arXiv subjects

Leonardo Solidoro

Publications and source records attributed to Leonardo Solidoro.

9 recordsLinked to original sources

arXiv2026

End state of the experimental black-hole bomb

Rotating black holes can amplify incident waves through superradiant scattering. When these waves are confined, repeated amplification gives rise to the black-hole bomb instability, whose nonlinear evolution remains poorly understood despite its central role in models of bosonic clouds around astrophysical black holes. Here, we reproduce the black-hole bomb mechanism in a laboratory setting using a gravity simulator based on a draining vortex in superfluid helium. Surface waves propagating on the superfluid interface experience an effective rotating spacetime and undergo repeated superradiant amplification within a cylindrical cavity. By tuning the temperature and flow parameters, we achieve exponential growth of a low-frequency resonant mode, followed by the arrest of the instability and the formation of a long-lived non-equilibrium steady state. Using spatially and temporally resolved measurements, we identify nonlinear frequency shifts, harmonic generation, and coherent three- and four-wave mixing that redistribute energy among interacting modes. This novel end state of the experimental black-hole bomb highlights the role of nonlinear wave interactions in quenching the runaway growth expected from linear theory and governing the system's late-time dynamics. Our results establish a laboratory framework for investigating the nonlinear evolution of black-hole bombs, with implications for analogous phenomena involving ultralight bosonic fields around rotating black holes.

gr-qc↗

arXiv2026

Spectroscopy of analogue black holes using simulation-based inference

The emergence of precision gravity simulators in quantum and fluid systems is opening new avenues for probing curved-spacetime physics and black-hole phenomenology under controlled laboratory conditions. In parallel, advances in understanding how fundamental physics can be probed in the spectral signatures of black holes and exotic compact objects motivate the development of modern spectroscopic techniques within analogue-gravity experiments. In this work, we model the spectral properties of analogue black holes sourced by broadband stochastic noise, a crucial aspect in realistic experiments that poses substantial challenges for established data-analysis techniques. Using simulation-based inference, we demonstrate that the physical parameters encoded in noisy spectra can be reliably extracted, showing that these techniques provide a powerful tool for studying both spacetime properties and boundary effects in gravity simulators.

gr-qc↗

arXiv2025

When is a sloshing vortex an analogue black hole bomb?

Draining vortices provide a powerful platform for simulating black hole phenomena in tabletop experiments. In realistic fluid systems confined within a finite container, low-frequency waves amplified by the vortex are reflected at the walls, rendering the system unstable. This process, known in the gravitational context as the black hole bomb, manifests as a sloshing motion of the free surface. The analogy, however, becomes more nuanced when a realistic vortex core with a non-singular vorticity distribution is considered. We investigate this by analysing a non-draining Rankine vortex in the shallow-water and inviscid limits. At low circulation, the sloshing corresponds to an instability of the vorticity field, whereas at high circulation where fluid is expelled from the vortex core, the destabilising mechanism coincides with that of the black hole bomb. Our variational framework distinguishes the energetic contributions of vorticity and irrotational perturbations, offering new insight into the rotating-polygons instability reported by, e.g. Jansson et al. (2006). From the analogue-gravity perspective, we identify hollow core vortices as an optimal regime for exploring black-hole-like instabilities in fluids.

physics.flu-dyn↗

arXiv2025

Digital holographic imaging for free surfaces of superfluid helium

Visualising the free surface of superfluid helium offers a rare opportunity to explore wave dynamics in the limit of vanishing viscosity. Such measurements are nonetheless challenging due to helium's low refractive index contrast, restricted optical access to the cryogenic setups required to maintain helium in its superfluid phase, and mechanical vibrations from the various cooling stages. Overcoming these limitations will enable quantitative studies of surface-wave dynamics with applications in fluid mechanics, quantum simulation, and quantum optomechanics. Here we report an implementation of off-axis digital holography for full-field imaging of the free surface of superfluid $^\text{4}$He. We perform non-contact measurements of nanometre- to micrometre-scale interface fluctuations in two cryogenic systems: a traditional helium bath cryostat and a cryogen-free refrigerator. We employ machine-learning-based analysis to isolate noise-driven normal modes and their spatial structure in both systems. This enables reconstruction of the dispersion relation for gravity-capillary waves in macroscopic samples and, for thick films, determination of the film thickness from the measured dispersion, providing a quantitative benchmark for our approach. These proof-of-concept experiments show that digital holography is a powerful and versatile tool for high-resolution, minimally invasive studies of superfluid surfaces, with strong potential for integration into diverse experimental platforms.

