Narrow Results

We propose and prove a theoretical scheme of realizing programmable and controlled remote quantum-state unambiguous discrimination (UD) based on nonlocal system–ancilla unitary evolution. By decomposing the evolution process from the initial state to the final state, we first construct the required nonlocal unitary evolution, which is a nonlocal conditional rotation. Utilizing the entanglement property of Greenberger–Horne–Zeilinger (GHZ) class state, we then design a quantum network for implementing the controlled nonlocal conditional rotation gate, and thus provide a feasible physical means to realize the remote UD. The features of the scheme is that the particular pair of states of system (data register) that can be remotely and unambiguously discriminated is specified by the state of the ancilla (program register). Furthermore, a third side is included, who may participate the process of quantum remote implementation as a supervisor. When the quantum channel is partially entangled, the third one can rectify the state distorted by the imperfect quantum channel. The success probability of implementing this remote UD is also investigated.

A scheme for asymmetric controlled bidirectional remote state preparation by utilizing 15-qubit entangled state as quantum channel is proposed. In this paper, we present a new protocol that Alice prepares a three-qubit equatorial state for Bob and Bob prepares a four-qubit equatorial state for Alice at the same time under Charlie’s control. The success of this scheme cannot be separated from the controller Charlie. In addition, we give some analysis and conclusions by comparing with other schemes. The auxiliary qubits and operations are not required in our scheme. In particular, the success probability of the receivers restoring the prepared states can reach 100%. Thus, our scheme has better performance.

In the existing research on cyclic teleportation protocols, it is generally discussed that the teleportation of single particle, two particle unknown quantum states with symmetrical structure or asymmetric special unknown quantum states (such as GHZ state) with three or four participants. In contrast, the scheme proposed in this paper has universality and stronger practicability. In this paper, we propose a novel scheme of asymmetric cyclic controlled teleportation. In our scheme, Alice can teleport an arbitrary single-qubit entangled state to Charlie, Charlie can teleport an arbitrary three-qubit entangled state to Bob and at the same time Bob can teleport an arbitrary two-qubit entangled state to Alice under the control of a controller David. It only needs Bell measurement and local unitary operation, and can realize three-party cyclic transmission with probability 1 by using a quantum channel composed of any six of the 16 G states.

In this paper, two three-party cyclic teleportation schemes for real arbitrary quantum states of a single particle and two particles are proposed for the first time. In the first ($1\sim 2\sim 1$) scheme, Alice sends any single particle state to Bob, Bob sends any two-particle states to Charlie, and meanwhile Charlie sends any single particle state to Alice. In the second ($2\sim 2\sim 1$) scheme, with the help of the controller David, Alice sends any two-particle states to Bob, Bob sends any two-particle states to Charlie, and Charlie sends any single particle state to Alice simultaneously. Based on the maximum entangled quantum channel shared in advance, the communication participants carry out some Bell state measurement (BSM) measurements and carry out corresponding unitary transformation according to the results published by each other. After that, the cyclic teleportation of predetermined quantum information can be successfully realized. The success probability of teleportation of both schemes can reach 100%. Finally, this paper briefly analyzes the security of the two schemes and compares them with some previously published schemes from the perspective of inherent efficiency. The results show that the two schemes proposed in this paper are safe and have high inherent efficiency. Different from the previous symmetric cyclic quantum teleportation methods, the asymmetric cyclic quantum teleportation schemes proposed in this paper are more universal.

We present a new multiparty controlled quantum secure direct communication protocol with phase encryption, in which the sender's secret message can only be recovered by the receiver under the permission of all the controllers. The security of this scheme is based on the basic principles of quantum mechanics and the secret order of encoding photons.