arXiv subjects

Thomás Fogarty

Publications and source records attributed to Thomás Fogarty.

At least 19 recordsLinked to original sources

arXiv2026

Boosting the performance of a Lipkin-Meshkov-Glick quantum battery via symmetry-breaking quenches or a single-mode bosonic charger

We explore the operation of quantum batteries in the Lipkin-Meshkov-Glick (LMG) model, when they are charged either through a sudden quench in the magnetic field strength or by coupling them to a single-mode bosonic charger. Through initializing the battery in either the symmetric or broken symmetry phases of the LMG model we analyze how the different spectral properties can affect the performance of both the charging and discharging of the battery. In particular, we show that by quenching the magnetic field strength from the symmetric phase to the broken phase, we can achieve a significant enhancement in stored energy, as well as stable and efficient ergotropy extraction. Similar observations can be made when introducing weak coupling between the battery with the bosonic charger, while the amount of stored work and ergotropy saturate at strong coupling. These findings emphasize the importance of the magnetic field dynamics or environmental coupling in optimizing charging performance, which could lead to practical applications in quantum energy storage.

quant-ph↗

arXiv2026

Enhancing ultracold atomic batteries using many-body resonances

We study the charging performance of a one-dimensional many-body bosonic quantum battery coupled to a harmonic-oscillator charger. In the weak-coupling regime, we show that the battery--charger dynamics can be accurately described by an effective two-level model, which predicts the resonance condition, optimal charging time, stored work, ergotropy, and charging power. We demonstrate that tuning the charger frequency to the interaction-shifted resonance enables complete energy transfer and maximum extractable work. A many-body charging advantage is observed: increasing the particle number reduces the quantum speed-limit time and enhances the charging power with a characteristic $\sqrt{N_B}$ scaling. We further introduce a decomposition of the switching cost into resonance-shifting and excitation contributions, allowing us to quantify the energetic overhead associated with the charging process. Owing to the small charging cost relative to the available charger energy, stronger battery--charger couplings can be employed to significantly boost the charging power while maintaining a low excitation cost. Our results highlight the role of resonance engineering and many-body effects in designing fast and efficient quantum batteries, and provide a promising route toward their realization in ultracold-atom platforms.

quant-ph↗

arXiv2026

Mobile impurity interacting with a Hubbard chain and the role of Friedel oscillations

This work examines a mobile impurity interacting with a bath of a few spin-$\uparrow$ and spin-$\downarrow$ fermions in a small one-dimensional open lattice system. We study ground-state properties using the exact diagonalization method, where the system is modeled by a three-component Fermi Hubbard Hamiltonian. We find that in addition to the standard phase separation between a strongly repulsive impurity and the bath, a strongly-attractive impurity also phase separates with the fermionic holes due to the particle-hole symmetry. Furthermore, we find that the impurity can show an oscillatory pattern in its density for intermediate attractive and repulsive bath-impurity interactions, which are induced by Friedel oscillations in the finite-size fermionic bath. This rich behavior of the impurity could be probed with fermionic ultracold mixtures in optical lattices.

cond-mat.quant-gas↗

arXiv2026

Roadmap on Quantum Thermodynamics

The last two decades has seen quantum thermodynamics become a well established field of research in its own right. In that time, it has demonstrated a remarkably broad applicability, ranging from providing foundational advances in the understanding of how thermodynamic principles apply at the nano-scale and in the presence of quantum coherence, to providing a guiding framework for the development of efficient quantum devices. Exquisite levels of control have allowed state-of-the-art experimental platforms to explore energetics and thermodynamics at the smallest scales which has in turn helped to drive theoretical advances. This Roadmap provides an overview of the recent developments across many of the field's sub-disciplines, assessing the key challenges and future prospects, providing a guide for its near term progress.

quant-ph↗

arXiv2025

Droplet-gas phases and their dynamical formation in particle imbalanced mixtures

We explore the ground state phase diagram and nonequilibrium dynamics of genuine two-component particle-imbalanced droplets in both isotropic and anisotropic three-dimensional confinements. A gradual transition from mixed droplet-gas to gas configurations is revealed as the average intercomponent attraction decreases or the transverse confinement becomes tighter. Within the mixed structures, a specific majority fragment binds to the minority droplet, satisfying the density ratio locking condition, while the remaining atoms are in a gas state. Our extended Gross-Pitaevskii numerical results are corroborated by a suitable variational approximation capturing the shape and characteristics of droplet-gas fragments. The tunability of the relatively low gas fraction is showcased through parametric variations of the atom number, the intercomponent imbalance, the trap aspect ratio, or the radius of a box potential. To validate the existence and probe the properties of these exotic phases, we simulate the standard time-of-flight and radio frequency experimental techniques. These allow to dynamically identify the resilience of the droplet fragment and the expansion of the gas fraction. Our results, amenable to current experimental cold atom settings, are expected to guide forthcoming investigations aiming to reveal unseen out-of-equilibrium droplet dynamics.

