arXiv subjects

Sergio Gaudio

Publications and source records attributed to Sergio Gaudio.

9 recordsLinked to original sources

arXiv2026

The Quantum Noise Fraction and the addressable fraction in High-Frequency Gravitational Wave Detection

The quantum noise fraction $\beta$ -- the share of a detector's noise power that is quantum in origin -- bounds the sensitivity gain from any quantum technique at $\mathcal{E}_{\max}=1/\sqrt{1-\beta}$. In the kHz--GHz band the readout is a bosonic mode and $\beta=1/(2\bar{n}_{\rm th}+1+\nu)$, so quantum noise dominates only below a thermal frontier $k_BT\ln 3=\hbar\omega$ (229 MHz at 10 mK) that governs mechanical resonators and electromagnetic cavities alike. On a multimode acoustic antenna the frontier is directly observable: the logarithmic slope of $\sqrt{S_hQ}$ along the odd-overtone comb increases by exactly one half across it, for any dependence of the quality factor on overtone number. Crossing the frontier costs more in classical sensitivity than quantum enhancement returns. For a GHz bulk acoustic wave mode at 10 mK, $\beta=0.984$, but the ceiling is unattainable: with intrinsic damping the zero-point term is the bath's force noise, fixed by the fluctuation--dissipation theorem. The addressable fraction $\beta_a$ measures what a quantum technique can actually remove: at the standard quantum limit $\beta=0.992$ yet $\beta_a=0.496$, an available factor 1.41 against a ceiling of 11.0. The remaining gap to the big-bang-nucleosynthesis bound is classical.

gr-qc↗

arXiv2026

Fundamental Limits of Quantum Sensors for Gravitational Wave Detection

Recent advances in quantum sensing---optical clocks, frequency-dependent squeezing below the standard quantum limit, and quantum magnetometers---raise a natural question: can these technologies detect gravitational waves directly, or enhance existing detectors? We show that the answer is set primarily by the \emph{coupling mechanism} between wave and sensor. From the tidal Hamiltonian in Fermi normal coordinates we identify three physically distinct mechanisms by which a gravitational wave couples directly to a quantum system, and derive their transducer gains within linearized general relativity and non-relativistic quantum mechanics. Internal atomic coupling yields a transducer gain $G_A = 2.4\times 10^{-20}$, with vanishing first-order energy shifts for all $J=0$ clock states---a $\sim\!10^{35}$ deficit relative to laser interferometry. Center-of-mass (Doppler) coupling reaches strain sensitivities of $\sim\!10^{-18}$, still $10^4$ above LISA requirements. Only light-propagation coupling provides the enormous transducer gain that makes laser and atom interferometry viable. For detectors of this third kind we quantify the quantum enhancement accessible through the noise architecture: LISA's noise budget is predominantly classical, capping the combined enhancement at $\mathcal{E}\approx 1.04$, while ground-based detectors in the shot-noise-dominated regime achieve $\mathcal{E}=1.6$--$2.1$. Atom interferometers exploit the same mechanism to target the 0.01--10~Hz band.

gr-qc↗

arXiv2020

Improving the background of gravitational-wave searches for core collapse supernovae: A machine learning approach

Based on the prior O1-O2 observing runs, about 30% of the data collected by Advanced LIGO and Virgo in the next observing runs are expected to be single-interferometer data, i.e., they will be collected at times when only one detector in the network is operating in observing mode. Searches for gravitational wave signals from supernova events do not rely on matched filtering techniques because of the stochastic nature of the signals. If a Galactic supernova occurs during single-interferometer times, separation of its unmodelled gravitational-wave signal from noise will be even more difficult due to lack of coherence between detectors. We present a novel machine learning method to perform single-interferometer supernova searches based on the standard LIGO-Virgo coherentWave-Burst pipeline. We show that the method may be used to discriminate Galactic gravitational-wave supernova signals from noise transients, decrease the false alarm rate of the search, and improve the supernova detection reach of the detectors.

astro-ph.IM↗

arXiv2007

Many body exchange effects close to the s-wave Feshbach resonance in two-component Fermi systems: Is a triplet superfluid possible?

