arXiv subjects

Alessandro Zenesini

Publications and source records attributed to Alessandro Zenesini.

At least 19 recordsLinked to original sources

arXiv2025

Observation of Temperature Effects on False Vacuum Decay in Atomic Quantum Gases

Temperature plays a crucial role in metastable phenomena, not only by contributing to determine the state (phase) of a system, but also ruling the decay probability to more stable states. Such a situation is encountered in many different physical systems, ranging from chemical reactions to magnetic structures. The characteristic decay timescale is not always straightforward to estimate since it depends on the microscopic details of the system. A paradigmatic example in quantum field theories is the decay of the false vacuum, manifested via the nucleation of bubbles. In this paper, we measure the temperature dependence of the timescale for the false vacuum decay mechanism in an ultracold atomic quantum spin mixture which exhibits ferromagnetic properties. Our results show that the false vacuum decay rate scales with temperature as predicted by the finite-temperature extension of the instanton theory, and confirm atomic systems as an ideal platform where to study out-of-equilibrium field theories.

cond-mat.quant-gas↗

arXiv2024

Progress toward a zero-magnetic-field environment for ultracold-atom experiments

The minimization of the magnetic field plays a crucial role in ultracold gas research. For instance, the contact interaction dominates all the other energy scales in the zero magnetic field limit, giving rise to novel quantum phases of matter. However, lowering magnetic fields well below the mG level is often challenging in ultracold gas experiments. In this article, we apply Landau-Zener spectroscopy to characterize and reduce the magnetic field on an ultracold gas of sodium atoms to a few tens of μG. The lowest magnetic field achieved here opens to observing novel phases of matter with ultracold spinor Bose gases.

cond-mat.quant-gas↗

arXiv2024

Ultracold atomic spin mixtures in ultrastable magnetic field environments

Ultracold atomic spin mixtures develop rich and intriguing magnetic properties when an external radiation coherently couples different spin states. In particular, the coupled mixture may acquire a critical behavior when the spin interactions equal the coupling energy. However, atomic mixtures generally feature a relatively high sensitivity to magnetic fields that can set a limitation to the observable phenomena. In this article, we present an overview of experimental studies of magnetism based on superfluid multicomponent gases in an ultrastable magnetic field environment, which recently became available.

cond-mat.quant-gas↗

arXiv2023

Quantum-torque-induced breaking of magnetic interfaces in ultracold gases

A rich variety of physical effects in spin dynamics arises at the interface between different magnetic materials. Engineered systems with interlaced magnetic structures have been used to implement spin transistors, memories and other spintronic devices. However, experiments in solid state systems can be difficult to interpret because of disorder and losses. Here, we realize analogues of magnetic junctions using a coherently-coupled mixture of ultracold bosonic gases. The spatial inhomogeneity of the atomic gas makes the system change its behavior from regions with oscillating magnetization -- resembling a magnetic material in the presence of an external transverse field -- to regions with a defined magnetization, as in magnetic materials with a ferromagnetic anisotropy stronger than external fields. Starting from a far-from-equilibrium fully polarized state, magnetic interfaces rapidly form. At the interfaces, we observe the formation of short-wavelength magnetic waves. They are generated by a quantum torque contribution to the spin current and produce strong spatial anticorrelations in the magnetization. Our results establish ultracold gases as a platform for the study of far-from-equilibrium spin dynamics in regimes that are not easily accessible in solid-state systems.

cond-mat.quant-gas↗

arXiv2023

Observation of false vacuum decay via bubble formation in ferromagnetic superfluids

In quantum field theory, the decay of an extended metastable state into the real ground state is known as ``false vacuum decay'' and it takes place via the nucleation of spatially localized bubbles. Despite the large theoretical effort to estimate the nucleation rate, experimental observations were still missing. Here, we observe bubble nucleation in isolated and highly controllable superfluid atomic systems, and we find good agreement between our results, numerical simulations and instanton theory opening the way to the emulation of out-of-equilibrium quantum field phenomena in atomic systems.

