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A special issue of Physics (ISSN 2624-8174). This special issue belongs to the section "High Energy Physics".

Deadline for manuscript submissions: closed (30 January 2023) | Viewed by 25025

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Prof. Dr. G. Jordan Maclay

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Guest Editor

Quantum Fields LLC, St. Charles, IL 60174, USA
Interests: quantum fields; symmetries and group theory; Casimir forces; vacuum fluctuations; foundations of quantum theory; history of science

Prof. Dr. Roberto Passante

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Guest Editor

Dipartimento di Fisica e Chimica – E. Segrè, Università degli Studi di Palermo, Via Archirafi 36, I-90123 Palermo, Italy
Interests: casimir physics; quantum electrodynamics; quantum fluctuations; radiative processes in static and dynamical structured environments; quantum field theory in accelerated frames and in a curved space-time; quantum optomechanics; resonances and dressed unstable states; microscopic origin of time asymmetry in quantum physics; cosmological axions and dark matter; axion electrodynamics
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Dear Colleagues,

Quantum electrodynamics (QED) describes the presence of a field of vacuum fluctuations in the quantized electromagnetic field. This fundamental field is present everywhere, even in the absence of matter and at absolute zero temperature. It consists of virtual photon creation and annihilation processes. The average value of the field <E> is 0, but <E^2> is not zero. This field is responsible for the Lamb shift and other phenomena in the QED that have been experimentally verified to 14 decimal places, the most precise predictions in modern science. The virtual electron–positron field is often included as a vacuum fluctuation. It produces a much smaller shifts in the atomic energy level due to the polarization of the vacuum. It is the source of Hawking radiation.

All quantum fields have vacuum fluctuations, but the effective distance of their influence decreases with the associated mass. Hence, the electromagnetic field has the greatest influence in most environments. In elementary particle physics, the vacuum fluctuations of the gluon and Higgs field are dominant.

One of the conundrums about vacuum energy is that QED predicts that the energy density of the quantum vacuum fluctuations is formally infinite or near infinite, which conflicts with General Relativity. There are several theories that may explain this disagreement. On the other hand, in all calculations to date of physically measureable phenomena, the changes in vacuum energy, which tend to be small, have precisely corresponded to predicted and measureable quantities.

The vacuum fluctuations of the electromagnetic field explain the origin of van der Waals forces and other dispersion forces, Casimir forces, and the atomic emission linewidth. Modifications in the boundary conditions of the vacuum fluctuations have been used, for example, to control spontaneous emission, to alter dispersion forces, to generate torques and repulsive forces, to enhance chemical reactions, to transfer heat in the vacuum, to transfer mechanical energy from one oscillator to an adjacent oscillator by the modulation of Casimir forces, and to tune attractive and repulsive forces in microelectromechanical systems. Vacuum fluctuations have also been linked to cosmological phenomena, for example, to dark energy, to the Big Bang, to inflation, and to the Cosmic Microwave Background radiation. Vacuum fluctuations have been used to induce entanglement. In some systems, vacuum fluctuations are a source of noise and may limit performance, for example, in quantum computation, or cause decoherence in electron diffraction.

Recent efforts are providing direct measurements of spectral regions of the virtual vacuum field using a variety of techniques.

The role of vacuum fluctuations can be enhanced in microcavity electrodynamics with subcycle control, where the strong coupling of matter to the vacuum fields has been achieved, for example, with graphene. New quantum states of matter, quantum cavity chemistry, cavity-controlled transport (for example, inducing a THz energy gap in the band structure of a carbon nanotube), and vacuum-modified superconductivity have been investigated.

