Effects Of Vacuum Fluctuations Research Articles

Effects of Non-Adiabatic Electromagnetic Vacuum Fluctuations on Internal Conversion.

To explore non-adiabatic effects caused by electromagnetic (EM) vacuum fluctuations in molecules, we develop a general theory of internal conversion (IC) in the framework of quantum electrodynamics and propose a new mechanism, "quantum electrodynamic internal conversion" (QED-IC). The theory allows us to compute the rates of the conventional IC and QED-IC processes at the first-principles level. Our simulations manifest that, under experimentally feasible weak light-matter coupling conditions, EM vacuum fluctuations can significantly affect IC rates by an order of magnitude. Moreover, our theory elucidates three key factors in the QED-IC mechanism: the effective mode volume, coupling-weighted normal mode alignment, and molecular rigidity. The theory successfully captures the nucleus-photon interaction in the factor "coupling-weighted normal mode alignment". In addition, we find that molecular rigidity plays a totally different role in conventional IC versus QED-IC rates. Our study provides applicable design principles for exploiting QED effects on IC processes.

Can Decoherence Solve the Measurement Problem?

The quantum decoherence program has become more attractive in providing an acceptable solution for the long-standing quantum measurement problem. Decoherence by quantum entanglement happens very quickly to entangle the quantum system with the environment including the detector. But in the final stage of measurement, acquiring the unentangled pointer states poses some problems. Recent experimental observations of the effect of the ubiquitous quantum vacuum fluctuations in destroying quantum entanglement appears to provide a solution.Quanta 2022; 11: 115–123.

Entanglement harvesting between two inertial Unruh-DeWitt detectors from nonvacuum quantum fluctuations

Entanglement harvesting from the quantum field is a well-known fact that, in recent times, is being rigorously investigated further in flat and different curved backgrounds. The usually understood formulation studies the possibility of two uncorrelated Unruh-DeWitt detectors getting entangled over time due to the effects of quantum vacuum fluctuations. Our current work presents a thorough formulation to realize the entanglement harvesting from non-vacuum background fluctuations. In particular, we further consider single excitation field states and a pair of inertial detectors, respectively, in $(1+1)$ and $(1+3)$ dimensions for this investigation. Our main observation asserts that entanglement harvesting is suppressed compared to the vacuum fluctuations in this situation. Our other observations confirm a non-zero individual detector transition probability in this background and vanishing entanglement harvesting for parallel co-moving detectors. We look into the characteristics of the harvested entanglement and discuss its dependence on different system parameters.

Effect of relativity and vacuum fluctuations on quantum measurement

Vacuum fluctuations can obscure the detection signal of the measurement of the smallest quantum objects like single particles seemingly implying a fundamental limit to measurement accuracy. However, as we show relativistic invariance implies the disappearance of fluctuations for the space-like spectrum of an observable at zero temperature. This complete absence of noise can be harnessed to perform noiseless measurement of single particles, as we illustrate for electrons or photons. We outline a general scheme to illustrate the noiseless measurement involving the space-like spectrum of observables based on the self-interference of counter-propagating paths of a single particle in a triangular Sagnac interferometer.

Boundary effects on classical liquid density fluctuations

In this paper, we study quantum vacuum fluctuation effects on the mass density of a classical liquid arising from the conical topology of an effective idealized cosmic string spacetime, as well as from the mixed, Dirichlet, and Neumann boundary conditions in Minkowski spacetime. In this context, we consider a phonon field representing quantum excitations of the liquid density, which obeys an effective Klein-Gordon equation with the sound velocity replaced by the light velocity. In the idealized cosmic string spacetime, the phonon field is subject to a quasi-periodic condition. Moreover, in Minkowski spacetime, the Dirichlet and Neumann boundary conditions are applied on one and also two parallel planes. We, thus, in each case, obtain closed analytic expressions for the two-point function and the renormalized mean-squared density fluctuation of the liquid. We point out specific characteristics of the latter by plotting their graphs.

