We study the dynamical effects following a sudden change of the transverse trapping frequency in an elongated BEC, which induces periodic oscillations of the radial density (the breathing mode). At early times, we observe an exponential growth of resonant longitudinal phonons, in agreement with the BdG predictions. We then observe an ordered sequence of phenomena induced by nonlinearities. The...

We study the Hawking radiation in an analogue black hole, in which sound plays the role of light. We find that the correlation spectrum of Hawking radiation agrees well with a thermal spectrum, and its temperature is given by the surface gravity. This confirms the predictions of Hawking’s theory. The Hawking radiation is in the regime of linear dispersion, in analogy with a real black hole....

“Backreaction” in gravitation and cosmology is a difficult yet important class of problems imbued with many challenging issues of theoretical physics. It studies how quantum field processes like cosmological particle creation affect the dynamics of the early universe, how Hawking radiation back-reacts and changes the fate of a black hole. Research in this field began in the late 70’s, with...

We consider an optical cavity enclosed by a freely moving mirror attached to a spring and we study the quantum friction exerted by the dynamical Casimir emission on the mechanical motion of the mirror at the mean-field level. Observable signatures of this simplest example of back-reaction effect are studied in both the ring-down oscillations of the mirror motion and in its steady-state motion...

Distinguishing spontaneous Hawking radiation from different thermal effects is possible by measuring correlations of Hawking pairs. However, measuring the local density is expected to be substantially more accurate than measuring density correlations. In our proposed sonic analogue, Hawking temperature can be extracted directly by studying the amplitude of a density modulation originated by...

Superradiant gain is the process in which waves are amplified via their interaction with a rotating body, examples including evaporation of a spinning black hole and electromagnetic emission from a rotating metal sphere.

We will first discuss the case of photon fluids, i.e. room temperature superfluids generated by a laser beam propagating in a nonlinear defocusing material. Prior work has...

The optical analogue of the Hawking radiation is based on the interaction between a pump and a probe through the optical Kerr effect. The phase-matching condition has been obtained previously by considering the conservation of energy in a frame co-moving with the pump. However, the origin of this interaction in nonlinear optics was not clear. In this work, we derive the conditions for the...

We have studied the scattering of light on a soliton propagating in a waveguide, which has been proposed as an experimental system in which one could observe the analog Hawking effect. The linearized wave equation governing perturbations is shown to have the same structure as that governing phonon propagation in an atomic Bose condensate. By taking into account the full dispersion relation,...

Quantum fluctuations on curved spacetimes cause the emission of entangled pairs, as in the Hawking effect from black hole horizons. We use an optical analogue to gravity to investigate the influence of the spacetime curvature on quantum emission. We calculate the mode conversion analytically for all frequencies. Due to dispersion, the spacetime curvature varies as a function of frequency and...

Ultralight bosonic fields (e.g. stringy axions, axion-like particles, dark photons, light spin-2 fields) are compelling dark-matter candidates and provide a serious alternative to the WIMP paradigm. These fields have eluded particle detectors so far, but can dramatically affect the strong-gravity dynamics of compact objects (black holes and compact stars) in various detectable ways. Light...

The Event Horizon Telescope (EHT) has mapped the central compact radio source of the elliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. These images show a prominent ring with a diameter of ~40 micro-arcsecond, consistent with the size and shape of the lensed photon orbit encircling the “shadow” of a supermassive black hole. The ring is persistent across four observing...

Generation of entangled particle pairs underlies several important phenomena in non-equilibrium field theories including Hawking radiation and dynamical Casimir effect. I will discuss application of these ideas to understanding pump and probe experiments in condensed matter systems and ultracold atoms. Examples include superconducting Higgs amplifiers, phonon-polariton lasing, shaken one...

Over the last decade, cavity polaritons have emerged as a powerful platform to explore the physics of quantum fluids of light [1]. They are quasi-particles arising from the strong coupling regime between photons trapped in a cavity and excitons confined in quantum wells. They propagate like photons but show strong interactions thanks to their matter part. Several theoretical works propose to...

