Chuanmei Xie

Four-party deterministic operation sharing with six-qubit cluster state

An efficient four-party scheme is proposed for remotely sharing an arbitrary single-qubit operation by using a six-qubit cluster state as quantum channel and local operation and classical communication. Some specific discussions are made, including the issues of the scheme determinacy, the sharer symmetry, the scheme security and the essential role of quantum channel as well as the current experimental feasibility.

Tripartite quantum operation sharing with two asymmetric three-qubit W states in five entanglement structures

Tripartite remote sharing of any single-qubit operation with two asymmetric three-qubit W states is amply treated. Five schemes are put forward with the W states in five different entanglement structures corresponding to five different distributions of two identical qubit trios in three locations. For all schemes, two features about the security and the agent symmetry are analyzed and confirmed. Moreover, resource consumption, necessary-operation complexity, success probability and efficiency are also worked out and compared mutually. For all schemes, quantum resource consumption and necessary-operation complexity are same. The last scheme needs to cost two additional classical bits than the former four schemes. Nonetheless, the last scheme is deterministic and has the highest efficiency in contrast to the other four probabilistic schemes with lower efficiencies. Through some analyses, it is found that both success probability and intrinsic efficiency of each scheme are completely determined by the corresponding entanglement structure of the two W states. The underlying physics of this feature is revealed. In addition, the implementation feasibility of all the schemes is analyzed and thus confirmed according to the current experimental techniques.

Quantum correlation swapping

Quantum correlations (QCs), including quantum entanglement and those different, are important quantum resources and have attracted much attention recently. Quantum entanglement swapping as a kernel technique has already been applied to quantum repeaters for successfully generating long-distance shared maximally entangled qubit states. Long-distance shared QCs containing shared entanglements are useful and important for some quantum information processing in future quantum networks. In this paper, the concept of quantum entanglement repeater is extended to that of QC repeater by generalizing quantum entanglement swapping to QC swapping. Specifically, the swapping of QCs in a pair of Werner states through a local bipartite von Neumann measurement is treated. Four different QC measures, i.e., entanglement of formation (William in Phys Rev Lett 80:2245, 1998), quantum discord (Ollivier and Zurek in Phys Rev Lett 88:017901, 2001), measurement-induced disturbance (MID) (Luo in Phys Rev A 77:022301, 2008) and ameliorated MID (Girolami et al. in J Phys A 44:352002, 2011), are employed to characterize and quantify QCs. Properties and thresholds of all QCs which occur in the swapping process are revealed, and two different phenomena are exposed and explained. It is found that a long-distance shared QC can be generated from two short-distance ones via QC swapping indeed; however, its amount cannot exceed the minimum one among the QCs in the two initial states and in the measuring state as far as the four quantifiers are concerned.

Shared quantum control via sharing operation on remote single qutrit

Two qubit-operation-sharing schemes (Zhang and Cheung in J. Phys. B 44:165508, 2011) are generalized to the qutrit ones. Operations to be shared are classified into three different classes in terms of different probabilities (i.e, 1/3, 2/3 and 1). For the latter two classes, ten and three restricted sets of operations are found out, respectively. Moreover, the two generalized schemes are amply compared from four aspects, namely, quantum and classical resource consumption, necessary-operation complexity, success probability and efficiency. It is found that the second scheme is overall more optimal than the first one as far as three restricted sets of operations are concerned. Moreover, the experimental feasibility of our schemes is confirmed with respect to the nowaday technique.

Probabilistic Three-Party Sharing of Operation on a Remote Qubit

A probabilistic tripartite single-qubit operation sharing scheme is put forward by utilizing a two-qubit and a three-qubit non-maximally entangled state as quantum channels. Some specific comparisons between our scheme and another probabilistic scheme are made. It is found that, if the product of the two minimal coefficients characterizing channel entanglements is greater than 3/16, our scheme is more superior than the other one. Nonetheless, the price is that more classical and quantum resources are consumed, and the operation difficulty is rather increased. Moreover, some important features of the scheme, such as its security, probability and sharer symmetry, are revealed through concrete discussions. Additionally, the experimental feasibility of our scheme is analyzed and subsequently confirmed according to the current experimental techniques.

