Hybrid Atom-optomechanical System Research Articles

The nonreciprocal optical bistability and nonreciprocal photon transmission in hybrid atom-optomechanical system

The nonreciprocal optical bistability and nonreciprocal photon transmission in hybrid atom-optomechanical system

Bose-Einstein condensates in an atom-optomechanical system with effective global nonuniform interaction

We consider a hybrid atom-optomechanical system consisting of a mechanical membrane inside an optical cavity and an atomic Bose-Einstein condensate outside the cavity. The condensate is confined in an optical lattice potential formed by a traveling laser beam reflected off one cavity mirror. We derive the cavity-mediated effective atom-atom interaction potential, and find that it is non-uniform, site-dependent, and does not decay as the interatomic distance increases. We show that the presence of this effective interaction breaks the Z$_2$ symmetry of the system and gives rise to new quantum phases and phase transitions. When the long-range interaction dominates, the condensate breaks the translation symmetry and turns into a novel self-organized lattice-like state with increasing particle densities for sites farther away from the cavity. We present the phase diagram of the system, and investigate the stabilities of different phases by calculating their respective excitation spectra. The system can serve as a platform to explore various self-organized phenomena induced by the long-range interactions.

Tunable fast–slow light conversion based on optomechanically induced absorption in a hybrid atom–optomechanical system

The fast and slow light effects of a transmitted probe light are researched in a hybrid atom–cavity optomechanical system, which is composed of an optical cavity, a mechanical resonator, and an atomic ensemble. The results show that the fast light generated in this hybrid system can be easily converted into slow light and vice versa, and that this fast–slow light conversion depends on a critical power of the control light, which corresponds to the fact that the probe light can be completely absorbed. Interestingly, this critical power can be modulated by changing the cavity coupling parameter or the atom–cavity coupling strength. Therefore, the fast–slow light conversion can be easily controlled.

Generation of the mechanical Schrödinger cat state in a hybrid atom-optomechanical system

In this paper, we propose a new theoretical scheme for generating a macroscopic Schrödinger cat state of a mechanical oscillator in a hybrid optomechanical system where a beam of two-level atoms passes through the cavity. In the model under consideration, the cavity field couples to the macroscopic mirror through the optomechanical interaction while it couples to the atom through a generalized Jaynes–Cummings interaction that involves the cavity-mode structure. The motion of the mirror modifies the cavity-mode function and therefore modulates the atom-field interaction, leading to the three-mode atom-field-mirror coupling or, equivalently, polariton-mirror coupling in a dressed picture. This interaction induces a controllable anharmonicity in the energy spectrum of the mechanical oscillator, which provides the possibility of generating a superposition of two time-dependent coherent states of the mechanical oscillator just by performing a conditional measurement on the internal states of the atoms exiting the optomechanical cavity. We also investigate the tripartite atom-field-mirror entanglement, which is controllable by adjusting the parameters of the system. In addition, we explore the effects of the mechanical dissipation and thermal noise on the tripartite quantum correlation in the system as well as the generated mechanical superposition state.

Nonequilibrium quantum phase transition in a spinor quantum gas in a lattice coupled to a membrane

Recently, a novel kind of hybrid atom-optomechanical system, consisting of atoms in a lattice coupled to a membrane, has been experimentally realized [Vochezer {\it et al.,} Phys. Rev. Lett. \textbf{120}, 073602 (2018)], which promises a viable contender in the competitive field of simulating non-equilibrium many-body physics. Here we are motivated to investigate a spinor Bose gas coupled to a vibrational mode of a nano-membrane, focusing on analyzing the role of the spinor degrees of freedom therein. Through an adiabatic elimination of the degrees of freedom of the quantum oscillator, we derive an effective Hamiltonian which reveals a competition between the force localizing the atoms and the membrane displacement. We analyze the dynamical stability of the steady state using Bogoliubov-de Gennes approach and derive the stationary phase diagram in the parameter space. We investigate the non-equilibrium quantum phase transition from a localized symmetric state of the atom cloud to a shifted symmetry-broken state, where we present a detailed analysis of the effects of the spin degree of freedom. Our work presents a simple way to study the effects of the spinor degree of freedom on the non-equilibrium nonlinear phenomena that is complementary to ongoing experiments on the hybrid atom-optomechanical system.

Tuning the order of the nonequilibrium quantum phase transition in a hybrid atom-optomechanical system

We show that a hybrid atom-optomechanical quantum many-body system with two internal atom states undergoes both first- and second-order nonequilibrium quantum phase transitions (NQPTs). A nanomembrane is placed in a pumped optical cavity, whose outcoupled light forms a lattice for an ultracold Bose gas. By changing the pump strength, the effective membrane-atom coupling can be tuned. Above a critical intensity, a symmetry-broken phase emerges which is characterized by a sizeable occupation of the high-energy internal states and a displaced membrane. The order of this NQPT can be changed by tuning the transition frequency. For a symmetric coupling, the transition is continuous below a certain transition frequency and discontinuous above. For an asymmetric coupling, a first-order phase transition occurs.

