Speed Geometric Quantum Logical Gate Based on Double-Hamiltonian Evolution under Large-Detuning Cavity QED Model

We introduce the double-Hamiltonian evolution technique approach to investigate the unconventional geometric quantum logical gate with dissipation under the model of many identical three-level atoms in a cavity~ driven by a classical fieM. Our concrete calculation is made for the case of two atoms for the large-detuning interaction of the atoms with the cavity mode. The main advantage of our scheme is of eliminating the photon flutuation in the cavity mode during the gating. The corresponding analytical results will be helpful for experimental realization of speed geometric quantum logical gate in real cavities.     

Unconventional Geometric Phase Gate with Superconducting Quantum Interference Device Qubits in Cavity QED

In the system with superconducting quantum interference devices （SQUID） in cavity, a scheme for constructing two-qubit quantum phase gate via a conventional geometric phase-shift is proposed by using a quantized cavity field and classical microwave pulses. In this scheme, the gate operation is realized in the subspace spanned by the two lower flux states of the SQUID system mud the population operator of the excited state has no effect on it. Thus the effect of decoherence caused from the levels of the SQUID system is possible to minimize. Under cavity decay, our strictly numerical simulation shows that it is also possible to realize the unconventional geometric phase gate. The experimental feasibility is discussed in detail.     

A Scheme of Conditional Quantum Phase Gate for Dissipative Cavity QED System

We propose a scheme to implement a two-qubit conditional quantum phase gate via a single mode cavity and a cascade four-level atom assisted by a classical laser. The quantum information is encoded on the Fock states of the cavity mode and the two metastable ground states of the atom. Even under the condition of systematic dissipations,this scheme can also be realized with fidelity of 98.6% and success probability of 0.767.     

A Scheme of Conditional Quantum Phase Gate for Dissipative Cavity QED System

We propose a scheme to implement a two-qubit conditional quantum phase gate via a single mode cavity and a cascade four-level atom assisted by a classical laser. The quantum information is encoded.on the Flock states of the cavity mode and the two metastable ground states of the atom. Even under the condition of systematic dissipations, this scheme can also be realized with fidelity of 98.6% and success probability of 0.767.     

Effect of Multiphoton Processes on Geometric Quantum Computation in Superconducting Circuit QED

We study the influence of multi-photon processes on the geometric quantum computation in the systems of superconducting qubits based on the displacement-like and the general squeezed operator methods. As an example, we focus on the question about how to implement a two-qubit geometric phase gate using superconducting circuit quantum electrodynamics with both single- and two-photon interaction between the qubits and the cavity modes. We find that the multiphoton processes are not only controllable but also improve the gating speed. The comparison with other physical systems and experimental feasibility are discussed in detail.     

Effect of Multiphoton Processes on Geometric Quantum Computation in Superconducting Circuit QED

We study the influence of multi-photon processes on the geometric quantum computation in the systems of superconducting qubits based on the displacement-like and the general squeezed operator methods. As an example, we focus on the question about how to implement a two-qubit geometric phase gate using superconducting circuit quantum electrodynamics with both single- and two-photon interaction between the qubits and the cavity modes. We find that the multiphoton processes are not only controllable but also improve the gating speed. The comparison with other physical systems and experimental feasibility are discussed in detail.     

Unconventional Geometric Phase-Shift Gates Based on Superconducting Quantum Interference Devices Coupled to a Single-Mode Cavity

We present a scheme to realize geometric phase-shift gate for two superconducting quantum interference device （SQUID） qubits coupled to a single-mode microwave field. The geometric phase-shift gate operation is performed in two lower flux states, and the excited state [2〉 would not participate in the procedure. The SQUIDs undergo no transitions during the gate operation. Thus, the docoherence due to energy spontaneous emission based on the levels of SQUIDs are suppressed. The gate is insensitive to the cavity decay throughout the operation since the cavity mode is displaced along a circle in the phase space, acquiring a phase conditional upon the two lower flux states of the SQUID qubits, and the cavity mode is still in the original vacuum state. Based on the SQUID qubits interacting with the cavity mode, our proposed approach may open promising prospects for quantum iogic in SQUID-system.     

Unconventional Geometric Phase-Shift Gates Based on Superconducting Quantum Interference Devices Coupled to a Single-Mode Cavity

We present a scheme to realize geometric phase-shift gate for two superconducting quantum interference device (SQUID) qubits coupled to a single-mode microwave field. The geometric phase-shift gate operation is performed transitions during the gate operation. Thus, the docoherence due to energy spontaneous emission based on the levels of SQUIDs are suppressed. The gate is insensitive to the cavity decay throughout the operation since the cavity mode is displaced along a circle in the phase space, acquiring a phase conditional upon the two lower flux states of the SQUID qubits, and the cavity mode is still in the original vacuum state. Based on the SQUID qubits interacting with the cavity mode, our proposed approach may open promising prospects for quantum logic in SQUID-system.     

Geometric Phase Gate Based on Both Displacement Operator and Squeezed Operators with a Superconducting Circuit Quantum Electrdynamics

We give the brief review on the related definition of the geometric phase independent of specific physical system based on the displacement opreator and
the sqeezed operator, then show how the displacement operator and the squeezed operator can induce the general geometric phase. By means of the displacement operator and the squeezed operator concerning the circuit cavity mode state along a closed path in the phase space, we discuss specifically how to implement a two-qubit geometric phase gate in circuit quantum electrodynamics with both single photon interaction and two-photon interaction between the superconducting qubits and the circuit cavity modes. The experimental feasibility is discussed in detail.     

