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The Conference on Quantum gases, fundamental interactions and cosmology- Second Edition (QFC 2019) will be held in Pisa from 23 to 25 October 2019.
Aim of the conference is to bring together scientists in both experimental and theoretical physics from the fields of ultracold quantum gases, fundamental interactions, and cosmology, with the aim of sharing and brainstorming on challenging open common problems, which can be zoomed in and out via a cross-disciplinary approach.
After QFC 2017, the Conference will be in its second edition of a series of appointments to be held each second year.
The mutual frontiers among these three apparently separated disciplines have been recently blossoming with new innovative, cutting edge research. To the well-established connections between cosmology and high-energy physics, current bright examples are the research activities in analogue gravity and superfluid analogies of cosmological phenomena, and of quantum simulations of lattice gauge theories using ultracold atoms in optical lattices. We intend to use this momentum and opportunities to establish strong collaborations among participants and leading groups to open new pathways leading to breakthrough results, in this spirit, the keynote speakers of the first edition, QFC2017, have been invited and have joined the Scientific Advisory Board.
Additional information on the spirit of the Conference can be found in the section of this website devoted to the first edition of QFC, QFC2017.
Q = Quantum Gases / F = Fundamental Physics / C = Cosmology¶
We propose a scheme for continuously measuring the evolving quantum phase of a collective spin composed of $N$ pseudospins. Quantum nondemolition measurements of a lossy cavity mode interacting with an atomic ensemble are used to directly probe the phase of the collective atomic spin without converting it into a population difference. Unlike traditional Ramsey measurement sequences, our scheme allows for real-time tracking of time-varying signals. As a bonus, spin-squeezed states develop naturally, providing real-time phase estimation significantly more precise than the standard quantum limit of $\Delta\phi_{\text{SQL}}=1/\sqrt{N}\,\text{rad}$.
Available as: Athreya Shankar, Graham P. Greve, Baochen Wu, James K. Thompson, and Murray Holland, Phys. Rev. Lett. 122, 233602 (2019).
We employ an effective field theory to study the detectability of sub-GeV dark matter through its interaction with the gapless excitations of superfluid He-4. In a quantum field theory language, the possible interactions between the dark matter and the superfluid phonon are solely dictated by symmetry. We compute the rate for the emission of one and two phonons, and show that these two observables combined allow for a large exclusion region for the dark matter masses. Our approach overcomes some limitations of standard techniques, and allows to easily compute differential distributions. The method presented here is extendible to different models of dark matter.
In the presence of external perturbations, astrophysical black holes (BHs) relax toward
a Kerr spacetime, as a consequence of the final state conjecture. During the relaxation
process (ringdown), BHs emit a spectrum given by a superposition of damped
sinusoids whose parameters are completely determined by the asymptotic BH mass and
spin. The ringdown emission is observable in binary black holes (BBH) coalescences by
means of the current and upcoming ground-based interferometers network. Employing
the known general relativistic predictions for the spectrum (both from linearized theory
and complete numerical solutions), it is possible to test for the existence of alternative
extreme compact objects, new particles surrounding BHs, hairy BHs or even wormholes.
In this talk, we present the first experimental implementation of BH spectroscopy,
test for the presence of multiple modes through Bayesian model comparison and
infer the transition time between the non-linear and the quasi-stationary regime of the
post-merger signal. We further place constraints on the excitation amplitudes of ringdown
modes and investigate classical bounds on the information emission rate of BHs.
Finally we show the constraints we can currently place on parametric deviations
from general relativity predictions for the spectrum
and how the increasing sensitivity of the current network of interferometers
will allow precision tests of general relativity in the ringdown regime.
In this talk, a series of experiments based on atom interferometry that can provide precision measurements and tests of gravitational interactions will be presented.
First, with rubidium atom interferometers, experiments aimed at the precision measurement of the Newtonian gravitational constant and at the test of the Equivalence Principle with quantum superpositions of internal states will be considered.
Second, with strontium atom interferometers, it will be shown that it is possible to implement gravimeters and gradiometers that can measure gravity. Finally, it will be shown that strontium interferometers can also be configured to operate on a single-photon transition, a condition that is interesting for the development of gravitational-wave detectors.
I will discuss how a class of Dark Energy models can be tested by studying the gravitational waves emitted during the ringdown phase after a black hole merger.
