Chen Ping-Xing

Relative Entropy of Entanglement of One Class of Two-Qubit System

The relative entropy of entanglement of a mixed state ? for a bipartite quantum system can be defined as the minimum of the quantum relative entropy over the set of completely disentangled states. Vedral et al. [Phys. Rev. A 57(1998)1619] have recently proposed a numerical method to obtain the relative entropy of entanglement Ere for two-qubit systems. This letter shows that the convex programming method can be applied to calculate Ere of two-qubit systems analytically, and discusses the conditions under which the method can be adopted.

Design of quantum VQ iteration and quantum VQ encoding algorithm taking O(N1/2) steps for data compression

Vector quantization (VQ) is an important data compression method. The key of the encoding of VQ is to find the closest vector among N vectors for a feature vector. Many classical linear search algorithms take O(N) steps of distance computing between two vectors. The quantum VQ iteration and corresponding quantum VQ encoding algorithm that takes O(N1/2) steps are presented in this paper. The unitary operation of distance computing can be performed on a number of vectors simultaneously because the quantum state exists in a superposition of states. The quantum VQ iteration comprises three oracles, by contrast many quantum algorithms have only one oracle, such as Shors factorization algorithm and Grovers algorithm. Entanglement state is generated and used, by contrast the state in Grovers algorithm is not an entanglement state. The quantum VQ iteration is a rotation over subspace, by contrast the Grover iteration is a rotation over global space. The quantum VQ iteration extends the Grover iteration to the more complex search that requires more oracles. The method of the quantum VQ iteration is universal.

Local distinguishability of orthogonal quantum states and generators of SU(N)

We investigate the possibility of distinguishing a set of mutually orthogonal multipartite quantum states by local operations and classical communication (LOCC). We connect this problem with generators of SU(N) and present a condition that is necessary for a set of orthogonal states to be locally distinguishable. We show that even in multipartite cases there exists a systematic way to check whether the presented condition is satisfied for a given set of orthogonal states. Based on the proposed checking method, we find that LOCC cannot distinguish three mutually orthogonal states in which two of them are Greenberger-Horne-Zeilinger-like states.

Quantum phase transition of light in a one-dimensional photon-hopping-controllable resonator array

We give a concrete experimental scheme for engineering the insulator-superfluid transition of light in a one-dimensional (1-D) array of coupled superconducting stripline resonators. In our proposed architecture, the on-site interaction and the photon hopping rate can be tuned independently by adjusting the transition frequencies of the charge qubits inside the resonators and at the resonator junctions, respectively, which permits us to systematically study the quantum phase transition of light in a complete parameter space. By combining the techniques of photon-number-dependent qubit transition and fast read-out of the qubit state using a separate low-Q resonator mode, the statistical property of the excitations in each resonator can be obtained with a high efficiency. An analysis of the various decoherence sources and disorders shows that our scheme can serve as a guide to coming experiments involving a small number of coupled resonators.

Realization of universal adiabatic quantum computation with fewer physical resources

The adiabatic quantum computation (AQC) has been proved to be equivalent with the standard circuit model. To realize AQC, we have to realize the target Hamiltonian. However, usually the target Hamiltonian contains k-local terms where k{>=}3 which is difficult to realize in experiment. It has been proved that a k-local Hamiltonian can be reduced to a two-local one. However, the reduction process needs a lot of auxiliary qubits which makes the system very complicated. Here we show that one can reduce a three-local Hamiltonian to a two-local one using only one third of the auxiliary qubits the previous approach needs and, in special cases, only three auxiliary qubits.

The Second Law of Thermodynamics in a Quantum Heat Engine Model

The second law of thermodynamics has been proven by many facts in classical world. Is there any new property of it in quantum world? In this paper, we calculate the change of entropy in T.D. Kieus model for quantum heat engine (QHE) and prove the broad validity of the second law of thermodynamics. It is shown that the entropy of the quantum heat engine neither decreases in a whole cycle, nor decreases in either stage of the cycle. The second law of thermodynamics still holds in this QHE model. Moreover, although the modified quantum heat engine is capable of extracting more work, its efficiency does not improve at all. It is neither beyond the efficiency of T.D. Kieus initial model, nor greater than the reversible Carnot efficiency.

Large Detuning Limit for the Multipartite Systems Interacting with Electromagnetic Fields

We study the dynamics of the multipartite systems nonresonantly interacting with electromagnetic fields and show that, since the coupling strength

Implementation of quantum partial search with superconducting quantum interference device qudits in cavity QED

g

One-way quantum computation with circuit quantum electrodynamics

is collectively enhanced by the square root of the number of microparticles involved, the more rigorous large detuning condition for neglecting the rapidly oscillating terms for the effective Hamiltonian should be

Entangled States with Positive Partial Transpose in Any-Dimensional Quantum System

\Delta\gg\sqrt{N}g