International Journal of Quantum Information

We generalize the symmetric multi-qubit states to their q-analogs, whose basis vectors are identified with the q-Dicke states. We study the entanglement entropy in these states and find that entanglement is extruded towards certain regions of the system due to the inhomogeneity aroused by q-deformation. We also calculate entanglement entropy in ground states of a related q-deformed Lipkin–Meshkov–Glick (LMG) model and show that the singularities of entanglement can correctly signify the quantum phase transition points for different strengths of q-deformation.

In this work, we study the dynamics of three entangled atoms coupled to a common structured reservoir. The atoms are initially prepared in different W-like states characterized by different relative phases. We examine the roles of initial relative phases on the energy transfers among the individual atoms as well as atomic entanglement dynamics. We show that the features of quantum interferences induced by initial relative phases greatly affect the energy transfers and entanglement dynamics. In particular, a suitable choice of initial phases can increase atomic stationary entanglement over their initial value. The results imply a possible control strategy for atomic entanglement dynamics.

In this paper, we propose three schemes for remotely state preparation (RSP) an arbitrary two-level one-atom state via cavity quantum electro dynamics (QED) with minimal resources consumption. In the first case, a Greenberger–Horne–Zeilinger (GHZ) state is used as quantum channel; in the second case, the sender needs to construct an quantum channel with both of the assistant of cavity QED and the knowledge about the state to be remotely prepared. In each scheme, only 1 cbit and 1 ebit are needed with the aid of cavity QED. In the third case, we combine the first two protocols and give a theoretical proposal for controlled RSP with only 2 cbits and 1 ebit resources consumption.

Reconciliation is a significant procedure in a continuous-variable quantum key distribution (CV-QKD) system. It is employed to extract secure secret key from the resulted string through quantum channel between two users. However, the efficiency and the speed of previous reconciliation algorithms are low. These problems limit the secure communication distance and the secure key rate of CV-QKD systems. In this paper, we proposed a high-speed reconciliation algorithm through employing a well-structured decoding scheme based on low density parity-check (LDPC) code. The complexity of the proposed algorithm is reduced obviously. By using a graphics processing unit (GPU) device, our method may reach a reconciliation speed of 25 Mb/s for a CV-QKD system, which is currently the highest level and paves the way to high-speed CV-QKD.

In this paper, we propose a quantum summation protocol, in which the genuinely maximally entangled six-qubit states found by Borras et al., are employed. Because of the excellent properties of the genuinely maximally entangled six-qubit states, the presented protocol allows three participants to compute the summation of their inputs without the help of a trusted third party and preserve the privacy of their inputs, respectively. The participants do not need any unitary operations. In addition, the proposed protocol utilizes the one-step quantum transmission and therefore is congenitally free from Trojan horse attacks. We have also shown that our protocol is secure against other well-known attacks over lossy and noisy quantum channels.

So far, one-way information deficit (OWID) has been calculated explicitly only for Bell-diagonal states and the four-parameter family of X-states with additional assumptions and expressions for more general quantum states are not known. In this paper, we derive explicit expressions for OWID for a larger class of two-qubit states, namely, a five-parameter family of two-qubit states. The dynamic behavior of the OWID under decoherence channel is investigated and it is shown that the OWID is more robust against the decoherence than the entanglement.

We explore the conditions under which identical particles in unitary linear networks behave as the other species, i.e. bosons as fermions and fermions as bosons. It is found that the Boson-sampling (BS) computer of Aaronson and Arkhipov can be implemented in an interference experiment with non-interacting fermions in an appropriately entangled state. Moreover, a scheme is proposed which simulates the scattershot version of the BS computer by preparing, on the fly, the required entangled state of fermions from an unentangled one.

Li and Luo [Phys. Rev. A 78 (2008) 024303] discovered a remarkable relation between discord and entanglement. It establishes that all separable states can be obtained via reduction of a classically-correlated state "living" in a space of larger dimension. Starting from this result, we discuss here an optimal classical extension of separable states and explore this notion for low-dimensional systems. We find that the larger the dimension of the classical extension, the larger the discord in the original separable state. Further, we analyze separable states of maximum discord in ℂ² ⊗ ℂ² and their associated classical extensions showing that, from the reduction of a classical state in (ℂ² ⊗ ℂ³) ⊗ ℂ², one can obtain a separable state of maximum discord in ℂ² ⊗ ℂ².

We propose a quantum blind signature scheme that achieves perfect security under the assumption of an honest offline repository. The security of the protocol also relies on perfect private quantum channels, which are achievable using quantum one-time pads with keys shared via a quantum key distribution (QKD) protocol. The proposed approach ensures that signatures cannot be copied and that the sender must compromise to a single message, which are important advantages over classical protocols for certain applications.

The Wigner rotation angle for a particle in a circular motion in the Schwarzschild spacetime is obtained via the Fermi–Walker transport of spinors. Then, by applying the Wentzel, Kramers, Brillouin (WKB) approximation, a possible application of the Fermi–Walker transport of spinors in relativistic Einstein–Podolsky–Rosen (EPR) correlations is discussed, where it is shown that the spins of the correlated particle undergo a precession in an analogous way to that obtained by Terashima and Ueda [H. Terashima and M. Ueda, Phys. Rev. A 69, 032113 (2004)] via the application of successive infinitesimal Lorentz transformations. Moreover, from the WKB approach, it is also shown that the degree of violation of the Bell inequality depends on the Wigner rotation angle obtained via the Fermi–Walker transport. Finally, the relativistic effects from the geometry of the spacetime and the accelerated motion of the correlated particles is discussed in the nonrelativistic limit.