Scheme for Preparation of W State Among Three Cavity Modes

We present a scheme of preparing the tripartite W state among three cavity modes of radiation field inside high-Q superconducting cavities. Our scheme is based on the interaction of a four-level atom with the cavity field for precalculated interaction times with every mode.     

Scheme for Preparation of the W State via Cavity QED

We put forward a scheme for preparation of an entangled multiparty W state between different modes of radiation field inside high-Q cavity QED. Our scheme is based on the interaction of a two-level atom with the cavity field with the assistance of a strong classical driving field for precalculated interaction time. In principle, the scheme can be extended to prepare an N-party W state. The required experimental techniques are within the scope of what can be obtained in the microwave cavity QED setup.     

Conditional large Fock state preparation and field state reconstruction in cavity QED

We propose a scheme for producing large Fock states in cavity QED via the implementation of a highly selective atom-field interaction. It is based on Raman excitation of a three-level atom by a classical field and a quantized field mode. Selectivity appears when one tunes to resonance a specific transition inside a chosen atom-field subspace, while other transitions remain dispersive, as a consequence of the field dependent electronic energy shifts. We show that this scheme can be also employed for reconstructing, in a new and efficient way, the Wigner function of the cavity field state.     

利用选择共振作用制备纠缠态

文章提出一个在高品质腔中利用选择性相互作用制备Bell态和W态的方案。该方案通过参数的选择来严格控制囚禁原子和腔场之间的相互作用,在所需要的子空间里实现共振跃迁,而让原子的其它跃迁处于大失谐,从而可以绝热去除。因此,本方案可以有效抑制原子的自发辐射,而且不需要对腔中原子独立寻址,使其在实验上更容易实现。     

Continuous-Variable Entanglement Generation from a Four-State Atom under Raman Excitation

We investigate the generation and the evolution of continuous-variable (CV) entanglement from a laser-driven four-state atom inside a doubly resonant cavity under Raman excitation. Two transitions in the four-state atom independently interact with the two cavity modes, while two other transitions are driven by coupling laser fields. By including the atomic relaxation as well as cavity losses, we show that the CV entanglement with large mean number of
photons can be generated in our scheme. We also show that the intensity of the coupling laser fields can influence effectively the entanglement period of the cavity field. Different from the conventional resonant excitation scheme where zero one-photon detuning are required, it is found that the intensity and period of entanglement between the two cavity modes as well as the total mean photon number of the cavity field can be adjusted by properly
modulating the frequency detuning.     

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.     

Preparation of steady-state entanglement via a laser-excited resonant interaction

In this paper we propose a scheme in which two-mode entanglement in a steady state is produced by using two lasers to resonantly drive a single four-level atom embedded inside a two-mode optical cavity.In this scheme,atomic coherence induced by a classical laser plays an important role in the process of preparing the entangled state.With the coupling of a strong control field,direct two-photon transition is generated and the relatively weak pump field induces the parametric interaction between two photons,which makes them entangle with each other.By numerical calculation,we find that the degree of entanglement depends strongly on the Rabi frequencies of the classical laser fields and the cavity losses.     

Amplification of entangled states of squeezed light

Two amplification schemes are considered for entangled squeezed states of light, including an Einstein-Podolsky-Rosen entangled state of continuous variables (EPR pair): propagation in a nonlinear medium and reflection from a cavity. Both schemes make use of a parametric process that can be implemented in a periodic nonlinear medium. The existence of an integral of motion makes it possible to amplify an entangled state of light while preserving the initial entanglement. To analyze the cavity-based scheme, a master equation is derived for the density matrix of the field inside the cavity. The feasibility of amplification that preserves entanglement of an EPR pair is demonstrated for this scheme.     

Generation of fully three-mode continuous-variable entanglement in a single-atom laser

We proposed a scheme for generating fully three-mode continuous-variable (CV) entanglement between three nondegenerate cavity modes in a single-atom laser. In our scheme, the single-atom laser consists of a four-level atom inside a triply resonant cavity, and the atomic coherence is induced by two classical laser fields driving the corresponding atomic transitions. To demonstrate the generation of entanglement, we numerically simulated the dynamics of this system, and the numerical simulation shows that the single-atom laser considered here can be seen as a three-mode CV entanglement amplifier even in the presence of cavity losses. Moreover, we also show that the generation of entanglement doesn’t depend intensively on the initial condition of cavity field, and the fully three-mode CV entanglement can be realized no matter the three entangled (nondegenerate) modes are initially in the same state or different states based on our scheme.     

Conditional quantum CNOT gate between two four-level atoms

We propose a scheme to implement a quantum controlled-NOT (CNOT) gate between two four-level atoms inside the detuned optical cavity. The system state is evolved inside the decoherence-free (DF) subspace through stimulated Raman processes, which yields the desired unitary evolution operation for the CNOT.Our scheme is immune to decoherence due to dissipation of cavity excitation and spontaneous emission from the excited atomic level.     

On the generation of a generalized superposition of displaced squeezed states

A feasible scheme is presented to generate a generalized superposition of displaced squeezed states, cosθ|α,z〉±sinθ|-α,z〉, in a single mode of the electromagnetic field inside a microwave cavity. The scheme employs a two-level (Rydberg) atom driven by an external classical field. The success probability and the interaction time of such generation are also considered.     

