Analogue Black Hole Research Articles

Accurate quasinormal modes of the analog black holes

Accurate quasinormal modes of the analog black holes

Violation of Bell inequalities in an analog black hole

Violation of Bell inequalities in an analog black hole

Exact phonon quasibound states around an optical black hole

In this work, we present an exact solution of phonon quasibound states in a vortex photon flow that creates an analogous black hole background. We worked out and successfully solve the governing differential equation of the systen that is similar with the relativistic Klein–Gordon equation. The exact radial solutions are discovered in terms of the confluent Heun functions that behaves as ingoing waves near the black hole’s horizon and decaying far away from the black hole’s horizon. The polynomial condition of the confluent Heun function leads to the discovery of the the complex valued quantized energy levels expression of the quasibound state of which depends on the phonon mass Ω0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Omega _0$$\\end{document}, the photon vortex horizon’s spin ΩH\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Omega _H$$\\end{document} and the azimuthal and the main quantum number (m, n). In the last section, by using the Damour–Ruffini method, the Hawking radiation of the analog black hole’s horizon is investigated to derive the phononic radiation distribution function from where, the Hawking temberature is obtained.

Rotating curved spacetime signatures from a giant quantum vortex.

Gravity simulators1 are laboratory systems in which small excitations such as sound2 or surface waves3,4 behave as fields propagating on a curved spacetime geometry. The analogy between gravity and fluids requires vanishing viscosity2-4, a feature naturally realized in superfluids such as liquid helium or cold atomic clouds5-8. Such systems have been successful in verifying key predictions of quantum field theory in curved spacetime7-11. In particular, quantum simulations of rotating curved spacetimes indicative of astrophysical black holes require the realization of an extensive vortex flow12 in superfluid systems. Here we demonstrate that, despite the inherent instability of multiply quantized vortices13,14, a stationary giant quantum vortex can be stabilized in superfluid 4He. Its compact core carries thousands of circulation quanta, prevailing over current limitations in other physical systems such as magnons5, atomic clouds6,7 and polaritons15,16. We introduce a minimally invasive way to characterize the vortex flow17,18 by exploiting the interaction of micrometre-scale waves on the superfluid interface with the background velocity field. Intricate wave-vortex interactions, including the detection of bound states and distinctive analogue black hole ringdown signatures, have been observed. These results open new avenues to explore quantum-to-classical vortex transitions and use superfluid helium as a finite-temperature quantum field theory simulator for rotating curved spacetimes19.

Acoustic pressure modulation driven by spatially non-uniform flow

The recent identification of a modulation of acoustic waves that is driven by spatial velocity gradients, using acoustic black and white hole analogues [see Schenke, Sewerin, van Wachem, and Denner, J. Acoust. Soc. Am. 154, 781–791 (2023)], has shed new light on the complex interplay of acoustic waves and non-uniform flows. According to the virtual acoustic black hole hypothesis, these findings should be applicable to acoustic waves propagating in non-uniform flows of arbitrary velocity. In this study, the propagation of acoustic waves in non-uniform flows is investigated by incorporating a leading-order model of acoustic pressure modulation into a Lagrangian wave tracking algorithm. Using this numerical method, the acoustic pressure modulation is recovered accurately in non-uniform subsonic flows. This suggests that spatial velocity gradients drive acoustic pressure modulations in any non-uniform flow, which can, as shown here, be readily quantified.

Listening to quantum gravity?

Recent experimental progresses in controlling classical and quantum fluids have made it possible to realize acoustic analogs of gravitational black holes, where a flowing fluid provides an effective spacetime on which sound waves propagate, demonstrating Hawking-like radiation and superradiance. We propose the exciting possibility that new hydrodynamic systems might provide insights to help resolve mysteries associated with quantum gravity, including the black hole information-loss paradox and the removal of spacetime singularities.

The holar wind

String theory in AdS3 with purely NS-NS fluxes and vanishing RR moduli has a continuum of winding string excitations in radial plane wave states. BTZ black holes can emit such strings, which then flow out toward the AdS3 boundary as a stream of massive quanta, and form a black hole analogue of the solar wind. The winding string sector thus provides a decay channel for the black hole to evaporate without having either to couple the system to an external reservoir or to match the AdS3 throat onto an asymptotically flat region. We compute the emission amplitude of this “holar wind” in the semi-classical approximation, and consider the associated version of the black hole information paradox.

