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Universe
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Quantum Field Theory of Open Systems
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Quantum Field Theory of Open Systems

A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Field Theory".

Deadline for manuscript submissions: closed (15 January 2024) | Viewed by 9131

Special Issue Editors

Prof. Dr. Janos Polonyi

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Guest Editor
CNRS-IPHC, Strasbourg University, 23 Rue du Loess, BP28 67037 Strasbourg, France
Interests: quantum field theory; renormalization group; electrodynamics; open quantum systems; quantum-classical transition; decoherence; time arrow
Special Issues, Collections and Topics in MDPI journals
Dr. Sandor Nagy

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Guest Editor
Department of Theoretical Physics, University of Debrecen, P.O. Box 5, H-4010 Debrecen, Hungary
Interests: quantum field theory; renormalization; phase transitions; open quantum systems

Special Issue Information

Dear Colleagues,

Relativistic quantum field theory, in particular QED, has been developed in the middle of the last century to describe high energy scattering experiments. The extension of the perturbation expansion in quantum mechanics to the transition amplitudes, given in the interaction representation, has been completed by the method using Feynman graphs. Ever since then, there has been a growing need for quantum field theory beyond scattering experiments, and the corresponding perturbation expansion has been introduced by J. Schwinger and bears the name Closed Time Path formalism. This scheme covers the calculation of expectation values and provides a more universal language of quantum theory. The effective theory approach to quantum field theory, developed within this formalism, can cope with open quantum systems. Similar results have been found by L. V. Keldysh by extending Feynman graph techniques to thermal equilibrium.

We believe that the Schwinger–Keldysh formalism is the natural language of quantum field theory since it covers both closed and open interactions in a natural manner. This issue is all the more important because the observed quantum systems tend to be open through interaction channels both at low and at high energy, reflecting the limit of our possibilities and knowledge, respectively. The uncontrollable small energy exchange with the environment leads to the violation of conservation laws, the dynamical breakdown of the time reversal invariance, dissipation, decoherence and relaxation. The last two phenomena are essential to the emergence of classical physics and statistical mechanics. The unknown high energy physics, beyond the current space resolution of the experiments, together with the UV divergences of realistic quantum field theoretical models, force us to use cutoff or effective theories which are valid up to some energy scale. Hence, the usual renormalization group procedure also has to be extended to open dynamics.

The quantum field theory of open systems allows us to access a number of important physical questions:

Why is the conventional quantum description, based on pure states and closed dynamics, so efficient in the presence of the ubiquitous entanglement?

What is the relation between decoherence and dissipation?

In what sense is equilibrium statistical physics the IR fixed point of an infinite open system?

How do the classical, macroscopic averages emerge from the quantum domain?

How can nanophysics be connected to micro- and macro-physics in a quantitative manner?

Contributions are expected to touch these and other issues of open many-body physics.

Prof. Dr. Janos Polonyi
Dr. Sandor Nagy
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • open quantum system
  • dissipation
  • decoherence
  • relaxation
  • renormalization

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Published Papers (5 papers)

