Hanwu Chen

Quantum secure direct communication with optimal quantum superdense coding by using general four-qubit states

From the perspective of quantum circuit, a construction framework and a measurement framework of a general kind of four-qubit states are sketched, respectively. By utilizing the properties of this kind of states, a quantum secure direct communication (QSDC) protocol is put forward, which adopts the idea of optimal quantum superdense coding to achieve a maximal efficiency and high resources capacity. The security of the proposed protocol is discussed in detail and it is proved to be secure theoretically. Moreover, the sufficient and necessary condition of which multipartite states are suitable for optimal quantum superdense coding in quantum secure direct communication is figured out.

Deterministic secure quantum communication without unitary operation based on high-dimensional entanglement swapping

By analysis of the basic properties of entanglement swapping of high-dimensional Bell states, a universal and general deterministic secure quantum communication (DSQC) protocol is proposed, in which unitary operation is not required. By making use of the results of high-dimensional Bell measurement, the sender and the receiver can encode and decode the message respectively by performing the modular addition and subtraction. Two mutually complementary bases are constructed; and according to the property of mutual complement, a method for checking security of the high-dimensional quantum channel is put forward. Some common attack strategies are analyzed, and the corresponding error rates are calculated. Then the upper bound of the threshold of error rate is deduced.

Refinements of the half-bit and factor-of-two bounds for capacity in Gaussian channel with feedback

We consider the upper bounds of the finite blocklength capacity C/sub n,FB/(P) of the discrete time Gaussian channel with feedback. We also let C/sub n/(p) be the nonfeedback capacity. We prove the relations C/sub n/(P)/spl les/C/sub n,FB/(P)/spl les/C/sub n/(/spl alpha/P)+ 1/2 ln(1+1//spl alpha/) and C/sub n/(P)/spl les/C/sub n,FB/(P)/spl les/(1+1//spl alpha/)C/sub n/(/spl alpha/P) for any P>0 and any /spl alpha/>0, which induce the half-bit and factor-of-two bounds given by Cover and Pombra (1989) in the special case of /spl alpha/=1.

Cryptanalysis and improvement of three-particle deterministic secure and high bit-rate direct quantum communication protocol

The three-particle deterministic secure and high bit-rate direct quantum communication protocol and its improved version are analyzed. It shows that an eavesdropper can steal the sender’s secret message by the intercept-resend attack and the entanglement attack. The original version is even fragile under denial-of-service attack. As a result, some suggestions to revise them are given.

ANALYZING AND REVISING A TWO-WAY PROTOCOL FOR QUANTUM CRYPTOGRAPHY WITH A NONMAXIMALLY ENTANGLED QUBIT PAIR

The security of the second (STF-B) protocol of quantum cryptography proposed by Shimizu, Tamaki and Fukasaka (STF) [Phys. Rev. A80 (2009) 022323] is analyzed in a general way, which shows that the STF-B protocol is vulnerable under a kind of generalized attack. Sufficient and necessary condition for which Eve can successfully attack the message M without introducing errors is deduced. It shows that the correlation-elicitation (CE) attack strategy found by Qin et al. [Phys. Rev. A82 (2010) 036301] is a special case of the sufficient and necessary condition. Next, we advance an effective and efficient strategy to prevent the general attack. Hence, the STF-B protocol is revised to a secure one by improving the control mode.

Fast algorithm for 4-qubit reversible logic circuits synthesis

Owing to the exponential nature of the memory or run-tune complexity, many existing methods can only synthesize 3-qubit circuits, however, (G.W. Yang et al., 2005) can achieve 12 steps for the CNP (controlled-Not gate, NOT gate and Peres gate) library in 4-qubit circuit synthesis with mini-length by using an enhanced bi-directional synthesis approach. We mainly absorb the ideas of our 3-qubit synthesis algorithms based on hash table and present a novel and efficient algorithm which can construct almost all optimal 4-qubit reversible logic circuits with various types of gates and mini-length cost based on constructing the shortest coding and the specific topological compression, whose lossless compression ratios of the space of n-qubit circuits is near 2timesn!. Our algorithm has created all 3120218828 optimal 4-qubit circuits whose length is less than 9 for the CNT (Toffoli gate) library, and it can quickly achieve 16 steps through cascading created circuits. To the best of our knowledge, there are no other algorithms to achieve the contribution.

High-dimensional deterministic multiparty quantum secret sharing without unitary operations

A deterministic multiparty quantum secret sharing scheme is put forward, in which Bell states in high-dimensional Hilbert space are used. Only by preforming High-dimensional Bell measurements, all agents can recover the secret according to the dealer’s announcement when collaborating with each other. It shows that unitary operation for encoding deterministic secret is unnecessary in quantum communication. The security of the transmission of the high-dimensional Bell states can be ensured by randomly using one of the two mutually unbiased bases for eavesdropping checking, and thus by which the proposed quantum secret sharing scheme is secure against usual attacks. In addition, the proposed scheme has three advantages: generality, high resource capacity and high security.

Selection of unitary operations in quantum secret sharing without entanglement

We propose a substitute-Bell-state attack strategy for quantum secret sharing schemes without entanglement, as well as a definition of the minimum failure probability of such attack strategy. A quantitative analysis of security degrees corresponding to different unitary operations is also provided, when the secret sharing schemes without entanglement are stricken by substitute-Bell-state attack. As a result, the relation between the selection of unitary operations and the effect of substitute-Bell-state attack is shown, which can serve as an important guidance for the selection of unitary operations in designing and implementing quantum secret sharing schemes.

A novel quantum-inspired evolutionary algorithm based on variable angle-distance rotation

By reviewing the original INIQGA algorithm, an improved algorithm (IINIQGA) is put forward by revising the lookup table. In addition, By introducing the variable angle-distance rotation method into the update Q(t) procedure, a novel quantum-inspired evolutionary algorithm, QEA-VAR, was proposed. Compared with previous algorithms, our update Q(t) procedure is more simple and feasible. Finally, the corresponding experiments on the 0–1 knapsack problem were carried out, and the results show that our improvement is efficient, and comparing with IINIQGA, QEA, and CGA, QEA-VAR has a faster convergence and better profits than other algorithms.

Improvement on "an efficient protocol for the quantum private comparison of equality with W state"

A quantum private comparison (QPC) protocol based on W states [W. Liu et al., Opt. Commun.284, 3160 (2011)] has pointed out there is a flaw of information leak [Y. B. Li et al., Eur. Phys. J. D.66, 110 (2012)]. In order to solve the problem, a special kind of W-class state is introduced, and its construction framework of quantum circuits is sketched. Based on this kind of W-class states, an improvement on Liu et al.s protocol is presented. Analysis shows the improvement can not only hold the characteristics of original protocol, but also avoid the information leak that Li et al. pointed out.