We propose to use quantum vortices for analog gravity. We implement an acoustic Kerr black hole with quantized angular momentum in a Bose-Einstein condensate. We show that the condensate's metric is equivalent to the Kerr's one, exhibiting a horizon and an ergosphere. We confirm that this metric is obeyed not only by weak density waves, but also by quantum vortices which behave as massive test...

Exciton-polaritons in semiconductor microcavities can be understood essentially as interacting photons that are confined into a bidimensional degree of freedom. Collectively, polaritons behave as a quantum fluid, with its typical features such as a superfluid state with sonic excitations. As such, and considering their photonic character, polaritons offer an exciting platform to simulate the...

Black holes are like bells; once perturbed they will relax through the emission of characteristic waves. The frequency spectrum of these waves is independent of the initial perturbation and, hence, can be thought of as a `fingerprint' of the black hole. Since the 1970s scientists have considered the possibility of using these characteristic modes of oscillation to identify astrophysical black...

In Poitiers has been realized a stationary transcritical flow of water in a flume that possesses the analogue of a black hole horizon for long-wavelength surface waves. The horizon has been probed via the scattering of an incident co-current wave, which partially scatters into counter-current waves on either side of the horizon, yielding three outgoing waves (of which one has negative energy)...

The talk will describe proposals for the quantum simulation of possible trans-Planckian effects on two fundamental phenomena in effective curved spacetime:

1. Scale Invariance of the Inflationary Power Spectrum. We consider an analogue de Sitter cosmos in an expanding quasi-two-dimensional Bose-Einstein condensate with dominant dipole-dipole interactions between the atoms or molecules in the...

Quenched or continuously driven quantum systems can show universal dynamics near non-thermal fixed points, generically in the form of scaling behaviour in space and time. Systems where such fixed points can be realized encompass post-inflationary evolution of the early universe, cold dark matter, dense neutron stars, heavy-ion collisions, to low-energy dynamics in cold gases. Key aspects of...

The early universe has undergone a transition from a super-cooled

state after cosmic inflation to a hot and thermal one. We propose an analog

experimental implementation of this cosmic reheating dynamics using an

ultra-cold Bose gas. In our mapping, a Bose-Einstein condensate plays the

role of the inflaton field, which describes the state of the universe after

inflation. The expansion of the...

We compute the density-density correlation function near an acoustic horizon realized in a Bose-Einstein condensate.

A correct normalization of the field of Bogoliubov excitations necessitates to account for the contribution of zero modes.

Once this is achieved, one obtains a very good description of the recent experimental results of Technion's group.

We give an overview on the possibile horizon geometries of black holes in four and five dimensions. In the four-dimensional case, we show that in presence of a cosmological constant or, more generally, of a scalar potential, there can exist actually more possibilities for the horizon geometry than the hitherto known spherical, hyperbolic or flat cases. In particular, there are black holes...

In this talk I will review the present status of the standard theoretical framework of cosmology and how it confronts observations, paying particular attention to the Early Universe physics (inflation models) and its observational probes (power-spectrum, non-Gaussian features, etc), possible connections between dark matter, dark energy and potential modifications of gravity, also accunting for...

Scalar-tensor and f(R) gravity can be described as general relativity plus an effective imperfect fluid corresponding to the scalar field degree of freedom of these theories. A symmetry of electrovacuum

Brans-Dicke gravity translates into a symmetry of the corresponding effective fluid. We present the formalism and an application to an anomaly in the limit of Brans-Dicke theory to Einstein...

The original Bose Einstein Condensate, BEC, black hole analog models and the experiments to date have been for BECs which are effectively one-dimensional and for which the mode functions have only longitudinal excitations. In this case, the corresponding phonons are massless. However, it is possible to have situations in which one or more transverse modes are excited with the result that a...

In the past years the experimental detection of the Hawking radiation in Bose-Einstein condensates (BECs) has taken a remarkable leap forward (J. Steinhauer, *Nature Physics* **12**, 2016 and J.R.M. De Nova et al., *Nature* **569**, 2019). Exploiting the particular features of hard core bosons in 1D, i.e. the Tonks-Girardeau gas (S. Giovanazzi, *Phys. Rev. Lett.* **94**, 2005), we are able to...

