Optomechanically induced transparency with Bose Einstein condensate in double-cavity optomechanical system

We propose a novel technique of generating multiple optomechanically induced transparency （OMIT） of a weak probe field in hybrid optomechanical system. This system consists of a cigar-shaped Bose-Einstein condensate （BEC）, trapped inside each high finesse Fabry-P6rot cavity. In the resolved sideband regime, the analytic solutions of the absorption and the dispersion spectrum are given. The tunneling strength of the two resonators and the coupling parameters of the each BEC in combination with the cavity field have the appearance of three distinct OMIT windows in the absorption spectrum. Furthermore, whether there is BEC in each cavity is a key factor in the number of OMIT windows determination. The technique presented may have potential applications in quantum engineering and quantum information networks.

Photon blockade in a cavity–atom optomechanical system

We study the single-photon blockade(1 PB),two-photon blockade(2 PB),and photon-induced tunneling(PIT)effects in a cavity–atom optomechanical system in which a two-level atom is coupled to a single-model cavity field via a twophoton interaction.By analyzing the eigenenergy spectrum of the system,we obtain a perfect 1 PB with a high occupancy probability of single-photon excitation,which means that a high-quality and efficient single-photon source can be generated.However,PIT often occurs in many cases when we consider 2 PB in analogy to 1 PB.In addition,we find that a 2 PB region will present in the optomechanical system,which can be proved by calculating the correlation function of the model analytically.

Optical nonreciprocity in a piezo-optomechanical system

We theoretically study the optical nonreciprocity in a piezo-optomechanical microdisk resonator,in which the cavity modes and the mechanical mode are optically pumped and piezoelectrically driven,respectively.For asymmetric optical pumping and different piezoelectrical drivings,our system shows some nonreciprocal optical responses.We find that our system can function as an optical isolator,a nonreciprocal amplifier,or a nonreciprocal phase shifter.

Review of cavity optomechanical cooling

Quantum manipulation of macroscopic mechanical systems is of great interest in both fundamental physics and ap- plications ranging from high-precision metrology to quantum information processing. For these purposes, a crucial step is to cool the mechanical system to its quantum ground state. In this review, we focus on the cavity optomechanical cooling, which exploits the cavity enhanced interaction between optical field and mechanical motion to reduce the thermal noise. Recent remarkable theoretical and experimental efforts in this field have taken a major step forward in preparing the mo- tional quantum ground state of mesoscopic mechanical systems. This review first describes the quantum theory of cavity optomechanical cooling, including quantum noise approach and covariance approach; then, the up-to-date experimental progresses are introduced. Finally, new cooling approaches are discussed along the directions of cooling in the strong coupling regime and cooling beyond the resolved sideband limit.

Electromagnetically induced transparency in a three-mode optomechanical system

We study a three-mode double-cavity optomechanical system in which an oscillating membrane of perfect reflection is inserted between two fixed mirrors of partial transmission. We find that electromagnetically induced transparency （EIT） can be realized and controlled in this optomechanical system by adjusting the relative intensity and the relative phase between left-hand and right-hand input （probe and coupling） fields. In particular, one perfect EIT window is seen to occur when the two probe fields are exactly out of phase and the EIT window＇s width is very sensitive to the relative intensity of two coupling fields. Our numerical findings may be extended to achieve optomechanical storage and switching schemes applicable in quantum information processing.

Tunable second-order sideband effects in hybrid optomechanical cavity assisted with a Bose-Einstein condensate

We theoretically investigated a second-order optomechanical-induced transparency(OMIT) process of a hybrid optomechanical system(COMS), which a Bose-Einstein condensate(BEC) in the presence of atom-atom interaction trapped inside a cavity with a moving end mirror. The advantage of this hybrid COMS over a bare COMS is that the frequency of the second mode is controlled by the s-wave scattering interaction. Based on the traditional linearization approximation, we derive analytical solutions for the output transmission intensity of the probe field and the dimensionless amplitude of the second-order sideband(SS). The numerical results show that the transmission intensity of the probe field and the dimensionless amplitude of the SS can be controlled by the s-wave scattering frequency. Furthermore, the control field intensities,the effective detuning, the effective coupling strength of the cavity field with the Bogoliubov mode are used to control the transmission intensity of the probe field and the dimensionless amplitude of the SS.