hep-ph↗

arXiv2023

Ferromagnetism in an extended coherently-coupled atomic superfluid

Ferromagnetism is an iconic example of a first-order phase transition taking place in spatially extended systems and is characterized by hysteresis and the formation of domain walls. In this paper we demonstrate that an extended atomic superfluid in the presence of a coherent coupling between two internal states exhibits a quantum phase transition from a para- to a ferromagnetic state. The nature of the transition is experimentally assessed by looking at the phase diagram as a function of the control parameters, at hysteresis phenomena, at the magnetic susceptibility and the magnetization fluctuations around the critical point. We show that the observed features are in good agreement with mean-field calculations. Additionally, we develop experimental protocols to deterministically generate domain walls that separate spatial regions of opposite magnetization in the ferromagnetic state. Thanks to the enhanced coherence properties of our atomic superfluid system compared to standard condensed matter systems, our results open the way towards the study of different aspects of the relaxation dynamics in isolated coherent many-body quantum systems.

cond-mat.quant-gas↗

arXiv2022

Hyperfine dependent atom-molecule loss analyzed by the analytic solution of few-body loss equations

We prepare mixtures of ultracold $^{39}$K atoms in various hyperfine spin states and $^{23}$Na$^{39}$K molecules in an optical dipole trap at a fixed magnetic field and study inelastic two-body atom-molecule collisions. We observe atom-molecule losses that are hyperfine dependent with a two-body loss rate far below the universal limit. We analyze the two-body loss dynamics based on the derivation of general and easy applicable analytic solutions for the differential equations describing the loss of an arbitrary number $γ$ of particles in a single collisional event.

physics.atom-ph↗

arXiv2022

Observation of Massless and Massive Collective Excitations with Faraday Patterns in a Two-Component Superfluid

We report on the experimental measurement of the dispersion relation of the density and spin collective excitation modes in an elongated two-component superfluid of ultracold bosonic atoms. Our parametric spectroscopic technique is based on the external modulation of the transverse confinement frequency, leading to the formation of density and spin Faraday waves. We show that the application of a coherent coupling between the two components reduces the phase symmetry and gives a finite mass to the spin modes.

cond-mat.quant-gas↗

arXiv2020

An Ultracold Gas of Bosonic $^{23}\textrm{Na}^{39}\textrm{K}$ Ground-State Molecules

We report the creation of ultracold bosonic dipolar $^{23}\textrm{Na}^{39}\textrm{K}$ molecules in their absolute rovibrational ground state. Starting from weakly bound molecules immersed in an ultracold atomic mixture, we coherently transfer the dimers to the rovibrational ground state using an adiabatic Raman passage. We analyze the two-body decay in a pure molecular sample and in molecule-atom mixtures and find an unexpectedly low two-body decay coefficient for collisions between molecules and $^{39}\textrm{K}$ atoms in a selected hyperfine state. The preparation of bosonic $^{23}\textrm{Na}^{39}\textrm{K}$ molecules opens the way for future comparisons between fermionic and bosonic ultracold ground-state molecules of the same chemical species.

cond-mat.quant-gas↗

arXiv2019

A pathway to ultracold bosonic $^{23}\textrm{Na}^{39}\textrm{K}$ ground state molecules

We spectroscopically investigate a pathway for the conversion of $^{23}\textrm{Na}^{39}\textrm{K}$ Feshbach molecules into rovibronic ground state molecules via STImulated Raman Adiabatic Passage (STIRAP). Using photoassociation spectroscopy from the diatomic scattering threshold in the $a^3Σ^+$ potential, we locate the resonantly mixed electronically excited intermediate states $|B^1Π, v=8\rangle$ and $|c^3Σ^+, v=30\rangle$ which, due to their singlet-triplet admixture, serve as an ideal bridge between predominantly $a^3Σ^+$ Feshbach molecules and pure $X^1Σ^+$ ground state molecules. We investigate their hyperfine structure and present a simple model to determine the singlet-triplet coupling of these states. Using Autler-Townes spectroscopy, we locate the rovibronic ground state of the $^{23}\textrm{Na}^{39}\textrm{K}$ molecule ($|X^1Σ^+, v=0, N=0\rangle$) and the second rotationally excited state $N=2$ to unambiguously identify the ground state. We also extract the effective transition dipole moment from the excited to the ground state. Our investigations result in a fully characterized scheme for the creation of ultracold bosonic $^{23}\textrm{Na}^{39}\textrm{K}$ ground state molecules.