It is often said that one cannot extract energy from the free quantum vacuum because it is the lowest state of the electromagnetic field. This statement is generally true but ignores some important nuances, for example, the stochastic transfer of energy. Theory indicates that charged particles in the vacuum will show Brownian motion. Vacuum fluctuations in the electromagnetic field induce current fluctuations in resistively shunted Josephson junctions that are measurable in terms of a physically relevant power spectrum, and vacuum fluctuations have been used to induce a persistent current in a quantum ring. One can reduce the energy density of the free vacuum by modifying the vacuum field, for example, by means of surfaces and therefore allow energy transfer. The attractive Casimir force between two metal surfaces could, in principle, perform positive work on the surfaces, moving them together quasistatically. One predicts theoretically that the energy density of the vacuum field between the plates would be reduced correspondingly to conserve energy. Unfortunately, this experiment, which would demonstrate the direct exchange of vacuum energy with mechanical energy, has not been conducted as far as I know.

A device has been described recently for which it is suggested that the boundary conditions of the vacuum field at a thin metal surface result in the transfer of energy from the vacuum fluctuations to electrons in the metal, injecting some into a dielectric and producing a small current. A theoretical calculation showing fluctuations in the kinetic energy of an electron near a surface supports this interpretation. It appears that under certain conditions, the exchange of quantum vacuum energy with mechanical or other forms of energy may be possible. The dynamical Casimir effect and the Unruh effect involve excitation of the vacuum field by mechanical means. Other dynamical vacuum excitation effects have been proposed. The recent demonstrations of the transfer of mechanical and thermal energy through the quantum vacuum also seem to support this possibility.

Over the past few decades, the role and significance of vacuum fluctuations have increased significantly as researchers have developed novel applications. With their pervasive role in physical phenomena, there is an opportunity to take advantage of this universal, tunable, vacuum field to accomplish scientific and engineering objectives with vacuum engineering.

Prof. Dr. G. Jordan Maclay
Prof. Dr. Roberto Passante
Guest Editors

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Keywords

vacuum fluctuations electromagnetic field
quantum vacuum
zero-point vibrations
Casimir force
Casimir effect
dynamical Casimir effect
virtual particles
vacuum boundary conditions
QED
microcavity electrodynamics
quantum fields

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Published Papers (11 papers)

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Research

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14 pages, 296 KiB

Open AccessArticle

Zero-Point Energy Density at the Origin of the Vacuum Permittivity and Photon Propagation Time Fluctuation

by Christophe Hugon and Vladimir Kulikovskiy

Physics 2024, 6(1), 94-107; https://doi.org/10.3390/physics6010007 - 10 Jan 2024

Viewed by 2257

Abstract

We give a vacuum description with zero-point density for virtual fluctuations. One of the goals is to explain the origin of the vacuum permittivity and permeability and to calculate their values. In particular, we improve on existing calculations by avoiding assumptions on the volume occupied by virtual fluctuations. We propose testing of the models that assume a finite lifetime of virtual fluctuation. If during its propagation, the photon is stochastically trapped and released by virtual pairs, the propagation velocity may fluctuate. The propagation time fluctuation is estimated for several existing models. The obtained values are measurable with available technologies involving ultra-short laser pulses, and some of the models are already in conflict with the existing astronomical observations. The phase velocity is not affected significantly, which is consistent with the interferometric measurements. Full article

(This article belongs to the Special Issue Vacuum Fluctuations)

36 pages, 4465 KiB

Open AccessEditor’s ChoiceArticle

Fluctuations-Induced Quantum Radiation and Reaction from an Atom in a Squeezed Quantum Field

by Matthew Bravo, Jen-Tsung Hsiang and Bei-Lok Hu

Physics 2023, 5(2), 554-589; https://doi.org/10.3390/physics5020040 - 24 May 2023

