Deterministic Generation of Quantum State Transfer Between Spatially Separated Single Molecule Magnets

We propose a new scheme for realizing deterministic quantum state transfer （QST） between two spatially separated single molecule magnets （SMMs） with the framework of cavity quantum eleetrodynamics （QED）. In the present scheme, two SMMs are trapped in two spatially separated optical cavities coupled by an optical fiber. Through strictly numerically simulating, we demonstrate that our scheme is robust with respect to the SMMs＇ spontaneous decay and fiber loss under the conditions of dispersive SMMs-field interaction and strong coupling of cavity fiber. In addition, we also discuss the influence of photon leakage out of cavities and show that our proposal is good enough to demonstrate the generation of QST with high fidelity utilizing the current experimental technology. The present investigation provides research opportunities for realizing QST between solid-state qubits and may result in a substantial impact on the progress of solid-state-based quantum communications network.     

Quantum State Transfer for Two Atoms with a Single Resonant Interaction

We present a scheme for transferring an unknown atomic entangled state with a single resonant interaction. This scheme only requires a single resonant interaction of two atoms with a cavity mode and does not use the cavity mode as the memory. Thus the scheme is very simple and the interaction time is very short, which is important, in view of decoherence. Quantum state can be directly transferred from two atoms to another two at, oms with a successful probability of 100 percent.     

Quantum State Transfer in Engineered Spin Chain under Influence of Spatially Distributed Environment

It has been shown that a quantum state could be perfectly transferred via a spin chain with engineered ＂always-on interaction＂. In this paper, we study a more realistic problem for such a quantum state transfer （QST） protocol, how the efficacy of QST is reduced by the quantum decoherence induced by a spatially distributed environment. Here, the environment is universally modeled as a bath of fermions located in different positions. By making use of the irreducible tensor method in angular momentum theory, we investigate the effect of environment on the efficiency of QST for both cases at zero and finite temperatures. We not only show the generic exponential decay of QST efficiency as the number of sites increase, but also find some counterintuitive effect, the QST can be enhanced as temperature increases in some cases.     

Quantum State Transfer in Engineered Spin Chain under Influence of Spatially Distributed Environment

It has been shown that a quantum state could be perfectly transferred via a spin chain with engineered ``always-on interaction". In this paper, we study a more realistic problem for such a quantum state transfer (QST) protocol, how the efficacy of QST is reduced by the quantum decoherence induced by a spatially distributed environment. Here, the environment is universally modeled as a bath of fermions located in different positions. By making use of the irreducible tensor method in angular momentum theory, we investigate the effect of environment on the efficiency of QST for both cases at zero and finite temperatures. We not onlyshow the generic exponential decay of QST efficiency as the number of sites increase, but also find some counterintuitive effect, the QST can be enhanced as temperature increases in some cases.     

Quantum Nonlocality and Generation of Multi-mode Schrodinger Cat States

We describe the Greenberger-Horne-Zeilinger (GHZ) paradox in the multi-mode Schroedinger cat states.We also show that the multi-mode cat states violate the Bell‘s inequality by an amount that grows exponentially with number of modes. The test of quantum nonlocality is based on parity measurement and displacement operation, which are experimentally feasible. We also describe a scheme for the generation of the cat states in cavity QED.     

Voltage-Controlled Quantum Dynamics and Generation Entanglement between Two Separated Quantum-Dot Molecules Embedded in Photonic Crystal Cavities

Voltage-controlled quantum dynamics of two quantum-dot molecules （QDMs） embedded in two separated photonic crystal cavities are theoretically investigated. We show numerically that generation of entangled states and population transfer between the two QDMs can be realized with the same coupling parameters. The effects of parameters deviation and dissipations on generation entangled states be used for realization of new-type of solid state quantum and populations transfer are also discussed. The results may devices and integrated electro-optical devices,     

Transferring a Multi-atom Entangled State via Adiabatic Passage

We present a scheme for transferring atomic entangled states via adiabatic passage. In the scheme, we use photons to achieve efficient quantum transmission among spatially distant atoms. The probability of the successful transferring quantum state approaches 1. Meanwhile, the scheme is robust against the effects of atomic spontaneous emission.     

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.     

Generation of a Genuine Six-Atom Entangled State in Cavity QED

We propose a potential scheme to generate a genuine six-atom entangled state [J. Phys. A 42 (2009) 415301] by using atoms in cavity QED system, where the atoms interact simultaneously with the highly detuned single-mode cavity and the strong classical driving field. Thus our approach is insensitive to both the cavity decay and thermal field.     

Transferring of a Two-Mode Entangled State Between Two Cavities via Cavity QED

We propose a scheme for transferring of a two-mode entanglement of zero- or one-photon entangled states between two cavities via atom-cavity field resonant interaction. In our proposal, in order to transfer the entangled state, we only need two identical two-level atoms and a two-mode cavity for receiving the teleported state. This scheme does not require Bell-state measurement and performing any transformations to reconstruct the initial state. And the transfer can occur with 100% success probability in a simple manner. And a network for transferring of a two-mode entangled state between cavities is suggested. This scheme can also be extended to transfer N-mode entangled state of cavity.     

