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Hu M.-L.,University of Posts and Telecommunications | Fan H.,CAS Institute of Physics
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

With the aid of a quantum memory, the uncertainty about the measurement outcomes of two incompatible observables of a quantum system can be reduced. We investigate this measurement uncertainty bound by considering an additional quantum system connected with both the quantum memory and the measured quantum system. We find that the reduction of the uncertainty bound induced by a quantum memory, on the other hand, implies it is increasing for a third participant. We also show that the properties of the uncertainty bound can be viewed from perspectives of both quantum and classical correlations, in particular, that the behavior of the uncertainty bound is a result of competitions of various correlations between different parties. © 2013 American Physical Society.


Hu M.-L.,University of Posts and Telecommunications | Fan H.,CAS Institute of Physics
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

By using the quantum-memory-assisted entropic uncertainty relation (EUR), we derive a computable tight upper bound for quantum discord, which applies to an arbitrary bipartite state. Detailed examples show that this upper bound is tighter than other known bounds in a wide regime. Furthermore, we show that for any tripartite pure state, the quantum-memory-assisted EUR imposes a constraint on the shareability of quantum correlations among the constituent parties. This conclusion amends the well-accepted result that quantum discord is not monogamous. © 2013 American Physical Society.


Hu M.-L.,University of Posts and Telecommunications | Fan H.,CAS Institute of Physics
New Journal of Physics | Year: 2015

Nonlocality is one unique property of quantum mechanics that differs from the classical world. One of its quantifications can be properly described as the maximum global effect caused by locally invariant measurements, known as measurement-induced nonlocality (MIN) (2011 Phys. Rev. Lett. 106 120401). Here, we propose quantifying the MIN by the trace norm. We show explicitly that this measure is monotonically decreasing under the action of a completely positive trace-preserving map, which is the general local quantum operation, on the unmeasured party for the bipartite state. This property avoids the undesirable characteristic appearing in the known measure of MIN defined by the Hilbert-Schmidt norm which may be increased or decreased by trivial local reversible operations on the unmeasured party. We obtain analytical formulas of the trace-norm MIN for any (2 x n)-dimensional pure state, two-qubit state, and certain high-dimensional states. As with other quantum correlation measures, the newly defined MIN can be directly applied to various models for physical interpretations. © 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.


Hu M.-L.,University of Posts and Telecommunications
Quantum Information Processing | Year: 2013

Based on the assumption that the receiver Bob can apply any unitary transformation, Horodecki et al. (Phys Lett A 222:21-25, 1996) proved that any mixed two spin-1/2 state which violates the Bell-CHSH inequality is useful for teleportation. Here, we further show that any X state which violates the Bell-CHSH inequality can also be used for nonclassical teleportation even if Bob can only perform the identity or the Pauli rotation operations. Moreover, we showed that the maximal difference between the two average fidelities achievable via Bob's arbitrary transformations and via the sole identity or the Pauli rotation is 1/9. © 2012 Springer Science+Business Media, LLC.


Hu M.-L.,University of Posts and Telecommunications
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2010

We investigate disentanglement dynamics of two coupled qubits and qutrits which interact uniformly to a general XY spin-chain environment with the Dzyaloshinsky-Moriya (DM) interaction. We obtained exact expression of the time evolution operator and analyzed the dynamical process of the decoherence factors. Through explicitly calculating the concurrence and the negativity, we examined disentanglement behaviors of two coupled central spins evolve from different initial pure states, which are found to be nontrivially different from those of the uncorrelated ones, in particular, the enhanced decay of the entanglement induced by quantum criticality of the surrounding environment may be broken by introducing self-Hamiltonian of the central spin system. Moreover, the DM interaction may have different influences on decay of the entanglement depending on the strength of the system-environment coupling, the anisotropy of the environmental spin chain and the intensity of the transverse magnetic field, as well as the explicit form of the initial states of the central spin system. © 2010 Elsevier B.V.


Li L.,University of Posts and Telecommunications
Materials Letters | Year: 2013

The SnO2 nanobelts were synthesized on silicon substrate by using simple thermal evaporation and condensation method at around 850 °C without catalysts assistant. The crystal structure and morphology of SnO 2 nanobelts were characterized using X-ray diffraction, Raman shift, scanning electron microscopy, selected area electron diffraction, transmission electron microscopy and energy-dispersive X-ray analysis. The mechanisms for the growth of SnO2 nanobelts have been discussed. The photoluminescence spectra of the nanobelts were measured from 77 K to 300 K. The results show that temperature has an obvious influence on the emission intensity of luminescence bands around 400 nm, 630 nm and 677 nm. © 2013 Elsevier B.V.


Shi G.-F.,University of Posts and Telecommunications
Optics Communications | Year: 2010

A bidirectional quantum secure communication protocol is presented. By introducing the auxiliary particle and utilizing the special character of Bell state, "correlation extractability", our scheme cannot only discard the drawback, "information leakage", but also is easy to implement. © 2010 Elsevier B.V. All rights reserved.


Hu M.-L.,University of Posts and Telecommunications
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2011

The one-qubit teleportation protocol is reexamined when it is executed in the presence of various decohering environments. The results revealed that this quantum protocol is more robust under the influence of dephasing environment than those under the influence of dissipative or noisy environment. The environment may deprive the quantum advantage of teleportation over purely classical communication in a finite or infinite lifetime, which is dependent on the type of environment. Also we found that except entanglement, the purity of the entangled state resource is also crucial in determining the quality of the teleported state. © 2011 Elsevier B.V. All rights reserved.


Hu M.-L.,University of Posts and Telecommunications
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2011

By solving analytically a master equation in the Lindblad form, we study quantum teleportation of the one-qubit state under the influence of different surrounding environments, and compared the robustness between Greenberger-Horne-Zeilinger (GHZ) and W states in terms of their teleportation capacity. The results revealed that when subject to zero temperature environment, the GHZ state is always more robust than the W state, while the reverse situation occurs when the channel is subject to infinite temperature or dephasing environment. © 2010 Elsevier B.V. All rights reserved.


Hu M.L.,University of Posts and Telecommunications
European Physical Journal D | Year: 2011

We study standard protocol \hbox{$\mathcal{P}-0$} 0 for teleporting the one-qubit state with both the transmission process of the two qubits constitute the quantum channel and the recovery operations performed by Bob disturbed by the decohering environment. The results revealed that Bob's imperfect operations do not eliminate the possibility of nonclassical teleportation fidelity provided he shares an ideal channel state with Alice, while the transmission process is constrained by a critical time t 0, c longer than which will result in failure of \hbox{$\ mathcal{P}-0$} 0 if the two qubits are corrupted by the decohering environment. Moreover, we found that under the condition of the same decoherence rate γ, the teleportation protocol is significantly more fragile when it is executed under the influence of the noisy environment than those under the influence of the dissipative and dephasing environments. © 2011 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.

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