Impact of trans-Planckian excitations on black-hole radiation in dipolar condensates

We consider a quasi-one-dimensional dipolar condensate in a steplike analog black hole setup. It is shown that the existence of roton excitations leaves significant imprints onto the Hawking radiation spectrum. The emitted radiation depends on the depth of the roton minimum, and is in general more intense. In addition, we find a novel spontaneous particle creation mechanism with no counterpart in nondipolar condensates. Our results establish that dipolar condensates offer a richer and more versatile environment for the simulation of particle production from the quantum vacuum in the presence of horizon interfaces than contact-interaction condensates.

Quantum simulation of Hawking radiation and curved spacetime with a superconducting on-chip black hole

Hawking radiation is one of the quantum features of a black hole that can be understood as a quantum tunneling across the event horizon of the black hole, but it is quite difficult to directly observe the Hawking radiation of an astrophysical black hole. Here, we report a fermionic lattice-model-type realization of an analogue black hole by using a chain of 10 superconducting transmon qubits with interactions mediated by 9 transmon-type tunable couplers. The quantum walks of quasi-particle in the curved spacetime reflect the gravitational effect near the black hole, resulting in the behaviour of stimulated Hawking radiation, which is verified by the state tomography measurement of all 7 qubits outside the horizon. In addition, the dynamics of entanglement in the curved spacetime is directly measured. Our results would stimulate more interests to explore the related features of black holes using the programmable superconducting processor with tunable couplers.

Analogous Black Holes in Type-III Dirac Semimetal Ni3In2X2 (X = S, Se)

Black holes are objects that have a large mass and curve space time, characterized by their event horizon and singularity. Recently, an interesting concept of analogous black holes has emerged in the field of condensed matter physics. In this work, the possibility of realizing analogous black holes in topological material is Ni3In2X2 (X = S, Se) discussed. This work shows that the type-III Dirac cones of the material can lead to the emergence of an event horizon and the formation of a black hole-like region near the Dirac point. In addition, the possible experimental signatures of such a system are discussed and the potential implications of an analogous black hole for the study of black hole physics in condensed matter systems.

Black hole mirages: Electron lensing and Berry curvature effects in inhomogeneously tilted Weyl semimetals

We study electronic transport in Weyl semimetals with spatially varying nodal tilt profiles. We find that the flow of electrons can be guided precisely by judiciously chosen tilt profiles. In a broad regime of parameters, we show that electron flow is described well by semiclassical equations of motion similar to the ones governing gravitational attraction. This analogy provides a physically transparent tool for designing tiltronic devices like electronic lenses. The analogy to gravity circumvents the notoriously difficult full-fledged description of inhomogeneous solids. A comparison to microscopic lattice simulations shows that it is only valid for trajectories sufficiently far from analogue black holes. We finally comment on the Berry curvature-driven transverse motion and relate the latter to spin precession physics.

Analog Schwarzschild black holes of Bose-Einstein condensates in a cavity: Quasinormal modes and quasibound states

Analog models of black holes have unequivocally proven to be extremely beneficial in providing critical information regarding black hole spectroscopy, superradiance, quantum phenomena and most importantly Hawking radiation and black hole evaporation; topics that have either recently begun to bloom through gravitational wave observations or have not yet been investigated in astrophysical setups. Black hole analog experiments have made astonishing steps toward the aforementioned directions and are paramount in understanding the quantum nature of the gravitational field. Recently, a tabletop analog Schwarzschild black hole has been proposed by placing Bose-Einstein condensates of photons inside a mirror's cavity, leading to a sink with a radial vortex that represents a velocity singularity. Here, we provide an extensive spectral analysis of both the tabletop acoustic black hole and its higher-dimensional gravitational analog. We find that quasinormal modes and quasibound states share qualitative similarities in both systems and show that the eikonal quasinormal modes of the analog acoustic black hole have a photon-sphere-like interpretation, which points to the existence of a phonon sphere in the analog black hole. Our results, complemented with the recently calculated graybody factors and Hawking radiation of the acoustic analog, can provide a theoretical test bed for future tabletop experiments with condensates of light in a mirror's cavity and provide significant insights regarding classical and quantum phenomena in higher-dimensional black holes.

