scholarly journals Daemonic Ergotropy: Generalised Measurements and Multipartite Settings

Entropy ◽  
2019 ◽  
Vol 21 (8) ◽  
pp. 771 ◽  
Author(s):  
Fabian Bernards ◽  
Matthias Kleinmann ◽  
Otfried Gühne ◽  
Mauro Paternostro
Keyword(s):  
Quantum System ◽  
Information Gain ◽  
Quantum Correlations ◽  
Maximum Energy ◽  
Extraction Protocol ◽  
Original Definition ◽  
Maximum Work ◽  
Classical Correlations ◽  
Projective Measurements ◽  
Classical States

Recently, the concept of daemonic ergotropy has been introduced to quantify the maximum energy that can be obtained from a quantum system through an ancilla-assisted work extraction protocol based on information gain via projective measurements [G. Francica et al., npj Quant. Inf. 3, 12 (2018)]. We prove that quantum correlations are not advantageous over classical correlations if projective measurements are considered. We go beyond the limitations of the original definition to include generalised measurements and provide an example in which this allows for a higher daemonic ergotropy. Moreover, we propose a see-saw algorithm to find a measurement that attains the maximum work extraction. Finally, we provide a multipartite generalisation of daemonic ergotropy that pinpoints the influence of multipartite quantum correlations, and study it for multipartite entangled and classical states.

scholarly journals Correlations in geometric states

2020 ◽  
Vol 2020 (8) ◽  
Author(s):  
Wu-zhong Guo
Keyword(s):  
Central Charge ◽  
Convex Combination ◽  
Vacuum State ◽  
Quantum Correlations ◽  
Quantum Field Theories ◽  
Quantum Field ◽  
Classical Geometry ◽  
Accessible Information ◽  
Classical Correlations ◽  
Quantum And Classical Correlations

Abstract In this paper we explore the correlations in the geometric states. Here the geometric state means the state in CFTs that can be effectively described by classical geometry in the bulk in the semi-classical limit G → 0. By using the upper bound of Holevo information we show the convex combination of geometric states cannot be a geometric state. To understand the duality between thermofield double state and eternal black hle, we construct several correlated states of two CFTs. In all the examples we show their correlations are too weak to produce the a connected spacetime. Then we review the measure named quantum discord and use it to characterize the classical and quantum correlations in quantum field theories. Finally, we discuss the correlations between two intervals A and B with distance d in the vacuum state of 2D CFTs with large central charge c. The feature is the phase transition of the mutual information I (ρAB). We analyse the quasi-product state of ρAB for large d. By using the Koashi-Winter relation of tripartite states the quantum and classical correlations between A and B can expressed as Holevo information, which provides a new understanding of the correlations as accessible information.

Non-Markovianity leading to coherence revivals in an open quantum system

2020 ◽  
pp. 2050040
Author(s):  
Y. Yugra ◽  
F. De Zela
Keyword(s):  
Quantum Information ◽  
Quantum System ◽  
Open Quantum System ◽  
Open Systems ◽  
Quantum Correlations ◽  
Experimental Proof ◽  
Optical Setup ◽  
Open Quantum ◽  
All Optical ◽  
Proof Of Principle

Coherence and quantum correlations have been identified as fundamental resources for quantum information tasks. As recently shown, these resources can be interconverted. In multipartite systems, entanglement represents a prominent case among quantum correlations, one which can be activated from coherence. All this makes coherence a key resource for securing the operational advantage of quantum technologies. When dealing with open systems, decoherence hinders full exploitation of quantum resources. Here, we present a protocol that allows reaching the maximal achievable amount of coherence in an open quantum system. By implementing our protocol, or suitable variants of it, coherence losses might be fully compensated, thereby leading to coherence revivals. We provide an experimental proof of principle of our protocol through its implementation with an all-optical setup.