Interatomic interaction of two ground-state atoms in vacuum: Contributions of vacuum fluctuations and radiation reaction

We generalize the formalism proposed by Dalibard, Dupont-Roc and Cohen-Tannoudji [the DDC formalism] to the fourth order of the coupling constant, which can be used to study the interatomic interaction of two ground-state atoms coupled with the vacuum scalar fields. We show that the interatomic potential can be attributed to the joint effect of both vacuum fluctuations and the radiation reaction of atoms. Remarkably, the formulae we derived for the contributions of vacuum fluctuations and the radiation reaction to the interatomic potential upon which future research on fourth-order effects in particular circumstances can be based differ from those in the existing literature [Phys. Rev. D 95, 085014 (2017)].

Quantum Fisher information in massless scalar field with a boundary

We explore the changes of Quantum Fisher information (QFI) for an uniformly accelerating atom coupling to fluctuating massless scalar field with a perfectly reflecting boundary. We first deduce the master equation that the system obeys. For the unbounded case, the vacuum fluctuation and Unruh thermal bath can rapidly degrade the QFI. However, with a boundary, the degradation, preservation, fluctuation and enhancement of QFI are dependent on the evolution time, boundary and acceleration. In addition, the existing boundary can effectively shield QFI from the influence of the vacuum fluctuation and Unruh thermal effect. Especially, the QFI seems to be unaffected by the vacuum fluctuation and acceleration when the atom is very close to the boundary. The efficient control of the boundary and acceleration can provide the feasible scheme of improving the parameter estimation precision.

Quantum vacuum fluctuation effects in a quasi-periodically identified conical spacetime

We consider a quasi-periodically identified conical spacetime, like the one of a cosmic string or disclination, to investigate nonzero averaged quantum vacuum fluctuations effects on the energy-momentum tensor and induced current density associated with a charged scalar field. We obtain exactly closed analytical expressions for the two-point Wightman function and the vacuum expectation value of the field squared, as well as for all components of the energy-momentum tensor. As to the induced current density, due to the quasi-periodic condition used, the only nonzero averaged component found is the azimuthal one. We also compare our results with previous ones found in literature.

Multipartite quantum coherence under electromagnetic vacuum fluctuation with a boundary

We investigate the dynamics of multipartite quantum coherence (QC) for accelerated detector qubit coupled with fluctuating electromagnetic field by presence of a perfectly reflecting boundary. We firstly derive the master equation that the detector evolution obeys. We find that without boundary, QC declines under the impact of Unruh thermal effect and vacuum fluctuation. However, with a boundary, the degradation, floating and protection of QC are closely related to boundary effect, detector polarization and acceleration. The presence of boundary can effectively protect QC under the influence of vacuum fluctuation and Unruh thermal effect in some certain conditions and give us more freedom of adjusting the QC behaviors. Besides, it is shown that the QC of W state manifests better robustness than that of GHZ state under the influence of the vacuum fluctuation and acceleration.

Vacuum induced dispersions on the motion of test particles in D+1 dimensions

When the vacuum state of a scalar or electromagnetic field is modified by the presence of a reflecting boundary, an interacting test particle undergoes velocity fluctuations. Such effect is regarded as a sort of quantum analog of the classical Brownian motion. Several aspects about this system have been recently investigated in the literature, for instance, finite temperature effects, curved spacetime framework, near-boundary regime, late time behavior, and subvacuum phenomena. Here, further steps are given in this analysis by considering the effect of vacuum fluctuations of a scalar field in the presence of a perfectly reflecting flat boundary over the motion of a scalar test particle when the background field does not satisfy the Huygens' principle. Specifically, the background field is allowed to have mass and the system is studied in $D+1$ dimensions. A method of implementing a smooth transition between distinct states of the field is also developed, rendering regularized analytic expressions describing the velocity fluctuations of the test particle. This method is applied to study some special behaviors of the system. Possible applications include fields known to occur in nature as, for instance, the massive Higgs' field, for which the velocity fluctuations are here predicted to acquire a characteristic oscillation, thus behaving differently from their electromagnetic counterparts.

