Quantum Computer Algorithm for Parity Determination Based on Quantum Counting

A new quantum computer algorithm is proposed for determining the parity of function f(x) by using quantum counting algorithm. The parity of function f(x) can be determined by counting exactly the number of satisfying f(x)=−1, which is equivalent to determine the number of solutions, M, to an N item search problem. The algorithm can be accomplished in time of order .     

Quantum State Transfer via Adiabatic Passage

我们采用周期极化KTP晶体为非线性介质，通过光学参量振荡器运转于阈值以下的简并参量振荡过程，产生了单模正交压缩真空态光场，在泵浦功率为123mW，Local光功率为842uW，晶体温度为32．1摄氏度时我们使用平衡零拍探测法测得输出场噪声功率低于散粒噪声基准3．41dB。     

Quantum state sharing with a genuinely entangled five-qubit state and Bell-state measurements

We construct several distinct schemes for tripartite Quantum state sharing (QSTS) of arbitrary single- and two-qubit states. Our schemes use genuinely entangled five-qubit state that has recently been introduced by Brown et al. [J. Phys. A 38 1119 (2005)] as the quantum channel. The Bell-state measurements and the single-qubit measurement are needed in our schemes. In comparison with the QSTS scheme using the same quantum channel [Phys. Rev. A 77 (2008) 032321], not joint measurement, which makes this scheme simpler than the latter.     

Generation and Transfer of Quantum Entangled State via Spin-Parity Measurements

We propose two schemes for entanglement generation and quantum state transfer via a double-quantum-dot system. Our schemes only need spin-parity measurements and single-qubit measurements combined with additional qubits. Discussions about the feasibility of the current scheme show that they would be realized within the current experimental technology.     

Quantum Generalized Measurement and Deterministic Generation of Maximum Entangled Pure State

We propose the concept of the quantum generalized projector measurement （QGPM） for finite-dimensional quantum systems by studying the quantum generalized measurement. This research reveals a distinguished property of this quantum generalized measurement： no matter what the system state is prior to the measurement and what the result of the measurement occurs, the state of the system after the measurement can be collapsed into any specified pure state, i.e., the state of quantum system can be deterministically reduced to any specified pure state just by a single QGPM. Subsequently. QGPM can be used to deterministically generate the maximum entangled pure state for quantum systems. We give three concrete theoretic schemes of generating the maximum quantum entangled pure states for two 2-Jevel particles, three 2-level particles and two 3-Jevel particles, respectively.     

Quantum Generalized Measurement and Deterministic Generation of Maximum Entangled Pure State

We propose the concept of the quantum generalized projector measurcment (QGPM) for finite-dimensional quantum systems by studying the quantum generalized measurement. This research reveals a distinguished property of this quantum generalized measurement: no matter what the system state is prior to the measurement and what the result of the measurement occurs, the state of the system after the measurement can be collapsed into any specified pure state, i.e., the state of quantum system can be deterministically reduced to any specified pure state just by a single QGPM. Subsequently, QGPM can be used to deterministically generate the maximum entangled pure state for quantum systems. We give three concrete theoretic schemes of generating the maximum quantum entangled pure stazes for two 2-level particles, three 2-level particles and two 3-level particles, respectively.     

基于cluster态任意单粒子态可控量子信息共享

基于cluster态具有较强的纠缠顽固性,提出两个利用四粒子cluster态传送任意单粒子态的量子信息共享方案.第一个方案中发送者Alice、控制者Charlie和接收者Bob共享一个四粒子纠缠态,首先Alice对自己拥有的粒子执行一个三粒子Von-Neumann联合测量,然后Charlie对其拥有粒子执行Z基测量,最后Bob根据发送者和控制者的测量结果,对所拥有的粒子做适当的幺正变换,就能重建共享的单粒子任意态.第二个方案利用一个辅助粒子,发送者Alice、控制者Charlie只需做Bell基测量,Bob通过比特位翻转和幺正变换即可得到Alice传送的量子态.与已有方案相比,两方案信息共享的成功概率为100%,且只需四粒子cluster态为载体,可在目前实验室技术条件下实现.     

Quantum State Transfer Between Any Pair of Qubits in a Quantum Network via Optical Fibers

We propose scheme for transferring quantum state between any pair of nodes in a quantum network. Each node consists of an atom and a cavity, with the atom acting as the quantum bit. Any two adjacent nodes are connected by an optical fiber. During the operation neither the atomic system nor the fibers are excited, which is important in view of decoherence. Under certain conditions, the probability that the cavities are excited is negligible. The method has an inherent robustness against the fluctuation perturbations in the classical control parameters and the randomness in the atomic position. The scheme can be generalized to implement quantum phase gate between any two remote qubits.     

基于奇偶校验门的非破坏性贝尔态测量

由于贝尔态测量是量子信息处理的前提,因此提出了一种针对贝尔态的非破坏性测量方案.在该方案中,将奇偶校验门作为关键器件,利用奇偶校验门不改变输入光子状态的特性实现了C-NOT门和Toffoli门.然后,将Toffoli门和Hadamard门结合实现了对4种贝尔态的确定性测量.所提方案可用于双光子纠缠态测量,并可推广到三光子纠缠态的应用场景中,为贝尔态测量与量子信息处理提供了新的思路.     