Hawking Radiation from the Boundary Scalar Field and the Information Loss Paradox

Hawking radiation is an essential property of the quantum black hole. It results in the information loss paradox and provides an important clue with regard to the unification of quantum mechanics and general relativity. In previous work, the boundary scalar fields on the horizon of black holes were used to determine the microstates of BTZ black holes and Kerr black holes. They account for Bekenstein–Hawking entropy. In this paper, we show that the Hawking radiation can also be derived from those scalar fields. Hawking radiation is a mixture of the thermal radiation of right- and left-moving sectors at different temperatures. Based on this result, for static BTZ black holes and Schwarzschild black holes, we propose a simple solution for the information loss paradox; i.e., the Hawking radiation is pure due to its entanglement between the left-moving sector and the right-moving sector. This entanglement may be detected in an analogue black hole in the near future.

An optical analogue for rotating BTZ black holes

We demonstrate an optical realization for the rotating BTZ black hole using the recent popular photon fluid model in an optical vortex but with a new proposed expression for the optical phase. We also give the numerical realization for the optical vortex to ensure that it can be generated experimentally. Different from the earlier suggestions for the analogue rotating black holes, our proposal includes an inner horizon in the analogue black hole structure. Such structure can keep for a long distance for the convenience of observing analogue Hawking or Penrose radiations.

Asymmetric tunneling of Bose–Einstein condensates

In his celebrated textbook, Quantum Mechanics: Nonrelativistic Theory, Landau argued that, for single particle systems in 1D, tunneling probability remains the same for a particle incident from the left or the right of a barrier. This left–right symmetry of tunneling probability holds regardless of the shape of the potential barrier. However, there are a variety of known cases that break this symmetry, e.g. when observing composite particles. We computationally (and analytically, in the simplest case) show this breaking of the left–right tunneling symmetry for Bose–Einstein condensates (BECs) in 1D, modeled by the Gross–Pitaevskii equation. By varying g, the parameter of inter-particle interaction in the BEC, we demonstrate that the transition from symmetric (g = 0) to asymmetric tunneling is a threshold phenomenon. Our computations employ experimentally feasible parameters such that these results may be experimentally demonstrated in the near future. We conclude by suggesting applications of the phenomena to design atomtronic diodes, synthetic gauge fields, Maxwell’s demons, and black-hole analogues.

Radiation shielding of analog Bañados-Teitelboim-Zanelli black holes

Although the theory of analog gravity suggests that we can simulate the space-time structure of black holes by using laboratory physical systems, it is difficult to find the analogs for rotating black holes in laboratory systems. In this work, we use a new field form for the optical vortex to study the analogous black hole structure close to the Bañados-Teitelboim-Zanelli (BTZ) black hole. We compare the similarities and differences between massless particles and sound waves by calculating their motions in space-time analogous to BTZ black holes and gravitational BTZ black holes. The effective potential energy values of massless particles and sound waves in both kinds of black hole spacetimes give the same forbidden-zone distributions of energy and angular momentum. The difference is that the classical forbidden area of the BTZ black hole will approach fixed energy values along the radial direction, while the classical forbidden area of the analogous BTZ black hole will be closed along the radial direction. Fortunately, near the event horizon and the ergosphere, the behaviors of massless particles and sound waves are almost the same. From this point of view, we can say that the analogous experimental system can simulate the BTZ black hole very well. In particular, the classically forbidden regions of particles with low energy and high angular momentum are wider in both types of black hole space-time.