Kerr Black Holes within a Modified Theory of Gravity

The Kerr black hole is studied within a modified theory of gravity, which adds the effects of vacuum fluctuations near a black hole. These vacuum fluctuations are treated as a dark energy. A parameter is introduced to account for these fluctuations. It is zero for the standard theory and acquires a maximal value, just before there would be no event horizon. The existence of an event horizon not only depends on the value of this parameter, but also on the spin of the black hole. In addition, we study the existence of a light-ring. We also elaborate on the relation of the appearance and vanishing of the event horizon and light-ring to phase transitions.

Vacuum fluctuation effects due to an Abelian gauge field in 2 + 1 dimensions, in the presence of moving mirrors

We study the Dynamical Casimir Effect (DCE) due to an Abelian gauge field in 2+1 dimensions, in the presence of semitransparent, zero-width mirrors, which may move or deform in a time-dependent way. We obtain general expressions for the probability of motion-induced pair creation, which we render in a more explicit form, for some relevant states of motion.

Quantum Coherence Behaviors for a Uniformly Accelerated Atom Immersed in Fluctuating Vacuum Electromagnetic Field with a Boundary

We investigate the dynamics of quantum coherence (QC) for a uniformly accelerated atom interacting with fluctuating electromagnetic field subject to a conductor boundary. We firstly derive the master equation that the atom evolution obeys. We find that without boundary, QC declines under the effect of Unruh thermal bath and vacuum fluctuation. However, with a boundary, the degradation, fluctuation, and preservation of QC are closely related to boundary effect, atomic polarization, and acceleration. Furthermore, in the presence of a boundary, QC can effectively be protected under the influence of the vacuum fluctuation and Unruh thermal effect when the atom is transversely polarizable and near this boundary, and the presence of boundary gives us more freedom of controlling the QC behaviors.

Exploration of entropic uncertainty relation for two accelerating atoms immersed in a bath of electromagnetic field

The uncertainty principle as an elementary theory of quantum mechanics plays an important role in quantum information science. In this paper, we study the dynamics of quantum-memory-assisted entropic uncertainty relation for two accelerating atoms coupled with a bath of fluctuating electromagnetic field. The master equation that the system evolution obeys is firstly derived. We find that the mixedness is bound up with the entropic uncertainty. For equilibrium state, the tightness of uncertainty vanishes. For the initial maximum entangled state, the tightness of uncertainty experiences a slight increase and then declines to zero with evolution time. It is found that the greater acceleration makes the uncertainty faster reach a maximum value and stable value. For a fixed acceleration, the uncertainty with different two-atom separations converges to a fixed value. Furthermore, we utilize weak measurement reversal to manipulate the entropic uncertainty. Our explorations may suggest a method of probing entanglement, acceleration effect and vacuum fluctuation effect with entropic uncertainty.

Instability Characteristics of Free-Standing Nanowires Based on the Strain Gradient Theory with the Consideration of Casimir Attraction and Surface Effects

AbstractSize-dependent dynamic instability of cylindrical nanowires incorporating the effects of Casimir attraction and surface energy is presented in this research work. To develop the attractive intermolecular force between the nanowire and its substrate, theproximity force approximation(PFA) for small separations, and the Dirichlet asymptotic approximation for large separations with a cylinder-plate geometry are employed. A nonlinear governing equation of motion for free-standing nanowires – based on the Gurtin-Murdoch model – and a strain gradient elasticity theory are derived. To overcome the complexity of the nonlinear problem in hand, a Garlerkin-based projection procedure for construction of a reduced-order model is implemented as a way of discretization of the governing differential equation. The effects of length-scale parameter, surface energy and vacuum fluctuations on the dynamic instability threshold and adhesion of nanowires are examined. It is demonstrated that in the absence of any actuation, a nanowire might behave unstably, due to the Casimir induction force.

