Quantum Discord, Quantum Entanglement, and Linear Entropy, and the Relationship Between Them

2010 ◽  
Author(s):  
Asma Al-Qasimi ◽  
Daniel F. V. James
Keyword(s):  
Quantum Entanglement ◽  
Quantum Discord ◽  
Linear Entropy ◽  
The Relationship

The impact of resource on remote quantum correlation Preparation

2015 ◽  
Vol 15 (13&14) ◽  
pp. 1223-1232
Author(s):  
Chengjun Wu ◽  
Bin Luo ◽  
Hong Guo
Keyword(s):  
Quantum Entanglement ◽  
Quantum Correlation ◽  
Quantum Discord ◽  
Entangled States ◽  
Shared Resources ◽  
Classical Communication ◽  
Bell Measurement ◽  
Measurement Results ◽  
The Impact

When Alice and Bob share two pairs of quantum correlated states, Alice can remotely prepare quantum entanglement and quantum discord in Bob’s side by measuring the parts in her side and telling Bob the measurement results by classical communication. For remote entanglement preparation, entanglement is necessary . We find that for some shared resources having the same amount of entanglement, when Bell measurement is used, the entanglement remotely prepared can be different, and more discord in the resources actually decreases the entanglement prepared. We also find that for some resources with more entanglement, the entanglement remotely prepared may be less. Therefore, we conclude that entanglement is a necessary resource but may not be the only resource responsible for the entanglement remotely prepared, and discord does not likely to assist this process. Also, for the preparation of discord, we find that some states with no entanglement could outperform entangled states.

REVIEW ON SYSTEM-SPIN ENVIRONMENT DYNAMICS OF QUANTUM DISCORD

2012 ◽  
Vol 27 (01n03) ◽  
pp. 1345055 ◽  
Author(s):  
BEN-QIONG LIU ◽  
BIN SHAO ◽  
JUN-GANG LI ◽  
JIAN ZOU
Keyword(s):  
Quantum Discord ◽  
Open Systems ◽  
Quantum Phase Transitions ◽  
Physical Models ◽  
Quantum Computers ◽  
Bipartite State ◽  
External Perturbations ◽  
Mathematical Properties ◽  
Spin Pairs ◽  
The Relationship

Recent work has relatively comprehensively studied the quantum discord, which is supposed to account for all the nonclassical correlations present in a bipartite state (including entanglement), and provide computational speedup and quantum enhancement even in separable states. Firstly, we introduce several different indicators of nonclassical correlations, including their definitions and interpretations, mathematical properties, and the relationship between them. Secondly, we review two major topics of quantum discord. One is the remarkable behavior at quantum phase transitions. The pairwise quantum discord for nearest neighbors as well as distant spin pairs can perfectly signal the critical behavior of many physical models, even at finite temperatures. The other is quantum discord dynamics in open systems, especially for "system-spin environment" models. Quantum discord is more robust than entanglement against external perturbations. It can be created, greatly amplified or protected under certain conditions, and presents promising applications in quantum technologies such as quantum computers.

QUANTUM CORRELATIONS IN THE ENTANGLEMENT DISTILLATION PROTOCOLS

2013 ◽  
Vol 11 (03) ◽  
pp. 1350029
Author(s):  
SHAO-XIONG WU ◽  
JUN ZHANG ◽  
CHANG-SHUI YU ◽  
HE-SHAN SONG
Keyword(s):  
Quantum Entanglement ◽  
Quantum Correlation ◽  
Quantum Discord ◽  
Quantum Correlations ◽  
The Other ◽  
Entangled States ◽  
Entanglement Distillation

We study the quantum correlations between source and target pairs in different protocols of entanglement distillation of one kind of entangled states. We find that there does not exist any quantum correlation in the standard recurrence distillation protocol, while quantum discord and even quantum entanglement are always present in the other two cases of the improved distillation protocols. In the three cases, the distillation efficiency improved with the quantum correlations enhanced.

