Single-mode Cavity Field Research Articles

Enhanced photon antibunching via interference effects in a Δ configuration

Photon antibunching based on a single two-level atom strongly coupled to a single-mode optical cavity has been demonstrated in experiments. Here, we put forward an improved version of such an antibunching by introducing a pump field and a microwave field in the coupled atom-cavity system to form both a three-level $\mathrm{\ensuremath{\Delta}}$-type transition and closed-loop coupling. Via calculating the zero-time-delay second-order correlation function ${g}^{(2)}(0)$ of the single-mode cavity field, we find that a complete photon blockade, namely, ${g}^{(2)}(0)=0$, can be well achieved without detuning the driving and cavity resonance. In addition, it is clearly shown that this strong photon antibunching effect appears in the weak-coupling regime of light-atom interactions. The enhanced photon antibunching is ascribed to quantum interference between the two transition paths from the three-level $\mathrm{\ensuremath{\Delta}}$ atom weakly coupled to the three involved fields (cavity, pump, and microwave). Our proposal is useful for the single-photon generation by photon blockade, which has applications in quantum information processing.

The occurrence of multistability and normal mode splitting in an optomechanical system

We provide a theoretical technique to study the occurrence of multistability and normal mode splitting in an optomechanical system driven by a single mode cavity field. For this purpose, we consider the position-dependent mass mechanical resonator (PDMR) which produces the nonlinearity in the system. This shifts the system from monostable to bistable regime and bistable to a multistable regime at different conditions of the nonlinearity. Further, we use the Fourier transform technique to find out the fluctuation in the position of the nano-mechanical resonator and their energy spectrum as well. Moreover, we used the input-output theory to analyze the transmitted field spectrum as well as x and y quadratures spectra of the output field. We explain the effect of the non-linearity on the normal mode splitting of the former and later spectra. In addition, we also explain the normal mode splitting as a function of cavity decay rate and laser power, respectively.

The damped interaction between a single-mode cavity field with Caldirola–Kanai Hamiltonian and a three-level atom

In this paper, we studied the damped interaction between a Λ-type three-level atom and a quantized single-mode cavity field, where the cavity field features a damped harmonic oscillator with a time-dependent mass that is described by the so-called Caldirola–Kanai (CK) Hamiltonian. Assuming that, initially, the atom is prepared in a superposition state and the field is prepared in coherent states, the temporal behavior of the atomic population inversion, von Neumann entropy, fidelity and Husimi function Q have been investigated by numerically solving the master equation.

Generation of entanglement between two three-level atoms interacting with a time-dependent damping field

In this article, the interaction between two Λ-type three-level atoms and a single-mode cavity field is discussed. The damping parameter is taken into account. Also, the field and the atoms are assumed to be coupled with modulated coupling parameter which depends explicitly on time. Even though the system seems complicated, the analytical form of the wave function and the probability amplitudes are exactly obtained. To comprehend the degree of entanglement between subsystems (field-atom and atom-atom), the dynamics of entanglement through various measures, namely, concurrence and negativity is evaluated. Also, the Mandel parameter and normal squeezing of the resultant state have been calculated. In each case, the influences of damping parameter on the above criteria are numerically analyzed, in detail. It is illustrated that the degree of entanglement can be generated by taking the evolved parameters, appropriately.

Dissipation-driven nonclassical-state generation in optomechanics with squeezed light

We study an optomechanical system for the purpose of generating a nonclassical mechanical state when a mechanical oscillator is quadratically coupled to a single-mode cavity field driven by a squeezed optical field. The system corresponds to a regime where the optical dissipation dominates both the mechanical damping and the optomechanical coupling. We identify that multi-phonon processes emerge in the optomechanical system and show that a mechanical oscillator prepared in the ground state will evolve into an amplitude-squared squeezed vacuum state. The Wigner distribution of the steady state of the mechanical oscillator is non-Gaussian exhibiting quantum interference and four-fold symmetry. This nonclassical mechanical state, generated via reservoir engineering, can be used for quantum correlation measurements of the position and momentum of the mechanics below the standard quantum limit.

