many experimental systems, cavity coupling decreases charge separation. Here, we theoretically study the quantum dynamics of a coherent and dissipative donor-acceptor cavity system, to investigate the dynamical mechanism and further discover the conditions under which polaritons may enhance free charge carrier generation. We use open quantum system methods based on single-pulse pumping to find that polaritons have the potential to connect excitonic states and charge separated states, further enhancing free charge generation on an ultrafast timescale of several hundred femtoseconds. The mechanism involves polaritons with optimal energy levels that allow the exciton to overcome the high Coulomb barrier induced by electron-hole attraction. Moreover, we propose that a second-hybridization between a polariton state and dark states with similar energy enables the formation of the hybrid charge separated states that are optically active. These two mechanisms lead to a maximum of 50% enhancement of free charge carrier generation on a short timescale. However, our simulation reveals that on the longer timescale of picoseconds, internal conversion and cavity loss dominate and suppress free charge carrier generation, reproducing the experimental results. Thus, our work shows that polaritons can affect the charge separation mechanism and promote free charge carrier generation efficiency, but predominantly on a short timescale after photoexcitation.

Low frequency-to-intensity noise conversion in a pulsed laser cavity locking by exploiting carrier envelope offset

We report on the dependence of the frequency-to-intensity noise conversion in the locking of an ultrafast laser against a high-finesse optical enhancement resonator from the carrier envelope offset frequency. By a proper combination of the cavity finesse and laser carrier envelope offset frequency, it is possible to optimize the signal-to-noise ratio of the laser intensity trapped into the optical resonator. In this paper, we describe the effect of the laser-enhancement cavity coupling on the intracavity power relative noise, and we demonstrate both theoretically and experimentally its reduction.

Synchronization of Optomechanical Oscillators in Coupled 1D Optomechanical Crystal Nanobeam Cavities

We proposed a new optomechanical system (OMS) based on parallel suspended one-dimensional optomechanical crystal (1D-OMC) nanobeam cavities for optomechanical synchronization. The optomechanical oscillators (OMOs) were spaced apart by an air-slot gap and coupled through optical radiation fields. The numerical simulation showed that the evolution process of 1D-OMC nanobeam cavities to mechanical synchronization could be divided into three clear stages. The synchronization of two mechanical breathing modes at 5.8846 GHz was achieved by using a single laser source. Finally, we investigated the relationship between the threshold power and detuning of an input laser for self-sustaining and synchronization states. Such chip-based structures hold great potential for large-scale synchronized oscillator networks.

Continuous-wave and passively Q-switched pulsed 1.5 µm Er:Yb:Ba3Gd(PO4)3 lasers.

An eye-safe 1567 nm continuous-wave laser with a maximum output power of 50 mW and a slope efficiency of 21.1% was demonstrated in an Er:Yb:Ba3Gd(PO4)3 crystal. By using a Co2+:MgAl2O4 crystal with an initial transmission of 95% as a saturable absorber, a stable passively Q-switched pulsed laser was also realized in the crystal. The effects of the output coupler transmission and cavity length on pulsed performance were investigated. At an absorbed pump power of 350 mW, a 1541 nm Er:Yb:Ba3Gd(PO4)3 pulsed laser with a repetition frequency of 0.86 kHz, duration of 38 ns, energy of 21.2 µJ, and peak output power of 0.56 kW was obtained.

High finesse bow-tie cavity for strong atom-photon coupling in Rydberg arrays.

We report a high-finesse bow-tie cavity designed for atomic physics experiments with Rydberg atom arrays. The cavity has a finesse of 51,000 and a waist of 7.1 μm at the cesium D2 line (852 nm). With these parameters, the cavity is expected to induce strong coupling between a single atom and a single photon, corresponding to a cooperativity per traveling mode of 35 at the cavity waist. To trap and image atoms, the cavity setup utilizes two in-vacuum aspheric lenses with a numerical aperture (NA) of 0.35 and is capable of housing NA = 0.5 microscope objectives. In addition, the large atom-mirror distance (≳1.5 cm) provides good optical access and minimizes stray electric fields at the position of the atoms. This cavity setup can operate in tandem with a Rydberg array platform, creating a fully connected system for quantum simulation and computation.