Excitations of optomechanically driven Bose Einstein condensates in a cavity: Photodetection measurements

We present a detailed study to analyze the Dicke quantum phase transition within the thermodynamic limit for an optomechanically driven Bose-Einstein condensate in a cavity. The photodetection-based quantum optical measurements have been performed to study the dynamics and excitations of this optomechanical Dicke system. For this, we discuss the eigenvalue analysis, fluorescence spectrum and the homodyne spectrum of the system. It has been shown that the normal phase is negligibly affected by the mechanical mode of the mirror while it has a significant effect in the superradiant phase. We have observed that the eigenvalues and the spectra both exhibit distinct features that can be identified with the photonic, atomic and phononic branches. In the fluorescence spectra, we further observe an asymmetric coherent energy exchange between the three degrees of freedom of the system in the superradiant phase arising as a result of optomechanical interaction and Bloch-Siegert shift.

Compound-induced transparency in three-cavity coupled structure

We propose a three-cavity coupled cavity optomechanical(COM)structure with tunable system parameters and theoretically investigate the probe-light transmission rate.Numerical calculation of the system’s spectra demonstrates distinctive compound-induced transparency(CIT)characteristics,including multiple transparency windows and sideband dips,which can be explained by a coupling between optomechanically-induced transparency(OMIT)and electromagnetically-induced transparency.The effects of optical loss(gain)in the cavity,number and topology of active cavity,tunneling ratio,and pump laser power on the CIT spectrum are evaluated and analyzed.Moreover,the optical group delay of CIT is highly controllable and fast–slow light inter-transition can be achieved.The proposed structure makes possible the advantageous tuning freedom and provides a potential platform for controlling light propagation and fast–slow light switching.

Ponderomotive squeezing and entanglement in a ring cavity with two vibrational mirrors

We investigate the properties of the ponderomotive squeezing and the entanglements in a ring cavity with two vibrational mirrors. In the part about squeezing, we find that the squeezing spectrum of the transmitted field shows a distinct feature when the two vibrational mirrors have different frequencies. We also study the effects of some external parameters such as the temperature and the laser power on the degree of squeezing. In the part concerning entanglement, we study the entanglements between the cavity field and one of the vibrational mirrors, and that between the two vibrational mirrors, with emphasis focusing on the robustness of entanglements with respect to the environment temperature.

Realization of quantum ground state in an optomechanical crystal cavity

Ground-state cooling of the mechanical degree of freedom is a fundamental requirement for quantum state transfer between relevant optical and mechanical systems.Here,we fabricate optomechanical crystal cavities with co-localized mechanical and optical modes on a monolithic chip.The typical linewidth of the optical modes at telecom wavelength is as low as 0.95 GHz,and the mechanical resonant frequency is around 5 GHz,which means the optomechanical system can be operated in the resolved sideband regime.With the statistics of the asymmetry in the scattering rates of red and blue detuning driving processes,we initialize and characterize the mechanical system in its quantum ground-state of motion,with a mean thermal phonon occupancy nth=0.018±0.0034,corresponding to a mode temperature of 57.3 m K.It is a general platform for quantum state transfer between relevant optical and mechanical systems,as well as the quantum entanglement between these systems.

