Approximate and Conditional Teleportation of?an?Unknown Atomic State with Dissipative Two-Photon Interaction in Cavity QED System

A scheme for approximate and conditional teleportation of an unknown atomic state via dissipative two-photon interaction in cavity QED is proposed. In our scheme, the dissipative two-photon interaction Jaynes-Cummings model is used to realize the approximate and conditional teleportation. We investigate analytically the influence of the cavity mode decay on the teleportation fidelity and show that the high fidelity teleportation can be implemented in dissipative case. Our scheme does not involve the Bell-state measurement and an additional atom, only requiring two atoms and one single-mode cavity. The scheme may be generalized to not only the teleportation of the state of a cavity mode to another mode by means of a single atom but also the teleportation of the state of a trapped ion.     

基于低Q腔光子Faraday旋转的远程态制备

基于低Q腔中单光子的输入与输出关系,提出了利用偏振光Faraday旋转分别遥远制备单原子态和两原子纠缠态的可行方案.研究结果表明,当初始原子态的系数为实数时,通过选择合适的偏振光、腔场与原子相互作用系统的参数,单原子态与两原子纠缠态的远程制备均可确定性地得以实现.与以前的原子态远程制备方案相比,本文方案采用光子作为飞行比特来传递量子信息,故原则上可实现原子态的真正长距离制备.由于原子态的信息编码在耗散单边腔囚禁的Λ型三能级原子的两个基态能级,且原子仅虚激发,因此本文方案对腔衰减和原子自发辐射不敏感.此外,本文所提出的两种方案不需要两体或多体正交测量,仅涉及单体直积态测量,而且两种方案都工作在低Q腔,不需要原子与光腔的强耦合,从而有效降低了实验难度.     

High efficient scheme for remote state preparation with cavity QED

In this paper, a scheme is proposed for remote state preparation （RSP） with cavity quantum electrodynamics （QED）. In our scheme, two observers share two-atom nonmaximally entangled state as quantum channels and can realize remote preparation of state of an atom. We also propose a generalization for remote preparation of N-atom entangled state by （N＋1）-atom GHZ-like state （N ≥ 2）. By this scheme, one single-atom projective measurement is enough for the RSP of a qubit or N-atom entangled state, and the probability of success for RSP is unity. Furthermore, we have considered the case where observers use W-like state as quantum channels to realize RSP of a qubit. We compare our scheme with existing ones.     

Approximate Teleportation of an Unknown Atomic-Entangled State with Dissipative Atom-Cavity Resonant Jaynes-Cummings Model

We propose a scheme for approximately and conditionally teleporting an unknown atomic-entangled state in dissipative cavity QED. It is the further development of the scheme of [Phys. Rev. A 69 (2004) 064302], where the cavity mode decay has not been considered and the state teleportated is an unknown atomic state. In this paper, we investigate the influence of the decay on the approximate and conditional teleportation of the unknown atomic-entangled state, which is different from that teleportated in [Phys. Rev. A 69 (2004) 064302] and then give the fidelity of the teleportation, which depends on the cavity mode decay. The scheme may be generalized to not only the teleportation of the cavity-mode-entangled-state by means of a single atom but also the teleportation of the unknown trapped-ion-entangled-state in a linear ion trap.     

Approximate and Conditional Teleportation of an Unknown Atomic State with Dissipative Jaynes-Cummings Model

A scheme for approximately and conditionally teleporting an unknown atomic state in dissipative cavity QED is proposed. It is the extension of the scheme of [Phys. Rev. A 69 （2004） 064302], where the cavity mode decay has not been considered and only a time point of system evolution and the corresponding fidelity implementing the teleportation are given. In fact, the cavity mode decay exists really and must be delt with. In this paper, we investigate the influence from the cavity mode decay on the implementation of the approximate and conditional teleportation by means of the dissipative Jaynes Cummings model and then show the analytical expression of the fidelity of realization of the teleportation. Alternatively, our scheme does not involve an additional atom, only requiring two atoms and one single-mode cavity.     

Approximate Toffoli Gate Originated from a Single Resonant Interaction of Cavity Dissipation and Atomic Spontaneous Emission

We propose a potentially practical scheme to implement an approximate three-qubit Toffoli gate by a single resonant interaction in dissipative cavity QED in which the cavity mode decay and atomic spontaneous emission are considered. The scheme does not require two-qubit controlled-NOT gates but uses a three-qubit phase gate and two Hadamard gates, where the approximate phase gate can be implemented by only a single dissipative resonant interaction of atoms with the cavity mode. Discussions are made for the advantages and the experimental feasibility of our scheme.     