Enhancing Squeezing and Nonclassicality of Light in Atom–Optomechanical Systems

AbstractQuadrature squeezing of light is investigated in a hybrid atom–optomechanical system comprising a cloud of two‐level atoms and a movable mirror mediated by a single‐mode cavity field. When the system is at high temperatures with quadrature fluctuations of light much above the standard quantum limit (SQL), excitation counting on the collective atomic state can effectively reduce the light noise close to the SQL. When the system is at low temperatures, considerable squeezing of light below the SQL is found at steady state. The squeezing is enhanced by simply increasing the atom–light coupling strength with the laser power optimized close to the unstable regime, and further noise reduction is achieved by decreasing the various losses in the system. The presence of atoms and excitation counting on the atoms lessen the limitation of thermal noise, and the squeezing can be achieved at an environment temperature of the order K. The nonclassicality of the light, embodied by the negative distributions of the Wigner function, is also studied by making non‐Gaussian measurements on the atoms. It is shown that with feasible parameters, excitation counting on the atoms is effective in inducing strongly optical nonclassicality.

One- and three-photon dynamical Casimir effects using a nonstationary cyclic qutrit

We consider the nonstationary circuit QED setup in which a 3-level artificial atom in the $\Delta$-configuration interacts with a single-mode cavity field of natural frequency $\omega $. It is demonstrated that when some atomic energy level(s) undergoes a weak harmonic modulation, photons can be generated from vacuum via effective 1- and 3-photon transitions, while the atom remains approximately in the ground state. These phenomena occur in the dispersive regime when the modulation frequency is accurately tuned near $\omega $ and $3\omega $, respectively, and the generated field states exhibit strikingly different statistics from the squeezed vacuum state attained in standard cavity dynamical Casimir effect.

A simple model for a minimal environment: the two-atom Tavis–Cummings model revisited

ABSTRACTIndividual quantum systems may be interacting with surrounding environments having a small number of degrees of freedom. Here we discuss a simple toy model: a system constituted by a two-level atom (atom 1) interacting with a single mode cavity field which is (weakly) coupled to a small environment (atom 2). We investigate the influence of the minimal environment on the dynamics of the linear entropy and the atomic dipole squeezing of atom 1, as well as the entanglement between atom 1 and the field. We also obtain the full analytical solution of the two-atom Tavis–Cummings model for both arbitrary coupling strengths and frequency detunings, necessary to analyse the influence of the field-environment detuning on the evolution of the system’s quantum properties. For complementarity, we discuss the role of the degree of mixedness of the environment by analysing the time-averaged linear entropy of atom 1.

Damping in the Interaction of a Field and Two Three-Level Atoms Through Quantized Caldirola–Kanai Hamiltonian

We investigate the damped interaction between two Λ-type three-level atoms and a quantized single-mode cavity field, for which the Hamiltonian of the field is rewritten in Caldirola–Kanai form. We obtain the wave functions for the case where the two atoms are initially prepared in arbitrary pure states and the field is initially prepared in the coherent state. We investigate numerically the influence of the damping parameter on the temporal behavior of the Mandel Q-parameter, linear entropy, and normal squeezing. We find the damping parameter and initial atomic states to play central roles in the nonclassical features and the degree of entanglement.

QuTiP-package applications to five-level atom with one mode

In this poster, we apply the Quantum Toolbox in Python (QuTiP) to study the interaction between a five-level atom and a single-mode cavity field. The non-classical statistical aspects such as the Mandel Q parameter, squeezing parameter, and linear entropy are investigated.

Multiple electromechanically-induced-transparency windows and Fano resonances in hybrid nano-electro-optomechanics

We show multiple electromechanically-induced transparency (EMIT) windows in a hybrid nano-electro-optomechanical system in the presence of two-level atoms coupled to a single-mode cavity field. The multiple EMIT-window profile can be observed by controlling the atom field coupling as well as Coulomb coupling between the two charged mechanical resonators. We derive the analytical expression of the multiple-EMIT-windows profile and describe the splitting of multiple EMIT windows as a function of optomechanical coupling, atom-field coupling, and Coulomb coupling. In particular, we discuss the robustness of the system against the cavity decay rate. We compare the results of identical mechanical resonators to different mechanical resonators. We further show how the hybrid nano-electro-optomechanics coupled system can lead to the splitting of the multiple Fano resonances (MFR). The Fano resonances are very sensitive to decay terms in such systems, i.e., atoms, cavities, and the mechanical resonators.

