Quantum Phase Gates for Trapped Ions via Adiabatic Passage

We propose a scheme to produce quantum phase gates for trapped ions. Taking advantage of the adiabatic evolution, the operation is insensitive to small fluctuations of experimental parameters. Furthermore, the spontaneous emission is suppressed since the ions have no probability of being populated in the electronic excited states.     

Robust Entanglement for Multiple Trapped Ions in Thermal Motion

A robust scheme is proposed for producing maximally entangled states for many trapped ions in thermal motion. In the scheme the ions are simultaneously illuminated by two standing-wave laser fields. During the operation the phases of the lasers are inverted, which not only cancels the vibration-dependent parts in the evolution operator, but also suppresses direct off-resonant coupling of the internal states. Thus, our scheme allows the production of entanglement for hot trapped ions with laser fields of high intensity, which makes the entanglement speed extremely high.     

Two Schemes for Generation of Entanglement for Vibronic Collective States of Multiple Trapped Ions

We propose two schemes to prepare entanglement for the vibronic collective states of multiple trapped ions. The first scheme aims to generating multipartite entanglement for vibrational modes of trapped ions, which only requires a single laser beam tuned to the ionic carrier frequency. Our scheme works in the mediated excitation regime, in which the corresponding Rabi frequency is equal to the trap frequency. Beyond their fundamental importance, these states may be of interest for experimental studies on decoherence since the present scheme operates in a fast way. The second scheme aims to preparing the continuous variable multimode maximal1y Greenberger-Horne-Zeilinger state. The distinct advantage is that the operation time is only limited by the available laser intensity, not by the inherent mechanisms such as off-resonant excitations. This makes it promising to obtain entanglernent of multiple coherent and squeezing states with desired amplitudes in a reasonable time.     

外场驱动的两囚禁离子的纠缠突然消失的研究(英文)

研究了两囚禁离子与一束激光场相互作用模型.通过幺正变换,这个系统被变换成Tavis—Cum-mings模型.通过计算共生纠缠度,分析了这个系统中两离子的纠缠动力学.与Tavis-Cummings模型不同,本文中两离子的纠缠演化经历周期性的消失和恢复.纠缠消失和恢复的周期与系统的初态有关.     

Generation of Three-Qutrit Singlet States with Two-Level Trapped Ions

We propose an adiabatic-passage scheme for the generation of three-qutrit singlet states with two-level trapped ions. Distinctly different from previous proposals, we encode qutrits in Dicke states with two-level ions and use the adiabatic-evolution techniques in order not to exactly control the laser pulses, making the realization of the scheme much easier. Furthermore, the phonon is only virtually excited in the procedure, so the effect of the phonon losses can be reduced.     

Entangled W State Generation via Adiabatic Passage in Cavity QED

A scheme is proposed to generate W state of N atoms trapped in a cavity, based on adiabatic passage along dark state. Taking advantage of adiabaticpassage, the atoms have no probability of being excited and thus the atomicspontaneous emission is suppressed. The scheme is simple. It does not needto adjust the interaction time accurately, and does not need to prepare thecavity field in one-photon state. Numerical simulation shows that thesuccessful probability of the scheme increases with the increasing of the atom number.     

Stark-Chirped Rapid Adiabatic Passage in Presence of Dissipation for Quantum Computation

Stark-chirped rapid adiabatic passage （SCRAP） is an important technique used for coherent quantum controls. In this paper we investigate how the practically-existing dissipation of the system influences on the efficiency of the passage, and thus the fidelities of the SCRAP-based quantum gates. With flux-biased Josephson qubits as a specifical example, our results show clearly that the efficiency of the logic gates implemented by SCRAP are robust against the weak dissipation. The influence due to the non-adiabtic transitions between the adiabatic passages is comparatively significantly small. Therefore, the SCRAP-based logic gates should be feasible for the realistic physical systems with noises.     

Three-Dimensional Quantum State Transferring Between Two Remote Atoms by Adiabatic Passage under Dissipation

Recently, Zhou et al. [Phys. Rev. A 79 （2009） 044304] proposed a scheme for transferring three-dimensional quantum states between remote atomic qubits confined in cavities connected by fibers through adiabatic passage. In order to avoid the decoherence due to spontaneous emission, Zhou et al. utilized the large detuning atom-field interaction. In the present paper, we discuss the influence of dissipation on the scheme in both the resonant atom-field interaction case and the large detuning case. We numerically analyze the success probability and the transferring fidelity. It is shown that the resonant case is a preferable choice for the technique of the stimulated Raman adiabatic passage （STIRAP） due to the shorter operation time and the smaller probability of dissipation.     

