Program
Talks will be 20 minutes + 5 minutes for questions except where indicated. Each day will end with a moderated discussion. Abstracts are below the schedule.
All times below are listed for GMT time zone
Day 1 (June 17)
12:00-12:10 Introduction and Technicalities of a Zoom workshop
Chair: Silke Weinfurtner
12:10 Aydin Keser (FLEET@UNSW) – Analogue stochastic gravity in strongly-interacting Bose–Einstein condensates
12:35 Ian Spielman (JQI: NIST and UMD) – Analog gravity metric control via dispersion engineering
1:00 Mathieu Isoard (LPTMS) – Departing from Thermality of Analogue Hawking Radiation in a Bose-Einstein Condensate
1:25 -1:35 Break
Chair: Maxime Jacquet
1:35 Jeff Steinhauer (Technion – Isreal Institute of Technology) – Spontaneous Hawking radiation and beyond: Observing the time evolution of an analogue black hole
2:00 Germain Rousseaux (CNRS) – Analogue Gravity in Classical Hydrodynamics: spacetimes and cosmic models of stationary and time-dependent processes
2:25 – 2:35 Break
Chair: David Bermudez
2:35 Iacopo Carusotto (INO-CNR BEC Center, Trento, Italy) – Quantum fields in curved space-times with atomic and optical systems: new directions from synthetic gauge fields and quantum emitters
3:00 Ted Jacobson (University of Maryland) – Phonons in an expanding BEC
3:25 – 3:35 Break
Chair: Steve Fulling
3:35 – 4:30 Discussion
Day 2 (June 18)
Chair: Mathieu Isoard
12:00-12:10 Introduction and Technicalities of a Zoom workshop
12:10 Subir Ghosh (Indian Statistical Institute, Kolkata, India) – On the possibility of stimulated Hawking radiation from (negative index) metamaterial-dielectric composite
12:35 Silke Weinfurtner (The University of Nottingham)- Hydrodynamic rotating black holes
1:00 David Bermudez – (Department of Physics, Cinvestav) Instabilities in an optical black-hole laser
1:25-1:35 Break
Chair: Justin Wilson
1:35 Ulf Leonhardt (Weizmann Institute of Science) – Casimir cosmology
2:00 Peter Skyba (Institute of Experimental Physics SAS, Košice, Slovakia) – Magnonic Analog of Black/White-Hole Horizons in Superfluid 3He-B
2:25-2:35 Break
Chair: Vladimir Eltsov
2:35 Maxime Jacquet (Université Paris Sorbonne) – Polariton hydrodynamics for analogue gravity
3:00 Feng Liu (University of Utah) – Fermionic Analogue of High Temperature Hawking Radiation in Black Phosphorus
3:25 – 3:35 Break
3:35 – 4:30 Discussion & Conclusions
Abstracts
Aydin Keser – Analogue stochastic gravity in strongly-interacting Bose–Einstein condensates
Collective modes propagating in a moving superfluid are known to satisfy wave equations in a curved space–time, with a metric determined by the underlying superflow. We use the Keldysh technique in a curved space–time to develop a quantum geometric theory of fluctuations in superfluid hydrodynamics. This theory relies on a “quantized” generalization of the two-fluid description of Landau and Khalatnikov, where the superfluid component is viewed as a quasi-classical field coupled to a normal component — the collective modes/phonons representing a quantum bath. This relates the problem in the hydrodynamic limit to the “quantum friction” problem of Caldeira–Leggett type. By integrating out the phonons, we derive stochastic Langevin equations describing a coupling between the superfluid component and phonons. These equations have the form of Euler equations with additional source terms expressed through a fluctuating stress–energy tensor of phonons. Conceptually, this result is similar to stochastic Einstein equations that arise in the theory of stochastic gravity. We formulate the fluctuation–dissipation theorem in this geometric language and discuss possible physical consequences of this theory.
Ian Spielman – Analog gravity metric control via dispersion engineering
Cold-atom based simulations of inflationary physics are constrained by both practical and in-principle limitations. For example, our experiments using Bose-Einstein condensates in ring-shaped geometries cannot have an expansion factor above about 10 before being limited by: the required laser power for trapping over a large area, the homogeneity of the confining potentials, as well as excitations of unwanted modes. It might seem that using Feshbach resonances to quench the interaction strength might be an idea solution, and indeed atomic systems such as 7Li have shown control over the scattering length with a dynamic range around 10^4, implying an inflation factor of around 100. Unfortunately, even in principle, the range of momentum states with linear dispersion (those described by an effective Lorentz invariant metric) approaches zero as the scattering length approaches zero.
Here I will describe an experimental proposal that bypasses these limitations by engineering the dispersion relation of the cold atom system, introducing a time-dependent effective mass m^*(t). I will describe 1D and 2D realizations of this concept in the continuum using spin orbit coupling, and discusses the practical limitations of these approaches (there is no free lunch).