cond-mat.quant-gas↗

arXiv2019

Beyond Born-Oppenheimer approximation in ultracold atomic collisions

We report on deviations beyond the Born-Oppenheimer approximation in the potassium inter-atomic potentials. Identifying three up-to-now unknown $d$-wave Feshbach resonances, we significantly improve the understanding of the $^{39}$K inter-atomic potentials. Combining these observations with the most recent data on known inter- and intra-isotope Feshbach resonances, we show that Born-Oppenheimer corrections can be determined from atomic collisional properties alone and that significant differences between the homo- and heteronuclear case appear.

physics.atom-ph↗

arXiv2019

Formation of ultracold weakly bound dimers of bosonic $^{23}\textrm{Na}^{39}\textrm{K}$

We create weakly bound bosonic $^{23}\textrm{Na}^{39}\textrm{K}$ molecules in a mixture of ultracold $^{23}\textrm{Na}$ and $^{39}\textrm{K}$. The creation is done in the vicinity of a so far undetected Feshbach resonance at about $196\,\text{G}$ which we identify in this work by atom-loss spectroscopy. We investigate the involved molecular state by performing destructive radio frequency binding energy measurements. For the constructive molecule creation we use radio frequency pulses with which we assemble up to $6000$ molecules. We analyze the molecule creation efficiency as a function of the radio frequency pulse duration and the atom number ratio between $^{23}\textrm{Na}$ and $^{39}\textrm{K}$. We find an overall optimal efficiency of $6\,\%$ referring to the $^{39}\textrm{K}$ atom number. The measured lifetime of the molecules in the bath of trapped atoms is about $0.3\,\textrm{ms}$.

cond-mat.quant-gas↗

arXiv2019

Feshbach resonances in $^{23}\mathrm{Na}+$$^{39}\mathrm{K}$ mixtures and refined molecular potentials for the NaK molecule

We present a detailed study of interspecies Feshbach resonances of the bosonic $^{23}\mathrm{Na}+$$^{39}\mathrm{K}$ mixture for magnetic fields up to $750 \, \mathrm{G}$ in various collision channels. A total of fourteen Feshbach resonances are reported, as well as four zero crossings of the scattering length and three inelastic two-body loss features. We use the observed magnetic field locations of the resonant features together with the known data on $^{23}\mathrm{Na}+$$^{40}\mathrm{K}$ to refine the singlet and triplet ground state potentials of NaK and achieve a consistent description of Feshbach resonances for both, the Bose-Bose mixture of $^{23}\mathrm{Na}+$$^{39}\mathrm{K}$ as well as the Bose-Fermi mixture of $^{23}\mathrm{Na}+$$^{40}\mathrm{K}$.

physics.atom-ph↗

arXiv2019

The mixing-demixing phase diagram of ultracold heteronuclear mixtures in a ring trimer

We derive the complete mixing-demixing phase-diagram relevant to a bosonic binary mixture confined in a ring trimer and modeled within the Bose-Hubbard picture. The mixing properties of the two quantum fluids, which are shown to be strongly affected by the fragmented character of the confining potential, are evaluated by means of a specific indicator imported from Statistical Thermodynamics and are shown to depend only on two effective parameters incorporating the asymmetry between the heteronuclear species. To closely match realistic experimental conditions, our study is extended also beyond the pointlike approximation of potential wells by describing the systems in terms of two coupled Gross-Pitaevskii equations. The resulting mean-field analysis confirms the rich scenario of mixing-demixing transitions of the mixture and also constitutes an effective springboard towards a viable experimental realization. We additionally propose an experimental realization based on a realistic optical-tweezers system and on mixtures of bosonic $^{23}\mathrm{Na}$ and $^{39}\mathrm{K}$, thanks to the large tunability of their intra- and inter-species scattering lengths.

