Coupled Cavity System Research Articles

Dissipative preparation of multibody entanglement via quantum feedback control

We investigate the generation of a multibody Dicke state in a coupled cavity system subject to environmental noise. Based on quantum feedback control, cavity decay may play a constructive role in obtaining the intended state. The required interaction time need not be accurately controlled. In addition, the feedback operations are only applied to a single atom in one cavity during the whole evolution process, and it is not necessary to change the control strategy as the number of atoms increases. Thus, our proposal can exploit the core advantage of coupled cavities to implement a scalable control scheme for preparing multibody entanglement.

DYNAMICS OF A COUPLED CAVITY SYSTEM COMPOSED OF THREE CAVITIES

We study the one-excitation dynamics of a coupled cavity system composed of three cavities, each containing a two-level atom. By adjusting the atom–cavity detuning Δ, cavity–cavity hopping rate v and the initial atomic excitation residential, a wide variety of time-evolution behaviors can be realized. Under certain conditions, the two-atom maximally entangled states and three-atom W states can be obtained. The results provide a theoretical basis for the manipulation of quantum states in such a system and will contribute to the understanding of more complex systems.

Geometric entangling gates for coupled cavity system in decoherence-free subspaces

We propose a scheme to implement geometric entangling gates for two logical qubits in a coupled cavity system in decoherence-free subspaces. Each logical qubit is encoded with two atoms trapped in a single cavity and the geometric entangling gates are achieved by cavity coupling and controlling the external classical laser fields. Based on the coupled cavity system, the scheme allows the scalability for quantum computing and relaxes the requirement for individually addressing atoms.

Control of two-atom entanglement with two thermal fields in coupled cavities

The dynamical evolution of a quantum system composed of two coupled cavities, each containing a two-level atom and a single-mode thermal field, is investigated under different conditions. The entanglement between the two atoms is controlled by the hopping strength and the detuning between the atomic transition and the cavities. We find that when the atomic transition is far off-resonant with both the eigenmodes of the coupled-cavity system, the maximally entangled state for the two atoms can be generated with the initial state in which one atom is in the ground state and the other is in the excited state. When both the two atoms are initially in the excited state, the entanglement exhibits periodical sudden birth and death. By choosing appropriate parameter values, the initial maximal entanglement of the two atoms can be frozen. The relation between the concurrence and the cooperative parameter is calculated.

Plasmonic coupled-cavity system for enhancement of surface plasmon localization in plasmonic detectors

A plasmonic coupled-cavity system, which consists of a quarter-wave coupler cavity, a resonant Fabry–Pérot detector nanocavity, and an off-resonant reflector cavity, is used to enhance the localization of surface plasmons in a plasmonic detector. The coupler cavity is designed based on transmission line theory and wavelength scaling rules in the optical regime, while the reflector cavity is derived from off-resonant resonator structures to attenuate transmission of plasmonic waves. We observed strong coupling of the cavities in simulation results, with an 86% improvement of surface plasmon localization achieved. The plasmonic coupled-cavity system may find useful applications in areas of nanoscale photodetectors, sensors, and an assortment of plasmonic-circuit devices.

All-optical tuning of a quantum dot in a coupled cavity system

We demonstrate a method for tuning a semiconductor quantum dot (QD) onto resonance with a cavity mode all-optically using a system comprised of two evanescently coupled cavities containing a single QD. One resonance of the coupled cavity system is utilized to generate a cavity enhanced optical Stark shift, enabling the QD to be resonantly tuned to the other cavity mode. A twenty-seven fold increase in photon emission from the QD is measured when the off-resonant QD is Stark shifted onto the cavity mode resonance, which is attributed to radiative enhancement of the QD. A maximum tuning of 0.06 nm is achieved for the QD at an incident power of 88 μW.

Quantum dynamic behaviour in a coupled cavities system

The dynamic behaviour of the two-site coupled cavities model which is doped with ta wo-level system is investigated. The exact dynamic solutions in the general condition are obtained via Laplace transform. The simple analytical solutions are obtained in several particular cases, which demonstrate the clear and simple physical picture for the quantum state transition of the system. In the large detuning or hoppling case, the quantum states transferring between qubits follow a slow periodic oscillation induced by the very weak excitation of the cavity mode. In the large coupling case, the system can be interpreted as two Jaynes-Cummings model subsystems which interact through photon hop between the two cavities. In the case of λ ≈ Δ ≫ g, the quantum states transition of qubits is accompanied by the excitation of the cavity, and the cavity modes have the same dynamic behaviours and the amplitude of probability is equal to 0.25 which does not change with the variation of parameter.

