利用V型三能级原子与相干态光场Raman相互作用传送未知奇偶相干态

描述了简并V型三能级原子与单模相干态光场的Raman相互作用，获得了处于激发态单态的原子与相干态光场相互作用的结果。利用探测原子与光场的相互作用将原子和探测光场制备成最大纠缠态，并将原子注入待测任一奇偶相干叠加态，通过原子与待测腔模构成的Bell基矢演化，对原子进行选择性探测，获得奇偶相干叠加态与原子相互作用后可能的量子状态，然后对待测腔场与原子进行联合探测，接着对所测奇偶相干态腔场的量子状态实施么正变换，就将探测腔场制备到待测腔场的初始量子态上，从而实现未知奇偶相干态的隐形传送。     

A Scheme for Teleportation of an Unknown Entangled Coherent State via Raman Interaction

A scheme is reported for the teleportation of entangled coherent states through the degenerate Raman interaction.The scheme uses an entangled state of an atom and two coherent states as a quantum channel.It makes full use of coherent cavity fields.Furthermore,it does not need any classical field to transform the atom states.     

通过Raman相互作用制备三个腔场的W型纠缠相干态

通过对比分立变量量子信息过程和连续变量量子信息过程的差别,利用相干态比较容易获得的这个特点,提出一种方案制备三个腔场的W型纠缠相干态.方案基于Λ型三能级原子与单模腔场的简并Raman 相互作用.三个相同的腔初始分别处于相干态,三个相同的原子初始处于W型纠缠态,通过三个原子分别与三个腔的Raman相互作用、选择适当的相互作用时间并探测作用后的三个原子,三个腔场坍缩为W型纠缠相干态.在原子与腔的相互作用过程中原子不处于高能级,可以忽略原子的自发辐射,系统的相干性能够得到较好的维持.基于当前的腔量子电动力学技术,相信方案能在实验上实现.该方案制备的三个腔场W型纠缠相干态有望在连续变量量子信息过程中有重要的应用价值.文中将方案推广到制备n(n〉3)个腔场的W型纠缠相干态.     

利用Raman相互作用实现未知原子态的传输

利用Λ型三能级原子与单模腔场之间的相互作用,研究简并喇曼相互作用过程中产生场-原子最大纠缠态的方法,实现量子逻辑门的方法,以及如何利用这种方法来实现未知原子态的量子隐形传送.     

Simultaneous Preparation of Two Optical Cat States Based on a Nondegenerate Optical Parametric Amplifier

The cat state, known as the superposition of coherent states, has broad applications in quantum computation and quantum metrology. Increasing the number of optical cat states is crucial to implement complex quantum information tasks based on them. Here, two optical cat states are prepared simultaneously based on a nondegenerate optical parametric amplifier. By subtracting one photon from each of two squeezed vacuum states, two odd cat states with orthogonal superposition direction in phase space are prepared simultaneously, which have similar fidelity of 60% and amplitude of 1.2. Compared with the traditional method to generate two odd optical cat states based on two degenerate optical parametric amplifiers, only one nondegenerate optical parametric amplifier is applied in this experiment, which saves half of the quantum resources of nonlinear cavities. The presented results make a step toward preparing the four-component cat state, which has potential applications in fault-tolerant quantum computation.     

Enhancement of coherent population transfer in a double Λ-type four-level system via a train of pulse pairs

We propose a flexible way to significantly enhance population transfer efficiency with a train of time-separated pump-Stokes pulse pairs when the non-adiabatic coupling between two degenerate adiabatic states exists in a double Λ-type four-level system, where the pump and Stokes pulses in each pair can be applied in either counterintuitive or intuitive order. It is shown that the needed Rabi frequency for achieving complete population transfer can be reduced dramatically with the increase of number of pump-Stokes pulse pairs, which results from temporal constructive quantum interference between the sequential transitions and subsequent coherent accumulation; moreover, an arbitrary coherent superposition between the two lower states can be realized by suitably tuning the Rabi frequency and the time delay between each pump-Stokes pair. The method may find applications in control of chemical reactions, quantum optics, and quantum information processing.     