Thermal quantum correlations in the two-qubit Heisenberg XYZ spin chain with Dzyaloshinskii–Moriya interaction

2021 ◽  
pp. 2150074
Author(s):  
Youssef Khedif ◽  
Mohammed Daoud
Keyword(s):  
Quantum Correlations ◽  
Thermal Fluctuations ◽  
Quantum Nonlocality ◽  
Chain Model ◽  
Trace Distance ◽  
Heisenberg Spin ◽  
Logarithmic Negativity ◽  
Qubit System ◽  
Classical Correlations ◽  
Moriya Interaction

We investigate the quantum correlations of a two-qubit XYZ Heisenberg spin-1/2 chain model with Dzyaloshinskii–Moriya interaction. The two-qubit system is considered in thermal equilibrium. The variations of logarithmic negativity, uncertainty-induced quantum nonlocality (UIN) and trace distance discord, versus the parameters characterizing the system, are analyzed. The results show that the UIN measure captures quantum correlations that cannot be revealed by entanglement and trace discord. We also show that the Dzyaloshinskii–Moriya interaction enhances the non-classical correlations between the spins and can weaken the undesirable destructive effects of thermal fluctuations. In addition, an entangled–unentangled phase transition can be detected from the behavior of logarithmic negativity.

scholarly journals Extracting classical correlations from a bipartite quantum system

2003 ◽  
Vol 67 (1) ◽  
Author(s):  
S. Hamieh ◽  
J. Qi ◽  
D. Siminovitch ◽  
M. K. Ali
Keyword(s):  
Quantum System ◽  
Bipartite Quantum System ◽  
Classical Correlations

Adiabatic demagnetization at absolute negative temperature: Generation of quantum correlations

2019 ◽  
Vol 17 (03) ◽  
pp. 1950023
Author(s):  
Gregory B. Furman ◽  
Shaul D. Goren ◽  
Victor M. Meerovich ◽  
Vladimir L. Sokolovsky
Keyword(s):  
Magnetic Field ◽  
Negative Temperature ◽  
Quantum Correlations ◽  
Zero Magnetic Field ◽  
Positive Temperature ◽  
Nuclear Spins ◽  
Adiabatic Demagnetization ◽  
Negative Temperatures ◽  
Classical Correlations ◽  
Quantum And Classical Correlations

In this paper, we study behavior of the correlations, both quantum and classical, under adiabatic demagnetization process in systems of nuclear spins with dipole–dipole interactions in an external magnetic field and in the temperature range including positive and negative temperatures. For a two-spin system, analytical expressions for the quantum and classical correlations are obtained. It is revealed that the field dependences of the quantum and classical correlations at positive and negative temperatures are substantially different. This difference most clearly appears in the case of zero magnetic field: at negative temperature, the measures of quantum correlations tend to the maximum values with a temperature increase. At positive temperature, these quantities tend to zero at a decrease of magnetic field. It is also found that, for the nearest-neighboring spins in the same field, the values of concurrence and discord are larger at negative temperatures than at positive ones.

scholarly journals MUTUAL INFORMATION OF BIPARTITE STATES AND QUANTUM DISCORD IN TERMS OF COHERENCE INFORMATION

2005 ◽  
Vol 03 (04) ◽  
pp. 691-728 ◽  
Author(s):  
FEDOR HERBUT
Keyword(s):  
Quantum Discord ◽  
Information Gain ◽  
Sufficient Conditions ◽  
Quantum Correlations ◽  
Global State ◽  
Final State ◽  
Global Coherence ◽  
State Formula ◽  
Necessary And Sufficient ◽  
Bipartite States

In relation to an observable and quantum state, the entity IC from previous work quantifies simultaneously coherence, incompatibility and quantumness. In this paper, its application to quantum correlations in bipartite states is studied. It is shown that Zurek's quantum discord can always be expressed as excess coherence information (global minus local). Strong and weak zero-discord cases are distinguished and investigated in terms of necessary and sufficient and sufficient conditions respectively. A unique string of relevant subsystem observables, each a function of the next, for "interrogating" the global state about the state of the opposite subsystem is derived with detailed entropy and information gain discussion. The apparent disappearance of discord in measurement is investigated, and it is shown that it is actually shifted from between subsystems 1 and 2 to between subsystems 1 and (2 + 3), where 3 is the measuring instrument. Finally, it is shown that the global coherence information IC(A2, ρ12) is shifted into the global coherence information [Formula: see text] in the final state [Formula: see text] of the measurement interaction.