Selective Atom-Cavity Interaction Scheme for Quantum Controlled-NOT Gate Using Four-Level Atoms in Cavity QED System

We propose a scheme for realization a quantum Controlled-NOT gate operation using two four-level atoms through a selective atom cavity interaction in cavity quantum electrodynamics system. In our protocol, the quantum information is encoded on the stable ground states of the two atoms. During the interaction between atoms and single-mode vacuum cavity-field, the atomic spontaneous emission is negligible as the large atom-cavity detuning effectively suppresses the spontaneous decay of the atoms. The influences of the dissipation and the deviation of interaction time on fidelity and corresponding success probability of the quantum Controlled-NOT gate and the experimental feasibility of our proposal are also discussed.     

腔场QED与量子点系统激子纠缠态的制备及消纠缠研究

利用量子点与单模腔场共振相互作用模型提出了激子Bell类和W类纠缠态的制备方案.借助于超算符方法和态的保真度考察了所制备的激子纠缠态的消相干特性,结果表明:激子Bell类和W态的纠缠特性非常脆弱,在极短的时间里演变为消纠缠态.基于腔场与两量子点共振相互作用模型设计了一个量子交换门.     

基于腔QED的一种非均匀量子行走

基于已有的文献,提出一种非均匀的量子行走,这种行走的特点是:针对不同的位置,手征态的变换具有不同的形式.在对该行走作一定的说明之后,我们进一步提出在腔QED体系中,实现该种行走的一种可能方案.     

Quantum Information Splitting Based on Current Cavity QED Techniques

We propose two schemes for quantum information splitting via W-class state. The first scheme is based on the interaction of single atom with single-mode field, while the second scheme is based on the simultaneous interaction of two atoms with single-mode cavity. For the first scheme, the difIiculty of two atoms required to be simultaneously sent through one cavity is avoid. For the second scheme, it is immune to thermal field. Both schemes are experimentally feasible based on current cavity QED techniques.     

腔QED中利用超导量子干涉仪实现Toffoli门

基于腔量子电动力学技术,提出了利用三能级超导量子干涉仪实现Toffoli门的理论方案.利用超导量子干涉仪与腔场发生耦合,以及与外加经典脉冲发生共振跃迁来实现量子态的演化控制.该方案可以拓展到N比特Toffoli门的实现.最后,讨论了逻辑门的实验可行性,四比特Toffoli门的作用时间约为30 nm,它远小于腔衰减时间和较高能级的能量驰豫时间,从而足以实现量子态的操控.并且随着比特数的增多,Toffoli门作用时间的增幅较慢.     

Quantum Superdense Coding Based on Coherent States in Cavity QED

A physical scheme for the implementation of quantum superdense coding has been proposed in Cavity QED. The detuned interaction between Λ-type three-level atoms and coherent fields constitute the main superdense coding process. The quantum superdense coding can be realized in an easier way, and the atoms are not excited during the whole process, so the effect of atomic decay is eliminated naturally.     

Quantum Logic Network for Cloning a State Near a Given One Based on Cavity QED

A quantum logic network is constructed to simulate a cloning machine which copies states near a given one. Meanwhile, a scheme for implementing this cloning network based on the technique of cavity quantum electrodynamics （QED） is presented. It is easy to implement this network of cloning machine in the framework of cavity QED and feasible in the experiment.     

Remote Three-Party Quantum State Sharing Based on Three-Atom Entangled States Assisted by Cavity QED and Flying Qubits

We present a remote three-party quantum state sharing (QSTS) schemewith three-atom Greenberger-Horne-Zeilinger (GHZ) states assisted bycavity QED and flying qubits. It exploits some photons to act as the flying qubits for setting up the quantum channel securely with three-atom systems in a GHZ state, which maybe make this remote QSTS scheme more practical than some other schemes based on atom systems only or ion-trap systems as photons interact with their environments weakly. The coherence of the stationary atom qubits in cavities provides the convenience for the parties in QSTS to check eavesdropping, different from entangled photon systems. Moreover, the present scheme works in a collective-noise condition and it may be more practical than others in applications in future.     

基于光克尔门空间扫描单次激光信噪比测量

提出一种基于光克尔门空间扫描的单次激光信噪比测量方法.在该方法中,门光和探测光在光克尔介质中正交传输,通过光克尔门对探测光的空间扫描实现激光信噪比测量.采用该测量方法进行了单次激光信噪比测量的实验研究,测得时间窗口和分辨率分别为88.2ps、2.7ps.由于取样门是由光克尔效应来控制,因此该激光信噪比测量方法对于待测激光的波长没有限制.     

Failure Impact,Availability and Cost Analysis of PONs Based on a Network Geometric Model

Passive Optical Networks(PONs)are considered as the preferred solution for broadband fibre-based access networks.This is because PONs present low cost deployment,low energy consumption and also meet high bandwidth demands from end users.In addition,end users expect a high availability for access networks,while operators are more concerned about reducing the failure impact(number of clients affected by failures).Moreover,operators are also interested in reducing the cost of the access network.This paper provides a deep insight into the consequences that the physical topology and design decisions cause on the availability,the failure impact and the cost of a PON.In order to do that,the physical layout of the PON deployment area is approximated by a network geometric model.A PON deployed according to the geometric model is then assessed in terms of failure impact,availability and cost.This way,the effects of different design decisions and the physical layout on these three parameters are evaluated.In addition,the tradeoffs between availability,failure impact and cost caused by planning decisions and the physical topology are identified and pinpointed.