Higher-order squeezing oscillations of the single-mode cavity field interacting with a three-level radiator

We study the two-photon interaction between a three-level equidistant radiator (atom, molecule) with different dipole transitions and the single-mode cavity field. It is supposed that the three-level radiator is laser cooled and trapped into the ground vibrational state, in which the vibrational quantum number [Formula: see text]. In the proposed two-photon Jaynes–Cummings model (JCM) of a three-level atom at the initial moment [Formula: see text], the quantized cavity field is prepared in the squeezed vacuum state and the three-level radiator in the first excited state [Formula: see text]. By using the exact analytical solution for the state-vector of the coupled atom-field system, the amplitude-squared squeezing of the quantized cavity field is examined as a function of the [Formula: see text] and [Formula: see text] parameters. In this situation, higher-order squeezing has the tendency towards oscillations, but the exact periodicity of these oscillations is violated by the analogy with the second-order squeezing.

Properties of Two Two-level Atoms Interacting with Intensity-Dependent Coupling

We discuss some new features of the model of two two-level atoms interacting with two single-mode thermal cavity field via multi-photon transitions under intensity-dependent coupling. We examine the dynamics of quantum and classical correlations of the system initially exists in Werner states. The results show that the sudden death and sudden birth of quantum entanglement occur but the geometric measure of quantum discord remains non-zero. It is observed that, by increasing the number of photons, the periods become shorter and the quantum discord and entanglement become irregular.

Steady-state entanglement in levitated optomechanical systems coupled to a higher order excited atomic ensemble

We investigate the steady-state entanglement in an optomechanical system with a levitated dielectric nanosphere and a higher order excited atomic ensemble. The single nanosphere is trapped by an external harmonic dipole trap and coupled to the single-mode cavity field by the effective optomechanical coupling, which depends on the steady-state position of the nanosphere. We show that the steady-state optomechanical entanglement can be generated via the effective optomechanical interaction between the mechanical motion and the cavity mode. Further, these exist an optimal effective cavity detuning that maximizes the optomechanical entanglement. We also analyze in detail the influences of the excitation number of atoms, the radius of the nanosphere and the thermal noise strength on the steady-state optomechanical entanglement. It is found that the steady-state entanglement can be enhanced by increasing the excitation number of atoms and the radius of the nanosphere.

Antibunching in an optomechanical oscillator

We theoretically analyze antibunching of the phonon field in an optomechanical oscillator employ- ing the membrane-in-the-middle geometry. More specifically, a single-mode mechanical oscillator is quadratically coupled to a single-mode cavity field in the regime in which the cavity dissipation is a dominant source of damping, and adiabatic elimination of the cavity field leads to an effective cubic nonlinearity for the mechanics. We show analytically in the weak coupling regime that the mechan- ics displays a chaotic phonon field for small optomechanical cooperativity, whereas an antibunched single-phonon field appears for large optomechanical cooperativity. This opens the door to control of the second-order correlation function of a mechanical oscillator in the weak coupling regime.

Relation between quantum probe and entanglement in n-qubit systems within Markovian and non-Markovian environments

We address in detail the process of parameter estimation for an n-qubit system dissipating into a cavity in which the qubits are coupled to the single-mode cavity field via coupling constant g which should be estimated. In addition, the cavity field interacts with an external field considered as a set of continuum harmonic oscillators. We analyse the behaviour of the quantum Fisher information (QFI) for both weak and strong coupling regimes. In particular, we show that in strong coupling regime, the memory effects are dominant, leading to an oscillatory variation in the dynamics of the QFI and consequently information flowing from the environment to the quantum system. We show that when the number of the qubits or the coupling strength rises, the oscillations, signs of non-Markovian evolution of the QFI, increase. This indicates that in the strong-coupling regime, increasing the size of the system or the coupling strength remarkably enhances the reversed flow of information. Moreover, we find that it is possible to retard the QFI loss during the time evolution and therefore enhance the estimation of the parameter using a cavity with a larger decay rate factor. Furthermore, analysing the dynamics of the QFI and negativity of the probe state, we reveal a close relationship between the entanglement of probes and their capability for estimating the parameter. It is shown that in order to perform a better estimation of the parameter, we should avoid measuring when the entanglement between the probes is maximized.