Large Single-Phonon Optomechanical Coupling Between Quantum Dots and Tightly Confined Surface Acoustic Waves in the Quantum Regime

Surface acoustic waves (SAWs) coupled to quantum dots (QDs), trapped atoms and ions, and point defects have been proposed as quantum transduction platforms, yet the requisite coupling rates and cavity lifetimes have not been experimentally established. Although the interaction mechanism varies, small acoustic cavities with large zero-point motion are required for high efficiencies. We experimentally establish the feasibility of this platform through electro- and optomechanical characterization of tightly focusing, single-mode Gaussian SAW cavities at approximately 3.6 GHz on $\mathrm{Ga}\mathrm{As}$. We explore the performance limits of the platform by fabricating SAW cavities with mode volumes approaching $6{\ensuremath{\lambda}}^{3}$ and linewidths less than 1 MHz. Employing strain-coupled single $\mathrm{In}\mathrm{As}$ QDs as optomechanical intermediaries, we measure single-phonon optomechanical coupling rates ${g}_{0}\ensuremath{\approx}2\ensuremath{\pi}\ifmmode\times\else\texttimes\fi{}1.2$ MHz. Sideband scattering rates thus exceed intrinsic phonon loss, indicating the potential for quantum optical readout and transduction of cavity phonon states. To demonstrate the feasibility of this platform for low-noise ground-state quantum transduction, we develop a fiber-based confocal microscope in a dilution refrigerator and perform single-QD resonance fluorescence sideband spectroscopy at millikelvin temperatures. These measurements show conversion between microwave phonons and optical photons with sub-natural linewidths.

Strong-coupling quantum thermodynamics far from equilibrium: Non-Markovian transient quantum heat and work

In this paper, we investigate the strong-coupling quantum thermodynamics of a hybrid quantum system far from equilibrium, based on the renormalization theory of quantum thermodynamics we developed recently [Phys. Rev. Research 4, 023141 (2022)]. The strong-coupling hybrid system consists of a superconducting microwave cavity and a spin ensemble of the NV centers in diamond under external driving. The non-Markovian dynamics of this strong-coupling hybrid system has been experimentally explored and theoretically investigated. We apply the renormalization theory of quantum thermodynamics to study the transient quantum heat and work in this strong-coupling hybrid system. We find that the dissipation and fluctuation dynamics of the system induce the transient quantum heat current which shows significant non-Markovian effects. On the other hand, the energy and driving field renormalization produces quantum work power. In particular, the driving-induced work power can be largely enhanced by non-Markovian dynamics through the cavity coupling strongly with the spin ensemble at the resonance. Our results show that non-Markovian dynamics makes faster energy conversion of the heat and work.

A review on quantum information processing in cavities

The processing of information and computation is undergoing a paradigmatic shift since the realization of the enormous potential of quantum features to perform these tasks. Coupled cavity array is one of the well-studied systems to carry out these tasks. It is a versatile platform for quantum networks for distributed information processing and communication. Cavities have the salient feature of retaining photons for longer durations, thereby enabling them to travel coherently through the array without losing them in dissipation. Many quantum information protocols have been implemented in arrays of coupled cavities. These advancements promise the suitability of cavity arrays for large-scale quantum communications and computations. This article reviews a few theoretical proposals and experimental realizations of quantum information tasks in cavities.

Unidirectional Coherent Phonon Emission in an Optomechanic Nanobeam Containing Coupled Cavities

Nonreciprocal phonon emission is predicted theoretically from the coherent excitation of two coupled optomechanical cavities arranged along a phoxonic crystal nanobeam. The latter consists of a periodic array of holes and stubs and exhibits simultaneous photonic and phononic bandgaps. It is shown that nonreciprocal phonon emission arises from a combined effect of the spatial symmetry of the cavities and their underlying coupled phononic modes and the temporal phase shift between the excitation sources. This demonstration paves the way for the development of advanced integrated phonon networks and circuits, in which mechanical waves connect different elements in phononic and optomechanical structures.