scholarly journals A Pedagogical Overview of Quantum Discord

2014 ◽  
Vol 21 (01n02) ◽  
pp. 1440006 ◽  
Author(s):  
Kavan Modi
Keyword(s):  
Quantum Computation ◽  
Quantum Entanglement ◽  
Quantum Discord ◽  
Historical Review ◽  
Point Of View ◽  
Many Body ◽  
Definition Of ◽  
Many Body Physics

Recent measures of nonclassical correlations are motivated by different notions of classicality and operational means. Quantum discord has received a great deal of attention in studies involving quantum computation, metrology, dynamics, many-body physics, and thermodynamics. In this article I show how quantum discord is different from quantum entanglement from a pedagogical point of view. I begin with a pedagogical introduction to quantum entanglement and quantum discord, followed by a historical review of quantum discord. Next, I give a novel definition of quantum discord in terms of any classically extractable information, an approach that is fitting for the current avenues of research. Lastly, I put forth several arguments for why discord is an interesting quantity to study and why it is of interest to so many researchers in the community.

scholarly journals Entanglement and impropriety

2021 ◽  
Author(s):  
Brian R. La Cour ◽  
Thomas W. Yudichak
Keyword(s):  
Quantum Entanglement ◽  
Random Variables ◽  
Squeezed States ◽  
Photon Detection ◽  
Gaussian Random Variables ◽  
Photon Pairs ◽  
Entangled Photon Pairs ◽  
The Relationship ◽  
Bogoliubov Transformations ◽  
Threshold Exceedance

AbstractThe relationship between quantum entanglement and classical impropriety is considered in the context of multi-modal squeezed states of light. Replacing operators with complex Gaussian random variables in the Bogoliubov transformations for squeezed states, we find that the resulting transformed variables are not only correlated but also improper. A simple threshold exceedance model of photon detection is considered and used to demonstrate how the behavior of improper Gaussian random variables can mimic that of entangled photon pairs when coincidence post-selection is performed.

Quantum Entanglement and Quantum Discord in Gaussian Open Systems

2011 ◽  
Author(s):  
Aurelian Isar ◽  
Madalin Bunoiu ◽  
Iosif Malaescu
Keyword(s):  
Quantum Entanglement ◽  
Quantum Discord ◽  
Open Systems

scholarly journals Quantum Entanglement and Quantum Discord of Two-Mode Gaussian States in a Thermal Environment

2011 ◽  
Vol 18 (02) ◽  
pp. 175-190 ◽  
Author(s):  
Aurelian Isar
Keyword(s):  
Sudden Death ◽  
Time Evolution ◽  
Quantum Entanglement ◽  
Quantum Discord ◽  
Thermal Environment ◽  
Quantum Correlations ◽  
Entangled State ◽  
Gaussian State ◽  
Thermal Bath ◽  
Bipartite State

In the framework of the theory of open systems based on completely positive quantum dynamical semigroups, we give a description of the continuous-variable quantum entanglement and quantum discord for a system consisting of two noninteracting modes embedded in a thermal environment. Entanglement and discord are used to quantify the quantum correlations of the system. For all values of the temperature of the thermal reservoir, an initially separable Gaussian state remains separable for all times. We study the time evolution of logarithmic negativity, which characterizes the degree of entanglement, and we show that in the case of an entangled initial Gaussian state, entanglement suppression (entanglement sudden death) takes place for non-zero temperatures of the environment. Only for zero temperature of the thermal bath the initial entangled state remains entangled for finite times. We analyze time evolution of Gaussian quantum discord, which is a measure of all quantum correlations in the bipartite state, including entanglement, and we show that quantum discord decays asymptotically in time under the effect of thermal bath. This is in contrast with the sudden death of entanglement. Before the suppression of entanglement, the qualitative evolution of quantum discord is very similar to that of the entanglement. We describe also time evolution of the degree of classical correlations and of quantum mutual information, which measures the total correlations of quantum system.

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