Optomechanical entanglement in a whispering-gallery cavity

The dynamics of the optomechanical entanglement between optical cavity field modes and a macroscopic mechanical breathing mode in a whispering-gallery cavity as well as the continuous variable entanglement between the phase-quadrature amplitudes of the two whispering-gallery modes have been analysed.Simulated results indicate that under state-of-the-art experimental conditions,optomechanical entanglement is obvious and can occur even at temperatures of above 40 K.Compared with the entanglement of the mechanical oscillator at the ground state temperature,optomechanical entanglement is more intense by several orders of magnitude.     

Optomechanical entanglement in a whispering-gallery cavity

The dynamics of the optomechanical entanglement between optical cavity field modes and a macroscopic mechanical breathing mode in a whispering-gallery cavity as well as the continuous variable entanglement between the phase-quadrature amplitudes of the two whispering-gallery modes have been analysed. Simulated results indicate that under state-of-the-art experimental conditions, optomechanical entanglement is obvious and can occur even at temperatures of above 40 K. Compared with the entanglement of the mechanical oscillator at the ground state temperature, optomechanical entanglement is more intense by several orders of magnitude.     

Entanglement of movable mirror and cavity field enhanced by an optical parametric amplifier

A scheme to generate entanglement in a cavity optomechanical system filled with an optical parametric amplifier is proposed. With the help of the optical parametric amplifier, the stationary macroscopic entanglement between the movable mirror and the cavity field can be notably enhanced, and the entanglement increases when the parametric gain increases.Moreover, for a given parametric gain, the degree of entanglement of the cavity optomechanical system increases with increasing input laser power.     

High finesse opto-mechanical cavity with a movable thirty-micron-size mirror

We report on the demonstration of a high finesse micro-optomechanical system and identify potential applications ranging from optical cooling to weak force detection to massive quantum superpositions. The system consists of a high quality diameter flat dielectric mirror cut from a larger substrate with a focused ion beam and attached to an atomic force microscope cantilever. Cavity ring-down measurements performed on a 25 mm long Fabry-Pérot cavity with the 30 microm mirror at one end show an optical finesse of 2100. Numerical calculations show that the finesse is not diffraction limited and that orders of magnitude higher finesse should be possible. A mechanical quality factor of more than 10(5) at pressures below 10(-3) mbar is demonstrated for the cantilever with a mirror attached.     

双模腔场中纠缠转移时纠缠与能量关系的研究

在初态为Bell态的两个二能级原子与双模腔场的耦合系统中,我们研究了其子系统纠缠转移时两原子的能量与其纠缠演化之间的关系。结果表明：两者的关系是密不可分的。而且,我们还讨论了原子间的偶极-偶极相互作用和腔场中的光子数对这种关系的影响。     

Multipartite entanglement in the interaction system between a single-mode microwave cavity field and superconducting charge qubits

This paper proposes a method of generating multipartite entanglement through using d.c. superconducting quantum interference devices (SQUID) inside a standing wave cavity. In this scheme, the d.c. SQUID works in the charge region. It is shown that, a large number of important multipartite entangled states can be generated by a controllable interaction between a cavity field and qubits. It is even possible to produce entangled states involving different cavity modes based on the measurement of charge qubits states. After such superpositions states are created, the interaction can be switched off by the classical magnetic field through the SQUID, and there is no information transfer between the cavity field and the charge qubits.     

Optomechanical properties of a degenerate nonperiodic cavity chain

Frontiers of Physics - Results of inelastic neutron scattering experiments and ab initio molecular dynamics simulations for GeTe–the parent compound of phase-change materials are reported....     

耗散系统中原子和场的熵交换与纠缠

研究耗散腔中,二能级原子与单模辐射场在相互作用过程中熵关联的情况。结果表明：原子与场之间存在熵交换现象,更重要的是证明了它们之间的熵交换需要满足一定的条件。同时也计算了原子与场之间的纠缠,发现两子系统间熵交换与纠缠的关系。     

Sudden death of entanglement in the two-mode cavity field

<正>The entanglement dynamics involving the so-called entanglement sudden death of atoms in two-photon Tavis-Cummings model is investigated.Various initial conditions that may have influences on the entanglement evolution of atoms,especially on the appearance of atomic entanglement sudden death,are studied. The appearance of entanglement sudden death is sensitive to the initial conditions of the whole system, i.e.,the concrete type of atomic initial state,the photon number in the cavity field,and the dipole-dipole interaction between atoms.It is shown that the strong dipole-dipole interaction between atoms can weaken the atomic entanglement sudden death.     

耗散系统中原子和场的熵交换与纠缠

研究耗散腔中, 二能级原子与单模辐射场在相互作用过程中熵关联的情况. 结果表明：原子与场之间存在熵交换现象, 更重要的是证明了它们之间的熵交换需要满足一定的条件. 同时也计算了原子与场之间的纠缠, 发现两子系统间熵交换与纠缠的关系.     

Optomechanical coupling in a two-dimensional photonic crystal defect cavity

Periodically structured materials can sustain both optical and mechanical modes. Here we investigate and observe experimentally the optomechanical properties of a conventional two-dimensional suspended photonic crystal defect cavity with a mode volume of ~3(λ/n)3. Two families of mechanical modes are observed: flexural modes, associated to the motion of the whole suspended membrane, and localized modes with frequencies in the GHz regime corresponding to localized phonons in the optical defect cavity of diffraction-limited size. We demonstrate direct measurements of the optomechanical vacuum coupling rate using a frequency calibration technique. The highest measured values exceed 80 kHz, demonstrating high coupling of optical and mechanical modes in such structures.     