Cavity optomechanical chaos

Cavity optomechanics provides a powerful platform for observing many interesting classical and quantum nonlinear phenomena due to the radiation-pressure coupling between its optical and mechanical modes.In particular,the chaos induced by optomechanical nonlinearity has been of great concern because of its importance both in fundamental physics and potential applications ranging from secret information processing to optical communications.This review focuses on the chaotic dynamics in optomechanical systems.The basic theory of general nonlinear dynamics and the fundamental properties of chaos are introduced.Several nonlinear dynamical effects in optomechanical systems are demonstrated.Moreover,recent remarkable theoretical and experimental efforts in manipulating optomechanical chaotic motions are addressed.Future perspectives of chaos in hybrid systems are also discussed.

Perfect optomechanically induced transparency in two-cavity optomechanics

Here,we study the controllable optical responses in a two-cavity optomechanical system,especially on the perfect optomechanically induced transparency(OMIT)in the model which has never been studied before.The results show that the perfect OMIT can still occur even with a large mechanical damping rate,and at the perfect transparency window the long-lived slow light can be achieved.In addition,we find that the conversion between the perfect OMIT and optomechanically induced absorption can be easily achieved just by adjusting the driving field strength of the second cavity.We believe that the results can be used to control optical transmission in modern optical networks.

Optomechanical Schrödinger cat states in a cavity Bose-Einstein condensate

Schrödinger cat states,consisting of superpositions of macroscopically distinct states,provide key resources for a large number of emerging quantum technologies in quantum information processing.Here we propose how to generate and manipulate mechanical and optical Schrödinger cat states with distinguishable superposition components by exploiting the unique properties of cavity optomechanical systems based on Bose-Einstein condensate.Specifically,we show that in comparison with its solid-state counterparts,almost a 3 order of magnitude enhancement in the size of the mechanical Schrödinger cat state could be achieved,characterizing a much smaller overlap between its two superposed coherent-state components.By exploiting this generated cat state,we further show how to engineer the quadrature squeezing of the mechanical mode.Besides,we also provide an efficient method to create multicomponent optical Schrödinger cat states in our proposed scheme.Our work opens up a new way to achieve nonclassical states of massive objects,facilitating the development of fault-tolerant quantum processors and sensors.

Remote weak-signal measurement via bound states in optomechanical systems

A scheme for remote weak-signal sensors is proposed,in which a coupled-resonator optical waveguide(CROW),as a transmitter,couples to a hybrid optomechanical cavity and an observing cavity at its two ends.Non-Markovian theory is employed to study the weak-force sensor by treating the CROW as a non-Markovian reservoir of cavity fields.The dissipationless bound states in the non-Markovian regime are conducive to remotely transmitting a signal in the CROW.Our results show that a sensor with ultrahigh sensitivity can be achieved with the assistance of bound states under certain parameter regimes.

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

An optomechanical cavity embedded with a V-type three-level atom is exploited to control single-photon transport in a one-dimensional waveguide. The effects of the atom–cavity detuning, the optomechanical effect,the coupling strengths between the cavity and the atom or the waveguide, and the atomic dissipation on the single-photon transport properties are analyzed systematically. Interestingly, the single-photon transmission spectra show multiple double electromagnetically induced transparency. Moreover, the double electromagnetically induced transparency can be switched to a single one by tuning the atom–cavity detuning.

Two-Mode Biomedical Sensor Build-up:Characterization of Optical Amplifier

Intracavity absorption spectroscopy is a strikingly sensitive technique that has been integrated with a two-wavelength setup to develop a sensor for human breath.Various factors are considered in such a scenario,out of which Relative Intensity Noise(RIN)has been exploited as an important parameter to characterize and calibrate the said setup.During the performance of an electrical based assessment arrangement which has been developed in the laboratory as an alternative to the expensive Agilent setup,the optical amplifier plays a pivotal role in its development and operation,along with other components and their significance.Therefore,the investigation and technical analysis of the amplifier in the system has been explored in detail.The algorithm developed for the automatic measurements of the system has been effectively deployed in terms of the laser’s performance.With this in perspective,a frequency dependent calibration has been pursued in depth with this scheme which enhances the sensor’s efficiency in terms of its sensitivity.In this way,our investigation helps us in a better understanding and implementation perspective of the proposed system,as the outcomes of our analysis adds to the precision and accuracy of the entire system.