Entanglement and excited-state quantum phase transition in an extended Dicke model

We investigate the properties of entanglement and excited-state quantum phase transition (ESQPT) in a hybrid atom-optomechanical system in which an optomechanical quadratic interaction is introduced into a normal Dicke model. Interestingly, by preparing the ancillary mode in a coherent state, both the quantum entanglement and ESQPT can be realized in a relative weak-coupling condition. Moreover, the entanglement is immune to the A2 term, and a reversed trend of the entropy is obtained when the A2 term is included. Density of states (DoS) and Peres lattice are used to investigate ESQPTs. Compared to a normal Dicke model, the DoS enlarges exp(2rα) times if the ancillary mode is prepared in a coherent state. This work is an extension of the ground-state quantum phase transition, which may inspire further exploration of the quantum criticality in many-body systems.

Control of atom-mirror entanglement versus Gaussian geometric discord with RWA

In this study, we control the quantum correlations existing between a movable mirror and atoms in hybrid atom-optomechanical system using rotating wave approximation (RWA) in adiabatic regime. We use the Mancini criterion to measure the entanglement, the purity to quantify the degree of mixedness and the Gaussian geometric discord (GGD) to characterize the quantum correlations even beyond entanglement. We study the effect of the optomechanical cooling rate and the cooperativity atomic on the transfer of quantum correlations between the movable mirror and atoms under the thermal effect. We also investigate the robustness of the GGD with respect to entanglement by exploiting recent experimental parameters.

Dynamic Manipulation of Single-Photon Transport along a Waveguide by Dipole-Coupled Two-Level Atoms in a Quadratic Optomechanical Cavity

Single-photon transport along a one-dimensional waveguide side coupled to a quadratic optomechanical cavity embedded in two two-level atoms with dipole-dipole interaction (DDI) are explored theoretically. The transmission and reflection amplitudes are derived using a real-space approach. The effects of the optomechanical coupling strength, the DDI, atom-cavity detuning, and atomic dissipation on the single-photon transport properties are analyzed. In single-photon strong-coupling regime, vacuum Rabi-splitting and electromagnetically induced transparency (EIT)-like transmission spectra are observed. It is found that the DDI can shift the reflected resonant points, change the distance and the minima of the two vacuum Rabi-splitting dips, and modify the EIT-like spectra. Therefore, single-photon transport can be well controlled by such a hybrid atom-optomechanical system.

Steady-state phase diagram of quantum gases in a lattice coupled to a membrane

In a recent experiment [Vochezer {\it et al.,} Phys. Rev. Lett. \textbf{120}, 073602 (2018)], a novel kind of hybrid atom-opto-mechanical system has been realized by coupling atoms in a lattice to a membrane. While such system promises a viable contender in the competitive field of simulating non-equilibrium many-body physics, its complete steady-state phase diagram is still lacking. Here we study the phase diagram of this hybrid system based on an atomic Bose-Hubbard model coupled to a quantum harmonic oscillator. We take both the expectation value of the bosonic operator and the mechanical motion of the membrane as order parameters, and thereby identify four different quantum phases. Importantly, we find the atomic gas in the steady state of such non-equilibrium setting undergoes a superfluid-Mott-insulator transition when the atom-membrane coupling is tuned to increase. Such steady-state phase transition can be seen as the non-equilibrium counterpart of the conventional superfluid-Mott-insulator transition in the ground state of Bose-Hubbard model. Further, no matter which phase the quantum gas is in, the mechanic motion of the membrane exhibits a transition from an incoherent vibration to a coherent one when the atom-membrane coupling increases, agreeing with the experimental observations. Our present study provides a simple way to study non-equilibrium many-body physics that is complementary to ongoing experiments on the hybrid atomic and opto-mechanical systems.

Four-wave mixing response in a hybrid atom-optomechanical system

We study the four-wave mixing (FWM) effect in a hybrid atom-optomechanical system, which is composed of an ensemble of two-level atoms trapped inside an optical cavity and a moveable cavity mirror serving as a mechanical resonator. It is shown that the FWM signal in this hybrid system can be significantly enhanced due to the coupling between the optical cavity and the atom ensemble. The larger the atom-cavity coupling strength is, the stronger the FWM will be. More interestingly, the FWM signal can be effectively modulated by the atom-pump detuning. It is demonstrated that, just by tuning this detuning to be positive or negative, the FWM signal can be easily switched on or off for the zero probe-pump detuning case. The obtained results may have potential applications in all-optical wavelength convertors, all-optical switches, or other optical devices.

Enhancing nanomechanical squeezing by atomic interactions in a hybrid atom-optomechanical system

In a hybrid atom-optomechanical system, the optical coupling of a mechanical mode of a nanomembrane in an optical cavity with a distant interacting atom gas permits highly non-classical quantum many-body states. We show that the mechanical mode can be squeezed by the back-action of internal excitations of the atoms in the gas. A Bogoliubov approach reveals that these internal excitations form a fluctuating environment of quasi-particle excitations for the mechanical mode with a gaped spectral density. Nanomechanical squeezing arises due to quasi-particle excitations in the interacting atom gas when the mechanical frequency is close to resonance with the internal atomic transitions. Interestingly, nanomechanical squeezing is enhanced by atom-atom interactions.