原子的选择测量对原子纠缠特性和场熵的影响*

考虑初始处于W态的三个二能级原子,将其中两个原子同时注入处于真空态的单模腔中,并与光场发生共振相互作用的情况。采用数值计算方法,通过对是否进行原子态选择性测量情况下,腔内原子间的纠缠性质和场熵的比较,讨论了对腔外原子的态选择性测量对腔内原子间的纠缠性质和场熵演化的影响。研究结果表明：对腔外原子的选择性测量,可增强腔内原子间的纠缠,但会减弱腔內原子与光场的关联。     

Squeezed States of Magnons and Phonons in a Cavity Magnomechanical System with a Microwave Parametric Amplifier

The cavity magnomechanical system has become a promising platform for preparing macroscopic quantum states. In this work, a scheme for generating the steady-state quadrature squeezing of the magnon and phonon modes in a cavity magnomechanical system is presented. This scheme uses a degenerate microwave parametric amplifier (PA) inside the microwave cavity. It is found that the squeezing of the cavity mode produced by the PA can be transferred to the magnon mode due to the cavity-magnon beamsplitter-like interaction, and the squeezing of the magnon mode can be further transferred to the phonon mode due to the magnon-phonon beamsplitter-like interaction induced by driving the magnon mode with a red-detuned microwave field. The effects of the parametric gain and phase of the PA, the magnon-cavity coupling strength, the power of the magnon drive, and the temperature of the environment on the squeezing of the magnon and phonon modes have been evaluated. The results show that the squeezing of the magnon and phonon modes is robust against the temperature of the environment.     

三纠缠原子与双模腔场相互作用系统的纠缠演化特性

研究了初始处于GHZ态的三个两能级原子与双模腔场相互作用系统的纠缠动力学特性,得到了并发度和线性熵的解析表达式.讨论了腔场初始纠缠度对腔内两原子之间纠缠的影响,对其余子系统求迹后结果表明腔内两原子之间的纠缠出现突然产生现象,腔内两原子之间产生纠缠的阈值时间和最大值依赖于双模腔场初始纠缠度;并且发现腔内两原子子系统和腔外原子与场子系统之间在整个的时间演化过程中一直保持着纠缠状态.     

Plasmon‐enhanced Raman scattering by suspended carbon nanotubes

We report plasmon‐enhanced Raman scattering of the order of 10³ by a metallic carbon nanotube partially suspended inside a near‐field cavity. The tube is part of a small bundle, and is interfaced with an Au nanodisc dimer using a recently developed assembly scheme based on dielectrophoretic deposition. Spatially resolved Raman measurements with two excitation wavelengths and two orthogonal polarizations confirm that the enhancement arises from a 65 nm long suspended tube segment. We show that the orientation of the tube inside the cavity can be as effective for generating enhancement as placing the nanotube precisely in a plasmonic hotspot. Position and shape of the G‐peak show that the suspended part of the tube is free of strain and doped with a Fermi energy shift ≤40 meV. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Quantum Dense Coding Based on Entangled Bell State in Cavity QED

We investigate quantum dense coding based on entangled Bell states in cavity QED. We implement a experimentally feasible new scheme in cavity QED with atomic qubits where the atoms interact with a highly detuned cavity mode with the assistance of a classical field. The scheme is insensitive to the cavity decay and the thermal field. Based on cavity QED techniques, the scheme can be realizable.     

Implementation of Deutsch-Jozsa Algorithm with Superconducting Quantum-Interference Devices via Raman Transition

In this paper, a theoretical scheme is proposed to implement the Deutsch-Jozsa algorithm with SQUIDs (superconducting quantum-interference devices) in cavity via Raman transition. The scheme only requires a quantized cavity field and classical microwave pulses. In this scheme, no transfer of quantum information between the SQUIDs and the cavity is required, the cavity field is only virtually excited and thus the cavity decay is suppressed.     

Teleportation of atomic states with a weak coherent cavity field

A scheme is proposed for the teleportation of an unknown atomic state. The scheme is based on the resonant interaction of atoms with a coherent cavity field. The mean photon-number of the cavity field is much smaller than one and thus the cavity decay can be effectively suppressed. Another advantage of the scheme is that only one cavity is required.     

开槽管微波腔中微波场分布初步研究

开槽管微波腔已被用于铷原子频标,但是其中的微波场分布尚不清楚. 利用高频结构仿真软件(HFSS)获得了开槽管微波腔内微波场的分布,利用激光-微波双共振方法实现了微波腔场分布的实验测量,所得结果与理论结果一致. 研究结果表明,腔内微波场磁力线呈轴向分布,这表明该种微波腔是适用于原子频标的. 研究结果还表明,腔内微波场存在明显的空间不均匀性,这会导致一些区域的原子不能充分利用,限制原子的钟跃迁信号强度. 因此,现有的开槽管腔结构还有改进的余地.     

Coherent effect of triple-resonant optical parametric amplification inside a cavity with injection of a squeezed vacuum field

In theory, we study the quantum tluctuatlons ot tlae suDllarmonlc renecteu nela Irom a ulplc-rc~ulltUtt IdU~ClIClatC optical parametric amplifier （OPA） inside an optical cavity. We discuss two cases, where the linewidth of the harmonic field is either much narrower or broader than the subharmonic field. Since an electromagnetically-induced-transparency （EIT）-like effect can be simulated in a triple-resonant OPA, the output spectra from a triple-resonant OPA with a squeezed vacuum input may simulate the phenomenon of the response of an EIT medium for squeezed states. This scheme can be implemented with present experimental setups.