scholarly journals Leggett-Garg Inequalities for Quantum Fluctuating Work

Entropy ◽  
2018 ◽  
Vol 20 (3) ◽  
pp. 200 ◽  
Author(s):  
◽  
Keyword(s):  
Quantum System ◽  
Quantum Correlations ◽  
Weak Measurement ◽  
Projective Measurement ◽  
Level System ◽  
Quantum Regime ◽  
Measurement Scheme ◽  
Temporal Correlations ◽  
Classical Thermodynamics ◽  
Work Done

The Leggett-Garg inequalities serve to test whether or not quantum correlations in time can be explained within a classical macrorealistic framework. We apply this test to thermodynamics and derive a set of Leggett-Garg inequalities for the statistics of fluctuating work done on a quantum system unitarily driven in time. It is shown that these inequalities can be violated in a driven two-level system, thereby demonstrating that there exists no general macrorealistic description of quantum work. These violations are shown to emerge within the standard Two-Projective-Measurement scheme as well as for alternative definitions of fluctuating work that are based on weak measurement. Our results elucidate the influences of temporal correlations on work extraction in the quantum regime and highlight a key difference between quantum and classical thermodynamics.

scholarly journals On the spectral dependence of separable and classical correlations in small quantum systems

2014 ◽  
Vol 14 (9&10) ◽  
pp. 857-887
Author(s):  
Gary McConnell ◽  
David Jennings
Keyword(s):  
Mutual Information ◽  
Spectral Dependence ◽  
Quantum Systems ◽  
Separable States ◽  
Small Quantum ◽  
Maximal Correlation ◽  
Full Analysis ◽  
Classical Correlations ◽  
Simple Systems ◽  
Classical States

We study the correlation structure of separable and classical states in $2\times2$-~and~$2\times3$-dimensional quantum systems with fixed spectra. Even for such simple systems the maximal correlation - as measured by mutual information - over the set of unitarily accessible separable states is highly non-trivial to compute; however for the $2\times2$ case a particular class of spectra admits full analysis and allows us to contrast classical states with more general separable states. We analyse a particular entropic binary relation on the set of spectra and prove for the qubit-qutrit case that this relation alone picks out a unique classical maximum state for mutual information. Moreover the $2\times3$ case is the largest system with such a property.

Fictitious spin-12 operators and correlations in quadrupole nuclear spin system

2018 ◽  
Vol 16 (01) ◽  
pp. 1850008 ◽  
Author(s):  
G. B. Furman ◽  
S. D. Goren ◽  
V. M. Meerovich ◽  
V. L. Sokolovsky
Keyword(s):  
Magnetic Field ◽  
Electric Fields ◽  
Nuclear Spin ◽  
Physical Phenomenon ◽  
Quantum Correlations ◽  
Zero Magnetic Field ◽  
Pauli Matrices ◽  
Nuclear Spin System ◽  
Classical Correlations ◽  
Limiting Values

The Hamiltonian and the spin operators for a spin 3/2 are represented in the basis formed by the Kronecker productions of the [Formula: see text] Pauli matrices. This reformulation allows us to represent a spin 3/2 as a system of two coupled fictitious spins 1/2. Correlations between these fictitious spins are studied using well-developed methods. We investigate the temperature and field dependences of correlations, such as mutual information, classical correlations, entanglement, and geometric and quantum discords in the fictitious spin-1/2 system describing a nuclear spin 3/2 which is placed in magnetic and inhomogeneous electric fields. It is shown that the correlations between the fictitious spins demonstrate properties which differ from those of real two-spin systems. In contrast to real systems all the correlations between the fictitious spins do not vanish with increasing external magnetic field; at a high magnetic field the correlations tend to their limiting values. Classical correlations, quantum and geometric discords reveal a pronounced asymmetry relative to the measurements on subsystems (fictitious spins) even in a uniform magnetic field and at symmetrical EFG, [Formula: see text]. The correlations depend also on the distribution of external charges, on the parameter of symmetry [Formula: see text]. At [Formula: see text] quantum and geometric discords have finite values in a zero magnetic field. The proposed approach may be useful in analysis of properties of particles with larger angular momentum, can provide the way to discover new physical phenomenon of quantum correlations, and can be a useful tool for similar definitions of other physical quantities of complex systems.

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