Observation of thermal Hawking radiation and its temperature in an analogue black hole

Abstract

We measure the correlation spectrum of the Hawking radiation emitted by an analogue black hole and find it to be thermal at the Hawking temperature implied by the analogue surface gravity. The Hawking radiation is in the regime of linear dispersion, in analogy with a real black hole. Furthermore, the radiation inside of the black hole is seen to be composed of negative-energy partners only. This work confirms the prediction of Hawking's theory regarding the value of the Hawking temperature, as well as the thermality of the spectrum. The thermality of Hawking radiation is the root of the information paradox. The correlations between the Hawking and partner particles imply that the analogue black hole has no analogue firewall.It was a profound realization that the entropy of a black hole [1] and Hawking radiation [2,3] should have the same temperature, within a numerical factor on the order of unity. It was further asserted that Hawking radiation should have a thermal spectrum, which creates an information paradox [4,5]. Furthermore, it was proposed that the physics of Hawking radiation could be verified in an analogue system [6]. This proposal was carefully studied and developed theoretically [7][8][9][10][11][12][13][14][15][16][17][18][19]. Classical white and black-hole analogues were also studied experimentally [20][21][22][23], as well as a variety of other analogue gravitational systems [24][25][26][27][28][29][30]. The theoretical works, combined with our long-term study of this subject [14,[31][32][33][34], allowed for the observation of spontaneous Hawking radiation in an analogue black hole [35]. Several theoretical works studied our observation [35], and made predictions about the thermality and Hawking temperature [36][37][38][39][40]. During the years since our observation [35], we have made many improvements to the experimental apparatus. This allows us to study the thermality of the Hawking spectrum, and compare its temperature with the prediction given by the analogue of the surface gravity. In this work, we find that the spectrum of Hawking radiation agrees well with a thermal spectrum, and its temperature is given by Hawking's prediction.The analogue black hole consists of a flowing Bose-Einstein condensate. The flow velocity out in the region < 0 is less than the speed of sound out , as indicated in Fig. 1a. This region corresponds to the outside of the black hole. For > 0, the flow is supersonic ( in > in ),

Slow sound laser in lined flow ducts

“…where j ∈ {B, S, A−, A+, N }. A direct evaluation of (22) shows that k N is of negative norm, while the four other roots have a positive norm (and the same follows for the energy since E = ω E s dx). To see this more simply, one can notice that in the correction term in δ, one can replace −M 0 k 3 j by (ω − M 0 k j ) 3 /M 2 0 to a good approximation (i.e.…”

“…This self-amplification is called the "black hole laser" in the analogue gravity community, and was studied in various contexts [15,16]. The analogue Hawking effect has lead to many experiments in the last decade, in media as diverse as water waves [17][18][19], nonlinear optics [20] or Bose-Einstein condensates [21,22], but despite many promising results, the full demonstration of the analogue Hawking radiation and its properties has not been achieved yet. Slow sound offers a promising system for its realization.…”

Analogues of gravity-induced instabilities in anisotropic metamaterials

“…The fact that Eqs. (7,8) are valid in the medium's instantaneous rest frame means that the fields E a , B a , D a , and H a appearing in them are related to F ab and G ab through Eqs. (3)(4)(5)(6) with u a = v a , the medium's four-velocity field.…”

Estimating the Unruh effect via entangled many-body probes

“…This means the detectable Unruh temperature lies far below the observable threshold with the experimentally achievable acceleration. Since experimental detection of the Unruh radiation is too difficult, people turn sight to the easier but still conceptually rich studies on the simulation [8] and estimation of this effect. We know that quantum metrology aims to improve the precision in estimating parameters via quantum strategies [9].…”