Three-Dimensional Quantum State Transferring Between Two Remote Atoms by Adiabatic Passage under Dissipation

Recently, Zhou et al. [Phys. Rev. A 79 (2009) 044304]proposed a scheme for transferring three-dimensional quantum statesbetween remote atomic qubits confined in cavities connected byfibers through adiabatic passage. In order to avoid the decoherencedue to spontaneous emission, Zhou et al. utilized the large detuningatom-field interaction. In the present paper, we discuss theinfluence of dissipation on the scheme in both the resonantatom-field interaction case and the large detuning case. Wenumerically analyze the success probability and the transferringfidelity. It is shown that the resonant case is a preferable choicefor the technique of the stimulated Raman adiabatic passage (STIRAP)due to the shorter operation time and the smaller probability of dissipation.     

N个热囚禁离子的GHZ态的制备

我们提出了一个简单的方法产生N个囚禁离子的GHZ态.在这个方法中,初始时处于相同态的N个两能级离子被囚禁在一个线性阱中,同时被两束均匀的经典激光照射.这个方法对振动模的加热不敏感,从退相干的观点来看这点很重要.     

Implementing a Universal Quantum Cloning Machine via Adiabatic Evolution in Ion-Trap System

A scheme for the realization of a universal quantum cloning machine is proposed in this paper. The present protocol does not need the vibrational mode to act as the memory and it is robust against small changes of experimental parameters due to adiabatic passages. Furthermore, the scheme may be realized based on current technology.     

Fast Preparation of W States for Hot Trapped Ions

A scheme is presented for generating W states for three o()four trapped ions in thermal motion. The scheme works in the regime, where the Rabi frequency of the laser field is on the order of the trap frequency, resulting a fast entanglement speed, which is of importance in view of decoherence.     

Fast Preparation of W States for Hot Trapped Ions

A scheme is presented for generating W states for three or four trapped ions in thermal motion. The scheme works in the regime, where the Rabi frequency of the laser field is on the order of the trap frequency, resulting a fast entanglement speed, which is of importance in view of decoherence.     

Two-qutrit maximally entangled states prepared via adiabatic passage in ion-trapped system

This paper considers a scheme for the preparation of two-qutrit entangled states via adiabatic passage in iontrapped system.In the proposal,the two three-level V-type ions are initially cooled to the ground states and need not be separately addressed.Moreover,only the ionic states act as memory and the system evolves in the dark space during the whole procedure,which makes the system robust against the decoherence and the fluctuation of the laser pulse.     

Motional Quantum-State Engineering and Implementation of a Quantum Phase-Gate for Multiple Trapped Ions

We propose a scheme to generate a superposition of motional coherent states with arbitrary coefficients on a line in phase space and implement a quantum controlled phase-gate for multiple trapped ions with a single standing-wave laser pulse whose carrier frequency is tuned to the ions transition. In the scheme each ion does not need to be exactly positioned at the node of the standing wave, which is very important from viewpoint of experiment. Furthermore, our scheme may allow the generation of a superposition of coherent states with large mean phonon number for a large number of trapped ions in a fast way by choosing suitable laser intensity. We show that it can also be used to generate maximally entangled states of multiple trapped ions.     

Motional Quantum-State Engineering and Implementation of a Quantum Phase-Gate for Multiple Trapped Ions

We propose a scheme to generate a superposition of motional coherent states with arbitrary coefficients on a line in phase space and implement a quantum controlled phase-gate for multiple trapped ions with a single standing-wave laser pulse whose carrier frequency is tuned to the ions transition. In the scheme each ion does not need to be exactly positioned at the node of the standing wave, which is very important from viewpoint of experiment, Furthermore, our scheme may allow the generation of a superposition of coherent states with large mean phonon number for a large number of trapped ions in a fast way by choosing suitable laser intensity. We show that it can also be used to generate maximally entangled states of multiple trapped ions.     

Teleportation of an Unknown Atomic State via Adiabatic Passage

We propose a scheme for teleporting an unknown atomic state via adiabatic passage. Taking advantage of adiabatic passage, the atom has no probability of being excited and thus the atomic spontaneous emission is suppressed. We also show that the fidelity can reach 1 under certain condition.