THANKS TO OPERA PRIMAZIALE AND COOPCULTURE
THANKS TO COMEL FOUNDATION
We study the collective dynamics of a clean Floquet system of cold atoms, numerically simulating two distinct realistic set-ups based on a regular chain of interacting Rydberg atoms driven by laser fields. In both cases, the population evolution and its Fourier spectrum display clear signatures of a discrete time crystal (DTC), exhibiting the appearance of a robust subharmonic oscillation which persists on a time scale increasing with the chain size, within a certain range of control parameters. We also characterize how the DTC stability is limited by dissipative processes, which are typically present in the system.
I will discuss, making use of on-shell amplitude methods, a possible ultraviolet completion of tree-level gravitational amplitudes. Contrary to "top-down" constructions like string theory, I will follow a "bottom-up" approach, solely based on fundamental properties (unitarity, locality and causality).
In corpuscular gravity black holes are condensates at the critical point, with a large number of bound gravitons and no central singularity. This innovative approach moves away from the semi-classical picture of quantum field theory on curved backgrounds and considers self-gravitating systems as truly quantum. We shall introduce a bootstrapped Newtonian gravitational potential which includes non-linearities inspired by general relativity and test the quantum corpuscular picture within this approach. Application to cosmology will also be briefly reviewed.
We discuss the problem of how Majorana mass terms can be generated in low-energy systems. We show that, while these terms imply the Majorana condition, the opposite is not always true when more than one flavour is involved. This is an important aspect for the low-energy realizations of the Majorana mass terms exploiting superfluid pairings, because in this case the Majorana condition is not implemented in the spinor space, but in an internal (flavour) space. Moreover, these mass terms generally involve opposite effective chiralities, similarly to a Dirac mass term. The net effect of these features is that the Majorana condition does not imply a Majorana mass term. Accordingly the obtained Majorana spinors, as well as the resulting symmetry breaking pattern and low-energy spectrum, are qualitatively different from the ones known in particle physics. This result has important phenomenological consequences, e.g. implies that these mass terms are unsuitable to induce an effective see-saw mechanism, proposed to give mass to neutrinos. Finally, we introduce and discuss schemes based on space-dependent pairings with nonzero total momentum to illustrate how genuine Majorana mass terms may emerge in low-energy quantum systems.
The idea that the area of a black hole (BH) horizon is quantized goes back to Bekenstein and Mukhanov [1,2,3]. The area is conjectured to be a multiple of the Planck area, but the constant of proportionality α is unknown and depends on the specific theory of quantum gravity. Expanding on this idea, recent studies [4,5] suggested that thermodynamic relations applied to an astrophysical Kerr BH would lead to a “quantized” quasinormal mode (QNM) spectrum that depends explicitly on α. In particular, the central frequencies of the ringdown signal from a BH (a superposition of QNMs) deviate measurably from GR predictions. We propose a method based on Bayesian inference designed to infer the properties of the remnant BHs from a time domain analysis of the ringdown part of the gravitational wave signal. We try to infer α from GW150914 and find that it is not yet measurable. From a population of simulated events observed by second generation instruments at design sensitivity, we investigate the measurability of α and assess potential stealth biases caused by ignoring the BH area quantisation in ringdown analyses.
References:
[1] J. D. Bekenstein, Lettere al Nuovo Cimento (1971-1985) 11, 467 (1974).
[2] V. F. Mukhanov, Pis. Eksp. Teor. Fiz. 44, 50 (1986).
[3] J. D. Bekenstein and V. F. Mukhanov, Phys. Lett. B 360, 7 (1995).
[4] J. D. Bekenstein, Phys. Rev. D 91, 124052 (2015).
[5] V. F. Foit and M. Kleban, Class. Quantum Grav. 36, 035006 (2019).
Hawking [1] predicted the emission of radiation by the event horizon of a black hole with a thermal spectrum whose temperature is given by the surface gravity. However, the temperature of emission is extremely low, making its direct detection an almost impossible task. As an alternative, Unruh [2] proposed that the analogue of Hawking radiation could be observed in the subsonic-supersonic interface of a flowing fluid.
Here, we report the first experimental observation of the emission of Hawking radiation with a thermal spectrum in an analogue black hole [3]. The experimental setup is an updated version of that used in previous measurements [4], based on a Bose-Einstein condensate of ultracold Rubidium atoms. The measured spectrum is in excellent agreement with a thermal spectrum with the measured Hawking temperature, given here by the gradients of the flow and sound velocities at the acoustic horizon. The experimental results are well reproduced by numerical simulations of the system.
[1] S. Hawking. Black hole explosions? Nature 248, 30–31 (1974).
[2] W. G. Unruh. Experimental black-hole evaporation? Phys. Rev. Lett. 46,
1351–1353 (1981).
