Complete and Nondestructive Atomic Greenberger–Horne–Zeilinger‐State Analysis Assisted by Invariant‐Based Inverse Engineering

A protocol to realize complete and nondestructive atomic Greenberger–Horne–Zeilinger (GHZ)‐state analysis in cavity quantum electrodynamics (QED) systems is presented. In this protocol, the three information‐carrier atoms and the three auxiliary atoms are trapped in six separated cavities, respectively. After ten‐step operations, the information for distinguishing the eight different GHZ states of the three information‐carrier atoms is encoded on the auxiliary atoms. Thus, by means of detecting the auxiliary atoms, complete and nondestructive GHZ‐state analysis with high success probability is realized. Moreover, the driving pluses of operations are designed as a simple superposition of Gaussian or trigonometric functions by using the invariant‐based inverse engineering. Therefore, the protocol can be realized experimentally and applied in some quantum information tasks based on complete GHZ‐state analysis with less physical entanglement resource.     

Deterministic nondestructive state analysis for polarization-spatial-time-bin hyperentanglement with cross-Kerr nonlinearity

We present a deterministic nondestructive hyperentangled Bell state analysis protocol for photons entangled in three degrees of freedom(DOFs),including polarization,spatial-mode,and time-bin DOFs.The polarization Bell state analyzer and spatial-mode Bell state analyzer are constructed by polarization parity-check quantum nondemolition detector(P-QND)and spatial-mode parity-check quantum nondemolition detector(S-QND)using cross-Kerr nonlinearity,respectively.The time-bin Bell state analyzer is constructed by the swap gate for polarization state and time-bin state of a photon(P-T swap gate)and P-QND.The Bell states analyzer for one DOF will not destruct the Bell states of other two DOFs,so the polarization-spatial-time-bin hyperentangled Bell states can be determinately distinguished without destruction.This deterministic nondestructive state analysis method has useful applications in quantum information protocols.     

A novel quantum information hiding protocol based on entanglement swapping of high-level Bell states

Using entanglement swapping of high-level Bell states, we first derive a covert layer between the secret message and the possible output results of the entanglement swapping between any two generalized Bell states, and then propose a novel high-efficiency quantum information hiding protocol based on the covert layer. In the proposed scheme, a covert channel can be built up under the cover of a high-level quantum secure direct communication(QSDC) channel for securely transmitting secret messages without consuming any auxiliary quantum state or any extra communication resource. It is shown that this protocol not only has a high embedding efficiency but also achieves a good imperceptibility as well as a high security.     

Nondestructive and complete Bell-state analysis for atomic qubit systems

This paper realizes a nondestructive and complete Bell-state analysis for atomic qubit systems by a designed nondestructive and complete Bell-state analyser. In the scheme, Bell states are completely discriminated by two bits of classical informations which comes from the locality single atom detection on two auxiliary atoms, during which the Bell states are not affected. The needed devices are well within the bounds of current technology, and then the scheme is experimentally feasible.     

Quantum Dialogue Without Information Leakage Using a Single Quantum Entangled State

At present, a lot of quantum dialogue protocols have the problem of information leakage, especially the ones merely using a single quantum state as the quantum resource. In this paper, the author successfully puts forward a novel kind of information leakage resistant quantum dialogue protocol merely using a single quantum entangled state. This kind of quantum dialogue protocol uses the measurement correlation property of a single quantum entangled state to prevent the information leakage problem. Its Bell state version is illustrated in detail at first in this paper, then it is generalized to the cases of three-particle, four-particle and five-particle quantum entangled states. Different from those previous information leakage resistant quantum dialogue protocols, the proposed protocol needs neither the auxiliary quantum state nor the entanglement swapping technology of quantum state.     

Generalized quantum state sharing of the arbitrary two particles state

This paper has proposed a generalized quantum state sharing protocol of an arbitrary two-particle state using non-maximally GHZ states and generalized Bell state measurement.The sender Alice performs two-particle generalized Bell state measurements on her two particles in the state sharing process and the controller takes measurements on his particles and transfers the quantum information to the receiver with entanglement swapping by the cooperation of the other agents.It is found that the use of nonmaximally entangled state in quantum state sharing has enabled the secure sharing of the quantum state.     