Superradiance is a radiation enhancement effect occurring by energy extraction from a rotating spacetime. Being a kinematical effect it can also happen in gravitational analogues, where the energy for the amplification is extracted from the fluid motion. We discuss such an effect in Bose-Einstein condensates with different geometries and show that the well known instability of multiply...

Ultra cold quantum gases are an ideal model system to quantum simulate field theories in the lab. Matter wave interferometry gives direct access to the quantum field and thereby offers an unprecedented view on its equilibrium properties and non-equilibrium evolution. We experimentally illustrate the particle creation when cutting a quantum field in two halfs, and demonstrate the establishment...

Neutron stars are the densest objects in the present Universe. These unique and irreproducible laboratories allow us to study physics in some of its most extreme regimes. The multifaceted nature of neutron stars involves a delicate interplay among astrophysics, gravitational physics, and nuclear physics. The recent direct detection of gravitational waves by merging black-holes and neutron...

This is the first of three talks exploring the feasibility building a quantum simulator for vacuum decay.

Vacuum decay is an important quantum phenomenon that could have occurred in the early universe, and has current importance due to the metastability of the Standard Model. I will review the toolkit we use in QFT and Gravity for computing the probability of vacuum decay, also showing how...

This is the second of three talks exploring the feasibility building a quantum simulator for testing vacuum decay.

I will describe some of the basic features that a BEC system would need in order to simulate cosmological vacuum decays in the laboratory. These include Klein-Gordon like behaviour and a ground state structure with metastable phases. Up to now, the proposals have suffered from a...

This is the third of three talks exploring the feasibility of building a quantum simulator for vacuum decay.

In this presentation I will briefly explain how the usual treatment of vacuum decay in relativistic field theories can be adapted to the case of a two-components, non-relativistic Bose-Einstein condensate, focusing on the contribution of defects and potential walls. I will motivate...

We propose a model describing the evolution of free electron current density in graphene giving rise to wormhole solutions. Based on the concept of M-branes, we perform the analysis using the difference between curvatures of parallel and antiparallel spins. In such a framework an effective graviton emerges in the form of gauge field exchange between electrons. In a plain graphene system, the...

In a previous work it was shown that the realization of the graphene topology on a Beltrami pseudosphere can lead to the analogue realization of the Hawking-Unruh effect [1]. This effect predicts that quantum fields in curved space-time with an horizon exhibit a thermal character due to the quantum vacuum and to the relativistic process of measurement.

Here we construct a computational model...

I shall present two orders of arguments in favor of the realization of a facility where to explore, with analogs, territories of the theoretical landscapes, otherwise unreachable. There, theorists (both of the HEP-TH and of the COND-MAT types) should sit next to experimentalists (mostly of the COND-MAT type). I shall call this facility HELIOS, an evocative name for something that should shed...

I will discuss how one can use tensor network state techniques, in particular matrix product states in 1D, to study the nonequilibrium dynamics of correlations in quantum lattice models in the presence of long-range interactions. For exponents larger than the lattice dimensionality, a Lieb-Robinson-type bound effectively restricts the spreading of correlations to a causal region, but allows...

Building on the analogy with superradiant amplification of waves scattered from a rotating black hole, this investigation considers the problem of a rotating detector embedded into a weakly interacting Bose gas. We observe a qualitative transition in the amplification of the ground state excitation rate of the detector at supersonic speeds. This results from the scattering of co-rotating...

We explore many-body entanglement in spinful Fermi gases with short-range interactions, for metrology purposes. We characterize the emerging quantum phases via Density-Matrix Renormalization Group simulations and quantify their entanglement content for metrological usability via the Quantum Fisher Information (QFI). Our study establishes a method, promoting the QFI to be an order parameter....

Analogue Gravity can be used to reproduce the phenomenology of Quantum Field Theory in Curved Spacetime and in particular phenomena such as cosmological particle creation and Hawking radiation.

In black hole physics, taking into account the backreaction of such effects on the metric requires an extension to semiclassical gravity and leads to an apparent inconsistency in the theory: the black...

We compute corrections to the Unruh effect and related Unruh temperature from the generalized uncertainty principle. First, by following a heuristic derivation, and then a more standard calculation in deformed QFT.

In the limit of small deformations, we recover the thermal character of the Unruh radiation. Corrections to the temperature at first order in the deforming parameter are compared...