cond-mat.quant-gas↗

arXiv2025

Correlated decoherence and thermometry with mobile impurities in a 1D Fermi gas

We theoretically investigate the correlated decoherence dynamics of two mobile impurities trapped within a gas of ultracold fermionic atoms. We use a mean-field approximation to self-consistently describe the effect of impurity-gas collisions on impurity motion, while decoherence of the impurities' internal state is computed exactly within a functional determinant approach. At equilibrium, we find that the impurities undergo bath-induced localisation as the impurity-gas interaction strength is increased. We then study the non-equilibrium dynamics induced by a sudden change of the impurities' internal state, which can be experimentally probed by Ramsey interferometry. Our theoretical approach allows us to investigate the effect of impurity motion on decoherence dynamics, finding strong deviations from the universal behaviour associated with Anderson's orthogonality catastrophe when the mass imbalance between impurity and gas atoms is small. Finally, we show that mobile impurities can be used as thermometers of their environment and that bath-mediated correlations can be beneficial for thermometric performance at low temperatures, even in the presence of non-trivial impurity motion. Our results showcase the interesting open quantum dynamics of mobile impurities dephasing in a common environment, and could help provide more precise temperature estimates of ultracold fermionic mixtures.

cond-mat.quant-gas↗

arXiv2025

Condensate-mediated dimerization of impurities in atomic BECs

We show that strongly correlated impurities confined in an optical lattice can form localized, molecule-like dimer states in the presence of a Bose-Einstein condensate (BEC). By systematically studying the effect of the lattice potential on this mixture, we reveal the two roles of the condensate in assisting the formation of dimerized impurities: mediating the attractive interaction among impurities and rescaling the lattice potential of impurities. At strong coupling between the impurities and the condensate, the two mechanisms cooperate to induce a structural transition, resulting in the rearrangement of dimers. We also show that the nonequilibrium dynamics of these states can be interpreted as a dimerized soliton train.

cond-mat.quant-gas↗

arXiv2025

Quantum correlations and spatial localization in trapped one-dimensional ultra-cold Bose-Bose-Bose mixtures

We systematically investigate and illustrate the complete ground-state phase diagram for a one-dimensional, three-species mixture of a few repulsively interacting bosons trapped harmonically. To numerically obtain the solutions to the many-body Schrödinger equation, we employ the improved Exact Diagonalization method [T. D. Anh-Tai {\it et al.}, SciPost Physics 15, 048 (2023)], which is capable of treating strongly-correlated few-body systems from first principles in an efficiently truncated Hilbert space. We present our comprehensive results for all possible combinations of intra- and interspecies interactions in the extreme limits that are either the ideal limit ($g=0$) or close to the hard-core limit ($g\to\infty$). These results show the emergence of unique ground-state properties related to correlations, coherence and spatial localization stemming from strongly repulsive interactions.

cond-mat.quant-gas↗

arXiv2025

Leveraging quantum statistics to enhance heat engines

A key focus of designing quantum thermal devices is the potential advantage that can be gleaned from genuine quantum effects when compared to classical devices. The recent experimental realization of the Pauli engine, where energy is extracted via changes in particle statistics as an alternative to conventional heat sources has opened new avenues of research where quantum statistics can be considered as a thermodynamic resource. In this work we propose hybrid quantum heat engines which utilize additional strokes that change the single particle statistics between bosonic and fermionic descriptions during the cycle. To accomplish this we consider the 1D Lieb Liniger gas whereby the s wave interactions can be tuned between the non interacting and the hard core limit, which are described by bosonic and fermionic statistics respectively. We show that by suitably choosing where to implement these statistical strokes during an Otto like cycle, the efficiency and work output can be significantly enhanced when compared to fully bosonic or fully fermionic engines. Furthermore, in the degenerate regime our engine can operate at the Carnot efficiency, due to the interplay between the different contributions of heat and work induced by the statistical strokes. Finally, we highlight how our thermodynamic cycles can realize other thermal operations,such as refrigerators, promising similar statistical enhancements for a wide range of temperatures.