薛定谔猫态的产生与探测及其对Jaynes-Cummings模型的影响

利用大失谐情况下的简并喇曼过程和双光子Jaynes-Cummings模型来产生电磁场中的宏观量子叠加态,即薛定旋风谔猫态,并探讨如何用零频检测的方法来探测这些态。研究了当电磁场初态为薛定谔猫态时,对强度耦合的Jaynes-Cummings模型中原子反转的崩塌与再生现象的影响,将在以相干态为初态所产生的原子反转的崩塌区产生不同程度的再生现象。 关键词：     

Implementing the Deutsch-Jozsa algorithm by using Schrodinger cat states in cavity QED

We propose a scheme to implement the Deutsch-Jozsa algorithm by using Schroedinger cat states in cavity quantum electron-dynamics （QED）. The scheme is based on the Raman interaction of a degenerate three-level A-type atom with a coherent state in a cavity. By using Schroedinger cat states, the atomic spontaneous emission can be minimized and the Hadamard transformation in our scheme is not needed.     

Classical breathers and quantum coherent states in discrete NLS systems

We present a comparison of quantum and “semiclassical” trajectories of coherent states that correspond to classical breather solutions of finite discrete nonlinear Schrödinger (DNLS) lattices. The main goal is to explain earlier numerical observations of recurrent return to the vicinity of initial coherent states corresponding to stable breathers that are also spatially localized. This effect can be considered as a quantum manifestation of classical spatial localization. We show that these phenomena are encoded in a simple expression for the distance between the quantum and semiclassical states that involves the basic frequencies of the classical and quantum systems, as well as the breather amplitude and quantum spectral decomposition of the system. A corollary is that recurrence phenomena are robust under perturbation of the initial conditions for stable breathers.     

Phase Properties of Photon-Added Coherent States for Nonharmonic Oscillators in a Nonlinear Kerr Medium

The potential of nonharmonic systems has several applications in the field of quantum physics. The photonadded coherent states for annharmonic oscillators in a nonlinear Kerr medium can be used to describe some quantum systems. In this paper, the phase properties of these states including number-phase Wigner distribution function,Pegg-Barnett phase distribution function, number-phase squeezing and number-phase entropic uncertainty relations are investigated. It is found that these states can be considered as the nonclassical states.     

Coherent state polarons in quantum wells

We investigate the polaronic effects of an electron confined in a quantum well, which we describe through its algebraic properties using su(1,1), taking into account the electron-bulk longitudinal-optical phonon interaction. We construct the variational wave function as the direct product of an electronic part and a part describing coherent phonons generated by the Low–Lee–Pines transformation from the vacuum state. We use two explicit forms of coherent states, Perelomov and Barut-Girardello states, to represent the electronic part in the quantum well spectrum. Our results show that in a coherent state basis for electrons the basic polaron parameters such as the energy gap shift and effective mass are further enhanced compared to those obtained with the conventional sinusoidal form of the basis. The difference between the two types of quantum well coherent states appears in polaronic interactions in quantum wells. We extend the calculations in order to estimate polaron lifetimes for a variety of different material systems.     

Coherent states in geometric quantization

In this paper we study overcomplete systems of coherent states associated to compact integral symplectic manifolds by geometric quantization. Our main goals are to give a systematic treatment of the construction of such systems and to collect some recent results. We begin by recalling the basic constructions of geometric quantization in both the Kähler and non-Kähler cases. We then study the reproducing kernels associated to the quantum Hilbert spaces and use them to define symplectic coherent states. The rest of the paper is dedicated to the properties of symplectic coherent states and the corresponding Berezin–Toeplitz quantization. Specifically, we study overcompleteness, symplectic analogues of the basic properties of Bargmann’s weighted analytic function spaces, and the ‘maximally classical’ behavior of symplectic coherent states. We also find explicit formulas for symplectic coherent states on compact Riemann surfaces.     

通过Raman相互作用隐形传送未知多原子纠缠态

基于多粒子纠缠态在证明量子非定域性和量子信息处理方面的重要应用,提出一种方案隐形传送未知原子纠缠态.方案基于Λ型三能级原子与单模腔场的简并Raman相互作用.首先让n个原子相继通过一个相干腔场来制备量子通道.然后发送者让携带未知纠缠态的另n个原子相继通过相干腔场并通过对原子与腔场的探测作联合测量.当｜α｜1时,可以用探测正交态的方法探测腔场.最后接收者根据由经典通道得到的联合测量结果重构初始态.方案的特点是用一个相干态与多个原子的纠缠态作为量子通道,简单易行.该方案有望在证明量子非定域性和量子信息过程中有重要的应用价值.     

