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Quantifying the Unitary Generation of Coherence from Thermal Quantum Systems

Coherence is associated with transient quantum states; in contrast, equilibrium thermal quantum systems have no coherence. We investigate the quantum control task of generating maximum coherence from an initial thermal state employing an external field. A completely controllable Hamiltonian is assum...

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Detalles Bibliográficos
Autores principales: Kallush, Shimshon, Aroch, Aviv, Kosloff, Ronnie
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2019
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7515339/
https://www.ncbi.nlm.nih.gov/pubmed/33267523
http://dx.doi.org/10.3390/e21080810
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author Kallush, Shimshon
Aroch, Aviv
Kosloff, Ronnie
author_facet Kallush, Shimshon
Aroch, Aviv
Kosloff, Ronnie
author_sort Kallush, Shimshon
collection PubMed
description Coherence is associated with transient quantum states; in contrast, equilibrium thermal quantum systems have no coherence. We investigate the quantum control task of generating maximum coherence from an initial thermal state employing an external field. A completely controllable Hamiltonian is assumed allowing the generation of all possible unitary transformations. Optimizing the unitary control to achieve maximum coherence leads to a micro-canonical energy distribution on the diagonal energy representation. We demonstrate such a control scenario starting from a given Hamiltonian applying an external field, reaching the control target. Such an optimization task is found to be trap-less. By constraining the amount of energy invested by the control, maximum coherence leads to a canonical energy population distribution. When the optimization procedure constrains the final energy too tightly, local suboptimal traps are found. The global optimum is obtained when a small Lagrange multiplier is employed to constrain the final energy. Finally, we explore the task of generating coherences restricted to be close to the diagonal of the density matrix in the energy representation.
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spelling pubmed-75153392020-11-09 Quantifying the Unitary Generation of Coherence from Thermal Quantum Systems Kallush, Shimshon Aroch, Aviv Kosloff, Ronnie Entropy (Basel) Article Coherence is associated with transient quantum states; in contrast, equilibrium thermal quantum systems have no coherence. We investigate the quantum control task of generating maximum coherence from an initial thermal state employing an external field. A completely controllable Hamiltonian is assumed allowing the generation of all possible unitary transformations. Optimizing the unitary control to achieve maximum coherence leads to a micro-canonical energy distribution on the diagonal energy representation. We demonstrate such a control scenario starting from a given Hamiltonian applying an external field, reaching the control target. Such an optimization task is found to be trap-less. By constraining the amount of energy invested by the control, maximum coherence leads to a canonical energy population distribution. When the optimization procedure constrains the final energy too tightly, local suboptimal traps are found. The global optimum is obtained when a small Lagrange multiplier is employed to constrain the final energy. Finally, we explore the task of generating coherences restricted to be close to the diagonal of the density matrix in the energy representation. MDPI 2019-08-19 /pmc/articles/PMC7515339/ /pubmed/33267523 http://dx.doi.org/10.3390/e21080810 Text en © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Kallush, Shimshon
Aroch, Aviv
Kosloff, Ronnie
Quantifying the Unitary Generation of Coherence from Thermal Quantum Systems
title Quantifying the Unitary Generation of Coherence from Thermal Quantum Systems
title_full Quantifying the Unitary Generation of Coherence from Thermal Quantum Systems
title_fullStr Quantifying the Unitary Generation of Coherence from Thermal Quantum Systems
title_full_unstemmed Quantifying the Unitary Generation of Coherence from Thermal Quantum Systems
title_short Quantifying the Unitary Generation of Coherence from Thermal Quantum Systems
title_sort quantifying the unitary generation of coherence from thermal quantum systems
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7515339/
https://www.ncbi.nlm.nih.gov/pubmed/33267523
http://dx.doi.org/10.3390/e21080810
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