Mathieu Isoard – Departing from Thermality of Analogue Hawking Radiation in a Bose-Einstein Condensate
We study the quantum fluctuations in a one-dimensional Bose-Einstein condensate realizing analogous acoustic black hole. The taking into account of evanescent channels and of zero modes makes it possible to accurately reproduce recent experimental measurements of the density correlation function. We discuss the determination of Hawking temperature and show that in our model some characteristics of the analogous radiation present significant departure from thermality.
Jeff Steinhauer – Spontaneous Hawking radiation and beyond: Observing the time evolution of an analogue black hole
We confirm the stationary character of the spontaneous Hawking radiation in an analogue black hole. Furthermore, we follow the time evolution of the Hawking radiation, and compare and contrast it with the predictions for real black holes. We observe the ramp up of the Hawking radiation, similar to a real black hole. The end of the spontaneous Hawking radiation is marked by the formation of an inner horizon. The Maryland group predicted that particles emanating from the inner horizon can cause stimulated Hawking radiation. We find that these stimulated Hawking pairs are directly observable.
Germain Rousseaux – Analogue Gravity in Classical Hydrodynamics: spacetimes and cosmic models of stationary and time-dependent processes
In this talk, we discuss some recent results on time-dependent experiments in open channel flows mimicking wave propagation in curved space-time and the black hole laser effect in Classical Hydrodynamics. We focus first on the many scattering effects at a black or white hole horizon in stationary settings both in analogue experiments and numerical simulations before switching to the birth and death of horizon(s) in time-dependent experiments.
Iacopo Carusotto – Quantum fields in curved space-times with atomic and optical systems: new directions from synthetic gauge fields and quantum emitters
In this talk I will review the state of the art and the new perspectives in the theoretical and experimental study of analog models of quantum field theories in flat, curved, or time-dependent backgrounds using condensed matter and optical systems. After a brief presentation of the theory and experiments on Hawking emission of phonons from acoustic horizons in quantum fluids of ultracold atoms and of light, I will present recent results (in collaboration with Luca Giacomelli) on superradiance effects in different geometries. In rotating configurations, the instability of multiply charged vortices can be understood in terms of an ergoregion instability at the vortex core. Introduction of synthetic gauge fields in planar geometries extends the range of space-time metrics that can be generated and allows for analytical insight into superradiant scattering processes. The relation between superradiant scattering and superradiant instabilities will be clarified. As a further extension of the analog model paradigm, I will present how impurity atoms in an atomic fluid can form two-level emitters coupled to the quantum field. Based on recent works with Jamir Marino, Gabriel Menezes and Alessio Recati, I will present observable predictions of Ginzburg radiation and superradiant lasing for moving emitters along linear or circular trajectories. I will finally outline the on-going investigations (in collaboration with Salvatore G. Butera) in the direction of observing back-reaction effects of the quantum Hawking emission onto the black hole background.”
Ted Jacobson – Phonons in an expanding BEC
Abstract: Like scalar waves in an expanding universe, phonons in an expanding BEC experience a Hubble friction, as observed in a recent experiment with a ring condensate (Eckel et al, 2018). The (rather uncertain) observed Hubble friction coefficient was about 0.55 times the one derived theoretically. Gomez-Llorente and Plata (2019) showed that this discrepancy is due to an oversimplified reduction from three spatial dimensions to the one azimuthal dimension. We have revisited this dimensional reduction, recovering their result in a different manner, hewing more closely to the spacetime analogue description, using an efficient, action formalism. Crucial to the result is the scaling with radius of the volume of the expanding BEC. Along the way, we recover in a simple manner the result of Zaremba (1998) for the phonon dispersion relation in a cylindrical condensate. (Based on work with Stephen Eckel.)
Subir Ghosh – On the possibility of stimulated Hawking radiation from (negative index) metamaterial-dielectric composite
We suggest a possibility of stimulated analogue Hawking radiation from negative index metamaterial-dielectric composite, in the presence of external electromagnetic field. We follow the complex path formalism, initiated by Srinivasan and Padmanabhan (PRD, 1999), to calculate the analogue Hawking temperature of the analogue horizon at the metamaterial-dielectric junction, where the dielectric parameters become singular.
Silke Weinfurtner – Hydrodynamic rotating black holes
I will present two recent analogue rotating black hole experiments:
Black hole ringdown: The late stages of the relaxation process of a black hole are expected to depend only on its mass and angular momentum, and not on the details of its formation process. Inspired by recent analogue gravity experiments which demonstrate that several black hole processes take place in gravitational and hydrodynamical systems alike, we conducted an experiment to search for quasinormal mode oscillations of the free surface of a hydrodynamical vortex flow. Our results demonstrate the occurrence and universality of quasinormal ringing in non-equilibrium analogue black hole experiments.