We suggest that the exchange fluctuations close to a Feshbach resonance in a two-component Fermi gas can result in an effective p-wave attractive interaction. On the BCS side of a Feshbach resonance, the magnitude of this effective interaction is comparable to the s-wave interaction, therefore leading to a possible spin-triplet superfluid in the range of temperatures of actual experiments. We also show that the particle-hole exchange fluctuations introduce an effective scattering length which does not diverge, as the standard mean-field one does. Finally, using the effective interaction quantities we are able to model the molecular binding energy on the BEC side of the resonance.

cond-mat.other↗

arXiv2007

Fermi liquid behavior and Luttinger's theorem close to a diverging scattering length

Based on the results obtained in a previous paper (S. Gaudio et al., cond-mat/0505309}, we derive the thermodynamic properties of a Fermi gas, deep into the quantum degenerate regime. We show that, if Luttinger's theorem holds, a first order phase transition occurs in the normal phase as a function of the interaction strength, U. We also show that a volume change occurs at finite temperatures from the BEC to the BCS side of a diverging s-wave scattering length, in the normal phase. The transition has an end point above the BCS critical temperature. Also we show that a paramagnetic system in equilibrium, close to the divergence of the scattering length, on the negative side, screens out any applied magnetic field.

cond-mat.str-el↗

arXiv2007

Acoustic attenuation probe for fermion superfluidity in ultracold atom gases

Dilute gas Bose-Einstein condensates (BEC's), currently used to cool fermionic atoms in atom traps, can also probe the superfluidity of these fermions. The damping rate of BEC-acoustic excitations (phonon modes), measured in the middle of the trap as a function of the phonon momentum, yields an unambiguous signature of BCS-like superfluidity, provides a measurement of the superfluid gap parameter and gives an estimate of the size of the Cooper-pairs in the BEC-BCS crossover regime. We also predict kinks in the momentum dependence of the damping rate which can reveal detailed information about the fermion quasi-particle dispersion relation.

cond-mat.other↗

arXiv2006

Acoustic attenuation rate in the Fermi-Bose model with a finite-range fermion-fermion interaction

We study the acoustic attenuation rate in the Fermi-Bose model describing a mixtures of bosonic and fermionic atom gases. We demonstrate the dramatic change of the acoustic attenuation rate as the fermionic component is evolved through the BEC-BCS crossover, in the context of a mean-field model applied to a finite-range fermion-fermion interaction at zero temperature, such as discussed previously by M.M. Parish et al. [Phys. Rev. B 71, 064513 (2005)] and B. Mihaila et al. [Phys. Rev. Lett. 95, 090402 (2005)]. The shape of the acoustic attenuation rate as a function of the boson energy represents a signature for superfluidity in the fermionic component.

cond-mat.other↗

arXiv2005

Density and spin response functions in ultracold fermionic atom gases

We propose a new method of detecting the onset of superfluidity in a two-component ultracold fermionic gas of atoms governed by an attractive short-range interaction. By studying the two-body correlation functions we find that a measurement of the momentum distribution of the density and spin response functions allows one to access separately the normal and anomalous densities. The change in sign at low momentum transfer of the density response function signals the transition between a BEC and a BCS regimes, characterized by small and large pairs, respectively. This change in sign of the density response function represents an unambiguous signature of the BEC to BCS crossover. Also, we predict spin rotational symmetry-breaking in this system.

cond-mat.other↗

arXiv2004

Zero sound in a single component fermion - Bose Einstein Condensate mixture

The resonant dynamics of mediated interactions supports zero-sound in a cold atom degenerate mixture of a single component fermion gas and a Bose-Einstein condensate (BEC). We characterize the onset of instability in the phase separation of an unstable mixture and we find a rich collective mode structure for stable mixtures with one undamped mode that exhibits an avoided crossing and a Landau-damped mode that terminates.

cond-mat.stat-mech↗