Robust Toffoli gate originating from Stark shifts

A method for synthesizing the Toffoli gate is proposed based solely on the Stark shifts of three superconducting quantum interference devices (SQUIDs). This scheme is robust against the effect of decoherence, since it operates with no excitation of SQUIDs and the coplanar waveguide cavity. The obtained fidelity of the Toffoli gate is high, corresponding to the current typical experimental parameters, and an equivalent physical model for conveniently addressing qubits is also constructed in the coupled-cavity array system.

Eigenpairs of a coupled rectangular cavity and its fundamental properties

This paper deals with the eigenvalue problem of a coupled rectangular cavity comprising five rigid walls and one flexible panel frequently employed in much literature. It is the purpose of this paper to derive explicitly the eigenpairs of the coupled cavity, which are yet to be found. First, the coupling orthogonality conditions the eigenpairs need to satisfy are derived, thereby enabling the verification of the eigenpairs newly sought or already existent. Using the coupling orthogonality conditions, the modal equation of the coupled cavity system is then obtained, permitting one to deal with a forced response of the coupled cavity. It is shown that the eigenfunctions governing the dynamics of the sound field are expressed as the infinite sum of degenerate eigenfunctions. The characteristic matrix equation is then derived, specifying the eigenpairs of the coupled cavity. In order to investigate the fundamental properties of the eigenpairs derived, a numerical analysis is conducted, revealing the presence of evanescent modes in addition to the conventional standing wave modes. Finally, an experiment is carried out, verifying the validity of the eigenpairs derived in the article.

High fidelity and flexible quantum state transfer in the atom-coupled cavity hybrid system

We investigate a system composed of N coupled cavities (linear array) and two-level atoms interacting one at a time. Adjusting appropriately the atom-field detuning, and making the hopping rate of photons between neighboring cavities, A, greater than the atom-field coupling g (i.e. A ? N 3/2 g), we can eliminate the interaction of the atom with the non-resonant normal modes reducing the dynamics to the interaction of the atom with only a single-mode. As an application of this interaction, we propose a two-step protocol for quantum communication of an arbitrary atomic quantum state between distant coupled cavities. In the ideal case, the coupled cavities system acts as a perfect quantum bus and we obtain a flexible and perfect quantum communication for any N. Considering the influence of dissipation, an interesting parity effect emerges and we still obtain a high fidelity quantum state transfer for an appreciable number of cavities with current experimental parameters. We also studied important sources of imperfections during the procedure.

Photon–quantum-dot dynamics in coupled-cavity photonic crystal slabs

We derive a master equation for the total-system density matrix to treat the evolution of quantum dots and photons in a photonic crystal slab with multiple, coupled, lossy defect cavities. In such systems, when the resonant lossy quasimodes of the system overlap in frequency and space, they are generally nonorthogonal. We find that this nonorthogonality can have important consequences for the system evolution. Our formalism allows for the calculation of multiple-photon effects in the presence of quasimode nonorthogonality. It can be applied to the calculation of strong- and weak-coupling dynamics and to first- and second-order photon correlation functions in a wide variety of complicated coupled-cavity systems. As an example, we apply the formalism to an asymmetric two-cavity photonic crystal slab and demonstrate how quasimode nonorthogonality results in oscillations in the decay of the photons out of the system.

Emission characteristics of laser-driven dissipative coupled-cavity systems

We consider a laser-driven and dissipative system of two coupled cavities with Jaynes-Cummings nonlinearity. In particular, we investigate both incoherent and coherent laser driving, corresponding to different experimental situations. We employ Arnoldi time evolution as a numerical tool to solve exactly the many-body master equation describing the nonequilibrium quantum system. We evaluate the fluorescence spectrum and the spectrum of the second-order correlation function of the emitted light field. Finally, we relate the measured spectra of the dissipative quantum system to excitations of the corresponding nondissipative quantum system. Our results demonstrate how to interpret spectra obtained from dissipative quantum systems and specify what information is contained therein.

Asymmetric Fano resonance analysis in indirectly coupled microresonators

We reveal that there exists an indirect interaction between two single-mode microcavities which have no direct coupling. This indirect interaction is mediated by coupling the two microcavities to a common waveguide, and it plays a key role in obtaining the asymmetric Fano line shape of the transport spectrum of the coupled cavity system. Finally, we show that this sharp Fano line shape can contribute to highly sensitive sensing, which is immune to most environmental variations.

Sudden change of the thermal contact between two quantum systems

In this paper, we address the issue of the stability of the thermal equilibrium of large quantum systems with respect to variations of the thermal contact between them. We study the Schrödinger time evolution of a free bosonic field in two coupled one-dimensional cavities after a sudden change of the contact between the cavities. Although this coupling is thermodynamically small, modifying it has a considerable impact on the two-point correlation functions of the system. We find that they do not return to equilibrium but essentially oscillate with a period proportional to the length of the cavities. We compare this coupled cavities system with the perfect gas, which is described by similar expressions but behaves very differently.