Resonant Coupling of Hermite-Gaussian Transverse Modes in the Triangular Cavity of a Cavity Ring-down Spectroscope

During resonance in resonant cavities, such as those used in laser or cavity ring-down spectroscopes (CRDS), resonant coupling between higher-order transverse modes and fundamental modes can seriously affect the quality of the beam and introduce measurement errors. Several coupling models, such as thermal deformation coupling and scattering coupling, have been established according to existing coupling theory and specific application scenarios; however, these coupling models have not been attributed to a unified theory. In this paper, we reveal that the same resonant coupling excitation factors exist under different types of environmental perturbation. The conditions and range of resonant coupling in a CRDS ring-down cavity are systematically analyzed, and a preferential coupling model of the middle-order modes is proposed. The time-domain characteristics of the CRDS are used in experiments to analyze the resonant coupling between the modes in a weak energy system. The order and coupling range of the middle-order modes involved in resonant coupling are verified using the modal filtering characteristics of the triangular cavity; this paper presents a unified explanation for various types of resonant coupling and also provides a new approach to resonant coupling experiments performed in high-finesse resonant cavities.

Role of Symmetry Breaking in Observing Strong Molecule-Cavity Coupling Using Dielectric Microspheres.

The emergence of dielectric open optical cavities has opened a new research avenue in nanophotonics. In particular, dielectric microspheres support a rich set of cavity modes with varying spectral characteristics, making them an ideal platform to study molecule–cavity interactions. The symmetry of the structure plays a critical role in the outcoupling of these modes and, hence, the perceived molecule–cavity coupling strength. Here, we experimentally and theoretically study molecule–cavity coupling mediated by the Mie scattering modes of a dielectric microsphere placed on a glass substrate and excited with far-field illumination, from which we collect scattering signatures both in the air and glass sides. Glass-side collection reveals clear signatures of strong molecule–cavity coupling (coupling strength 2g = 74 meV), in contrast to the air-side scattering signal. Rigorous electromagnetic modeling allows us to understand molecule–cavity coupling and unravel the role played by the spatial mode profile in the observed coupling strength.

Study of SGEMP Field-Coupling Inside and Outside Reentrant Cavity

This article studies system-generated electromagnetic pulse (EMP) and coupling in a reentrant cavity—a simplified spacecraft model with the annular slit and internal shaft, numerically by using the three-dimensional conformal particle-in-cell method. The results indicate that when the electromagnetic fields arrive at the annular slit, obvious field-coupling will be induced that EMP may enter or escape from the slit without many restrictions at the low-irradiation fluence. In this case, the total field can be acquired by linearly summing the EMPs derived from the moving electrons released separately by the external and internal emitting surfaces. The reentrant cavity is to form a repetitive-oscillating capacitor model, while the electromagnetic waves of damped oscillation with comparatively large amplitude are found near the annular slit and the internal shaft. The frequency of the damped oscillation is mainly influenced by the cavity geometrical factor and is going to converge to the natural frequency of the reentrant cavity. Furthermore, the reason accounting for the change of both the frequencies is revealed.

A Triple-Quasi-TEM-Resonance Dielectric Cavity for Bandpass Filter Design

This letter presents a triple-quasi-TEM-resonance dielectric cavity for compact bandpass filter design. The proposed dielectric cavity is silver coated and has three blind holes which form three distinct quasi-TEM mode resonators. The external coupling structure for the resonator is realized by tapping hole. The inter-resonator couplings are realized and controlled by slots on the outer surfaces of the dielectric block. A three-pole filter with two controllable transmission zeros is designed and implemented. The measured results agree well with the simulated results, verifying the proposed triple-resonance dielectric cavity structure and coupling mechanisms.