Influence of atomic mass centre moving on spontaneous emission in double-well potential

The interaction between a two-level atom trapped in symmetric double-well potential and a single mode cavity field is investigated. By solving Schrödinger equation, the analytical expressions of the total wave function and inversion of the atomic energy level for the whole system are given. Time evolution of the atomic population inversion is analyzed for different initial states of the cavity field, such as fock and coherent states. Influence of atomic mass centre motion on population inversion is considered. Results show that by choosing appropriate cavity field initial state, potential well location and related factors, the spontaneous emission rate of an atom can be effectively controlled and the atomic moving centre of mass can suppress Rabi oscillation.

Quasi-lattices of qubits for generating inequivalent multipartite entanglements

The mesoscopic scale of superconducting qubits makes their inter-spacings comparable to the scale of wavelength of a circuit cavity field to which they commonly couple. This comparability results in inhomogeneous coupling strengths for each qubit and hence asynchronous Rabi excitation cycles among the qubits that form a quasi-lattice. We find that such inhomogeneous coupling benefits the formation of multi-photon resonances between the single-mode cavity field and the quasi-lattice. The multi-photon resonances lead, in turn, to the simultaneous generation of inequivalent and types of multipartite entanglement states, which are not transformable to each other through local operations with classical communications. Applying the model on the 3-qubit quasi-lattice and using the entanglement measures of both concurrence and 3-tangle, we verify that the inhomogeneous coupling specifically promotes the generation of the totally inseparable state.

Damping effect in the interaction of a Ξ-type three-level atom with a single-mode field: Caldirola–Kanai approach

In this paper the damped interaction between a -type three-level atom and a quantized single-mode cavity field is studied, where the Hamiltonian of the field is performed based on the Caldirola–Kanai damping Hamiltonian. The amplitude probabilities of the atom–field entangled state associated with the system considered have been explicitly deduced and the time evolution of a few of its physical properties is discussed. In detail, the influence of the damping parameter on the temporal behavior of the linear entropy, sub-Poissonian statistics as well as quadrature and amplitude squared squeezing is numerically investigated. Besides these, as an additional purpose of the paper, the effects of the initial field type as well as the initial mean photon number of the field on the above-mentioned properties are evaluated numerically. It is shown that via adjusting the damping parameter, initial field and its intensity, one can tune the degree of entanglement and other nonclassicality features.

Entanglement of a damped non-degenerate $\Diamond$ -type atom interacting nonlinearly with a single-mode cavity

In this paper, we investigate the entanglement of a non-degenerate $ \Diamond$ -type four-level atom interacting with a single-mode cavity field with multi-photon transitions in the intensity-dependent (atom-field) coupling regime. We consider the non-degenerate atom in the intermediate levels and with different detunings between the frequencies of the atom and quantized light field. The decay of the atom from the topmost state to the two intermediate states and also that from the two intermediate states to the bottom state are taken into account. In spite of the fact that the system seems to be complicated, the explicit form of the state vector of the entire system is analytically obtained by using the Laplace transform technique. Then, the entanglement between the atom and field is evaluated with the help of I concurrence measure. The effects of intensity-dependent coupling, decay rates, multi-photon processes and detuning parameters on the concurrence are numerically analyzed, in detail. The results indicate that, the larger the decay coefficients, the more rapid the entanglement decrement between the atom and the field. The intensity-dependent coupling enhances the entanglement between atom and field in most of the interaction times. Furthermore, the degeneracy of the intermediate atomic levels in the presence of decay parameters increases the asymptotic value of the concurrence in the linear and nonlinear regimes. Finally, the amount of entanglement between atom and field in the presence of decay parameters for two-photon transition is greater than that for the one-photon transition.