Quantum Brownian motion in an analog Friedmann-Robertson-Walker geometry

In this paper we study the effects of quantum scalar field vacuum fluctuations on scalar test particles in an analog model for the Friedmann-Robertson-Walker spatially flat geometry. In this scenario, the cases with one and two perfectly reflecting plane boundaries are considered as well as the case without a boundary. We find that the particles can undergo Brownian motion with a nonzero mean squared velocity induced by the quantum vacuum fluctuations due to the time-dependent background and the presence of the boundaries. Typical singularities which appear due to the presence of the boundaries in flat spacetime can be naturally regularized for an asymptotically bounded expanding scale function. Thus, shifts in the velocity could be, at least in principle, detectable experimentally. The possibility to implement this observation in an analog cosmological model by the use of a Bose-Einstein condensate is also discussed.

Dynamic instability and bifurcation of electrically actuated circular nanoplate considering surface behavior and small scale effect

In this paper, the dynamic pull-in instability and bifurcation characteristics of circular nanoplate subjected to electrostatic and Casimir forces are studied. Surface effect originates from high surface/volume ratio of nanostructures, where atoms at a free surface experience distinct local environments with respect to those in the bulk material. Thus, the surface free energy being negligible in classical elastic theory, becomes significant in dynamic behaviors of nanostructures. Based on Eringen's nonlocal elasticity and Gurtin-Murdoch surface model, the nonlinear governing equation of electrically actuated circular nanoplate is derived in polar coordinate. The closed-form solution of dynamic frequency and electrostatic voltage is obtained by utilizing the homotopy perturbation method (HPM). Furthermore, the coupling effects of nonlocal parameter and surface characteristics on the dynamic pull-in instability of circular nanoplate are investigated, and the nonlinear dynamics behaviors, time histories and phase diagrams of electrically actuated circular nanoplate are discussed. Some new results obtained in this work could be helpful in design of 2-D circular nanoplate-type actuator considering size-dependency and quantum vacuum fluctuation effects.

The effects of vacuum fluctuations on teleportation of quantum Fisher information

The teleported quantum Fisher information of the phase parameter of atomic state is studied in consideration of vacuum fluctuations. Our results show that the teleported information is determined by the wavelength of the atoms as well as the distance of teleportation. When the wavelength of the atoms is much smaller than the teleportation distance, the teleported information decays with time and the decay rates are determined by the spontaneous emission rate of the atoms. However, when the wavelength of the atoms is much larger than the teleportation distance, the teleported information remains unchanged with time. The information of the phase parameter of atomic state has been absolutely transmitted.

The Effect of Vacuum Fluctuations on Quantum Metrology for a Uniformly Accelerated Atom

We studied, in the framework of open quantum systems, the dynamics of the quantum Fisher information of the parameters of the initial atomic state and atomic transition frequency for a uniformly accelerated polarizable two-level atom coupled in the multipolar scheme to a bath of fluctuating vacuum electromagnetic fields in Minkowski space-time. Our results show that the vacuum fluctuations in Minkowski space-time always make the quantum Fisher information decay, thus degrade the precision of the parameter estimation. The acceleration of the atom makes the quantum Fisher information of initial parameters of atomic state decay faster than those in case with static atom in Minkowski vacuum and even those in case with static atom in Minkowski thermal bath with corresponding Unruh temperature. The maxima of quantum Fisher information of atomic frequency and the optimal measurement time are shown to be smaller than those in the static atom in vacuum case as well as those in the corresponding thermal case.

Nonlinear vibration and adhesion instability of Casimir-induced nonlocal nanowires with the consideration of surface energy

The following research work deals with the size-dependent dynamic instability of suspended nanowires in the presence of Casimir force and surface effects. Specifically, the Casimir-induced instability of nanostructures with circular cross-section and cylinder-plate geometry is studied. Following the Gurtin–Murdoch model and nonlocal elasticity, the governing equation of motion for nanowires is derived. To express the Casimir attraction of cylinder-plate geometry, two approaches, e.g. proximity force approximation (PFA) for small separations and Dirichlet asymptotic approximation for large separations are studied. To overcome the difficulties for solving a nonlinear problem, a step-by-step numerical method is utilized. The effects of nonlocal parameter, surface energy and vacuum fluctuations on the dynamic instability characteristic and adhesion time of nanowires are studied. It is observed that the phase portrait of Casimir-induced nanowires exhibit periodic and homoclinic orbits.