Remote interactions between two d-dimensional distributed quantum systems： nonlocal generalized quantum control-NOT gate and entanglement swapping

We present a systematic simple method to implement a generalized quantum control-NOT （CNOT） gate on two d-dimensional distributed systems. First, we show how the nonlocal generalized quantum CNOT gate can be implemented with unity fidelity and unity probability by using a maximally entangled pair of qudits as a quantum channel. We also put forward a scheme for probabilistically implementing the nonlocal operation with unity fidelity by employing a partially entangled qudit pair as a quantum channel. Analysis of the scheme indicates that the use of partially entangled quantum channel for implementing the nonlocal generalized quantum CNOT gate leads to the problem of ＇the general optimal information extraction＇. We also point out that the nonlocal generalized quantum CNOT gate can be used in the entanglement swapping between particles belonging to distant users in a communication network and distributed quantum computer.[第一段]     

Implementation of nonlocal quantum swap operation on two entangled pairs

We propose a scheme for the implementation of nonlocal quantum swap operation on two spatially separated entangled pairs and we show that the operation can swap two qubits of these entangled pairs.We discuss the resources of the entangled qubits and classical communication bits required for the optimal implementation of the nonlocal quantum swap operation.We also put forward a scheme for probabilistic implementation of nonlocal swap operation via a nonmaximally entangled quantum channel.The probability of a successful nonlocal swap operation is obtained by introducing a collective unitary transformation.     

Arbitrary Partially Entangled Three-Electron W State Concentration with Controlled-Not Gates

We describe an efficient entanglement concentration protocol （ECP） for an arbitrary partially entangled threeelectron W state. We show that with the help of two ancillary single electrons, the concentration task can be well completed. This ECP has several advantages： Firstly, we only require one pair of partially entangled states. Secondly, only two single electrons are used during the whole protocol. Thirdly, we do not require all the parties to participate in the whole process, and only two parties are needed to perform the operation. Fourthly, the protocol can 5e repeated to obtain a high success probability. This ECP may be useful in current quantum computation and quantum communication.     

Implementation of non-local quantum controlled-NOT gate with multiple targets

We show how a non-local quantum controlled-NOT (CNOT) gate with multiple targets can be implemented with unit fidelity and unit probability.The explicit quantum circuit for implementing the operation is presented.Two schemes for probabilistic implementing the operation via partially entangled quantum channels with unit fidelity are put forward.The overall physical resources required for accomplishing these schemes are different,and the successful implementation probabilities are also different.     

Non-local implementation of single-qubit rotation operation

We present two optimal schemes for non-local implementing a single-qubit rotation operation via a maximally entangled quantum channel. We report on the quantitative relations between the quantum action, entangled and classical communication resources required in the implementation. We also put forward two schemes for conclusive implementing the non-local quantum single-qubit rotation via a partially entangled quantum channel. Both these methods can appropriately be referred to as qubit-assisted processes.     

Multiparty Quantum Cryptographic Protocol

We propose a multiparty quantum cryptographic protocol. Unitary operators applied by Bob and Charlie, on their respective qubits of a tripartite entangled state encoding a classical symbol that can be decoded at Alice＇s end with the help of a decoding matrix. Eve＇s presence can be detected by the disturbance of the decoding matrix. Our protocol is secure against intercept resend attacks. Furthermore, it is eifficient and deterministic in the sense that two classical bits can be transferred per entangled pair of qubits. It is worth mentioning that in this protocol, the same symbol can be used for key distribution and Eve＇s detection that enhances the etfficiency of the protocol.     

Remote interactions on two distributed quantum systems： nonlocal unambiguous quantum-state discrimination

Remote quantum-state discrimination is a critical step for the implementation of quantum communication network and distributed quantum computation. We present a protocol for remotely implementing the unambiguous discrimination between nonorthogonal states using quantum entanglements, local operations, and classical communications. This protocol consists of a remote generalized measurement described by a positive operator valued measurement （POVM）. We explicitly construct the required remote POVM. The remote POVM can be realized by performing a nonlocal controlled-rotation operation on two spatially separated qubits, one is an ancillary qubit and the other is the qubit which is encoded by two nonorthogonal states to be distinguished, and a conventional local Von Neumann orthogonal measurement on the ancilla. The particular pair of states that can be remotely and unambiguously distinguished is specified by the state of the ancilla. The probability of successful discrimination is not optimal for all admissible pairs. However, for some subset it can be very close to an optimal value in an ordinary local POVM.     

Multipartite entanglement concentration of electron-spin states with CNOT gates

We propose a different entanglement concentration protocol (ECP) for nonlocal N-electron systems in a partially entangled Bell-type pure state using the CNOT gates and the projection measurements on an additional electron. For each nonlocal N-electron system, Alice first entangles it with the additional electron, and then she projects the additional electron onto an orthogonal basis for dividing the N-electron systems into two groups. In the first group, the N parties obtain a subset of N-electron systems in a maximally entangled state directly. In the second group, they obtain some less-entangled N-electron systems, which are the resource for the entanglement concentration in the next round. By iterating the entanglement concentration process several times, the present ECP has the maximal success probability, which is the theoretical limit of an ECP, equal to the entanglement of the partially entangled state, and higher than the others. This ECP may be useful in quantum computers based on electron-spin systems in the future.     

Quantum Teleportation of a Three—Particle Entangled State

We present a scheme for teleporting a three-particle entangled state to three remote particles.In this scheme,three pairs of pure nonmaximally entangled states are considered as quantum channels.It is found that by means of optimal discrimination between two nonorthogonal quantum states,probabilistic teleportation of the three-particle entangled state can be achieved.     

Implementation of non-local multiple qubits controlled-not operation via partially entangled channels

We propose two different schemes for probabilistic implementing a non-local multiple qubits controlled-not operation via partially entangled quantum channels. The overall physical resources required for accomplishing these schemes are different, and the successful implementation probabilities are also different.