Locality in quantum and Markov dynamics on lattices and networks

We consider gapped systems governed by either quantum or Markov dynamics, with the low-lying states below the gap being approximately degenerate. For a broad class of dynamics, we prove that ground or stationary state correlation functions can be written as a piece decaying exponentially in space plus a term set by matrix elements between the low-lying states. The key to the proof is a local approximation to the negative energy, or annihilation, part of an operator in a gapped system. Applications to numerical simulation of quantum systems and to networks are discussed.     

Number-phase entropic uncertainty relations and Wigner functions for solvable quantum systems with discrete spectra

In this Letter, the “number-phase entropic uncertainty relation” and the “number-phase Wigner function” of generalized coherent states associated to a few solvable quantum systems with non-degenerate spectra are studied. We also investigate time evolution of “number-phase entropic uncertainty” and “Wigner function” of the considered physical systems with the help of temporally stable Gazeau-Klauder coherent states.     

几类宏观量子态的内部结构及其压缩特性

谐振子,变形振子,非简谐振子以及变形非简谐振子湮没算符高次幂的正交归一本征态都具有奇偶结构形式.正是由于这种结构特点决定了它们振幅的高次幂压缩性质.     

Inserting single Cs atoms into an ultracold Rb gas

We report on the controlled insertion of individual Cs atoms into an ultracold Rb gas at ≈400 nK. This requires one to combine the techniques necessary for cooling, trapping and manipulating single laser cooled atoms around the Doppler temperature with an experiment to produce ultracold degenerate quantum gases. In our approach, both systems are prepared in separated traps and then combined. Our results pave the way for coherent interaction between a quantum gas and a single or few neutral atoms of another species.     

Coherent States and Modified de Broglie-Bohm Complex Quantum Trajectories

This paper examines the nature of classical correspondence in the case of coherent states at the level of quantum trajectories. We first show that for a harmonic oscillator, the coherent state complex quantum trajectories and the complex classical trajectories are identical to each other. This congruence in the complex plane, not restricted to high quantum numbers alone, illustrates that the harmonic oscillator in a coherent state executes classical motion. The quantum trajectories we consider are those conceived in a modified de Broglie-Bohm scheme. Though quantum trajectory representations are widely discussed in recent years, identical classical and quantum trajectories for coherent states are obtained only in the present approach. We may note that this result for standard harmonic oscillator coherent states is not totally unexpected because of their holomorphic nature. The study is extended to coherent states of a particle in an infinite potential well and that in a symmetric Poschl-Teller potential by solving for the trajectories numerically. For the Gazeau-Klauder coherent state of the infinite potential well, almost identical classical and quantum trajectories are obtained whereas for the Poschl-Teller potential, though classical trajectories are not regained, a periodic motion results as t→∞. Similar features were found for the SUSY quantum mechanics-based coherent states of the Poschl-Teller potential too, but this time the pattern of complex trajectories is quite different from that of the previous case. Thus we find that the method is a potential tool in analyzing the properties of generalized coherent states.     

Generalized Coherent States for Position-Dependent Effective Mass Systems

A generalized scheme for the construction of coherent states in the context of position-dependent effective mass systems has been presented. This formalism is based on the ladder operators and associated algebra of the system which are obtained using the concepts of supersymmetric quantum mechanics and the property of shape invariance. In order to exemplify the general results and to analyze the properties of the coherent states, several examples have been considered.     

Quantum qualitative dynamics

We describe our work on qualitative methods for visualizing the quantum eigenstates of systems with nonlinear classical dynamics. For two-degree-of-freedom systems, our approach is based on the use of generalized coherent states, and allows systems with nonoscillator kinematics to be investigated. The general approach is illustrated with two examples involving vibration-rotation interaction in polyatomic molecules. We apply the coherent states of the Lie groupH ₄SU(2) to define quantum surfaces of section for a model involving centrifugal coupling of a harmonic bend with molecular rotation, andSU(2)SU(2) coherent states to study two harmonic normal modes coupled to overall molecular rotation through coriolis interaction. In both systems, quantum states are visualized on the rotational surface of section and compared with the corresponding classical phase space structure. Striking classical-quantum correspondence is observed. We then describe recent results on the quantum states of (N 3)-dimensional systems of coupled nonlinear oscillators, which reveal a quantum delocalization that is reminiscent of classical Arnold diffusion.