Black hole backreaction: In general relativity, the interaction between a black hole and the fields around it (a process known as backreaction) proceeds via the evolution of the black holes mass and angular momentum. Analogue models of gravity, particularly fluid mechanical analogues, have been very successful in mimicking the propagation of fields, and the effects they experience, around black holes. However, hydrodynamic black holes are externally driven systems whose effective mass and angular momentum are set by experimental parameters, and as such no significant internal backreaction processes are expected to take place. We show, using a rotating draining vortex flow, that a fluid system of finite size exhibit a memory that keeps track of scattering processes in the system. This memory is encoded in the total mass of the system and hence, the backreaction arises as a significant global change in the background parameters, as opposed to a small local correction. More importantly, this backreaction is encapsulated by a dynamical metric, raising the possibility of studying wave-background interaction around evolving black hole spacetimes.
David Bermudez – Instabilities in an optical black-hole laser
Department of Physics, Cinvestav, Mexico
A fluctuation of the quantum field of light can be generated by a light pulse in an optical fiber through the analog Hawking effect. Two close light pulses can amplify this fluctuation as an instability inside a cavity, similar to a laser. This system is called black-hole laser and its emission resonant Hawking radiation. In this talk, we will discuss applications, resonances, instabilities, and phenomenology.
Ulf Leonhardt – Casimir cosmology
Weizmann Institute of Science
Astrophysics has given empirical evidence for the cosmological constant that accelerates the expansion of the universe. Atomic, Molecular, and Optical Physics has proven experimentally that the quantum vacuum exerts forces – the van der Waals and Casimir forces – on neutral matter. It has long been conjectured [Ya. B. Zel’dovich, Usp. Fiz. Nauk 95, 209 (1968)] that the two empirical facts, the cosmological constant and the Casimir force, have a common theoretical explanation, but all attempts of deriving both from a unified theory in quantitative detail have not been successful so far. In AMO Physics, Lifshitz theory has been the standard theoretical tool for describing the measured forces of the quantum vacuum. The lecture explains how a version of Lifshitz theory [U. Leonhardt, Ann. Phys. (New York) 411, 167973 (2019)] accounts for the electromagnetic contribution to the cosmological constant with the correct order of magnitude. At the heart of this connection between AMO Physics and astrophysics lies the analogy between gravitational fields and dielectric media. Analogues of gravity may thus shed light on what has been called dark energy.
Peter Skyba – Magnonic Analog of Black/White-Hole Horizons in Superfluid 3He-B
Marcel Človečko, Emil Gažo, Martin Kupka, Peter Skyba
Centre of low temperature physics, Institute of Experimental Physics SAS, Watsonova 47, 04001 Košice, Slovakia
An aim of this lecture is to introduce and present as a theoretical model, so experimental results of the experiment made in limit of absolute zero temperature studying a spin-wave analogue of the black/white hole horizon using a spin (magnonic) superfluidity in superfluid 3He-B. As an experimental tool simulating properties of the black/white holes horizon we used the spin-precession waves propagating on the background of the spin super-currents between two Bose-Einstein condensates of magnons in form of homogeneously precessing domains. We provide an experimental details and evidence of the white hole formation for the spin precession waves in this system, together with observation of an amplification effect. This system seems to be a promising tool to study the effects of spontaneous Hawking radiation.
Maxime Jacquet – Polariton hydrodynamics for analogue gravity
Analogue gravity enables the study of fields on curved spacetimes in the laboratory. There are numerous experimental platforms in which amplification at the event horizon or the ergoregion has been observed. For example, polaritons in semiconductor microcavities may be made to behave as “fluids of light” and their flow can be engineered to create various geometries with, eg horizons and ergosurfaces. In this talk, I introduce the physics of fluids of light with polaritons, explain how to characterise their flow and how to measure emission in these systems. I then explain how to create a horizon and discuss theoretical results on spontaneous emission by the Hawking effect. I also comment on the quantum statistics of emission “at the horizon” in all dispersive systems, from nonlinear optics to BECs.
Feng Liu- Fermionic Analogue of High Temperature Hawking Radiation in Black Phosphorus
Time-periodic laser driving can create nonequilibrium states not accessible in equilibrium, opening new regimes in materials engineering and topological phase transitions. In this talk, I will report our recent studies to show that black phosphorus exhibits spatially nonuniform topological Floquet–Dirac states under laser illumination, mimicking the “gravity” felt by fermionic quasiparticles in the same way as that for a Schwarzschild black hole (SBH). Quantum tunneling of electrons from a type-II Dirac cone (inside BH) to a type-I Dirac cone (outside BH) emits an SBH-like Planck radiation spectrum. The Hawking temperature 𝑇H obtained for a fermionic analog of BH in the bilayer BP is approximately 3 K, which is several orders of magnitude higher than that in previous works. Our work sheds light on increasing 𝑇H from the perspective of engineering 2D materials by time-periodic light illumination. The predicted SBH-like Hawking radiation, accessible in BP thin films, provides clues to probe analogous astrophysical phenomena in solids.