Gui Lu Long

Two-step quantum direct communication protocol using the Einstein-Podolsky-Rosen pair block

A protocol for quantum secure direct communication using blocks of Einstein-Podolsky-Rosen (EPR) pairs is proposed. A set of ordered N EPR pairs is used as a data block for sending secret message directly. The ordered N EPR set is divided into two particle sequences, a checking sequence and a message-coding sequence. After transmitting the checking sequence, the two parties of communication check eavesdropping by measuring a fraction of particles randomly chosen, with random choice of two sets of measuring bases. After insuring the security of the quantum channel, the sender Alice encodes the secret message directly on the message-coding sequence and sends them to Bob. By combining the checking and message-coding sequences together, Bob is able to read out the encoded messages directly. The scheme is secure because an eavesdropper cannot get both sequences simultaneously. We also discuss issues in a noisy channel.

Theoretically efficient high-capacity quantum-key-distribution scheme

A theoretical quantum key distribution scheme using Einstein-Podolsky-Rosen (EPR) pairs is presented. This scheme is efficient in that it uses all EPR pairs in distributing the key except those chosen for checking eavesdroppers. The high capacity is achieved because each EPR pair carries 2 bits of key code.

Secure direct communication with a quantum one-time pad

Quantum secure direct communication is the direct communication of secret messages without first producing a shared secret key. It may be used in some urgent circumstances. Here we propose a quantum secure direct communication protocol using single photons. The protocol uses batches of single photons prepared randomly in one of four different states. These single photons serve as a one-time pad which is used directly to encode the secret messages in one communication process. We also show that it is unconditionally secure. The protocol is feasible with present-day technique.

Efficient multiparty quantum-secret-sharing schemes

In this work, we generalize the quantum-secret-sharing scheme of Hillery, Buzek, and Berthiaume [Phys. Rev. A 59, 1829 (1999)] into arbitrary multiparties. Explicit expressions for the shared secret bit is given. It is shown that in the Hillery-Buzek-Berthiaume quantum-secret-sharing scheme the secret information is shared in the parity of binary strings formed by the measured outcomes of the participants. In addition, we have increased the efficiency of the quantum-secret-sharing scheme by generalizing two techniques from quantum key distribution. The favored-measuring-basis quantum-secret-sharing scheme is developed from the Lo-Chau-Ardehali technique [H. K. Lo, H. F. Chau, and M. Ardehali, e-print quant-ph/0011056] where all the participants choose their measuring-basis asymmetrically, and the measuring-basis-encrypted quantum-secret-sharing scheme is developed from the Hwang-Koh-Han technique [W. Y. Hwang, I. G. Koh, and Y. D. Han, Phys. Lett. A 244, 489 (1998)] where all participants choose their measuring basis according to a control key. Both schemes are asymptotically 100% in efficiency, hence nearly all the Greenberger-Horne-Zeilinger states in a quantum-secret-sharing process are used to generate shared secret information.

Multi-step quantum secure direct communication using multi-particle Green–Horne–Zeilinger state

Abstract A multi-step quantum secure direct communication protocol using blocks of multi-particle maximally entangled state is proposed. In this protocol, the particles in a Green–Horne–Zeilinger state are sent from Alice to Bob in batches in several steps. It has the advantage of high efficiency and high source capacity.

Grover algorithm with zero theoretical failure rate

In a standard Grovers algorithm for quantum searching, the probability of finding the marked item is not exactly 1. In this paper we present a modified version of Grovers algorithm that searches a marked state with full successful rate. The modification is done by replacing the phase inversion by phase rotation through angle phi. The rotation angle is given analytically to be phi = 2 arcsin(sin [pi/(4J+6)]/sin beta), where sin beta = 1/rootN, N is the number of items in the database, and J is any integer equal to or greater than the integer part of [(pi /2)-beta]/(2 beta). Upon measurement at the (J+1)th iteration, the marked state is obtained with certainty.

Entanglement and squeezing in solid-state circuits

We investigate the dynamics of a system consisting of a Cooper-pair box and two superconducting transmission line resonators. There exist both linear and nonlinear interactions in such a system. We show that a single-photon entanglement state can be generated in a simple way in the linear interaction regime. In the nonlinear interaction regime, we propose a scheme for generating squeezed states of microwaves using three-wave mixing in solid-state circuits.

Quantum Secure Direct Communication

Quantum secure direct communication transmits secret messages directly without another classical transmission. We describe its principle and working procedure through example protocols. Distinctions from QKD are pointed out, and its wide applications are given.

Quantum Direct Communication

Gui Lu Long1,2, Chuan Wang1,3, Fu-Guo Deng4, and Wan-Ying Wang1 1Key Laboratory of Atomic and Molecular Nanosciences and Department of Physics, Tsinghua University, Beijing 100084, 2Tsinghua National Laboratory for Information Science and Technology, Beijing 100084, 3School of Science and Key Laboratory of Optical Communication and Lightwave Technologies, Beijing University of Posts and Telecommunications, Beijing, 100876, 4Department of Physics, Beijing Normal University, Beijing 100875, Peoples Republic of China

Entanglement and Squeezing in Solid State Circuits

We investigate the dynamics of a system consisting of a Cooper‐pair box and two superconducting transmission line resonators. There exist both linear and nonlinear interactions in such a system. We show that single‐photon entanglement state can be generated in a simple way in the linear interaction regime. In nonlinear interaction regime, we derive the Hamiltonian of degenerate three‐wave mixing and propose a scheme for generating squeezed state of microwave using the three‐wave mixing in solid state circuits. In the following, we design a system for generating squeezed states of nanamechanical resonator.