56,309 research outputs found
On the development of QPOs in Bondi-Hoyle accretion flows
The numerical investigation of Bondi-Hoyle accretion onto a moving black hole
has a long history, both in Newtonian and in general-relativistic physics. By
performing new two-dimensional and general-relativistic simulations onto a
rotating black hole, we point out a novel feature, namely, that quasi-periodic
oscillations (QPOs) are naturally produced in the shock cone that develops in
the downstream part of the flow. Because the shock cone in the downstream part
of the flow acts as a cavity trapping pressure perturbations, modes with
frequencies in the integer ratios 2:1 and 3:1 are easily produced. The
frequencies of these modes depend on the black-hole spin and on the properties
of the flow, and scale linearly with the inverse of the black-hole mass. Our
results may be relevant for explaining the detection of QPOs in Sagittarius A*,
once such detection is confirmed by further observations. Finally, we report on
the development of the flip-flop instability, which can affect the shock cone
under suitable conditions; such an instability has been discussed before in
Newtonian simulations but was never found in a relativistic regime.Comment: 11 pages, 7 figure
Fluctuations, dissipation and the dynamical Casimir effect
Vacuum fluctuations provide a fundamental source of dissipation for systems
coupled to quantum fields by radiation pressure. In the dynamical Casimir
effect, accelerating neutral bodies in free space give rise to the emission of
real photons while experiencing a damping force which plays the role of a
radiation reaction force. Analog models where non-stationary conditions for the
electromagnetic field simulate the presence of moving plates are currently
under experimental investigation. A dissipative force might also appear in the
case of uniform relative motion between two bodies, thus leading to a new kind
of friction mechanism without mechanical contact. In this paper, we review
recent advances on the dynamical Casimir and non-contact friction effects,
highlighting their common physical origin.Comment: 39 pages, 4 figures. Review paper to appear in Lecture Notes in
Physics, Volume on Casimir Physics, edited by Diego Dalvit, Peter Milonni,
David Roberts, and Felipe da Rosa. Minor changes, a reference adde
Current status of the Dynamical Casimir Effect
This is a brief review of different aspects of the so-called Dynamical
Casimir Effect and the proposals aimed at its possible experimental
realizations. A rough classification of these proposals is given and important
theoretical problems are pointed out.Comment: 12 pages, the text corresponds to the final published version, except
for the layout and reference styl
Stimulating uncertainty: Amplifying the quantum vacuum with superconducting circuits
The ability to generate particles from the quantum vacuum is one of the most
profound consequences of Heisenberg's uncertainty principle. Although the
significance of vacuum fluctuations can be seen throughout physics, the
experimental realization of vacuum amplification effects has until now been
limited to a few cases. Superconducting circuit devices, driven by the goal to
achieve a viable quantum computer, have been used in the experimental
demonstration of the dynamical Casimir effect, and may soon be able to realize
the elusive verification of analogue Hawking radiation. This article describes
several mechanisms for generating photons from the quantum vacuum and
emphasizes their connection to the well-known parametric amplifier from quantum
optics. Discussed in detail is the possible realization of each mechanism, or
its analogue, in superconducting circuit systems. The ability to selectively
engineer these circuit devices highlights the relationship between the various
amplification mechanisms.Comment: 27 pages, 10 figures, version published in Rev. Mod. Phys. as a
Colloquiu
Motion Induced Radiation from a Vibrating Cavity
We study the radiation emitted by a cavity moving in vacuum. We give a
quantitative estimate of the photon production inside the cavity as well as of
the photon flux radiated from the cavity. A resonance enhancement occurs not
only when the cavity length is modulated but also for a global oscillation of
the cavity. For a high finesse cavity the emitted radiation surpasses radiation
from a single mirror by orders of magnitude.Comment: 4 pages, to appear in Physical Review Letter
Non-perturbative Dynamical Casimir Effect in Optomechanical Systems: Vacuum Casimir-Rabi Splittings
We study the dynamical Casimir effect using a fully quantum-mechanical
description of both the cavity field and the oscillating mirror. We do not
linearize the dynamics, nor do we adopt any parametric or perturbative
approximation. By numerically diagonalizing the full optomechanical
Hamiltonian, we show that the resonant generation of photons from the vacuum is
determined by a ladder of mirror-field {\em vacuum Rabi splittings}. We find
that vacuum emission can originate from the free evolution of an initial pure
mechanical excited state, in analogy with the spontaneous emission from excited
atoms. By considering a coherent drive of the mirror, using a master-equation
approach to take losses into account, we are able to study the dynamical
Casimir effect for optomechanical coupling strengths ranging from weak to
ultrastrong. We find that a resonant production of photons out of the vacuum
can be observed even for mechanical frequencies lower than the cavity-mode
frequency. Since high mechanical frequencies, which are hard to achieve
experimentally, were thought to be imperative for realizing the dynamical
Casimir effect, this result removes one of the major obstacles for the
observation of this long-sought effect. We also find that the dynamical Casimir
effect can create entanglement between the oscillating mirror and the radiation
produced by its motion in the vacuum field, and that vacuum Casimir-Rabi
oscillations can occur.Comment: 30 pages, 8 figure
- …