Search

In this paper, we show that for sufficiently strong atomic interactions, there exist analytical solutions of current-carrying nonlinear Bloch states at the Brillouin zone edge to the model of spin-orbit-coupled Bose-Einstein condensates (BECs) with symmetric spin interaction loaded into optical lattices. These simple but generic exact solutions provide an analytical demonstration of some intriguing properties which have neither an analog in the regular BEC lattice systems nor in the uniform spin-orbit-coupled BEC systems. It is an analytical example for understanding the superfluid and other related properties of the spin-orbit-coupled BEC lattice systems., 9 pages, 6 figures, a couple of typos in equation are corrected

We study the multimagnon blockade and magnon-induced tunneling in the hybrid ferromagnet-superconductor system, where a magnon mode representing the collective motion of spins in the yttrium iron garnet (YIG) sphere is coupled with a three-level $\mathrm{\ensuremath{\Delta}}$-type fluxonium qubit via the virtual-photon excitation from the microwave cavity. By appropriately choosing the parameters, the single magnon blockade, multimagnon blockade including two- and three-magnon blockades, and magnon-induced tunneling could be achieved. Fortunately, the switch from magnon blockade to magnon-induced tunneling could be obtained via controlling the overall phase of the loop transition determined by the driving fields. Furthermore, the single-magnon blockade could be transformed into a multimagnon blockade via the phase modulation. The scheme we present may provide an alternative method to manipulate the few-magnon states and have potential applications in quantum communication and quantum information processing.

We propose theoretically an optomechanical system with double cavities to explore the thermophonon transport from the thermal bath of the mechanical oscillator to the coupled system. We find that the direction and magnitude of thermophonon flux in the system can be controlled flexibly by coupling an active cavity with gain to the driven cavity. In particular, the injected squeezing vacuum can reverse the nonequilibrium characteristics of the system and change the thermophonon flux from positive to negative. We also investigate in detail the influence of the driving power and the photon tunneling strength on the flux, which can widen the energy transfer channel of the system. The results obtained here have a potential application in the thermal noise energy harvesting and rectification by the optomechanical setup.

We theoretically explore the tunneling dynamics for the tight-binding (TB) model of a single spin-orbit-coupled atom trapped in an optical lattice subjected to lattice shaking and to time-periodic Zeeman field. By means of analytical and numerical methods, we demonstrate that the spin-orbit (SO) coupling adds some new results to the tunneling dynamics in both multiphoton resonance and far-off-resonance parameter regimes. When the driving frequency is resonant with the static Zeeman field (multi-photon resonances), we obtain an unexpected new dynamical localization (DL) phenomenon where the single SO-coupled atom is restricted to making perfect two-site Rabi oscillation accompanied by spin flipping.By using the unconventional DL phenomenon, we are able to generate a ratchetlike effect which enables directed atomic motion towards different directions and accompanies periodic spin-flipping under the action of SO coupling. For the far-off-resonance case, we show that by suppressing the usual inter-site tunneling alone, it is possible to realize a type of spin-conserving second-order tunneling between next-nearest-neighboring sites, which is not accessible in the conventional lattice system without SO coupling. We also show that simultaneous controls of the usual inter-site tunneling and the SO-coupling-related second-order-tunneling are necessary for quasienergies flatness (collapse) and completely frozen dynamics to exist. These results may be relevant to potential applications such as spin-based quantum information processing and design of novel spintronics devices., 12 pages, 7 figures

Finding the optimal estimator capable of saturating the Cram\'er-Rao bound is important for quantum parameter estimation. The maximum likelihood estimator (MLE) is well known to be asymptotically optimal, but it is usually nonanalytic and hence requires extensive numerical computation. On the other hand, the inversion estimator is widely used in experiments due to its simplicity, but it is usually suboptimal. Here we derive an estimator based on the linear combination of multiple inversion estimators associated with the occurrence probability of different measurement outcomes. This linear combination estimator shares the asymptotic optimality of the MLE and the simplicity of the inversion estimator and is applicable to general multi-outcome measurements, irrespective of the specific system and the noise in the system. We demonstrate this estimator for the intensity-difference measurement to a six-photon twin-Fock input state.