AnaBHEL (Analog Black Hole Evaporation via Lasers) Experiment: Concept, Design, and Status

Accelerating relativistic mirrors have long been recognized as viable settings where the physics mimic those of the black hole Hawking radiation. In 2017, Chen and Mourou proposed a novel method to realize such a system by traversing an ultra-intense laser through a plasma target with a decreasing density. An international AnaBHEL (Analog Black Hole Evaporation via Lasers) collaboration was formed with the objectives of observing the analog Hawking radiation, shedding light on the information loss paradox. To reach these goals, we plan to first verify the dynamics of the flying plasma mirror and characterize the correspondence between the plasma density gradient and the trajectory of the accelerating plasma mirror. We will then attempt to detect the analog Hawking radiation photons and measure the entanglement between the Hawking photons and their “partner particles”. In this paper, we describe our vision and strategy of AnaBHEL using the Apollon laser as a reference, and we report on the progress of our R&D concerning the key components in this experiment, including the supersonic gas jet with a graded density profile, and the superconducting nanowire single-photon Hawking detector. In parallel to these hardware efforts, we performed computer simulations to estimate the potential backgrounds, and derived analytic expressions for modifications to the blackbody spectrum of the Hawking radiation for a perfectly reflecting point mirror, due to the semi-transparency and finite-size effects specific to flying plasma mirrors. Based on this more realistic radiation spectrum, we estimate the Hawking photon yield to guide the design of the AnaBHEL experiment, which appears to be achievable.

Artificial Hawking radiation, weak pseudo-Hermiticity, and Weyl semimetal blackhole analogy

We examine the possibility of artificial Hawking radiation by proposing a non-PT-symmetric weakly pseudo-Hermitian two-band model containing a tilting parameter by pursuing Weyl semimetal blackhole analogy. We determine the tunneling probability using such a Hamiltonian through the event horizon that acts as a classically forbidden barrier.

Symplectic circuits, entanglement, and stimulated Hawking radiation in analogue gravity

We introduce a convenient set of analytical tools (the Gaussian formalism) and diagrams (symplectic circuits) to analyze multimode scattering events in analogue gravity, such as pair creation \`a la Hawking by black hole and white hole analogue event horizons. The diagrams prove to be valuable Ans\"atze for the scattering dynamics, especially in settings where direct analytic results are not straightforward and one must instead rely on numerical simulations. We use these tools to investigate entanglement generation in single- and multihorizon scenarios, in particular when the Hawking process is stimulated with classical (e.g., thermal noise) and nonclassical (e.g., single-mode squeezed vacuum) input states---demonstrating, for instance, that initial squeezing can enhance the production of entanglement and overcome the deleterious effects that initial thermal fluctuations have on the output entanglement. To make further contact with practical matters, we examine how attenuation degrades quantum correlations between Hawking pairs. The techniques that we employ are generally applicable to analogue gravity setups of (Gaussian) bosonic quantum systems, such as analogue horizons produced in optical analogues and in Bose-Einstein condensates, and should be of great utility in these domains. We show the applicability of these techniques by putting them in action for an optical system containing a pair white-black hole analogue, extending our previous analysis of [Phys. Rev. Lett. 128, 091301 (2022)].

Confirmation of stimulated Hawking radiation, but not of black hole lasing

Stimulated Hawking radiation in an analog black hole in a Bose-Einstein condensate was reported in 2014, and it was claimed that the stimulation was of the black hole lasing variety. The study was based on the observation of rapidly growing negative-energy waves. We find that the correlations between the Hawking and partner particles are directly observable in the experimental plots, which confirms the stimulated Hawking radiation. We further verify this result with new measurements. Also, the observed Hawking/partner correlations provide a sensitive, background-free probe of the underlying mechanism of the stimulation. The experiment inspired the prediction of the Bogoliubov-Cherenkov-Landau (BCL) mechanism of stimulated Hawking radiation. Through a numerical simulation in which the BCL mechanism is suppressed, we find that the partner particles have an infrared cutoff due to the finite distance between the outer and inner horizons, which limits the rate of black hole lasing. We compute this cutoff for the experiment, and the resulting Bogoliubov coefficient, and black hole lasing rate. This analysis shows that the growth rate of black hole lasing is too slow to explain the observations. It is likely that the observed stimulation was due to the BCL mechanism. Furthermore, zero frequency lasing modes play no role in our numerical simulation.