Fast Hybrid Quantum State Transfer and Entanglement Generation via No Transition Passage

Quantum information processing requires information or entanglement that can be transferred or distributed from one location to another with high fidelity. Here, a scheme for faithful quantum state transfer and entanglement generation based on the hybrid opto‐electro‐mechanical (OEM) systems in a fast and deterministic way is proposed. By applying invariant‐based inverse engineering to the interaction Hamiltonian, the couplings in the OEM system can be controlled by asynchronized driving fields, which is convenient to be realized in practice. Taking the systematic decoherence into consideration, the numerical simulation shows that the scheme can be implemented with less time and high fidelity. Therefore, the scheme provides a promising way for robust on‐chip converting of low‐frequency electrical signal into much higher‐frequency optical signal, and thus enabling large‐scale quantum information networks to grow in size and complexity.     

Perfect Transfer of Many-Particle Quantum State via High-Dimensional Systems with Spectrum-Matched Symmetry

The quantum state transmission through the medium of high-dimensional many-particle system (boson or spinless fermion) is generally studied with a symmetry analysis. We discover that, if the spectrum of a Hamiltonian matches the symmetry of a fermion or boson system in a certain fashion, a perfect quantum state transfer can be implemented without any operation on the medium with pre-engineered nearest neighbor (NN). We also study a simple but realistic near half-filled tight-binding fermion system with uniform NN hopping integral. We show that an arbitrary many-particle state near the fermi surface can be perfectly transferred to its translational counterpart.     

Perfect Transfer of Many-Particle Quantum State via High-Dimensional Systems with Spectrum-Matched Symmetry

The quantum state transmission through the medium of high-dimensional many-particle system （boson or spinless fermion） is generally studied with a symmetry analysis. We discover that, if the spectrum of a Hamiltonian matches the symmetry of a fermion or boson system in a certain fashion, a perfect quantum state transfer can be implemented without any operation on the medium with pre-engineered nearest neighbor （NN）. We also study a simple but realistic near half-filled tight-bindlng fermion system wlth uniform NN hopping integral. We show that an arbitrary many-particle state near the fermi surface can be perfectly transferred to its translational counterpart.     

Quantum State Transfer Using the Four-Ion Cluste State

We demonstrate that a four-ion cluster state can be used to realize the quantum state transfer in the ion-trap systems. The scheme does not involve Bell-state measurement and is insensitive to both the initial motional state and heating.     

Engineering of Two Quantum States via Conditional Measurement on Two-Mode Squeezed State

We propose a scheme for the simultaneously preparation radiation-field modes of a single photon and a superposition of zero- and one-photon states, based on the coherent quantum state displacement and photon subtraction from two-mode squeezed state. It is shown that the single-photon and the superposition states can be obtained by only choosing the suitable parameter of displacements. The experimental feasibility to accomplish this scheme is also discussed.     

Quantum State Transfer in Trapped-Ion-Cavity Systems

We study the information transfer and entanglement transfer in a system consisting of single trapped ions in cavities by the three-mode cross-Kerr-like interaction among the cavity field （photons）, the centre-of-mass motion （phonons） and the internal state of the trapped ion in the Lamb-Dicke and large detuning regime.     

基于四粒子GHZ态的可控量子双向隐形传态及安全性

提出一个基于四粒子GHZ纠缠态实现未知单粒子态的可控量子双向传态方案.通信双方Alice和Bob以及控制方事先密享两对四粒子GHZ纠缠态以构建量子信道,根据纠缠粒子的不同分发方式,以及测量时所选择的不同测量基,可以分别实现三方和四方参与的可控量子双向传态.通信开始后,Alice和Bob分别对自己拥有的部分粒子作量子投影测量,若控制方同意双方通信,则对自己拥有的粒子作测量并通过经典信道公布测量结果.通信双方根据控制方公布的测量结果对各自的某个粒子作相应的幺正变换,即可在己方的粒子上重建对方待传的量子态.由于第三方Charlie以及第四方Dennis的加入,整个双向传态的安全性大为提高.     

Conclusive Teleportation of an Arbitrary Three-Particle State via Positive Operator-Valued Measurement

We present a scheme for conclusive teleportation of an arbitrary and unknown three-particle state by performing three Bell-state measurements at the sender＇s side and a positive operator-valued measurement at the receiver＇s side. Moreover, we obtain the successful probability of teleportation and make a brief discussion on the average fidelity for the conclusive teleportation scheme.     

Quantum State Transfer between Two Distant Atoms by Connecting Two Cavities via Optical Fibres

A scheme is proposed to unconditionally implement state transfer between two distant atoms by sending the atoms across two distant cavities connected via an optical fibre, respectively. The field state, which preserves the information about the first atom, is transmitted from one cavity to the other along the fibre. A Faraday rotator integrated in the fibre can be designed to completely stop the fields reflected from the second cavity, thus after the field interacts with the second atom for a defined time, the state transfer can be accomplished with unit efficiency.     

Retrocausality and Quantum Measurement

A retrocausal interpretation of quantum mechanics is examined and is applied to the problem of measuring an optical qubit before the qubit is actually created. Although the predictions of the retrocausal interpretation are the same as for the conventional causal picture, it provides a new perspective which should give a useful way of understanding some quantum mechanical processes.