[3] Juan Ramón Muñoz de Nova, Katrine Golubkov, Victor I. Kolobov and Jeff Steinhauer. Observation of thermal Hawking radiation and its temperature in an analogue black hole. Nature 569, 688–691 (2019)
[4] J. Steinhauer. Observation of quantum Hawking radiation and its entanglement in an analogue black hole. Nat. Phys. 12, 959–965 (2016).
A holographic model of QCD axion is presented. It describes a composite axion in the KSVZ class. Having a gravity dual, based on the Witten-Sakai-Sugimoto model, it is calculable in the strongly coupled regime and its UV completion is under control. Its basic properties are derived, including the low energy Lagrangian, from which the axion couplings to nucleons can be derived. Basic features in the deconfined phase are studied as well. In particular, the temperature dependence of the axion mass is extracted from the topological susceptibility.
Dipolar quantum gases are an extremely interesting playground for studies of quantum phase transitions in the presence of anisotropic, long-range interactions. We present here our recent observation that a dipolar quantum gas under proper conditions, due to the combination of the roton instability and the quantum stabilization, reveals supersolid properties [1]. We also show a study of collective oscillations in this system, which reflect the Goldstone modes associated with the spontaneous breaking of two continuous symmetries: the breaking of phase invariance, corresponding to the locking of the phase of the atomic wave functions at the origin of superfluid phenomena, and the breaking of translational invariance due to the lattice structure of the system. [2]. Our observations thus reveal that the dipolar supersolid has properties similar to those originally hypothesized for supersolid Helium.
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 hole evaporation induces a breakdown of the unitary quantum evolution leading to the so called information loss problem. Here we show that analogue gravity can provide an interesting perspective on the resolution of this problem, albeit the back reaction in analogue systems is not described by semiclassical Einstein equations. In particular, by looking at the simpler problem of cosmological particle creation, we show, in the context of BEC analogue gravity, that the emerging analogue geometry and quasi-particles have correlations due to the quantum nature of the atomic degrees of freedom underlying the emergent spacetime. As a consequence the quantum evolution is always unitary on the whole Hilbert space which cannot be exactly factorised a posteriori in geometry and quasi-particle components.
In analogy, in a black hole evaporation one should expect a continuous process creating correlations between the Hawking quanta and the microscopic quantum degrees of freedom of spacetime, implying so that only a full Quantum Gravity treatment would be able to resolve the information loss problem by proving the unitary evolution on the full Hilbert space.
Using relativistic hydrodynamic equations for polarized spin 1/2 particles we determine the space-time evolution of the spin polarization in the system. In our approach we use the forms of the energy-momentum and spin tensors based on de Groot, van Leeuwen, and van Weert. The calculations are done in a boost-invariant and transversely homogeneous setup. We present how the formalism of hydrodynamics with spin can be used for the determination of physical observables related to the spin polarization required for the modeling of the experimental data.
Studying solutions to Cosmological models through the Wheeler DeWitt (WDW) equation with deformed phase space could be interpreted as studying quantum effects to Cosmology. In this talk we make an analysis of scalar field cosmology
Bragg interferometers, operating using pseudospin-1/2 systems composed of two momentum states, have become a mature technology for precision measurements. State-of-the-art Bragg interferometers are rapidly surpassing technical limitations and are soon expected to operate near the projection noise limit set by uncorrelated atoms. Despite the use of large numbers of atoms, their operation is governed by single-atom physics. Motivated by recent proposals and demonstrations of Raman gravimeters in cavities, we propose a scheme to squeeze directly on momentum states that is capable of surpassing the projection noise limit in Bragg interferometers. We consider unique issues that arise when a spin squeezing protocol is applied to momentum pseudospins, such as the effects of the momentum width of the atomic cloud and the coupling to momentum states outside the pseudospin manifold. Our scheme promises to be feasible using current technology and is experimentally attractive because it requires no additional setup beyond what is required to operate Bragg interferometers in cavity geometries. We anticipate that our scheme will be an effective protocol for demonstrating appreciable levels of spin squeezing on momentum pseudospins.
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 quantized vortices can be attributed to a dispersive version of the ergoregion instability based on superradiant amplification in rotating spacetimes with no horizon.
Functional integration of a nonrelativistic scalar field is an elegant formulation of
Quantum Field Theory to study the Thermodynamics of Bose-Einstein condensates,
made with dilute ultracold atomic gases.
In a beyond mean field approach one can derive the static and dynamical properties
of a condensate confined in different geometries and with D-spatial dimensions.
In particular, we have applied this method recently to calculate the condensate fraction
and the superfluid one of a dilute Bose-Einstein condensate in three and in two dimensions.
