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15 pages, 5968 KiB

Open AccessArticle

The Dynamical Casimir Effect in a Dissipative Optomechanical Cavity Interacting with Photonic Crystal

by Satoshi Tanaka and Kazuki Kanki

Physics 2020, 2(1), 34-48; https://doi.org/10.3390/physics2010005 - 07 Feb 2020

Cited by 7 | Viewed by 4714

Abstract

We theoretically study the dynamical Casimir effect (DCE), i.e., parametric amplification of a quantum vacuum, in an optomechanical cavity interacting with a photonic crystal, which is considered to be an ideal system to study the microscopic dissipation effect on the DCE. Starting from [...] Read more.

We theoretically study the dynamical Casimir effect (DCE), i.e., parametric amplification of a quantum vacuum, in an optomechanical cavity interacting with a photonic crystal, which is considered to be an ideal system to study the microscopic dissipation effect on the DCE. Starting from a total Hamiltonian including the photonic band system as well as the optomechanical cavity, we have derived an effective Floquet–Liouvillian by applying the Floquet method and Brillouin–Wigner–Feshbach projection method. The microscopic dissipation effect is rigorously taken into account in terms of the energy-dependent self-energy. The obtained effective Floquet–Liouvillian exhibits the two competing instabilities, i.e., parametric and resonance instabilities, which determine the stationary mode as a result of the balance between them in the dissipative DCE. Solving the complex eigenvalue problem of the Floquet–Liouvillian, we have determined the stationary mode with vanishing values of the imaginary parts of the eigenvalues. We find a new non-local multimode DCE represented by a multimode Bogoliubov transformation of the cavity mode and the photon band. We show the practical advantage for the observation of DCE in that we can largely reduce the pump frequency when the cavity system is embedded in a narrow band photonic crystal with a bandgap. Full article

(This article belongs to the Special Issue The Quantum Vacuum)

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10 pages, 1075 KiB

Open AccessArticle

On the Non-Local Surface Plasmons’ Contribution to the Casimir Force between Graphene Sheets

by Yan Francescato, Simon R. Pocock and Vincenzo Giannini

Physics 2020, 2(1), 22-31; https://doi.org/10.3390/physics2010003 - 19 Jan 2020

Viewed by 2883

Abstract

Herein we demonstrate the dramatic effect of non-locality on the plasmons which contribute to the Casimir forces, with a graphene sandwich as a case study. The simplicity of this system allowed us to trace each contribution independently, as we observed that interband processes, [...] Read more.

Herein we demonstrate the dramatic effect of non-locality on the plasmons which contribute to the Casimir forces, with a graphene sandwich as a case study. The simplicity of this system allowed us to trace each contribution independently, as we observed that interband processes, although dominating the forces at short separations, are poorly accounted for in the framework of the Dirac cone approximation alone, and should be supplemented with other descriptions for energies higher than 2.5 eV. Finally, we proved that distances smaller than 200 nm, despite being extremely relevant to state-of-the-art measurements and nanotechnology applications, are inaccessible with closed-form response function calculations at present. Full article

(This article belongs to the Special Issue The Quantum Vacuum)

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8 pages, 324 KiB

Open AccessArticle

QED Response of the Vacuum

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

Physics 2020, 2(1), 14-21; https://doi.org/10.3390/physics2010002 - 18 Jan 2020

Cited by 5 | Viewed by 4850

Abstract

We present a new perspective on the link between quantum electrodynamics (QED) and Maxwell’s equations. We demonstrate that the interpretation of the electric displacement vector

D = ε_{0} E

, where

E

is the electric field vector and

ε_{0}

is the [...] Read more.

We present a new perspective on the link between quantum electrodynamics (QED) and Maxwell’s equations. We demonstrate that the interpretation of the electric displacement vector

D = ε_{0} E

, where

E

is the electric field vector and

ε_{0}

is the permittivity of the vacuum, as vacuum polarization is consistent with QED. A free electromagnetic field polarizes the vacuum, but the polarization and magnetization currents cancel giving zero source current. The speed of light is a universal constant, while the fine structure constant, which couples the electromagnetic field to matter runs, as it should. Full article

(This article belongs to the Special Issue The Quantum Vacuum)