Optomechanical dynamics in detuned whispering-gallery modes cavity

The dynamics of a microresonator in detuned whispering-gallery modes (WGM) cavity opto-mechanical system are investigated by the quantum Langevin equation. A WGM cavity coupling to two parallel waveguides is devised to study the transmission and reflection of this system. In single mode WGM cavity, without optomechanical coupling, both the transmission and reflection of the cavity present a Lorentzian dip and peak. When the coupling between the cavity mode and mechanical mode is considered, the transmission and reflection of the optomechanical cavity show “W” and “M” shape mode splitting. Moreover, under the action of a controlling and a probe laser, the output field at the probe frequency presents electromagnetically induced transparency (EIT)-like spectrum in the system. We give the physical origin of EIT-like and the pump-probe response for the WGM shares all the features of the Λ system in atoms. Further, due to backscattering, the two traveling waves in WGM are coupled with a rate γ. The transmission and reflection of the optomechanical cavity display three modes splitting in the spectra with optomechanical coupling between the two cavity modes and the mechanical mode.     

On the observation of decoherence with a movable mirror

Following almost a century of debate on possible “independent of measurement" elements of reality, or “induced" elements of reality - originally invoked as an ad-hoc collapse postulate, we propose a novel line of interference experiments which may be able to examine the regime of induced elements of reality. At the basis of the proposed experiment, lies the hypothesis that models of “induced" elements of reality should exhibit symmetry breaking within quantum evolution. The described symmetry experiment is thus aimed at being able to detect and resolve spatial symmetry breaking signatures. The proposed experiment stands at the edge of present day technological abilities and will be, so we believe, realizable in the near future. Received 2 December 1999 and Received in final form 6 April 2000     

Optomechanical cavity cooling of an atomic ensemble

We demonstrate cavity sideband cooling of a single collective motional mode of an atomic ensemble down to a mean phonon occupation number ?n?(min?)=2.0(-0.3)(+0.9). Both ?n?(min) and the observed cooling rate are in good agreement with an optomechanical model. The cooling rate constant is proportional to the total photon scattering rate by the ensemble, demonstrating the cooperative character of the light-emission-induced cooling process. We deduce fundamental limits to cavity cooling either the collective mode or, sympathetically, the single-atom degrees of freedom.     

Control of the entanglement of a two-level atom in a dissipative cavity via a classical field

We investigate the entanglement dynamics and purity of a two-level atom, which is additionally driven by a classical field, interacting with a coherent field in a dissipative environment. It is shown that the amount of entanglement and the purity of the system can be improved by controlling the classical field.     

Sudden birth of entanglement between two atoms successively passing a thermal cavity

We study the dynamics of entanglement of two initially separate atoms passing through a cavity one after another by employing the concurrence and negativity. The effects of the atomic coherence and mean photon number on the time evolution of atom-atom entanglement are examined when the field is initially in thermal field. We show that the phenomenon of sudden birth of entanglement occurs in some certain conditions and the threshold time for the creation of the entanglement can be controlled by the atomic coherence and mean photon number of the field. It is also shown that the entanglement between two atoms can be created even if the two atoms are initially in excited states.     

Generation of entanglement molecules via weak coherent field in cavity QED

This paper presents a method for generating entanglement molecules, which is introduced by Dur (2001 Phys. Rev. A). In this scheme, N ladder-type three-level atoms are sent through a resonant weak coherent cavity field, then the system states are measured. And the system field may collapse onto some possible types of entanglement molecules. Meanwhile it discusses about the interaction time from the experimental point of view, and compare the result with the previous scheme proposed by Huang (2004 J. Phys. B: At. Mol. Opt. Phys.).     

Information entropy and entanglement of a superconducting qubit coupled to a cavity field with its spontaneous decay

The quantum entanglement between superconducting qubit and cavity field is described quantitatively in the presence of spontaneous decay. Depending on how how a system is quantum correlated with its environment, the entanglement dynamics between the qubit and cavity is evaluated and investigated during the dissipative process. The motivation based on recent experiments wherein the Cooper box can be used to probe the decay of the resonator superposition state due to environmental decoherence, we theoretically investigate the dynamics of entanglement measured by the negativity. Wehrl entropy and Wehrl phase distribution of a superconducting qubit coupled to a cavity field induced by a superconducting qubit-damping reservoir governed by a master equation.     

选择原子测量对原子与光场纠缠特性的影响

考虑将初始处于纠缠态的一个原子注入处于Fock态的单模腔中,并且原子与光场发生共振相互作用的情况,采用Negativity熵来描述两子系统间的纠缠,运用数值计算方法研究了腔内原子与光场间的纠缠特性.通过是否进行原子态选择性测量情况下,对腔内原子与光场间的纠缠特性的比较,讨论了腔外原子的测量对纠缠特性的影响.研究结果表明...     

Manipulating mixed state entanglement between a time-dependent field and a three-level trapped ion

In this paper, we extend earlier investigations (Q.C. Zhou, S.N. Zhu, Opt. Commun. 248 (2005) 437) on the pure state entanglement to the mixed state entanglement. In particular, analysis of the pattern of entanglement arising in the interaction between a three-level trapped ion with a time-dependent frequency interacting with a laser field is presented. By working out an exact analytic solution, we conclusively calculate the mixed state entanglement formula. Numerical calculations under current experimental conditions are carried out. Depending on the initial state of the system and in the presence of a time-dependent interaction, long surviving entanglement between the trapped ion and field can be obtained.