physics.optics↗

arXiv2025

Black-hole spectroscopy from a giant quantum vortex

Black-hole spectroscopy aims to infer the fundamental properties of black holes by analysing the spectrum of gravitational waves emitted as they settle into equilibrium. These resonances, known as quasinormal modes (QNMs), decay rapidly, which limits the time-domain analysis of gravitational-wave data or numerical simulations to the longest-lived mode, except for a particularly loud event. Owing to the analogy between fields in curved spacetime and waves propagating in a flowing medium, QNMs can be equally excited in a laboratory. In these finite-sized systems, the QNM spectrum is expected to alter: compared to their counterparts in unbounded settings, the real frequencies of QNMs shift while their damping rates (imaginary frequencies) reduce, thereby enhancing their detectability. Here we show that multiple QNMs can be extracted from noise-driven interface waves surrounding a giant quantum vortex in superfluid helium-4, which emulates a spacetime geometry indicative of a rotating black hole. By resolving waves with different azimuthal periodicity, we find that both fundamental modes and their higher-frequency overtones are excited, and oscillate at frequencies given by the size of our system. Since similar effects may arise in astrophysical scenarios due to the interstellar medium or dark matter, gravity simulators now complement numerical and observational approaches to black-hole spectroscopy.

gr-qc↗

arXiv2024

On the origin of quasinormal modes in semi-open systems

Astrophysical black holes are open systems which, when perturbed, radiate quasi-normal modes (QNMs) to infinity. By contrast, laboratory analogues are necessarily finite-sized, presenting a potential obstacle to exciting QNMs in experiments. We explore how the QNM spectrum of a toy-model black hole changes when enclosed by a partially reflecting wall with adjustable reflectivity. Our results reveal a continuous connection between the QNM spectra of open and finite-sized systems. Additionally, we demonstrate that QNMs in this setup are easily excited by incoherent background noise. This work opens new avenues for studying QNMs of black holes and compact objects in laboratory settings, where finite-size effects and noise are unavoidable.

gr-qc↗

arXiv2023

Rotating Curved Spacetime Signatures from a Giant Quantum Vortex

Gravity simulators are laboratory systems where small excitations like sound or surface waves behave as fields propagating on a curved spacetime geometry. The analogy between gravity and fluids requires vanishing viscosity, a feature naturally realised in superfluids like liquid helium or cold atomic clouds. Such systems have been successful in verifying key predictions of quantum field theory in curved spacetime. In particular, quantum simulations of rotating curved spacetimes indicative of astrophysical black holes require the realisation of an extensive vortex flow in superfluid systems. Here we demonstrate that despite the inherent instability of multiply quantised vortices, a stationary giant quantum vortex can be stabilised in superfluid $^4$He. Its compact core carries thousands of circulation quanta, prevailing over current limitations in other physical systems such as magnons, atomic clouds and polaritons. We introduce a minimally invasive way to characterise the vortex flow 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 utilise superfluid helium as a finite temperature quantum field theory simulator for rotating curved spacetimes.

gr-qc↗

arXiv2022

From the delay time in Quantum Mechanics to the Goos-Hänchen shift in Optics

Delay times in quantum mechanics always represented an intriguing challenge for physicists. Due to the fact that quantum mechanical experiments are, often, hard to be implemented, the possibility to connect delay times with laser lateral displacements gives us the opportunity to prepare, in optical laboratories, experiments which are equivalent to the quantum mechanical ones in detecting delay times. In this article, we will show in detail not only the relationship between delay times and Goos-Haenchen shifts, but also the close connection between the impulse change in quantum mechanics and angular deviations in optics. Lateral shifts are caused by the phase of Fresnel coefficients whereas angular deviations by the breaking of symmetry of the wave number distributions. The classical formula for the delay time is based on the use of the stationary phase method and contains a divergence for incidence at a critical potential energy. For Gaussian beams, the mean value calculation removes such a divergence. The closed expression for the delay time for incidence at critical energy show an excellent agreement with the numerical calculation. The three-dimensional analysis of delay times allow to find the final and definitive connection between wave packets reflected by a potential in quantum mechanics and optical beams reflected by a dielectric/air interface.

quant-ph↗

arXiv2020

Quasinormal modes in Lorentz violating black hole analogues

Analogue models of black holes typically have collective excitations with a dispersion relation that breaks the effective Lorentz symmetry at high energy. We investigate the consequences of such Lorentz violations on the quasinormal modes (QNMs) of the system, that is, the modes of energy dissipation. The model involves low frequency capillary-gravity waves (whose dispersion relation can be adjusted between sub- and superluminal modifications) around a draining vortex, which mimics a rotating black hole spacetime. For a subluminal/superluminal modification, the frequency and decay rate of co-rotating modes can be reduced/increased substantially, whilst counter-rotating modes are barely affected. A further consequence of the superluminal modification is that there are no corotating QNMs above a critical rotation and no counter-rotating ones below a critical rotation for strong enough Lorentz violations.

gr-qc↗