The squeezed state of a macroscopic mechanical oscillator can be exploited to enhance the sensitivity of precision measurements. Here, we theoretically demonstrate that the displacement squeezing of a mechanical oscillator in a dissipative optomechanical system can be generated by the use of two driving tones tuned to the first upper and lower mechanical sidebands. We find that the displacement squeezing of the mechanical oscillator is determined by the powers of the two driving tones and the temperature of the environment. Even when the temperature of the environment is as high as 20 mK, the mechanical squeezing beyond 3 dB can be achieved. Moreover, we show that the mechanical squeezing can be detected by directly measuring the cavity output spectrum.

We theoretically investigate the generation of steady-state entanglement in a levitated optomechanical system with a cascade three-level atomic medium and a dielectric nanosphere. There are two cavity modes, driven by two external laser beams with different frequencies, which are responsible for trapping and cooling the nanosphere. Atoms prepared in coherent superposition are injected into the cavity to manipulate the optical fields and the effective optomechanical coupling. We show that the entanglement between the nanosphere and the cavity modes can be enhanced by selecting properly the initial population of the lower atomic level. In particular, when the atoms are prepared at that level, the corresponding optomechanical entanglement increases with the increase of the atom-field coupling strength. We also investigate in detail the influence of the effective cavity field detunings, the atomic detunings, the driving power, and the nanosphere's radius and found that there exist optimal values of the effective cavity field detuning and the driving power that maximize the optomechanical entanglement. By selecting the system's parameters properly, we further demonstrate the generation of genuine tripartite entanglement between three degrees of freedom in the system. The findings here may help flexible control of the steady-state entanglement in hybrid optomechanical systems.

Einstein-Podolsky-Rosen (EPR) steering has potential applications in quantum information processing. Here the genuine tripartite EPR steering is investigated in cascaded nonlinear process of spontaneous parametric down-conversion cascaded with a sum-frequency generation in an optical cavity for a wide range of the nonlinear parameters. The threshold properties of the cascaded nonlinear precess are also analyzed both below and without threshold regime, respectively. The genuine tripartite EPR steering is demonstrated based on the criteria for genuine multipartite EPR steering. Our scheme of the generation of genuine tripartite EPR steering can be used as a suggestion for the potential experiments and the applications in quantum communication and computation.

We investigate thermo-phonon transport and its nontrivial Berry-phase-like effect in an optomechanical system with a squeezed vacuum injection. By taking the cumulant generation function approach the exact expressions of the thermo-phonon flux and optomechanical Berry phase are derived analytically. Further, the quantum master equation approach is invoked to verify the analytical results of the transport properties. It is shown that the steady-state thermo-phonon flux can be modulated by varying optically the nonequilibrium characteristics of the system via the squeezed vacuum. In particular, an adiabatic modulation of squeezing parameters induces an optomechanical Berry-phase-like effect and as a result provides an additional geometric phonon response across the macroscopic mechanical motion near the quantum regime, which can also be seen as a consequence of the asymmetric jumping probability between transition associated with phonon absorption and emission in a thermal bath. The present method and results are general and can be straightforwardly extended to any multimode oscillator systems and therefore pave the way to the thermal noise energy harvesting and rectification in coupled oscillator systems with inertial terms.

The spontaneous emission spectrum of a multi-level atom or molecule with nonreciprocal transition is investigated. It is shown that the nonreciprocal transition can lead to the elimination of a spectral line in the spontaneous emission spectrum. As an application, we show that nonreciprocal transition arises from the phase-related driving fields in chiral molecules with cyclic three-level transitions, and the elimination of a spectral line induced by nonreciprocal transition provides us a method to determine the enantiomeric excess for the chiral molecules without requiring the enantio-pure samples., Comment: 8 pages, 6 figures

We theoretically demonstrate that an especially tuned degenerate optical parametric amplifier (OPA) inside a cavity can lead to the momentum squeezing of a moving membrane in a dissipative optomechanical system. The momentum squeezing of the membrane depends on the parametric gain and the parametric phase of the OPA, the power of the external laser driving the cavity, and the temperature of the environment. The best achievable momentum squeezing is about 2.53 dB, which is limited by the OPA. Moreover, we show that the momentum squeezing of the membrane can be detected by directly measuring the cavity output field. In addition, we find that the mechanical squeezing can be enhanced to about 10.36 dB under the joint effect of the OPA and an input broadband squeezed vacuum field.

