Detecting Rotational Superradiance in Fluid Laboratories

Cardoso, Vítor; Coutant, Antonin; Richartz, Maurício; Weinfurtner, Silke

doi:10.1103/physrevlett.117.271101

Cited by 54 publications

(57 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…[36], which shows that non-zero vorticity can act as an effective mass term, thus allowing quasibound states to appear in vortex flows). For superradiance, the presence of an event horizon is not mandatory [7,[37][38][39]: it can be replaced by any dissipative material, as in the case of Zel'dovich's cylinder that scatters electromagnetic waves [40] or in the case of a rotating cylinder that dissipates the energy of water waves [41]. Here, building on the ideas of Refs.…”

Section: Introductionmentioning

confidence: 99%

Synchronized stationary clouds in a static fluid

Benone¹,

Crispino²,

Herdeiro³

et al. 2018

Physics Letters B

View full text Add to dashboard Cite

The existence of stationary bound states for the hydrodynamic velocity field between two concentric cylinders is established. We argue that rotational motion, together with a trapping mechanism for the associated field, is sufficient to mitigate energy dissipation between the cylinders, thus allowing the existence of infinitely long lived modes, which we dub stationary clouds. We demonstrate the existence of such stationary clouds for sound and surface waves when the fluid is static and the internal cylinder rotates with constant angular velocity Ω. These setups provide a unique opportunity for the first experimental observation of synchronized stationary clouds. As in the case of bosonic fields around rotating black holes and black hole analogues, the existence of these clouds relies on a synchronization condition between Ω and the angular phase velocity of the cloud.

show abstract

Section: Introductionmentioning

confidence: 99%

Synchronized stationary clouds in a static fluid

Benone¹,

Crispino²,

Herdeiro³

et al. 2018

Physics Letters B

View full text Add to dashboard Cite

show abstract

“…The present experiment does not reveal the mechanism behind the absorption of the negative energies. The likely possibilities are that they are dissipated away in the vortex throat, in analogy to superradiant cylinders 4,22 , that they are trapped in the hole 23 and unable to escape, similarly to what happens in black holes 24,25 , or a combination of both. A possible way to distinguish between the two in future experiments would be to measure the amount of energy going down the throat.…”

mentioning

confidence: 99%

Rotational superradiant scattering in a vortex flow

et al. 2017

Self Cite

View full text Add to dashboard Cite

When an incident wave scatters o of an obstacle, it is partially reflected and partially transmitted. In theory, if the obstacle is rotating, waves can be amplified in the process, extracting energy from the scatterer. Here we describe in detail the first laboratory detection of this phenomenon, known as superradiance [1][2][3][4] . We observed that waves propagating on the surface of water can be amplified after being scattered by a draining vortex. The maximum amplification measured was 14% ± 8%, obtained for 3.70 Hz waves, in a 6.25-cm-deep fluid, consistent with the superradiant scattering caused by rapid rotation. We expect our experimental findings to be relevant to black-hole physics, since shallow water waves scattering on a draining fluid constitute an analogue of a black hole [5][6][7][8][9][10] , as well as to hydrodynamics, due to the close relation to over-reflection instabilities [11][12][13] . In water, perturbations of the free surface manifest themselves by a small change ξ(t, x) of the water height. On a flat bottom, and in the absence of flow, linear perturbations are well described by superpositions of plane waves of definite frequency f (Hz) and wavevector k (rad m −1 ). When surface waves propagate on a changing flow, the surface elevation is generally described by the sum of two contributions ξ = ξ I + ξ S , where ξ I is the incident wave produced by a source, for example, a wave generator, while ξ S is the scattered wave, generated by the interaction between the incident wave and the background flow. In this work, we are interested on the properties of this scattering on a draining vortex flow which is assumed to be axisymmetric and stationary. At the free surface, the velocity field is given in cylindrical coordinates by v = v r e r + v θ e θ + v z e z .Due to the symmetry, it is appropriate to describe ξ I and ξ S using polar coordinates (r, θ). Any wave ξ(t, r, θ ) can be decomposed into partial waves 10,14 ,where m ∈ Z is the azimuthal wavenumber and ϕ f ,m (r) denotes the radial part of the wave. Each component of this decomposition has a fixed angular momentum proportional to m, instead of a fixed wavevector k. (To simplify notation, we drop the indices f ,m in the following.) Since the background is stationary and axisymmetric, waves with different f and m propagate independently. Far from the centre of the vortex, the flow is very slow, and the radial part ϕ(r) becomes a sum of oscillatory solutions,where k = ||k|| 2 is the wavevector norm. This describes the superposition of an inward wave of (complex) amplitude A in propagating towards the vortex, and an outward wave propagating away from it with amplitude A out . These coefficients are not independent. The A in values, one for each f and m component, are fixed by the incident part ξ I . If the incident wave is a plane wave ξ = ξ 0 e −2iπft+ik·x , then the partial amplitudes are given by A in = ξ 0 e imπ+iπ/4 / √ 2πk. In other words, a plane wave is a superposition containing all azimuthal waves, something that we have exploited...

show abstract

“…[2] for a detailed review about this topic). Analogue gravity models of this kind are often used to probe kinematical aspects of general relativity and quantum field theory on curved spacetimes, such as cosmological particle production [3][4][5], superradiance [6][7][8][9][10] and Hawking radiation [11][12][13][14]. In particular, the transition between sub-and supercritical fluid flows can be set up in a laboratory, generating a dumb hole, the analogue of a black hole [1,15], which allows the classical analogue of the Hawking radiation to be tested experimentally [16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Analogue model for anti-de Sitter as a description of point sources in fluids

2016

View full text Add to dashboard Cite

We introduce an analogue model for a nonglobally hyperbolic spacetime in terms of a twodimensional fluid. This is done by considering the propagation of sound waves in a radial flow with constant velocity. We show that the equation of motion satisfied by sound waves is the wave equation on AdS2 × S 1 . Since this spacetime is not globally hyperbolic, the dynamics of the KleinGordon field is not well defined until boundary conditions at the spatial boundary of AdS2 are prescribed. On the analogue model end, those extra boundary conditions provide an effective description of the point source at r = 0. For waves with circular symmetry, we relate the different physical evolutions to the phase difference between ingoing and outgoing scattered waves. We also show that the fluid configuration can be stable or unstable depending on the chosen boundary condition.

show abstract

Detecting Rotational Superradiance in Fluid Laboratories

Cited by 54 publications

References 40 publications

Synchronized stationary clouds in a static fluid

Synchronized stationary clouds in a static fluid

Rotational superradiant scattering in a vortex flow

Analogue model for anti-de Sitter as a description of point sources in fluids

Contact Info

Product

Resources

About