Cited by 1 | Viewed by 1649

Abstract

In this third of a series on quantum radiation, we further explore the feasibility of using the memories (non-Markovianity) kept in a quantum field to decipher certain information about the early universe. As a model study, we let a massless quantum field be subjected to a parametric process for a finite time interval such that the mode frequency of the field transits from one constant value to another. This configuration thus mimics a statically-bounded universe, where there is an ‘in’ and an ‘out’ state with the scale factor approaching constants, not a continuously evolving one. The field subjected to squeezing by this process should contain some information of the process itself. If an atom is coupled to the field after the parametric process, its response will depend on the squeezing, and any quantum radiation emitted by the atom will carry this information away so that an observer at a much later time may still identify it. Our analyses show that (1) a remote observer cannot measure the generated squeezing via the radiation energy flux from the atom because the net radiation energy flux is canceled due to the correlation between the radiation field from the atom and the free field at the observer’s location. However, (2) there is a chance to identify squeezing by measuring the constant radiation energy density at late times. The only restriction is that this energy density is of the near-field nature and only an observer close to the atom can use it to unravel the information of squeezing. The second part of this paper focuses on (3) the dependence of squeezing on the functional form of the parametric process. By explicitly working out several examples, we demonstrate that the behavior of squeezing does reflect essential properties of the parametric process. Actually, striking features may show up in more complicated processes involving various scales. These analyses allow us to establish the connection between properties of a squeezed quantum field and details of the parametric process which performs the squeezing. Therefore, (4) one can construct templates to reconstitute the unknown parametric processes from the data of measurable quantities subjected to squeezing. In a sequel paper these results will be applied to a study of quantum radiations in cosmology. Full article

(This article belongs to the Special Issue Vacuum Fluctuations)

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25 pages, 714 KiB

Open AccessEditor’s ChoiceArticle

The Asymmetric Dynamical Casimir Effect

by Matthew J. Gorban, William D. Julius, Patrick M. Brown, Jacob A. Matulevich and Gerald B. Cleaver

Physics 2023, 5(2), 398-422; https://doi.org/10.3390/physics5020029 - 11 Apr 2023

Cited by 3 | Viewed by 2633 | Correction

Abstract

A mirror with time-dependent boundary conditions will interact with the quantum vacuum to produce real particles via a phenomenon called the dynamical Casimir effect (DCE). When asymmetric boundary conditions are imposed on the fluctuating mirror, the DCE produces an asymmetric spectrum of particles. We call this the asymmetric dynamical Casimir effect (ADCE). Here, we investigate the necessary conditions and general structure of the ADCE through both a waves-based and a particles-based perspective. We review the current state of the ADCE literature and expand upon previous studies to generate new asymmetric solutions. The physical consequences of the ADCE are examined, as the imbalance of particles produced must be balanced with the subsequent motion of the mirror. The transfer of momentum from the vacuum to macroscopic objects is discussed. Full article

(This article belongs to the Special Issue Vacuum Fluctuations)

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9 pages, 1030 KiB

Open AccessCommunication

Finite-Size Effects of Casimir–van der Waals Forces in the Self-Assembly of Nanoparticles

by Raul Esquivel-Sirvent

Physics 2023, 5(1), 322-330; https://doi.org/10.3390/physics5010024 - 21 Mar 2023

Cited by 6 | Viewed by 2605

Abstract

Casimir–van der Waals forces are important in the self-assembly processes of nanoparticles. In this paper, using a hybrid approach based on Lifshitz theory of Casimir–van der Waals interactions and corrections due to the shape of the nanoparticles, it is shown that for non-spherical nanoparticles, the usual Hamaker approach overestimates the magnitude of the interaction. In particular, the study considers nanoplates of different thicknesses, nanocubes assembled with their faces parallel to each other, and tilted nanocubes, where the main interaction is between edges. Full article

(This article belongs to the Special Issue Vacuum Fluctuations)

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14 pages, 314 KiB

Open AccessArticle

van der Waals Dispersion Potential between Excited Chiral Molecules via the Coupling of Induced Dipoles

by A. Salam

Physics 2023, 5(1), 247-260; https://doi.org/10.3390/physics5010019 - 24 Feb 2023

