Upper bound and shareability of quantum discord based on entropic uncertainty relations

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.Comment: 5 pages, 1 figure, the final version as that published in Phys. Rev.

Electromagnetic form factors of Λc\Lambda_c in the Bethe-Salpeter equation approach

We study the electromagnetic form factors (EMFFs) of $\Lambda_c$ and the quark and diquark current contributes to the EMFFs of $\Lambda_c$ in the space-like (SL) region in the Bethe-Salpeter equation approach. In this picture, the heavy baryon $\Lambda_c$ is regarded as composed of a heavy quark and a scalar diquark. We find that for different values of parameters the quark and diquark current contribute to the EMFFs of $\Lambda_c$ is very different, but the total contribute to the EMFFs of $\Lambda_c$ is similarly. The EMFFs of $\Lambda_c$ are similar to those of other baryons (proton, $\Xi^-$, $\Sigma^+$) with a peak at $\omega =1$ ($\omega=v^\prime \cdot v$ is the velocity transfer between the initial state (with velocity $v$) and the final state (with velocity $v^\prime$) of $\Lambda_c$).Comment: arXiv admin note: substantial text overlap with arXiv:1612.0608

Evolution equation for quantum coherence

The estimation of the decoherence process of an open quantum system is of both theoretical significance and experimental appealing. Practically, the decoherence can be easily estimated if the coherence evolution satisfies some simple relations. Based on the coherence quantification method, we prove a simple factorization relation for the $l_1$ norm measure of coherence, and analyze under which condition this relation holds. We also obtain a more general relation which applies to arbitrary $N$-qubit state, and determine a condition for the transformation matrix of the quantum channel which can support permanently freezing of the $l_1$ norm of coherence. These results simplify determination of a general decoherence dynamics to that the investigation of evolution about the representative probe state.Comment: 9 pages (including the Supplemental Material), 1 figure, minor corrections being mad

Studying the bound state of the K−pK^-p system in the Bethe-Salpeter formalism

We study the $s$-wave kaon-nucleon bound state with the strangeness $S=-1$ in the Bethe-Salpeter formalism in the ladder and instantaneous approximations. We solve the Bethe-Salpeter equation of the bound state and obtain the Bethe-Salpeter amplitude. It is shown that the $K^-p$ bound state exists in this formalism. We also study the decay width of the bound state based on the Bethe-Salpeter techniques. The mass of this bound state is 1422 MeV and its decay width is obviously smaller than that of $\Lambda(1405)$. These results indicate that there may be some other structures in the observed resonance.Comment: 7 pages, 4 Figure

Measurement-induced nonlocality based on the trace norm

Nonlocality is one unique property of quantum mechanics differing from classical world. One of its quantifications can be properly described as the maximum global effect caused by locally invariant measurements, termed as measurement-induced nonlocality (MIN) (2011 \emph{Phys. Rev. Lett.} {\bf 106} 120401). Here, we propose to quantify the MIN by the trace norm. We show explicitly that this measure is monotonically decreasing under the action of 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 that 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 $2\times n$ dimensional pure state, two-qubit state, and certain high-dimensional states. As other quantum correlation measures, the new defined MIN can be directly applied to various models for physical interpretations.Comment: 6 pages, 1 figure, the final version as that published in New J. Phy

Dynamics of entropic measurement-induced nonlocality in structured reservoirs

We propose the entropic measurement-induced nonlocality (MIN) as the maximal increment of von Neumann entropy induced by the locally non-disturbing measurement, and study behaviors of it both in the independent and common structured reservoirs. We present schemes for preserving the MIN, and show that for certain initial states the MIN, including the quantum correlations, can even be enhanced by the common reservoir. Additionally, we also show that the different measures of MIN may give different qualitative characterizations of nonlocal properties, i.e., it is rather measure dependent than state dependent.Comment: 8 pages, 6 figure

Evolution equation for geometric quantum correlation measures

A simple relation is established for the evolution equation of quantum information processing protocols such as quantum teleportation, remote state preparation, Bell-inequality violation and particularly dynamics of the geometric quantum correlation measures. This relation shows that when the system traverses the local quantum channel, various figures of merit of the quantum correlations for different protocols demonstrate a factorization decay behavior for dynamics. We identified the family of quantum states for different kinds of quantum channels under the action of which the relation holds. This relation simplifies the assessment of many quantum tasks.Comment: 7 pages, 2 figure

Nonlocal advantage of quantum coherence in high-dimensional states

By local measurements on party $A$ of a system $AB$ and classical communication between its two parties, one can achieve a nonlocal advantage of quantum coherence (NAQC) on party $B$. For the $l_1$ norm of coherence and the relative entropy of coherence, we generalized the framework of NAQC for two qubits and derived the criteria which capture NAQC in the $(d\times d)$-dimensional states when $d$ is a power of a prime. We also presented a new framework for formulating NAQC, and showed through explicit examples its capacity on capturing the NAQC states. Moreover, we proved that any bipartite state with NAQC is quantum entangled, thus the obtained criteria can also be used as an entanglement witness.Comment: 5 pages, 2 figures; Final version to be published in Phys. Rev.

Accuracy of Range-Based Cooperative Localization in Wireless Sensor Networks: A Lower Bound Analysis

Accurate location information is essential for many wireless sensor network (WSN) applications. A location-aware WSN generally includes two types of nodes: sensors whose locations to be determined and anchors whose locations are known a priori. For range-based localization, sensors' locations are deduced from anchor-to-sensor and sensor-to-sensor range measurements. Localization accuracy depends on the network parameters such as network connectivity and size. This paper provides a generalized theory that quantitatively characterizes such relation between network parameters and localization accuracy. We use the average degree as a connectivity metric and use geometric dilution of precision (DOP), equivalent to the Cramer-Rao bound, to quantify localization accuracy. We prove a novel lower bound on expectation of average geometric DOP (LB-E-AGDOP) and derives a closed-form formula that relates LB-E-AGDOP to only three parameters: average anchor degree, average sensor degree, and number of sensor nodes. The formula shows that localization accuracy is approximately inversely proportional to the average degree, and a higher ratio of average anchor degree to average sensor degree yields better localization accuracy. Furthermore, the paper demonstrates a strong connection between LB-E-AGDOP and the best achievable accuracy. Finally, we validate the theory via numerical simulations with three different random graph models.Comment: 11 pages, 6 figures, 1 tabl

Competitions between quantum correlations in the quantum-memory-assisted entropic uncertainty relation

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 its 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, the behavior of the uncertainty bound is a result of competitions of various correlations between different parties.Comment: 5 pages, 2 figures, the final version as that published in Phys. Rev.