Experimental demonstration of impedance match locking and control for coupled resonators

We describe and verify the dynamic behavior of a novel technique to optimize and actively control the optical impedance matching condition of a coupled resonator system. The technique employs radio frequency modulation and demodulation to interrogate the reflection amplitude response of the coupled cavity system. The sign and magnitude of the demodulated signal is used in a closed loop feedback system which controls the coupling condition of a three-mirror resonator. This was done by actuating on the spacing between two of mirrors, effectively using the pair as a variable reflectivity compound mirror. We propose that this technique can be used for controlling the signal bandwidth of next-generation gravitational wave detectors, as well as optimizing circulating optical carrier power in the instrument.

Coupled mode theory analysis of mode-splitting in coupled cavity system

We analyze transmission characteristics of two coupled identical cavities, of either standing-wave (SW) or traveling-wave (TW) type, based on temporal coupled mode theory.Mode splitting is observed for both directly (cavity-cavity) and indirectly (cavity-waveguide-cavity) coupled cavity systems. The effects of direct and indirect couplings, if coexisting in one system, can offset each other such that no mode splitting occurs and the original single-cavity resonant frequency is retained. By tuning the configuration of the coupled cavity system, one can obtain different characteristics in transmission spectra, including splitting in transmission, zero transmission, Fano-type transmission, electromagnetically-induced-transparency (EIT)-like transmission, and electromagnetically-induced-absorption (EIA)-like transmission. It is also interesting to notice that a side-coupled SW cavity system performs similarly to an under-coupled TW cavity. The results are useful for the design of cavity-based devices for integration in nanophotonics.

Broadly Tunable Laser Using Double-Rings Vertically Coupled to a Passive Waveguide

A widely tunable laser source based on double microrings is presented which exhibits tuning range up to 46 nm. Two microrings consisting of active GaInAsP/InP material are vertically coupled with a straight transparent waveguide using full wafer bonding techniques. Wafer bonding allows the fabrication of ultra short couplers where the critical coupling gap can be epitaxially controlled. The microrings are operated above threshold and act as laser sources forming a coupled cavity system. Their respective radii are chosen to be slightly different, greatly extending the coupled cavity free spectral range (FSR) providing sufficiently high mode suppression ratio ( MSR > 30 dB). The isolation of adjacent rings allows an individual electrical control and enables a wavelength tuning with pm accuracy. The tuning mechanism benefits from the Vernier effect resulting in a broad range of achievable wavelengths in a systematic and repeatable way.

Development of a signal-extraction scheme for resonant sideband extraction

As a future plan, an advanced gravitational-wave detector will employ an optical configuration of resonant sideband extraction (RSE), achieved with an additional mirror at the signal-detection port of the power-recycled Fabry–Perot Michelson interferometer. To control the complex coupled cavity system, one of the most important design issues is how to extract the longitudinal control signals of the cavities. We have developed a new signal-extraction scheme which provides an appropriate sensing matrix. The new method uses two sets of sidebands: one of the sideband components satisfies the critical coupling condition for the RSE interferometer and reaches the signal-extraction port, and the other sideband is completely reflected by the Michelson interferometer. They provide a diagonalized sensing matrix and enable the RSE control to be robust.

Techniques in the optimization of length sensing and control systems for a three-mirror coupled cavity

The control of coupled cavity systems, as employed in interferometric gravitational wave detectors, depends to a large extent on the design and optimization of sensing systems that can correctly read out the length and angle degrees of freedom. As interferometer configurations become more complex, and new sensing schemes are introduced, it is important to ensure that methods are available to optimize the system parameters to allow the experimental realization to match the theoretical design. In an experimental test, on a suitable model apparatus, we show that currently available numerical modelling tools allow the development and implementation of reliable methods of setting the key system parameters. Here we present an example technique showing how these parameters can be optimized and compare the numerical model with the experimental reality. The effects of mode-matching and misalignment on the sensing signals and on the process of optimizing them are also considered.

GENERATION OF AN EPR PAIR OF ATOMS IN COUPLED CAVITIES SYSTEM VIA AN OPTICAL FIBER

The interaction between identical two-level atoms with a system that consists of two coupled cavities connected by an optical fiber was investigated. With new bosonic operators, the interaction Hamiltonian between the fiber and the cavities can be diagonalized (Pellizzari's model1). In the strong coupling regime (cavity field-fiber), the interaction between atoms and the non-resonant normal modes can be eliminated, simplifying our system to that of one atom interacting with a single-mode cavity. For this interaction, we have analyzed the entanglement between distant atoms. We present two simple procedures to generate two atoms in a maximally entangled state, interacting (i) successively and (ii) simultaneously with the coupled cavities system.