Dissipative Dynamics of Quantum Discord of Two Strongly Driven Qubits

The exact dynamics of quantum discord (QD) of two strongly driven qubits, which are initially prepared in the X-type quantum states and inserted in two independent dissipative cavities or in a common dissipative cavity, are studied. The results indicate that both in the two cases, the evolution of QD is independent of the initial cavity state. For the two independent dissipative cavities, it is found that the phenomenon of sudden transition between classical and quantum decoherence exists and the transition time can be greatly delayed by suitably choosing the initial state parameter of the two qubits, the cavity mode-driving field detunning and the decay rate of the cavity. For the common dissipative cavity, it is shown that for some initial states of the two qubits, the QD can increase for a finite time at first, and then it decreases to a steady value, while for some other initial states, the QD can increase monotonously or with oscillation till a stable value is reached. Moreover, the creation of QD for the two qubits in a common cavity is discussed.     

远程制备双原子纠缠态

提出一种远程制备双原子纠缠态的方案,该方案基于两个原子与单模腔场的同时非共振相互作用.由于双粒子纠缠态比三粒子纠缠态容易制备,方案用两对双原子纠缠态作为量子通道.Alice 拥有的两个相同原子同时与一单模腔场非共振相互作用.Alice已知她要制备的纠缠态,她选择适当的相互作用时间、测量她所拥有的两个原子并通过经典通道通知Bob.Bob引入一个相同的辅助原子和一个单模腔场来实现方案.方案对腔场状态和腔损耗不敏感,基于当前的腔QED 技术,方案能在实验上实现.该方案有望在量子信息过程中有重要的应用价值.     

Dissipative generation for steady-state entanglement of two transmons in circuit QED

We present a dissipative scheme to generate an entangled steady-state between two superconducting transmon qutrits separately embedded in two coupled transmission line resonators in a circuit quantum electrodynamics(QED) setup. In our scheme, the resonant qutrit-resonator interaction and photon hopping between resonators jointly induce asymmetric energy gaps in the dressed state subspaces. The coherent driving fields induce the specific dressed state transition and the dissipative processes lead to the gradual accumulation in the population of target state, combination of both drives the system into a steady-state entanglement. Numerical simulation shows that the maximally entangled state can be produced with high fidelity and strong robustness against the cavity decay and qutrit decay, and no requirements for accurate time control. The scheme is achievable with the current experimental technologies.     

Preparation and decoherence of superpositions of electromagnetic field states

In a recent experiment the progressive decoherence of a mesoscopic superposition of two coherent field states in a high-Q cavity, known as Schr?dinger cat state, has been measured for the first time [Brune et al., Phys. Rev. Lett. 77, 4887 (1996)]. Here, the full master equation governing the coupled dissipative dynamics of the atom-field system studied in the experiment is formulated and solved numerically for the experimental parameters. The model simulated avoids the approximations underlying an analytically solvable model which is based on a harmonic expansion of the energies of the dressed atomic states and on a treatment of their dynamics within the adiabatic approximation. In particular, the numerical simulations reveal that the coupling of the cavity field mode to its environment causes important decoherence effects already during the initial preparation phase of the Schr?dinger cat state. This phenomenon is investigated in detail with the help of a measure for the purity of states. Moreover, the Hilbert-Schmidt distance of the intended target state, the Schr?dinger cat, to the state that is actually prepared in the experiment is determined. Received 13 September 2000 and Received in final form 22 December 2000     

Entanglement transfer from two-mode squeezed vacuum light to spatially separated mechanical oscillators via dissipative optomechanical coupling

In this paper, we propose a scheme to generate an entangled state between two spatially separated movable mirrors by injecting the two-mode squeezed optical reservoir to the dissipative optomechanics, in which the movable mirrors can modulate the linewidth of the cavity modes. When the coupling between the mirrors and the corresponding cavity modes is weak, the two driven cavity fields can respectively behave as the squeezed-vacuum reservoir for the two movable mirrors by utilizing the effect of completely destructive interference of quantum noise. Thus the mechanical modes are prepared in a two-mode squeezed vacuum state. Moreover,when the coupling between the two mirrors and the cavities modes is strong, the entanglement between the two movable mirrors decreases because photonic excitation can preclude the completely destructive interference of quantum noise, but the movable mirrors are still entangled.     

Quantum state engineering by superpositions of coherent states along a straight line with a single atomic state measurement

A new scheme is proposed for preparation of a type of nonclassical state in cavity QED. In the scheme, an atom either flying through or trapped within a cavity, is controlled by the classical Stark effect; this makes it interact alternately with a (resonant) classical field and with the (dispersive) cavity field. The cavity field, which allows an arbitrary displacement operation during the process, after the detection on the atom, finally collapses to the specific superpositions of coherent states, with their weighting factors controllable. The scheme is also applied for preparation of superpositions of motional coherent states for a trapped ion. The scheme is in contrast to all the previous ones, and thus provides a new perspective for quantum state engineering.     

Remote Preparation of an Arbitrary Two-atom State in the Cavity QED

A simple scheme for remote preparation of an arbitrary two-atom state in the cavity QED. An arbitrary two-atom entangled state can be prepared perfectly. Our protocol only need single qubit measurement instead of the conventional Bell-state measurement, then it is quite simple but also very robust to the cavity decay and the influence of the thermal field. The probability of the success in our scheme is 1.0.     