cond-mat.quant-gas↗

arXiv2018

Feshbach spectroscopy and dual-species Bose-Einstein condensation of $^{23}\mathrm{Na}-$$^{39}\mathrm{K}$ mixtures

We present measurements of interspecies Feshbach resonances and subsequent creation of dual-species Bose-Einstein condensates of $^{23}\mathrm{Na}$ and $^{39}\mathrm{K}$. We prepare both optically trapped ensembles in the spin state $\left|f = 1,m_{f}=-1\right\rangle$ and perform atom loss spectroscopy in a magnetic field range from 0 to $700 \, \mathrm{G}$. The observed features include several s-wave poles and a zero crossing of the interspecies scattering length as well as inelastic two-body contributions in the $\mathcal{M} = m_{\mathrm{Na}}+m_{\mathrm{K}} = -2$ submanifold. We identify and discuss the suitability of different magnetic field regions for the purposes of sympathetic cooling of \K and achieving dual-species degeneracy. Two condensates are created simultaneously by evaporation at a magnetic field of about $150 \, \mathrm{G}$, which provides sizable intra- and interspecies scattering rates needed for fast thermalization. The impact of the differential gravitational sag on the miscibility criterion for the mixture is discussed. Our results serve as a promising starting point for the magnetoassociation into quantum degenerate $^{23}\mathrm{Na}^{39}\mathrm{K}$ Feshbach molecules.

cond-mat.quant-gas↗

arXiv2014

Resonant atom-dimer collisions in cesium: Testing universality at positive scattering lengths

We study the collisional properties of an ultracold mixture of cesium atoms and dimers close to a Feshbach resonance near 550G in the regime of positive $s$-wave scattering lengths. We observe an atom-dimer loss resonance that is related to Efimov's scenario of trimer states. The resonance is found at a value of the scattering length that is different from a previous observation at low magnetic fields. This indicates non-universal behavior of the Efimov spectrum for positive scattering lengths. We compare our observations with predictions from effective field theory and with a recent model based on the van der Waals interaction. We present additional measurements on pure atomic samples in order to check for the presence of a resonant loss feature related to an avalanche effect as suggested by observations in other atomic species. We could not confirm the presence of such a feature.

cond-mat.quant-gas↗

arXiv2013

Feshbach resonances, weakly bound molecular states and coupled-channel potentials for cesium at high magnetic fields

We explore the scattering properties of ultracold ground-state Cs atoms at magnetic fields between 450 G (45 mT) and 1000 G. We identify 17 new Feshbach resonances, including two very broad ones near 549 G and 787 G. We measure the binding energies of several different dimer states by magnetic field modulation spectroscopy. We use least-squares fitting to these experimental results, together with previous measurements at lower field, to determine a new 6-parameter model of the long-range interaction potential, designated M2012. Coupled-channels calculations using M2012 provide an accurate mapping between the s-wave scattering length and the magnetic field over the entire range of fields considered. This mapping is crucial for experiments that rely on precise tuning of the scattering length, such as those on Efimov physics.

cond-mat.quant-gas↗

arXiv2009

Exploring dynamic localization with a Bose-Einstein condensate

We report on the experimental observation of dynamic localization of a Bose-Einstein condensate in a shaken optical lattice, both for sinusoidal and square-wave forcing. The formulation of this effect in terms of a quasienergy band collapse, backed by the excellent agreement of the observed collapse points with the theoretical predictions, suggests the feasibility of systematic quasienergy band engineering.

cond-mat.other↗