Reservoir-engineered entanglement in an unresolved-sideband optomechanical system

We study theoretically the generation of strong entanglement of two mechanical oscillators in an unresolved-sideband optomechanical cavity,using a reservoir engineering approach.In our proposal,the effect of unwanted counter-rotating terms is suppressed via destructive quantum interference by the optical field of two auxiliary cavities.For arbitrary values of the optomechanical interaction,the entanglement is obtained numerically.In the weak-coupling regime,we derive an analytical expression for the entanglement of the two mechanical oscillators based on an effective master equation,and obtain the optimal parameters to achieve strong entanglement.Our analytical results are in accord with numerical simulations.

Highly tunable broadband coherent wavelength conversion with a fiber-based optomechanical system

Modern information networks are built on hybrid systems working at disparate optical wavelengths.Coherent interconnects for converting photons between different wavelengths are highly desired.Although coherent interconnects have conventionally been realized with nonlinear optical effects,those systems require demanding experimental conditions,such as phase matching and/or cavity enhancement,which not only bring difficulties in experimental implementation but also set a narrow tuning bandwidth(typically in the MHz to GHz range as determined by the cavity linewidth).Here,we propose and experimentally demonstrate coherent information transfer between two orthogonally propagating light beams of disparate wavelengths in a fiber-based optomechanical system,which does not require phase matching or cavity enhancement of the pump beam.The coherent process is demonstrated by interference phenomena similar to optomechanically induced transparency and absorption.Our scheme not only significantly simplifies the experimental implementation of coherent wavelength conversion but also extends the tuning bandwidth to that of an optical fiber(tens of THz),which will enable a broad range of coherent-optics-based applications,such as optical sensing,spectroscopy,and communication.

Nonequilibrium thermodynamics in cavity optomechanics

Classical thermodynamics has been a great achievement in dealing with systems that are in equilibrium or near equilibrium.As an emerging field,nonequilibrium thermodynamics provides a general framework for understanding the nonequilibrium processes,particularly in small systems that are typically far-from-equilibrium and are dominated by thermal or quantum fluctuations.Cavity optomechanical systems hold great promise among the various experimental platforms for studying nonequilibrium thermodynamics owing to their high controllability,excellent mechanical performance,and ability to operate deep in the quantum regime.Here,we present an overview of the recent advances in nonequilibrium thermodynamics with cavity optomechanical systems.The experimental results in entropy production assessment,fluctuation theorems,heat transfer,and heat engines are highlighted.

Phonon and photon lasing dynamics in optomechanical cavities

Lasers differ from other light sources in that they are coherent,and their coherence makes them indispensable to both fundamental research and practical application.In optomechanical cavities,photon and phonon lasing is facilitated by the ability of photons and phonons to interact intensively and excite one another coherently.The lasing linewidths of both phonons and photons are critical for practical application.This study investigates the lasing linewidths of photons and phonons from the underlying dynamics in an optomechanical cavity.We find that the linewidths can be accounted for by two distinct physical mechanisms in two regimes,namely the normal regime and the reversed regime,where the intrinsic optical decay rate is either larger or smaller than the intrinsic mechanical decay rate.In the normal regime,an ultra-narrow spectral linewidth of 5.4 kHz for phonon lasing at 6.22 GHz can be achieved regardless of the linewidth of the pump light,while these results are counterintuitively unattainable for photon lasing in the reversed regime.These results pave the way towards harnessing the coherence of both photons and phonons in silicon photonic devices and reshaping their spectra,potentially opening up new technologies in sensing,metrology,spectroscopy,and signal processing,as well as in applications requiring sources that offer an ultra-high degree of coherence.