Atomic swap gate, driven by position fluctuations, in dispersive cavity optomechanics

ABSTRACTTracing the dynamics of a quantum system using a mesoscopic device is an important topic of interest nowadays. Here we show how a mesoscopic mechanical oscillator can be used to steer the dynamics of a coupled two-atom system and thereby to implement a two-qubit universal gate. We have theoretically studied a generic hybrid atom-optomechanical system where two identical atoms in Λ configuration are trapped inside the cavity and the cavity mode mediates the interaction between the atoms and the mechanical oscillator. Adiabatic elimination of the lossy channels, namely, cavity decay and spontaneous emission, is adopted to obtain an effective Hamiltonian. This Hamiltonian is responsible for two-atom swap and gates, controlled by the position fluctuation of the oscillator. The validity of the proposal for successful implementation is assessed using presently available experimental parameters.

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.

Controlling single-photon transport in an optical waveguide coupled to an optomechanical cavity with a Λ-type three-level atom

We theoretically study the single-photon transport along a one-dimensional optical waveguide coupled to an optomechanical cavity containing a Λ-type three-level atom. Our numerical results show that the transmission spectra of the incident photon can be well controlled by such a hybrid atom-optomechanical system. The effects of the optomechanical coupling strength, the classical laser beam applied to the atom, atom-cavity detuning, and atomic dissipation on the single-photon transport properties are analyzed. It is of particular interest that an analogous double electromagnetically induced transparency emerges in the single-photon transmission spectra.

Light-Mediated Collective Atomic Motion in an Optical Lattice Coupled to a Membrane.

We observe effects of collective atomic motion in a one-dimensional optical lattice coupled to an optomechanical system. In this hybrid atom-optomechanical system, the lattice light generates a coupling between the lattice atoms as well as between atoms and a micromechanical membrane oscillator. For large atom numbers we observe an instability in the coupled system, resulting in large-amplitude atom-membrane oscillations. We show that this behavior can be explained by light-mediated collective atomic motion in the lattice, which arises for large atom numbers, small atom-light detunings, and asymmetric pumping of the lattice, in agreement with previous theoretical work. The model connects the optomechanical instability to a phase delay in the global atomic backaction onto the lattice light, which we observe in a direct measurement.

Controllable single-photon transport in an optical waveguide coupled to an optomechanical cavity with a V-type three-level atom

We theoretically study the single-photon transport along a one-dimensional optical waveguide coupled to an optomechanical cavity containing a Lambda-type three-level atom. Our numerical results show that the transmission spectra of the incident photon can be well controlled by such a hybrid atom-optomechanical system. The effects of the optomechanical coupling strength, the classical laser beam applied to the atom, atom-cavity detuning, and atomic dissipation on the single-photon transport properties are analyzed. It is of particular interest that an analogous double electromagnetically induced transparency emerges in the single-photon transmission spectra.

Perfect photon absorption in hybrid atom-optomechanical system

We propose a scheme to investigate the perfect photon absorption in a hybrid atom-optomechanical system under and beyond the low-excitation limit. The perfect photon absorption is present in both cases and always accompanied by the optical bistability or multistability. We find that the coupling with the atomic ensemble provides the sufficient and necessary condition for the perfect photon absorption in such a system, but the optomechanical coupling is only a necessary condition for the bistability (in the low-excitation regime)/multistability (beyond the low-excitation limit). It is especially interesting that the optical nonlinearities induced by the nonlinear optomechanical interaction and nonlinear atomic excitation can be overlap-added, which results in the optical multistability and further causes an additional perfect photon absorption point.

The Correlated Two-Photon Transport in a One-Dimensional Waveguide Coupling to a Hybrid Atom-Optomechanical System

We investigate the two-photon transport properties inside one-dimensional waveguide side coupled to an atom-optomechanical system, aiming to control the two-photon transport by using the nonlinearity. By generalizing the scheme of Phys. Rev. A 90, 033832, we show that Kerr nonlinearity induced by the four-level atoms is remarkable and can make the photons antibunching, while the nonlinear interaction of optomechanical coupling participates in both the single photon and the two photon processes so that it can make the two photons exhibiting bunching and antibunching.

Steady-state mechanical squeezing in a hybrid atom-optomechanical system with a highly dissipative cavity.

Quantum squeezing of mechanical resonator is important for studying the macroscopic quantum effects and the precision metrology of weak forces. Here we give a theoretical study of a hybrid atom-optomechanical system in which the steady-state squeezing of the mechanical resonator can be generated via the mechanical nonlinearity and cavity cooling process. The validity of the scheme is assessed by simulating the steady-state variance of the mechanical displacement quadrature numerically. The scheme is robust against dissipation of the optical cavity, and the steady-state squeezing can be effectively generated in a highly dissipative cavity.