We investigate corner states in a photonic two-dimensional (2D) Su-Schrieffer-Heeger (SSH) model on a square lattice with zero gauge flux. By considering intracelluar next-nearest-neighbor (NNN) hoppings, we discover a broad class of corner states in the 2D SSH model and show that they are robust against certain fabrication disorders. Moreover, these corner states are located around the corners but not at the corner points. We analytically identify that these corner states are induced by the intracelluar NNN hoppings (long-range interactions) and split off from the edge-state bands. Thus, we refer to them as general bounded corner states. Our paper shows a simple way to induce unique corner states by the long-range interactions and offers opportunities for designing novel photonic devices.

We discuss the Fano resonance and amplification in a quadratically coupled optomechanical system with a nonlinear Kerr medium. We find that effective cavity detuning and the strength of the Kerr nonlinearity lead to the appearance of the Fano resonance in the output probe field at room temperature, respectively. We show that the Kerr nonlinearity causes the asymmetric line shape to appear in the intensities of the output Stokes field and the second-order upper sideband generation. We also show that the Kerr nonlinearity can amplify the intensities of the output Stokes field and the second-order upper sideband generation, and the amplification factor is related to the strength of the Kerr nonlinearity. The findings of this study have potential applications in optical switching and frequency conversion.

We propose the use of the second-order magnetic-gradient-induced coupling between the nitrogen-vacancy center and the mechanical resonator for exploring the phonon-blockade effect in a hybrid system. This quantum effect essentially originates from the energy-level anharmonicity of the spin-mechanical system. Specifically, the second-order magnetic gradient could induce the two-phonon nonlinear coupling between spin qubits and phonons, which ultimately allows for the generation of phonon blockade. Moreover, this magnetically induced nonlinearity can be adjusted and enhanced to the strong-coupling regime. In this regime, we investigate the statistical characteristics of phonons by calculating the second-order correlation function numerically and analytically. In particular, we find that the antibunching effect of phonons is robust against the spin dephasing rate. This could provide an advantage and relax the required conditions for observing the phonon quantum effects from the perspective of experimental feasibility. Our work provides an alternative way, i.e., magnetically induced mechanical nonlinearity, to manipulate the mechanical quantum effects. Combined with the current quantum technologies, this study may extend the functionalities of hybrid systems and has potential applications in quantum information processing.

We theoretically study the dynamics of the ground-state cooling and the quantum entanglement in a modulated optomechanical system, where the frequency of the mechanical oscillator and the optical field or the strength of the driving laser is time dependent. In this paper, we focus mainly on the fact that the system works in the regime of blue detuning. It is found that in the long-time limit the steady-state phonon number can be decreased significantly so that the mechanical oscillator is cooled to the ground state by appropriately selecting the frequency and the amplitude of the modulation. Further, with the help of the dynamical modulation in the system, the time evolution of the entanglement preevaluation value displays the death and rebirth of quantum entanglement between the mechanical oscillator and the optical field, which correspond, respectively, to the increase and decrease of the effective phonon number of the mechanical oscillator. In particular, when the steady-state dynamics of the system is quasiperiodic, the dynamics of the entanglement preevaluation value exhibits a quasiperiodic behavior, which means that the quantum phenomena can be represented in nonlinear classical dynamics.

Quantum blockade and entanglement play important roles in quantum information and quantum communication as quantum blockade is an effective mechanism to generate single photons (phonons) and entanglement is a crucial resource for quantum information processing. In this work, we propose a method to generate single entangled photon-phonon pairs in a hybrid optomechanical system. We show that photon blockade, phonon blockade, and photon-phonon correlation and entanglement can be observed via the atom-photon-phonon (tripartite) interaction, under the resonant atomic driving. The correlated and entangled single photons and single phonons, i.e., single entangled photon-phonon pairs, can be generated in both the weak and strong tripartite interaction regimes. Our results may have important applications in the development of highly complex quantum networks., Comment: 9 pages, 7 figures

We propose a scheme for producing the phase squeezing of the output light in a dissipative optomechanical coupling system. This is achieved by applying a degenerate parametric drive on the mechanical oscillator. We also show that this scheme is capable of generating the stationary entanglement between an optical cavity field and a macroscopic mechanical oscillator. The effects of the strength of the mechanical parametric drive, the power of the input laser, the temperature of the environment on the output phase squeezing, and the optomechanical entanglement are investigated. For a temperature of 20 mK, we find that up to 9 dB of the output phase squeezing and the large optomechanical entanglement can be achieved.