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13 pages, 946 KiB

Open AccessArticle

Progress in a Vacuum Weight Search Experiment

by Saverio Avino, Enrico Calloni, Sergio Caprara, Martina De Laurentis, Rosario De Rosa, Tristano Di Girolamo, Luciano Errico, Gianluca Gagliardi, Marco Grilli, Valentina Mangano, Maria Antonietta Marsella, Luca Naticchioni, Giovanni Piero Pepe, Maurizio Perciballi, Gabriel Pillant, Paola Puppo, Piero Rapagnani, Fulvio Ricci, Luigi Rosa, Carlo Rovelli, Paolo Ruggi, Naurang L. Saini, Daniela Stornaiuolo, Francesco Tafuri and Arturo Tagliacozzo Show full author list Hide full author list

Physics 2020, 2(1), 1-13; https://doi.org/10.3390/physics2010001 - 25 Dec 2019

Cited by 12 | Viewed by 4399

Abstract

We present the status of the art of the Archimedes experiment, devoted to measuring the debated interaction of quantum vacuum fluctuations and gravity. The method is essentially the weighing of the transition energy of a layered superconductor where the contribution of vacuum energy [...] Read more.

We present the status of the art of the Archimedes experiment, devoted to measuring the debated interaction of quantum vacuum fluctuations and gravity. The method is essentially the weighing of the transition energy of a layered superconductor where the contribution of vacuum energy to the transition energy is expected to be relevant. The transition is obtained by modulating the temperature of the superconducting sample at a frequency of about 10 mHz and the expected change of weight is measured with a suitably designed high sensitivity cryogenic beam balance. In this paper, we present an overview of the experiment, discussing the expected signal to be measured, and presenting in particular the result of a prototype balance operated in our present laboratory. In the frequency range of the measurement, the sensitivity is affected mainly by seismic, thermal, sensor, and control noise. We discuss these points showing in particular the design of the cryogenic apparatus, the final balance, and the quiet seismic site that will host the final measurement. Full article

(This article belongs to the Special Issue The Quantum Vacuum)

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15 pages, 299 KiB

Open AccessArticle

Atom-Field Interaction: From Vacuum Fluctuations to Quantum Radiation and Quantum Dissipation or Radiation Reaction

by Jen-Tsung Hsiang and B. L. Hu

Physics 2019, 1(3), 430-444; https://doi.org/10.3390/physics1030031 - 17 Dec 2019

Cited by 14 | Viewed by 3956

Abstract

In this paper, we dwell on three issues: (1) revisit the relation between vacuum fluctuations and radiation reaction in atom-field interactions, an old issue that began in the 1970s and settled in the 1990s with its resolution recorded in monographs; (2) the fluctuation–dissipation [...] Read more.

In this paper, we dwell on three issues: (1) revisit the relation between vacuum fluctuations and radiation reaction in atom-field interactions, an old issue that began in the 1970s and settled in the 1990s with its resolution recorded in monographs; (2) the fluctuation–dissipation relation (FDR) of the system, pointing out the differences between the conventional form in linear response theory (LRT) assuming ultra-weak coupling between the system and the bath, and the FDR in an equilibrated final state, relaxed from the nonequilibrium evolution of an open quantum system; (3) quantum radiation from an atom interacting with a quantum field: We begin with vacuum fluctuations in the field acting on the internal degrees of freedom (idf) of an atom, adding to its dynamics a stochastic component which engenders quantum radiation whose backreaction causes quantum dissipation in the idf of the atom. We show explicitly how different terms representing these processes appear in the equations of motion. Then, using the example of a stationary atom, we show how the absence of radiation in this simple cases is a result of complex cancellations, at a far away observation point, of the interference between emitted radiation from the atom and the local fluctuations in the free field. In so doing we point out in Issue 1 that the entity which enters into the duality relation with vacuum fluctuations is not radiation reaction, which can exist as a classical entity, but quantum dissipation. Finally, regarding issue 2, we point out for systems with many atoms, the co-existence of a set of correlation-propagation relations (CPRs) describing how the correlations between the atoms are related to the propagation of their (retarded non-Markovian) mutual influence manifesting in the quantum field. The CPR is absolutely crucial in keeping the balance of energy flows between the constituents of the system, and between the system and its environment. Without the consideration of this additional relation in tether with the FDR, dynamical self-consistency cannot be sustained. A combination of these two sets of relations forms a generalized matrix FDR relation that captures the physical essence of the interaction between an atom and a quantum field at arbitrary coupling strength. Full article

(This article belongs to the Special Issue The Quantum Vacuum)

10 pages, 285 KiB

Open AccessArticle

Proposal of a Computational Approach for Simulating Thermal Bosonic Fields in Phase Space

by Alessandro Sergi, Roberto Grimaudo, Gabriel Hanna and Antonino Messina

Physics 2019, 1(3), 402-411; https://doi.org/10.3390/physics1030029 - 03 Dec 2019

Cited by 5 | Viewed by 2719

Abstract

When a quantum field is in contact with a thermal bath, the vacuum state of the field may be generalized to a thermal vacuum state, which takes into account the thermal noise. In thermo field dynamics, this is realized by doubling the dimensionality [...] Read more.