Conditional Generation of Multiparticle Entanglement via Cavity QED

We propose a simple scheme to not only generate GHZ states and W states of the multiparticle but also form a new category of multiparticle entangled states by letting the λ-type three-level atoms simultaneously interacting with a coherent cavity field followed by the selective measurements on the cavity mode. We investigate the influence of the cavity dissipation on the generated entangled state and discuss the experimental feasibility of our scheme. It is shown that the intensity of the coherent cavity field plays an instructive role in contribution to state preparation process while the cavity decay and the detuning between the atoms and cavity mode result in the deterioration of the generated entangled state.     

Preparation of Steady 3D Dark State Entanglement in Dissipative Rydberg Atoms via Electromagnetic Induced Transparency

A scheme to prepare a 3D entangled state between a pair of Rydberg atoms via dissipative dynamics and electromagnetic induced transparency associated with the single-atom dark state is proposed. The prepared entangled state is the dark state of the whole system. The scheme is also feasible regardless of initial purity or mixed state. Since the proposed scheme is based on the Rydberg block regime, the Rydberg–Rydberg interaction strength does not need to satisfy a certain relation with laser detuning, which is very different to the Rydberg-antiblock-based dissipative schemes. One group of Rydberg states and corresponding parameters to simulate the fidelity are used, which verify the feasibility of the scheme.     

Qubit-assisted squeezing of mirror motion in a dissipative cavity optomechanical system

In this study, we investigate a hybrid system consisting of an atomic ensemble trapped inside a dissipative optomechanical cavity assisted with perturbative oscillator-qubit coupling. Such a system is generally very suitable for generating stationary squeezing of the mirror motion in the long-time limit under the unresolved sideband regime. Based on the master equation and covariance matrix approaches, we discuss in detail the respective squeezing effects. We also determine that in both approaches, simplifying the system dynamics with adiabatic elimination of the highly dissipative cavity mode is very effective. In the master equation approach, we find that the squeezing is a resulting effect of the cooling process and is robust against thermal fluctuations of the mechanical mode. In the covariance matrix approach, we can approximately obtain the analytical result of the steady-state mechanical position variance from the reduced dynamical equation. Finally, we compare the two approaches and observe that they are completely equivalent for the stationary dynamics. Moreover, the scheme may be useful for possible ultraprecise quantum measurement that involves mechanical squeezing.     

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.     

Deterministic controlled bidirectional remote state preparation in dissipative environments

It is a significant subject to explore effective quantum communication protocol and enhance the efficiency of the transmission process in noisy environments. In this paper, we investigate the bidirectional controlled remote preparation of an arbitrary single-qubit state in the presence of dissipative environments by using two EPR states as the entanglement source. We first construct the quantum circuit of our scheme by means of unitary matrix decomposition procedure, then the effects of the Markovian and non-Markovian environmental noises acting on the EPR states are considered through the analytical derivation and numerical calculations of the corresponding average fidelity. Moreover, we adopt two methods of weak measurement reversal (WMR) and detuning modulation to improve the average fidelity. Our results show that the average fidelity can be remarkably enhanced under appropriate conditions of the WMR strength and the detuning. Compared with the average fidelity behaviors in dissipative environments, it is also shown that the two methods for fidelity improvement are more efficient in the non-Markovian regime than in the Markovian regime.     

Hidden Vacuum Rabi Oscillations:Dynamical Quantum Superpositions of On/Off Interaction between a Single Quantum Dot and a Microcavity

We show that it is possible to realize quantum superpositions of switched-on and-off strong light-matter interaction in a single quantum dot-semiconductor microcavity system.Such superpositions enable the observation of counterintuitive quantum conditional dynamics effects.Situations are possible where cavity photons as well as the emitter luminescence display exponential decay but their joint detection probability exhibits vacuum Rabi oscillations.Remarkably,these quantum correlations are also present in the nonequilibrium steady state spectra of such coherently driven dissipative quantum systems.     

Approximate and Conditional Teleportation of an Unknown Atomic State Without the Bell-state Measurement with Multi-photon Interaction

A scheme for approximately and conditionally teleporting an unknown atomic state via multi-photon interaction in cavity quantum electro dynamics (QED) is proposed. It is the extension of the scheme of Zheng (2004) [Physical Review A69, 064302], which is based on Jaynes–Cummings model in QED and where only a time point of system evolution and the corresponding Fidelity implementing the teleportation are given. In our scheme, the cavity field may be Fock state and the multi-photon interaction Jaynes–Cummings model is used to realize the approximate and conditional teleportation. Our scheme does not involve the Bell-state measurement and an additional atom, only requiring two atoms and one single-mode cavity. The fidelity of the scheme is higher than that of Zheng (2004) [Physical Review A69, 064302]. The scheme may be generalized to not only the teleportation of the state of a cavity mode to another mode by means of a single atom but also the teleportation of the state of a trapped ion. PACS: 03.67.-Ta, 03.65.Ta, 42.50.Dv