Efficient nonlocal two-step entanglement concentration protocol for three-level atoms in an arbitrary less-entangledW state using cavity input-output process

We present an efficient two-step entanglement concentration protocol (ECP) for three-level atoms trapped in one-sided optical micro-cavities in an arbitrary three-particle less-entangled W state, using the coherent state input-output process in low-Q cavity quantum electrodynamics system. In each step of the new proposed protocol, one of the three remote users prepares the auxiliary coherent optical pulses to perform cavity input-output process and then utilizes the standard homodyne measurement to discriminate the final outgoing coherent states. When both of the two steps are successful, remote parties can deterministically concentrate the less-entangled W state atoms to a standard maximally entangled W state. Compared with previous ECPs for W state, this protocol has some advantages and can be widely used in current quantum repeater and some quantum information processing tasks.     

Emission Spectrum from Two Atoms in Bell States in a Cavity

By means of time-evolution operator, the emission spectrum from two two-level entangled atoms in Bell states interacting with a single-mode cavity field in the Fock state has been studied in the paper. The physical spectrum expression of radiation emitted by the atoms is given out for each Bell state. In general, the spectrum shows the symmetrical multi-peak structure and the symmetrical three-peak structure with the strong optical input. Bell states composed of two identical atoms can be partially distinguished in view of the characterizations of their emission spectrum.     

Simulation of the Ising model,memory for Bell states and generation of four-atom entangled states in cavity QED

A scheme is proposed to simulate the Ising model and preserve the maximum entangled states (Bell states) in cavity quantum electrodynamics (QED) driven by a classical field with large detuning. In the strong driving and large-detuning regime, the effective Hamiltonian of the system is the same as the standard Ising model, and the scheme can also make the initial four Bell states of two atoms at the maximum entanglement all the time. So it is a simple memory for the maximal entangled states. The system is insensitive to the cavity decay and the thermal field and more immune to decoherence. These advantages can warrant the experimental feasibility of the current scheme. Furthermore, the genuine four-atom entanglement may be acquired via two Bell states through one-step implementation on four two-level atoms in the strong-driven model, and when two Greenberger-Horne-Zeilinger (GHZ) states are prepared in our scheme, the entangled cluster state may be acquired easily. The success probability for the scheme is 1. Supported by the National Natural Science Foundation of China (Grant No. 10774088) and the Key Program of the National Natural Science Foundation of China (Grant No. 10534030)     

Emission Spectrum from Two Atoms in Bell States in a Cavity

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Discrete photodetection for protocols of linear optical quantum calculations and communications

A theory of a discrete photodetection method is developed in which an atomic packet in a microresonator is used as a probe. Such a detector is adjusted by selecting the number of atoms in the packet, the constant of interaction between the mode under study and atoms and the interaction duration. The possibility is analyzed for using this detector to distinguish one-photon and two-photon Fock states and applications in protocols of linear optical quantum measurements and communications. A protocol of a Bell-state analyzer is prepared that allows one to distinguish all the four Bell states constructed on the polarization states of a photon pair.     

Complete deterministic linear optics Bell state analysis

We show how hyperentanglement allows us to deterministically distinguish between all four polarization Bell states of two photons. In this proof-of-principle experiment, we employ the intrinsic time-energy correlation of photon pairs generated with high temporal definition in addition to the polarization entanglement obtained from parametric down-conversion. For the identification, no nonlinear optical elements or auxiliary photons are needed. The new possibilities this complete Bell measurement offers are demonstrated by realizing an optimal dense coding protocol.     

与两等同Bell态纠缠原子相互作用光场的量子场熵

利用全量子理论,并通过数值计算,研究了初始处于Fock态的单模光场与两等同双能级纠缠原子单光子共振相互作用过程中单模光场量子场熵的时间演化特性.结果发现:当两原子初始处于第一种Bell态时,光场量子场熵的时间演化周期为π/g2(2n+1);随着初始光强的增大,光场与原子之间的量子纠缠现象减弱;特别是当时间t为演化周期的整数倍时,场－原子系统处于退纠缠状态.当两原子初始处于第二种Bell态时,光场量子场熵不随时间变化,恒为零.当两原子初始分别处于第三种和第四种Bell态时,光场量子场熵的时间演化曲线呈现不等幅周期振荡现象;并且随着初始光场光子数的增加,光场量子场熵的振荡周期逐渐增大,但振荡幅值逐渐减小.     