When a quantum field is in contact with a thermal bath, the vacuum state of the field may be generalized to a thermal vacuum state, which takes into account the thermal noise. In thermo field dynamics, this is realized by doubling the dimensionality of the Fock space of the system. Interestingly, the representation of thermal noise by means of an augmented space is also found in a distinctly different approach based on the Wigner transform of both the field operators and density matrix, which we pursue here. Specifically, the thermal noise is introduced by augmenting the classical-like Wigner phase space by means of Nosé–Hoover chain thermostats, which can be readily simulated on a computer. In this paper, we illustrate how this may be achieved and discuss how non-equilibrium quantum thermal distributions of the field modes can be numerically simulated. Full article

(This article belongs to the Special Issue The Quantum Vacuum)

18 pages, 748 KiB

Open AccessArticle

Vacuum Energy Decay from a q-Bubble

by Frans R. Klinkhamer, Osvaldo P. Santillán, Grigory E. Volovik and Albert Zhou

Physics 2019, 1(3), 321-338; https://doi.org/10.3390/physics1030024 - 01 Nov 2019

Cited by 4 | Viewed by 2906

Abstract

We consider a finite-size spherical bubble with a nonequilibrium value of the q-field, where the bubble is immersed in an infinite vacuum with the constant equilibrium value

q_{0}

for the q-field (this

q_{0}

has already cancelled an initial cosmological [...] Read more.

We consider a finite-size spherical bubble with a nonequilibrium value of the q-field, where the bubble is immersed in an infinite vacuum with the constant equilibrium value

q_{0}

for the q-field (this

q_{0}

has already cancelled an initial cosmological constant). Numerical results are presented for the time evolution of such a q-bubble with gravity turned off and with gravity turned on. For small enough bubbles and a q-field energy scale sufficiently below the gravitational energy scale

E_{Planck}

, the vacuum energy of the q-bubble is found to disperse completely. For large enough bubbles and a finite value of

E_{Planck}

, the vacuum energy of the q-bubble disperses only partially and there occurs gravitational collapse near the bubble center. Full article

(This article belongs to the Special Issue The Quantum Vacuum)

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Review

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45 pages, 2264 KiB

Open AccessReview

History and Some Aspects of the Lamb Shift

by G. Jordan Maclay

Physics 2020, 2(2), 105-149; https://doi.org/10.3390/physics2020008 - 13 Apr 2020

Cited by 8 | Viewed by 7200

Abstract

Radiation is a process common to classical and quantum systems with very different effects in each regime. In a quantum system, the interaction of a bound electron with its own radiation field leads to complex shifts in the energy levels of the electron, [...] Read more.

Radiation is a process common to classical and quantum systems with very different effects in each regime. In a quantum system, the interaction of a bound electron with its own radiation 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 and the imaginary part to the width of the energy level. The most celebrated radiative shift is the Lamb shift between the

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 calculation of the shift showed how to deal with the divergences plaguing the existing theories and led to the understanding that interactions with the zero-point vacuum field, the lowest energy state of the quantized electromagnetic field, have measurable effects, not just resetting the zero of energy. This understanding led to the development of modern quantum electrodynamics (QED). This historical pedagogic paper explores the history of Bethe’s calculation and its significance. It explores radiative effects in classical and quantum systems from different perspectives, with the emphasis on understanding the fundamental physical phenomena. Illustrations are drawn from systems with central forces, the H atom, and the three-dimensional harmonic oscillator. A first-order QED calculation of the complex radiative shift for a spinless electron is explored using the equations of motion and the

m a s s^{2}

operator, describing the fundamental phenomena involved, and relating the results to Feynman diagrams. Full article

(This article belongs to the Special Issue The Quantum Vacuum)

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38 pages, 681 KiB

Open AccessReview

Fifty Years of the Dynamical Casimir Effect

by Viktor Dodonov

Physics 2020, 2(1), 67-104; https://doi.org/10.3390/physics2010007 - 14 Feb 2020

Cited by 96 | Viewed by 9289

Abstract

This is a digest of the main achievements in the wide area, called the Dynamical Casimir Effect nowadays, for the past 50 years, with the emphasis on results obtained after 2010. Full article

(This article belongs to the Special Issue The Quantum Vacuum)

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