Cited by 2 | Viewed by 1466

Abstract

The retarded van der Waals dispersion potential between two excited chiral molecules was calculated using an approach, in which electric and magnetic dipole moments are induced in each particle by fluctuations in the vacuum electromagnetic field. An expectation value of the coupling of the moments at different centres to the dipolar interaction tensors was taken over excited matter states and the ground state radiation field, the former yielding excited molecular polarisabilities and susceptibilities, and the latter field–field spatial correlation functions. The dispersion potential term proportional to the mixed dipolar polarisability is discriminatory, dependent upon molecular handedness, and contains additional terms due to transitions that de-excite each species as well as the usual u-integral term over imaginary frequency, which applies to both upward and downward transitions. Excited state dispersion potentials of a comparable order of magnitude involving paramagnetic and diamagnetic couplings were also computed. Pros and cons of the method adopted are compared to other commonly used approaches. Full article

(This article belongs to the Special Issue Vacuum Fluctuations)

18 pages, 358 KiB

Open AccessArticle

Two New Methods in Stochastic Electrodynamics for Analyzing the Simple Harmonic Oscillator and Possible Extension to Hydrogen

by Daniel C. Cole

Physics 2023, 5(1), 229-246; https://doi.org/10.3390/physics5010018 - 21 Feb 2023

Cited by 1 | Viewed by 1298

Abstract

The position probability density function is calculated for a classical electric dipole harmonic oscillator bathed in zero-point plus Planckian electromagnetic fields, as considered in the physical theory of stochastic electrodynamics (SED). The calculations are carried out via two new methods. They start from a general probability density expression involving the formal integration over all probabilistic values of the Fourier coefficients describing the stochastic radiation fields. The first approach explicitly carries out all these integrations; the second approach shows that this general probability density expression satisfies a partial differential equation that is readily solved. After carrying out these two fairly long analyses and contrasting them, some examples are provided for extending this approach to quantities other than position, such as the joint probability density distribution for positions at different times, and for position and momentum. This article concludes by discussing the application of this general probability density expression to a system of great interest in SED, namely, the classical model of hydrogen. Full article

(This article belongs to the Special Issue Vacuum Fluctuations)

9 pages, 560 KiB

Open AccessEditor’s ChoiceCommunication

Electron as a Tiny Mirror: Radiation from a Worldline with Asymptotic Inertia

by Michael R. R. Good and Yen Chin Ong

Physics 2023, 5(1), 131-139; https://doi.org/10.3390/physics5010010 - 28 Jan 2023

Cited by 7 | Viewed by 1985

Abstract

We present a moving mirror analog of the electron, whose worldline possesses asymptotic constant velocity with corresponding Bogoliubov

β

coefficients that are consistent with finite total emitted energy. Furthermore, the quantum analog model is in agreement with the total energy obtained by integrating [...] Read more.

We present a moving mirror analog of the electron, whose worldline possesses asymptotic constant velocity with corresponding Bogoliubov

β

coefficients that are consistent with finite total emitted energy. Furthermore, the quantum analog model is in agreement with the total energy obtained by integrating the classical Larmor power. Full article

(This article belongs to the Special Issue Vacuum Fluctuations)

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25 pages, 695 KiB

Open AccessArticle

New Insights into the Lamb Shift: The Spectral Density of the Shift

by G. Jordan Maclay

Physics 2022, 4(4), 1253-1277; https://doi.org/10.3390/physics4040081 - 19 Oct 2022

Cited by 3 | Viewed by 2284

Abstract

In an atom, the interaction of a bound electron with the vacuum fluctuations of the electromagnetic field leads to complex shifts in the energy levels of the electron, with the real part of the shift corresponding to a shift in the energy level [...] Read more.