An Novel Protocol for the Quantum Secure Multi-Party Summation Based on Two-Particle Bell States

A protocol for the quantum secure multi-party summation based on two-particle Bell states is proposed. In this protocol, two-particle Bell states are used as private information carriers. Without using the entangled character of Bell states, we also use Pauli matrices operations to encode information and Hadamard matrix to extract information. The proposed protocol can also resist various attacks and overcomes the problem of information leakage with acceptable efficiency. In theory, our protocol can be used to build complex secure protocols for other multiparty computations and also lots of other important applications in distributed networks.     

Deterministically distinguishing a remote Bell state

It has been proven that, with a single copy provided, the four Bell states cannot be distinguished by local operations and classical communications (LOCC). Traditionally, a Bell basis projective measurement is needed to distinguish the four Bell states, which is usually carried out with a local interference between two particles. This paper presents an interesting protocol that allows two remote parties to distinguish four Bell states deterministically. We prove that our protocol of distinguishing remote Bell states is beyond LOCC.     

Fault-Tolerant Quantum Dialogue Without Information Leakage Based on Entanglement Swapping between Two Logical Bell States

At present, the anti-noise property and the information leakage resistant property are two great concerns for quantum dialogue(QD). In this paper, two anti-noise QD protocols without information leakage are presented by using the entanglement swapping technology for two logical Bell states. One works well over a collective-dephasing noise channel, while the other takes effect over a collective-rotation noise channel. The negative influence of noise is erased by using logical Bell states as the traveling quantum states. The problem of information leakage is avoided by swapping entanglement between two logical Bell states. In addition, only Bell state measurements are used for decoding, rather than four-qubit joint measurements.     

High-Efficiency Three-Party Quantum Key Agreement Protocol with Quantum Dense Coding and Bell States

We propose a high-efficiency three-party quantum key agreement protocol, by utilizing two-photon polarization-entangled Bell states and a few single-photon polarization states as the information carriers, and we use the quantum dense coding method to improve its efficiency. In this protocol, each participant performs one of four unitary operations to encode their sub-secret key on the passing photons which contain two parts, the first quantum qubits of Bell states and a small number of single-photon states. At the end of this protocol, based on very little information announced by other, all participants involved can deduce the same final shared key simultaneously. We analyze the security and the efficiency of this protocol, showing that it has a high efficiency and can resist both outside attacks and inside attacks. As a consequence, our protocol is a secure and efficient three-party quantum key agreement protocol.

     

High-capacity Deterministic Secure Four-qubit <Emphasis Type="Italic">W</Emphasis> State Protocol for Quantum Communication Based on Order Rearrangement of Particle Pairs

A novel high-capacity protocol for deterministic secure quantum communication with four-qubit symmetric W state is proposed. In the presented protocol, the secret messages can be encoded on the four-qubit symmetric W states by employing four two-particle unitary operations and directly decoded by utilizing the corresponding measurements in Bell basis or single particle basis. It has a high capacity as each W state can carry two bits of secret information, and has a high intrinsic efficiency because almost all the instances are useful. The security of this communication can be ensured by the decoy photon checking technique and the order rearrangement of particle pairs technique. Furthermore, this protocol is feasible with present-day technique.     

High-Dimensional Bell State Analysis for Photon-Atoms Hybrid System

High-dimensional Bell state analysis (HDBSA) has great application potential in the high-capacity quantum communication and quantum information processing. In this paper, we propose a scheme to completely distinguish the 2^N-dimensional Bell states of a hybrid system with the help of the nonlinear interaction between the Λ-type atoms and a photon system. We use the unit-probability quantum teleportation with non-maximum entanglement as an example to show the application of HDBSA. Finally, we discuss its possible realization with current experimental techniques. Our HDBSA protocol may pave a new way for high-capacity long-distance quantum communication.

     

Coherent Preservation of Two-Qubit Quantum Entanglement in the Strong Coupling Region

The entanglement of two qubits is investigated in the range of their ultra-strongly coupling with a quantum oscillator. The two qubits are initially in four Bell states and they are under the control mechanism of the coherent state of the quantum oscillator. There are four parameters: the average number of the coherent state, the ultra-strong coupling strength, the ratio of two frequencies of qubit and oscillator, and the inter-interaction coupling of the two qubits in the mechanism, and they all are influential parameters on the entanglement of the two qubits. One Bell state |0>is easyily kept and is trivial case. The novel results show that there is one state |I₀> among the other three Bell states which the entanglement of the two qubits could be almost completely preserved. The possibility is made into reality by the appropriate choice of the four influential parameters. We give two different schemes to choose the respective parameters to maintain the entanglment of |I₀> almost undiminished. The results will be useful for the quantum information process.