665 research outputs found
Some aspects of dispersive horizons: lessons from surface waves
Hydrodynamic surface waves propagating on a moving background flow experience
an effective curved space-time. We discuss experiments with gravity waves and
capillary-gravity waves in which we study hydrodynamic black/white-hole
horizons and the possibility of penetrating across them. Such possibility of
penetration is due to the interaction with an additional "blue" horizon, which
results from the inclusion of surface tension in the low-frequency gravity-wave
theory. This interaction leads to a dispersive cusp beyond which both horizons
completely disappear. We speculate the appearance of high-frequency
"superluminal" corrections to be a universal characteristic of analogue gravity
systems, and discuss their relevance for the trans-Planckian problem. We also
discuss the role of Airy interference in hybridising the incoming waves with
the flowing background (the effective spacetime) and blurring the position of
the black/white-hole horizon.Comment: 29 pages. Lecture Notes for the IX SIGRAV School on "Analogue
Gravity", Como (Italy), May 201
Horizon effects for surface waves in wave channels and circular jumps
Surface waves in classical fluids experience a rich array of black/white hole
horizon effects. The dispersion relation depends on the characteristics of the
fluid (in our case, water and silicon oil) as well as on the fluid depth and
the wavelength regime. In some cases, it can be tuned to obtain a relativistic
regime plus high-frequency dispersive effects. We discuss two types of ongoing
analogue white-hole experiments: deep water waves propagating against a
counter-current in a wave channel and shallow waves on a circular hydraulic
jump.Comment: 4 pages, 2 figs. To appear in: Proceedings of the Spanish Relativity
Meeting (ERE2010
Observation of noise correlated by the Hawking effect in a water tank
We measured the power spectrum and two-point correlation function for the
randomly fluctuating free surface on the downstream side of a stationary flow
with a maximum Froude number reached above a
localised obstacle. On such a flow the scattering of incident long wavelength
modes is analogous to that responsible for black hole radiation (the Hawking
effect). Our measurements of the noise show a clear correlation between pairs
of modes of opposite energies. We also measure the scattering coefficients by
applying the same analysis of correlations to waves produced by a wave maker.Comment: 11 pages, 14 figures. several points clarified; two new subsections
in the Supplemental Material on the wave equation and the links with
experiments in BEC
Modelling the electric field applied to a tokamak
The vector potential for the Ohmic heating coil system of a tokamak is
obtained in semi-analytical form. Comparison is made to the potential of a
simple, finite solenoid. In the quasi-static limit, the time rate of change of
the potential determines the induced electromotive force through the
Maxwell-Lodge effect. Discussion of the gauge constraint is included.Comment: 13 pages, 7 figures, final versio
Visco-elastic Cosmology for a Sparkling Universe?
We show the analogy between a generalization of the Rayleigh-Plesset equation of bubble dynamics including surface tension, elasticity and viscosity effects with a reformulation of the Friedmann-Lemaître set of equations describing the expansion of space in cosmology assuming a homogeneous and isotropic universe. By comparing both fluid and cosmic equations, we propose a bold generalization of the newly-derived cosmic equation mapping three continuum mechanics contributions. Conversely, the addition of a cosmological constant-like term in the fluid equation would lead also to a new phenomenology. Our work is purely speculative and does not rely on any observations or theoretical derivations from first principles
Mode-selective quantization and multimodal effective models for spherically layered systems
We propose a geometry-specific, mode-selective quantization scheme in coupled
field-emitter systems which makes it easy to include material and geometrical
properties, intrinsic losses as well as the positions of an arbitrary number of
quantum emitters. The method is presented through the example of a spherically
symmetric, non-magnetic, arbitrarily layered system. We follow it up by a
framework to project the system on simpler, effective cavity QED models.
Maintaining a well-defined connection to the original quantization, we derive
the emerging effective quantities from the full, mode-selective model in a
mathematically consistent way. We discuss the uses and limitations of these
effective models
Experimental demonstration of the supersonic-subsonic bifurcation in the circular jump: A hydrodynamic white hole
We provide an experimental demonstration that the circular hydraulic jump
represents a hydrodynamic white hole or gravitational fountain (the
time-reverse of a black hole) by measuring the angle of the Mach cone created
by an object in the "supersonic" inner flow region. We emphasise the general
character of this gravitational analogy by showing theoretically that the white
hole horizon constitutes a stationary and spatial saddle-node bifurcation
within dynamical-systems theory. We also demonstrate that the inner region has
a "superluminal" dispersion relation, i.e., that the group velocity of the
surface waves increases with frequency, and discuss some possible consequences
with respect to the robustness of Hawking radiation. Finally, we point out that
our experiment shows a concrete example of a possible "transplanckian
distortion" of black/white holes.Comment: 5 pages, 5 figures. New "transplanckian effect" described. Several
clarifications, additional figures and references. Published versio
Hawking tunneling and boomerang behaviour of massive particles with E < m
Copyright © 2012 American Institute of PhysicsTowards New Paradigms: Proceeding of the Spanish Relativity Meeting 2011 (ERE2011), 29 August–2 September 2011, Madrid, SpainMassive particles are radiated from black holes through the Hawking mechanism together with the more familiar radiation of massless particles. For E ≥ m, the emission rate is identical to the massless case. But E < m particles can also tunnel across the horizon. A study of the dispersion relation and wave packet simulations show that their classical trajectory is similar to that of a boomerang. The tunneling formalism is used to calculate the probability for detecting such E < m particles, for a Schwarzschild black hole of astrophysical size or in an analogue gravity experiment, as a function of the distance from the horizon and the energy of the particle
Semiclassical analysis of dark-state transient dynamics in waveguide circuit QED
The interaction between superconducting qubits and one-dimensional microwave transmission lines has been studied experimentally and theoretically in the past two decades. In this work, we investigate the spontaneous emission of an initially excited artificial atom which is capacitively coupled to a semi-infinite transmission line, shorted at one end. This configuration can be viewed as an atom in front of a mirror. The distance between the atom and the mirror introduces a time delay in the system, which we take into account fully. When the delay time equals an integer number of atom oscillation periods, the atom converges into a dark state after an initial decay period. The dark state is an effect of destructive interference between the reflected part of the field and the part directly emitted by the atom. Based on circuit quantization, we derive linearized equations of motion for the system and use these for a semiclassical analysis of the transient dynamics. We also make a rigorous connection to the quantum optics system-reservoir approach and compare these two methods to describe the dynamics. We find that both approaches are equivalent for transmission lines with a low characteristic impedance, while they differ when this impedance is higher than the typical impedance of the superconducting artificial atom
Transmon in a semi-infinite high-impedance transmission line: Appearance of cavity modes and Rabi oscillations
In this paper, we investigate the dynamics of a single superconducting artificial atom capacitively coupled to a transmission line with a characteristic impedance comparable to or larger than the quantum resistance. In this regime, microwaves are reflected from the atom also at frequencies far from the atom\u27s transition frequency. Adding a single mirror in the transmission line then creates cavity modes between the atom and the mirror. Investigating the spontaneous emission from the atom, we then find Rabi oscillations, where the energy oscillates between the atom and one of the cavity modes
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