2 s_{1 / 2}

and the

2 p_{1 / 2}

levels of the hydrogen atom. The measurement of this shift in 1947 by Willis Lamb Jr. proved that the prediction by Dirac theory that the energy levels were degenerate was incorrect. Hans Bethe’s non-relativistic calculation of the shift using second-order perturbation theory demonstrated the renormalization process required to deal with the divergences plaguing the existing theories and led to the understanding that it was essential for theory to include interactions with the zero-point quantum vacuum field. This was the birth of modern quantum electrodynamics (QED). Numerous calculations of the Lamb shift followed including relativistic and covariant calculations, all of which contain a nonrelativistic contribution equal to that computed by Bethe. The semi-quantitative models for the radiative shift of Welton and Power, which were developed in an effort to demonstrate physical mechanisms by which vacuum fluctuations lead to the shift, are also considered here. This paper describes a calculation of the shift using a group theoretical approach which gives the shift as an integral over frequency of a function, which is called the “spectral density of the shift.“ The energy shift computed by group theory is equivalent to that derived by Bethe yet, unlike in other calculations of the non-relativistic radiative shift, no sum over a complete set of states is required. The spectral density, which is obtained by a relatively simple computation, reveals how different frequencies of vacuum fluctuations contribute to the total energy shift. The analysis shows, for example, that half the radiative shift for the ground state 1S level in H comes from virtual photon energies below 9700 eV, and that the expressions of Power and Welton have the correct high-frequency behavior, but not the correct low-frequency behavior, although they do give approximately the correct value for the total shift. Full article

(This article belongs to the Special Issue Vacuum Fluctuations)

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Review

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14 pages, 417 KiB

Open AccessReview

Centenary of Alexander Friedmann’s Prediction of the Universe Expansion and the Quantum Vacuum

by Galina L. Klimchitskaya and Vladimir M. Mostepanenko

Physics 2022, 4(3), 981-994; https://doi.org/10.3390/physics4030065 - 31 Aug 2022

Cited by 3 | Viewed by 2656

Abstract

We review the main scientific pictures of the universe developed from ancient times to Albert Einstein and underline that all of them treated the universe as a stationary system with unchanged physical properties. In contrast to this, 100 years ago Alexander Friedmann predicted that the universe expands starting from the point of infinitely large energy density. We briefly discuss the physical meaning of this prediction and its experimental confirmation consisting of the discovery of redshift in the spectra of remote galaxies and relic radiation. After mentioning the horizon problem in the theory of the hot universe, the inflationary model is considered in connection with the concept of quantum vacuum as an alternative to the inflaton field. The accelerated expansion of the universe is discussed as powered by the cosmological constant originating from the quantum vacuum. The conclusion is made that since Alexander Friedmann’s prediction of the universe expansion radically altered our picture of the world in comparison with the previous epochs, his name should be put on a par with the names of Ptolemy and Copernicus. Full article

(This article belongs to the Special Issue Vacuum Fluctuations)

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Other

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4 pages, 197 KiB

Open AccessCorrection

Correction: Gorban et al. The Asymmetric Dynamical Casimir Effect. Physics 2023, 5, 398–422

by Matthew J. Gorban, William D. Julius, Patrick M. Brown, Jacob A. Matulevich and Gerald B. Cleaver

Physics 2024, 6(1), 422-425; https://doi.org/10.3390/physics6010028 - 15 Mar 2024

Cited by 1 | Viewed by 565

Abstract

There was an error in the original paper [1], which occurred in the calculation of the DCE spectrum from the time-dependant perturbations on

λ (t)

[...] Full article

(This article belongs to the Special Issue Vacuum Fluctuations)

14 pages, 2290 KiB

Open AccessOpinion

Physical Mechanisms Underpinning the Vacuum Permittivity

by Gerd Leuchs, Margaret Hawton and Luis L. Sánchez-Soto

Physics 2023, 5(1), 179-192; https://doi.org/10.3390/physics5010014 - 8 Feb 2023

Cited by 5 | Viewed by 2552

Abstract

The debate about the emptiness of space goes back to the prehistory of science and is epitomized by the Aristotelian ‘horror vacui’, which can be seen as the precursor of the ether, whose modern version is the dynamical quantum vacuum. In this paper, [...] Read more.

ε_{0}

, and permeability,

μ_{0}

, by modelling their dynamical response by three-dimensional harmonic oscillators. Full article

(This article belongs to the Special Issue Vacuum Fluctuations)

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