Shu-Qian Shen

Entanglement detection via some classes of measurements

Based on the mutually unbiased bases, the mutually unbiased measurements and the general symmetric informationally complete positive-operator-valued measures, we propose three separability criteria for

Improved separability criteria via some classes of measurements

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Detection and measure of genuine tripartite entanglement with partial transposition and realignment of density matrices

-dimensional bipartite quantum systems, which are more powerful than the corresponding ones introduced previously [C. Spengler, M. Huber, S. Brierley, T. Adaktylos, and B. C. Hiesmayr, Phys. Rev. A 86, 022311 (2012); B. Chen, T. Ma, and S. M. Fei, Phys. Rev. A 89, 064302 (2014); and B. Chen, T. Li, and S. M. Fei, arXiv:1406.7820v1 [quant-ph] (2014)]. Some states such as Werner states and Bell-diagonal states are used to further illustrate the efficiency of the presented criteria.

Tight upper bound for the maximal quantum value of the Svetlichny operators

The entanglement detection via local measurements can be experimentally implemented. Based on mutually unbiased measurements and general symmetric informationally complete positive-operator-valued measures, we present separability criteria for bipartite quantum states, which, by theoretical analysis, are stronger than the related existing criteria via these measurements. Two detailed examples are supplemented to show the efficiency of the presented separability criteria.

Improved Separability Criteria Based on Bloch Representation of Density Matrices.

It is challenging task to detect and measure genuine multipartite entanglement. We investigate the problem by considering the average based positive partial transposition(PPT) criterion and the realignment criterion. Sufficient conditions for detecting genuine tripartite entanglement are presented. We also derive lower bounds for the genuine tripartite entanglement concurrence with respect to the conditions. While the PPT criterion and the realignment criterion are powerful for detecting bipartite entanglement and for providing lower bounds of bipartite concurrences, our results give an effective operational way to detect and measure the genuine tripartite entanglement.

The norms of Bloch vectors and a trade-off relation of Svetlichny inequalities

It is a challenging task to detect genuine multipartite nolocality (GMNL). In this paper, the problem is considered via computing the maximal quantum value of Svetlichny operators for three-qubit systems and a tight upper bound is obtained. The constraints on the quantum states for the tightness of the bound are also presented. The approach enables us to give the necessary and sufficient conditions of violating the Svetlichny inequalities (SI) for several quantum states, including the white and color noised GHZ states. The relation between the genuine multipartite entanglement concurrence and the maximal quantum value of the Svetlichny operators for mixed GHZ class states is also discussed. As the SI is useful for the investigation on GMNL, our results give an effective and operational method to detect the GMNL for three-qubit mixed states.

Construction of Bell inequalities based on the CHSH structure

The correlation matrices or tensors in the Bloch representation of density matrices are encoded with entanglement properties. In this paper, based on the Bloch representation of density matrices, we give some new separability criteria for bipartite and multipartite quantum states. Theoretical analysis and some examples show that the proposed criteria can be more efficient than the previous related criteria.

Realignment criteria for recognizing multipartite entanglement of quantum states

We investigate the norms of Bloch vectors in four-partite quantum systems. An upper bound for the sum of the norms of three-order Bloch vectors has been obtained. We then present a trade-off relation of the Svetlichny inequality for any multipartite qubits systems by the upper bound. We show that for four-qubit systems, the reduced triple qubits cannot reach the maximal violate value simultaneously, while for any six-qubit state, the reduced triple qubits cannot violate Svetlichny inequality in the same time.

Measure and Detection of Genuine Multipartite Entanglement for Tripartite Systems

It is a computationally hard task to find all Bell inequalities for a given number of parties, measurement settings, and measurement outcomes. We investigate the construction of the Clauser-Horne-Shimony-Holt Bell inequalities, based on which we present a set of new Bell inequalities. The maximal violations of the constructed Bell inequalities are analysed, and computable formulas are derived.

New Separability Criteria Based on Two Classes of Measurements

By multiple realignments of density matrices, we present a new separability criterion for the multipartite quantum state, which includes the computable cross-norm or realignment criterion and the multipartite partial realignment criterion as special cases. An example is used to show that the new criterion can be more efficient than the corresponding multipartite realignment criteria given in Horodecki et al. (Open Syst Inf Dyn 13:103–111, 2006) and Shen et al. (Phys Rev A 92:042332, 2015).