A note on quantum correlations in Werner states under two collective noises

Influences of two collective noises, i.e., the dephasing noise and the rotating noise, on quantum correlations in Werner states are considered in this note. It is found that the collective noises do not alter the correlations as far as quantum discord and geometry discord as quantifiers are concerned. Alternatively, quantum correlations in Werner states are robust against the noises.

Study of quantum correlation swapping with relative entropy methods

To generate long-distance shared quantum correlations (QCs) for information processing in future quantum networks, recently we proposed the concept of QC repeater and its kernel technique named QC swapping. Besides, we extensively studied the QC swapping between two simple QC resources (i.e., a pair of Werner states) with four different methods to quantify QCs (Xie et al. in Quantum Inf Process 14:653–679, 2015). In this paper, we continue to treat the same issue by employing other three different methods associated with relative entropies, i.e., the MPSVW method (Modi et al. in Phys Rev Lett 104:080501, 2010), the Zhang method (arXiv:1011.4333 [quant-ph]) and the RS method (Rulli and Sarandy in Phys Rev A 84:042109, 2011). We first derive analytic expressions of all QCs which occur during the swapping process and then reveal their properties about monotonicity and threshold. Importantly, we find that a long-distance shared QC can be generated from two short-distance ones via QC swapping indeed. In addition, we simply compare our present results with our previous ones.

Deterministic tripartite sharing of eight restricted sets of single-qubit operations with two Bell states or a GHZ state

Two tripartite schemes with a pair of Bell states and a Greenberger–Horne–Zeilinger (GHZ) state respectively have been proposed recently by Zhang and Cheung for remotely sharing two restricted sets of operations in a deterministic manner [J. Phys. B 44 (2011) 165508]. In this paper, we generalize the schemes with the same quantum channels so that another six restricted sets of operations can be shared deterministically, too. Features about scheme security, sharer symmetry, fulfillment determinacy and experimental feasibility are discussed and revealed. Moreover, some comparisons are also made from the aspects of quantum and classical resource consumption, necessary operation complexity and efficiency.

Generalized three-party sharing of operations on remote single qutrit

Two three-party schemes are put forward for sharing quantum operations on a remote qutrit with local operation and classical communication as well as shared entanglements. The first scheme uses a two-qutrit and three-qutrit non-maximally entangled states as quantum channels, while the second replaces the three-qutrit non-maximally entangled state with a two-qutrit. Both schemes are treated and compared from the four aspects of quantum and classical resource consumption, necessary-operation complexity, success probability and efficiency. It is found that the latter is overall more optimal than the former as far as a restricted set of operations is concerned. In addition, comparisons of both schemes with other four relevant ones are also made to show their two features, including degree generalization and channel-state generalization. Furthermore, some concrete discussions on both schemes are made to expose their important features of security, symmetry and experimental feasibility. Particularly, it is revealed that the success probabilities and intrinsic efficiencies in both schemes are completely determined by the shared entanglement.

Quantum correlations in a family of bipartite separable qubit states

Quantum correlations (QCs) in some separable states have been proposed as a key resource for certain quantum communication tasks and quantum computational models without entanglement. In this paper, a family of nine-parameter separable states, obtained from arbitrary mixture of two sets of bi-qubit product pure states, is considered. QCs in these separable states are studied analytically or numerically using four QC quantifiers, i.e., measurement-induced disturbance (Luo in Phys Rev A77:022301, 2008), ameliorated MID (Girolami et al. in J Phys A Math Theor 44:352002, 2011),quantum dissonance (DN) (Modi et al. in Phys Rev Lett 104:080501, 2010), and new quantum dissonance (Rulli in Phys Rev A 84:042109, 2011), respectively. First, an inherent symmetry in the concerned separable states is revealed, that is, any nine-parameter separable states concerned in this paper can be transformed to a three-parameter kernel state via some certain local unitary operation. Then, four different QC expressions are concretely derived with the four QC quantifiers. Furthermore, some comparative studies of the QCs are presented, discussed and analyzed, and some distinct features about them are exposed. We find that, in the framework of all the four QC quantifiers, the more mixed the original two pure product states, the bigger QCs the separable states own. Our results reveal some intrinsic features of QCs in separable systems in quantum information.