An Alternative Scheme for Transferring Quantum States and Preparing a Quantum Network in Cavity QED

An alternative scheme is proposed to transfer quantum states and prepare a quantum network in cavity QED. It is based on the interaction of a two-mode cavity field with a three-level V-type atom. In the scheme, the atom-cavity field interaction is resonant, thus the time required to complete the quantum state transfer process is greatly shortened, which is very important in view of decoherence. Moreover, the present scheme does not require one mode of the cavities to be initially prepared in one-photon state, thus it is more experimentally feasible than the previous ones.     

Transferring Multi-Dimensional Quantum States and Preparing Quantum Networks in Cavity QED

In this paper we propose a scheme for transferring quantum states and preparing quantum networks. Compared with the previous schemes, this scheme is more efficient, since three or four-dimensional quantum states can be transferred with a single step and information interchange of three-dimensional quantum states can be realized, which is a significant improvement. It is based on the resonant interaction of a three-mode cavity field with an atom. As a consequence, the interaction time is shortened greatly. Furthermore, we give some discussions about the feasibility of the scheme.     

Teleportation of A Single Qubit State via Unique W State

We propose a scheme for teleporting a single qubit state employing a unique three-particle W state as quantum channel. By adopting QED cavity technologies, our scheme does not involve the Bell-state measurements(BMs). An unknown state a|0〉 + b|1〉 can be probabilistically teleported by communicators' single particle measurements, unitary operations and classical communications. We can perfectly teleport quantum state ½1√2(|0〉 +|1〉) with 100% probability.     

Generation of a Genuine Six-Atom Entangled State in Cavity QED

We propose a potential scheme to generate a genuine six-atom entangled state [J. Phys. A 42 (2009) 415301] by using atoms in cavity QED system, where the atoms interact simultaneously with the highly detuned single-mode cavity and the strong classical driving field. Thus our approach is insensitive to both the cavity decay and thermal field.     

Preparation of n-Atom GHZ State and Implementation of Quantum-State Transfer via Cavity Decay

We propose schemes to prepare n-atom Greenberger-Horn-Zeilinger （GHZ） state via two-sided cavities interacting with single-photon pulses, and achieve quantum state transfer （QST） from one atom to another atom. Entanglement particle pair and the control of coupling between qu bits are of no need in the QST process. Some practical quantum noises only decrease the success probabilities of the schemes but have no influence on the fidelity of prepared state. In addition, the success probabilities of our schemes are close to unity in the ideal case.     

关于单模最小关联混态的量子隐性传态及其保真度的研究

基于Braunstein和Kimble方案以双模压缩真空态作为量子信道实施对单模最小关联混态量子隐性传态的可行性进行了研究.我们发现,单模最小关联混态在一定参数范围内呈现出压缩效应这种非经典性质,利用双模压缩真空态作为量子通道可以高保真的传递没有压缩效应的单模最小关联混态,但对呈现压缩效应的单模最小关联混态进行量子隐性传送时得到输出态的保真度较低.而且发现通过调节输出端位移因子的方法不能实现对单模最小关联混态保真度的优化.     

Highly Efficient Transfer of Quantum State and Robust Generation of Entanglement State Around Exceptional Lines

Exceptional points (EPs) are non-Hermitian degeneracies or branch points where eigenvalues and their corresponding eigenvectors coalesce. Due to the complex non-trivial topology of Riemann surfaces associated with non-Hermitian Hamiltonians, the dynamical encirclement or proximity of EPs in parameter space has been shown to lead to topological mode conversions and some novel physical phenomena. In fact, degeneracies can also form continuous line geometries, which are called exceptional lines (ELs). The problem is whether the state transfer around the ELs can show different characteristics from the EPs, which is less explored. Here, novel properties of quantum state transfer around the ELs based on a quantum walk platform are explored. It is found that the evolutionary state around the ELs is independent of the initial state and evolution direction, and the transfer of quantum state is more efficient than the case around the EPs. Furthermore, based on such a property, an entangled state generation insensitive to the incident state is realized experimentally. The work opens up a new way for the application of non-Hermitian physics in the field of quantum information.     

Preparation of Genuinely Entangled Six-Atom State via Cavity Quantum Electrodynamics

A cavity quantum electrodynamics scheme for preparing a genuinely entangled state [A. Borras, et al., J. Phys. A 40 (2007) 13407] on six two-level atoms is proposed. In the scheme, the atom-cavity detuning is much bigger than the atom-cavity coupling strength and the necessary preparation time is much shorter than the Rydberg-atom lifespan. Hence the scheme has two distinct features, i.e., insensitive to the cavity decay and the atom radiation.     

Quantum States Transfer by Analogous Bell States

Transmitting quantum states by channels of analogous Bell states is studied in this paper. We analyze the transmitting process. constructed the probabilitic unitary operator, and gain the largest successful transfer quantum state probability.