In another work, we have studied the condensation of an interacting Bose gas
confined on a thin spherical shell, a work triggered by the forthcoming experiments
with bubble traps in microgravity settings.
The development of new laser-beam shaping methods is important in a variety of fields within optics, atomic physics and biophotonics. Spatial light modulators offer a highly versatile method of time-dependent beam shaping, based on imprinting a phase profile onto an incident laser beam which then determines the intensity in the far field, where the atoms are trapped. The calculation of the required phase is a well-known inverse problem, which can be tackled with different approaches. Our method based on conjugate gradient minimisation [1] not only allows the calculation of smooth and accurate intensity profiles suitable for trapping cold atoms, but can also be used to generate multi-wavelength traps [2] and for simultaneous control over both the intensity and the phase of the light [3], with exceptionally high reconstruction fidelity.
Here we describe our experimental progress of trapping ultracold atoms in arbitrary SLM-generated traps. In this experiment, we demonstrate two reservoirs connected by a channel, a guide interrupted by a junction, and a cross shape with a junction at the centre. The width of the junctions in these light patterns is determined by the diffraction limit of our optics. The cross pattern has a possible future application to the simulation of the topological Kondo effect with ultracold atoms [4].
[1] T Harte et al., Opt. Express 22, 26548 (2014).
[2] D. Bowman et al., Opt. Express 23, 8365 (2015).
[3] D. Bowman et al., Opt. Express 25, 11692 (2017).
[4] F. Buccheri et al., New J. Phys. 18, 075012 (2016).
The $SU(2)\bigotimes U(1) $ gauge model unifying
the electromagnetic and weak interactions, which is initially free of the auxiliary self-interaction scalar field, is developed. We narrow the initial symmetry up to $SU_L(2)\bigotimes U_R(1) $ by eliminating the right neutrinos current from the Lagrangian by means of the bosonization of this current into the $SU(2)$ current of the charged scalar field that leads to the $SU_L(2)\bigotimes U_R(1) $ gauge invariant Lagrangian containing the arbitrary $SU(2)$ invariant charged scalar field. The interaction of such a field with leptons and gauge fields provides them with the required masses, and mixes the lepton families under spontaneous breaking the symmetry of the scalar field. The obtained Pontecorvo-Maki-Nakagawa-Sakata matrix elements is entirely governed by both the coupling constant of leptons with the scalar field and the parameters of the spontaneously arisen vacuum.
We unify and generalize the notions of vacuum and amplitude in linear quantum field theory in curved spacetime. Crucially, the generalized notion admits a localization in spacetime regions and on hypersurfaces. The underlying concept is that of a Lagrangian subspace of the space of complexified germs of solutions of the equations of motion on hypersurfaces. Traditional vacua and traditional amplitudes correspond to the special cases of definite and real Lagrangian subspaces respectively. Further, we introduce both infinitesimal and asymptotic methods for vacuum selection that involve a localized version of Wick rotation.A recurrent theme is the occurrence of mixed vacua, where propagating solutions yield definite Lagrangian subspaces and evanescent solutions yield real Lagrangian subspaces. We provide examples that cover Minkowski space, Rindler space, Euclidean space and de Sitter space. A simple formula allows for the calculation of expectation values for observables in the generalized vacua.
In recent years, experiments using cold atoms in Rydberg states have emerged as a powerful platform for the quantum simulation of condensed matter Hamiltonians with extended-range interactions (ERI). This perspective for experimental realization has led to strong cross-fertilization between atomic and condensed matter physics, with considerable theoretical work being dedicated to the study of ERI Hamiltonians. As a result, several interesting equilibrium and out-of-equilibrium scenarios have been discovered in this kind of system.
I will present my numerical results for two classes of ERI Hamiltonians: namely, i) the determination [1] of the phase diagram of the Fendley-Sengupta-Sachdev model (recently realized via quantum simulation in Rydberg atom experiments) in the so-called doubly-blockaded regime, where the critical behavior of the system is still not fully understood, and ii) the demonstration of a phase transition between two supersolid states in an extended Bose-Hubbard model, whose interactions are of interest for experiments with atoms in Rydberg-dressed states.
[1] G. Giudici, AA, G. Magnifico, Z. Zeng, G. Giudice, T. Mendes-Santos, M. Dalmonte, Phys. Rev. B 99, 094434 (2019)
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. Short-range interactions reveal to build up metrologically promising entanglement in the XY-ferromagnetic and cluster ordering, the cluster physics being unexplored so far.
THANKS TO PALAZZO BLU