We theoretically investigate the enhanced charge-dependent generation of the optical second-order sidebands (OSS) in a gain-cavity-assisted optomechanical (GCAOM) system coupled to a charged object. The hybrid optomechanical system is coherently driven by an external two-tone laser field which consists of a continuous-wave pump field and a pulsed probe field. Beyond the conventional linearized description of optomechanical interactions, the nonlinear optomechanical interactions are included in the Heisenberg-Langevin equations and are treated analytically by means of the perturbation method. It is shown that an assisted gain cavity can significantly enhance the OSS generation and can also lead to higher charge dependence of the output OSS spectrum than that achieved from a lossy cavity optomechanical system. Subsequently we discuss the application of such a GCAOM system as a family of high-sensitivity sensor for measuring the charges. Using experimentally achievable parameters, we identify the conditions under which the assisted gain cavity allows us to enhance the OSS generation and improve sensitivity of the sensor beyond what is achievable in a lossy cavity optomechanical system. The present investigation may provide a route toward modulating the nonlinear optical properties of the electro-optic hybrid system, as well as to guide the design of sensitive devices.

The ground-state cooling of a macroscopic mechanical oscillator is a crucial prerequisite for implementing the quantum manipulation of the mechanical oscillator. Here we show that a degenerate optical parametric amplifier (OPA) can significantly improve the cooling of the mechanical membrane in the purely dissipative coupling system in the unresolved sideband regime. In the presence of the OPA with a parametric phase $\ensuremath{\pi}/2$, the mechanical membrane can be cooled from room temperature 293 K to 10 mK, a factor of 112 lower than that in the absence of the OPA. If the mechanical oscillator is precooled to 0.1 K, the mechanical membrane can be cooled into the microkelvin regime.

We propose theoretically a four-mode coupled optomechanical system to explore the optical-response properties of an optical trimer system consisting of a passive cavity, a no-loss-gain cavity, and an active cavity coupled with a mechanical oscillator. In the study, the passive cavity is driven by an external laser so that the stability of the coupled system depends strongly on the gain-to-loss ratio and the photon tunneling between the adjacent cavities. We find that in the regime near the stable-unstable critical point, the resonance absorption of the optical trimer system changes quickly with the increasing gain of the active cavity. In contrast, when the mechanical oscillator is coupled to the passive cavity, the center absorption peak is split and a phenomenon of optomechanically induced transparency appears. Consequently, two additional resonance peaks in the absorption profile are induced by the optomechanical coupling, which hinges on the tunneling between the optical cavities and also on the gain of the active cavity. The dependence of the width of the transparency window on the optomechanical coupling and the driving strength is also discussed in detail. The results obtained here indicate that the optical properties of the trimer system can be manipulated by coupling a mechanical oscillator to the system and therefore have a potential application in quantum optics and quantum information processing.

We study photon, phonon statistics and the cross-correlation between photons and phonons in a quadratically coupled optomechanical system. Photon blockade, phonon blockade and strongly anticorrelated photons and phonons can be observed in the same parameter regime with the effective nonlinear coupling between the optical and mechanical modes, enhanced by a strong optical driving field. Interestingly, an optimal value of the effective nonlinear coupling strength for the photon blockade is not within the strong nonlinear coupling regime. This abnormal phenomenon results from the destructive interference between different paths for two-photon excitation in the optical mode with a moderate effective nonlinear coupling strength. Further more, we show that phonon (photon) pairs and correlated photons and phonons can be generated in the strong nonlinear coupling regime with a proper detuning between the weak mechanical driving field and mechanical mode. Our results open up a way to generate anticorrelated and correlated photons and phonons, which may have important applications in quantum information processing., 9 pages, 6 figures