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Research

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29 pages, 458 KiB  
Article
Symmetries and the Hilbert Space of Large N Extended States
by Antal Jevicki, Xianlong Liu and Junjie Zheng
Universe 2024, 10(2), 99; https://doi.org/10.3390/universe10020099 - 17 Feb 2024
Cited by 1 | Viewed by 1297
Abstract
We discuss the large N expansion in backgrounds of extended states with a focus on the implementation of Goldstone symmetries and the construction of the associated Hilbert space. The formulation is given in the general framework of collective field theory. The case of [...] Read more.
We discuss the large N expansion in backgrounds of extended states with a focus on the implementation of Goldstone symmetries and the construction of the associated Hilbert space. The formulation is given in the general framework of collective field theory. The case of translational symmetry is described first as a basic example. The large N thermofield represents the main topics, with the emergent dynamics of left–right bulk fields and collective symmetry coordinates. These give the basis for a 1/N expansion. Full article
(This article belongs to the Special Issue Quantum Field Theory of Open Systems)
10 pages, 453 KiB  
Article
Radiation of High-Energy Gamma Quanta by Ultrarelativistic Electrons on Nuclei in Strong X-ray Fields
by Sergei Roshchupkin, Alexander Dubov and Stanislav Starodub
Universe 2022, 8(4), 218; https://doi.org/10.3390/universe8040218 - 29 Mar 2022
Cited by 4 | Viewed by 1634
Abstract
The possibility of radiation of high-energy gamma quanta with energies of the order of 100 GeV by ultrarelativistic electrons on nuclei in strong X-ray fields with intensities up to ∼1027Wcm−2 was theoretically studied. It is shown that this effect [...] Read more.
The possibility of radiation of high-energy gamma quanta with energies of the order of 100 GeV by ultrarelativistic electrons on nuclei in strong X-ray fields with intensities up to ∼1027Wcm−2 was theoretically studied. It is shown that this effect can be realized under special experimental conditions in the process of resonant spontaneous bremsstrahlung radiation of ultrarelativistic electrons on nuclei in an external electromagnetic field. These special experimental conditions determine the characteristic energy of the electrons. This characteristic energy should be significantly less than the energy of the initial electrons. Under these conditions, spontaneous gamma quanta are emitted in a narrow cone with energies close to the energy of the initial electrons. Moreover, the resonant differential cross-sections of such processes can exceed the corresponding differential cross-section without an external field by twenty orders of magnitude. The results obtained can explain the occurrence of high-energy gamma quanta near pulsars and magnetars. Full article
(This article belongs to the Special Issue Quantum Field Theory of Open Systems)
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22 pages, 586 KiB  
Article
Renormalizing Open Quantum Field Theories
by Sandor Nagy and Janos Polonyi
Universe 2022, 8(2), 127; https://doi.org/10.3390/universe8020127 - 16 Feb 2022
Cited by 4 | Viewed by 2061
Abstract
The functional renormalization group flow of a scalar field theory with quartic couplings and a sharp spatial momentum cutoff is presented in four-dimensional Minkowski space-time for the bare action by retaining the entanglement of the IR and the UV particle modes. It is [...] Read more.
The functional renormalization group flow of a scalar field theory with quartic couplings and a sharp spatial momentum cutoff is presented in four-dimensional Minkowski space-time for the bare action by retaining the entanglement of the IR and the UV particle modes. It is argued that the open interaction channels have to be taken into account in quantum field theory defined by the help of a cutoff, and a non-perturbative UV-IR entanglement is found in closed or almost closed models. Full article
(This article belongs to the Special Issue Quantum Field Theory of Open Systems)
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23 pages, 355 KiB  
Article
Dynamical Symmetry and the Thermofield State at Large N
by Antal Jevicki, Xianlong Liu, Junggi Yoon and Junjie Zheng
Universe 2022, 8(2), 114; https://doi.org/10.3390/universe8020114 - 10 Feb 2022
Cited by 8 | Viewed by 1627
Abstract
We discuss thermofield double QFT at real time, in the large N limit. First, we establish a (dynamical) symmetry, which we argue holds in general for the real-time portion of the Schwinger–Kelydish contour. At large N, this symmetry is seen to generate [...] Read more.
We discuss thermofield double QFT at real time, in the large N limit. First, we establish a (dynamical) symmetry, which we argue holds in general for the real-time portion of the Schwinger–Kelydish contour. At large N, this symmetry is seen to generate a one-parameter degeneracy of stationary collective solutions. The construction is explicitly worked out on an example of the O(N) vector QFT. As a nontrivial application, we describe the construction of the corresponding (large N) thermofield double state in real-time collective formalism. Full article
(This article belongs to the Special Issue Quantum Field Theory of Open Systems)

Other

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43 pages, 639 KiB  
Tutorial
Graviton Physics: A Concise Tutorial on the Quantum Field Theory of Gravitons, Graviton Noise, and Gravitational Decoherence
by Jen-Tsung Hsiang, Hing-Tong Cho and Bei-Lok Hu
Universe 2024, 10(8), 306; https://doi.org/10.3390/universe10080306 - 24 Jul 2024
Viewed by 940
Abstract
The detection of gravitational waves in 2015 ushered in a new era of gravitational wave (GW) astronomy capable of probing the strong field dynamics of black holes and neutron stars. It has opened up an exciting new window for laboratory and space tests [...] Read more.
The detection of gravitational waves in 2015 ushered in a new era of gravitational wave (GW) astronomy capable of probing the strong field dynamics of black holes and neutron stars. It has opened up an exciting new window for laboratory and space tests of Einstein’s theory of classical general relativity (GR). In recent years, two interesting proposals have aimed to reveal the quantum nature of perturbative gravity: (1) theoretical predictions on how graviton noise from the early universe, after the vacuum of the gravitational field was strongly squeezed by inflationary expansion; (2) experimental proposals using the quantum entanglement between two masses, each in a superposition (gravitational cat, or gravcat) state. The first proposal focuses on the stochastic properties of quantum fields (QFs), and the second invokes a key concept of quantum information (QI). An equally basic and interesting idea is to ask whether (and how) gravity might be responsible for a quantum system becoming classical in appearance, known as gravitational decoherence. Decoherence due to gravity is of special interest because gravity is universal, meaning, gravitational interaction is present for all massive objects. This is an important issue in macroscopic quantum phenomena (MQP), underlining many proposals in alternative quantum theories (AQTs). To fully appreciate or conduct research in these exciting developments requires a working knowledge of classical GR, QF theory, and QI, plus some familiarity with stochastic processes (SPs), namely, noise in quantum fields and decohering environments. Traditionally a new researcher may be conversant in one or two of these four subjects: GR, QFT, QI, and SP, depending on his/her background. This tutorial attempts to provide the necessary connective tissues between them, helping an engaged reader from any one of these four subjects to leapfrog to the frontier of these interdisciplinary research topics. In the present version, we shall address the three topics listed in the title, excluding gravitational entanglement, because, despite the high attention some recent experimental proposals have received, its nature and implications in relation to quantum gravity still contain many controversial elements. Full article
(This article belongs to the Special Issue Quantum Field Theory of Open Systems)
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