quant-ph↗

arXiv2025

Phases and dynamics of quantum droplets in the crossover to two-dimensions

We explore the ground states and dynamics of ultracold atomic droplets in the crossover region from three to two dimensions by solving the two-dimensional and the quasi two-dimensional extended Gross-Pitaevskii equations numerically and with a variational approach. By systematically comparing the droplet properties, we determine the validity regions of the pure two-dimensional description, and therefore the dominance of the logarithmic nonlinear coupling, as a function of the sign of the averaged mean-field interactions and the size of the transverse confinement. One of our main findings is that droplets become substantially extended upon transitioning from negative-to-positive averaged mean-field interactions. This is accompanied by a significant reduction of their binding energies which are approximately inversely proportional to the square of their size. To explore fundamental dynamical properties in the crossover region, we study interaction quenches and show that the droplets perform a periodic breathing motion for modest quench strengths, while larger quench amplitudes lead to continuous expansion exhibiting density ring structures. We also showcase that it is possible to form complex bulk and surface density patterns in anisotropic geometries following the quench. Since we are working with realistic parameters, our results can directly facilitate future experimental realizations.

cond-mat.quant-gas↗

arXiv2025

Bose-Fermi $N$-polaron state emergence from correlation-mediated blocking of phase separation

We study $N$ fermionic impurities in a one-dimensional lattice bosonic bath at unit filling. Using DMRG and mixed boundary conditions-periodic for bosons, open for fermions -- we find an $N$-polaron ground state replacing phase separation at high interspecies repulsion. This tightly bound state of clustered particles emerges due to strong impurity-bath correlations, which induce large impurity-impurity correlations that we quantify via the von Neumann entropy and bipartite mutual information, respectively. This system also reveals a fermionic self-localization effect from a Mott insulator background due to local correlations between the impurities and the bath. The growth of long-range correlations breaks this Mott phase, resulting in the transition to impurity clusters delocalized along the system. Finally, we show that there is a critical impurity number, which depends on intraspecies bosonic interaction, beyond which phase separation is recovered.

cond-mat.quant-gas↗

arXiv2025

Dynamical invariant based shortcut to equilibration in open quantum systems

We propose using the dynamical invariant also known as the Lewis-Riesenfeld invariant, to speed-up the equilibration of a driven open quantum system. This allows us to reverse engineer the time-dependent master equation that describes the dynamics of the open quantum system and systematically derive a protocol that realizes a shortcut to equilibration. The method does not require additional constraints on the timescale of the dynamics beside the Born-Markov approximation and can be generically applied to boost single particle quantum engines significantly. We demonstrate it with the damped harmonic oscillator, and show that our protocol can achieve a high-fidelity control in shorter timescales than simple non-optimized protocols. We find that the system is heated during the dynamics to speed-up the equilibration, which can be considered as an analogue of the Mpemba effect in quantum control.

quant-ph↗

arXiv2024

Quench dynamics in topologically non-trivial quantum many-body systems

We investigate the nonequilibrium dynamics of a groundstate fermionic many body gas subjected to a quench between parameter regimes of a topologically nontrivial Hamiltonian. By focusing on the role of the chiral edge states inherent to the system, we calculate the many body overlap and show that the characteristic monotonic decay of the orthogonality catastrophe with increasing system size is notably altered. Specifically, we demonstrate that the dynamics are governed not solely by the total particle number but rather by the number of occupied single particle edge states. This behavior is further explained through an analysis of the full work probability distribution, providing a deeper understanding of the system's dynamics.

quant-ph↗

arXiv2024

Shortcuts to Adiabaticity in Anisotropic Bose-Einstein Condensates

We propose shortcut to adiabaticity protocols for Bose-Einstein condensates trapped in generalized anisotropic harmonic traps in three dimensions. These protocols enable high-fidelity tuning of trap geometries on time scales much faster than those required for adiabatic processes and are robust across a wide range of interaction strengths, from weakly interacting regimes to the Thomas-Fermi limit. Using the same approach, we also design STA paths to rapidly drive interaction strengths in both isotropic and anisotropic traps. Comparisons with standard linear ramps of system parameters demonstrate significant improvements in performance. Finally, we apply these STA techniques to a unitary engine cycle with a BEC as the working medium. The STA methods significantly enhance the engine's power output without reducing efficiency and remain highly effective even after multiple consecutive cycles.

cond-mat.quant-gas↗

arXiv2024

Engineering impurity Bell states through coupling with a quantum bath

We theoretically demonstrate the feasibility of creating Bell states in multi-component ultra-cold atomic gases by solely using the ability to control the inter-particle interactions via Feshbach resonances. For this we consider two distinguishable impurities immersed in an atomic background cloud of a few bosons, with the entire system being confined in a one-dimensional harmonic trap. By analyzing the numerically obtained ground states we demonstrate that the two impurities can form spatially entangled bipolaron states due to mediated interactions from the bosonic bath. Our analysis is based on calculating the correlations between the two impurities in a two-mode basis, which is experimentally accessible by measuring the particles positions in the left or right sides of the trap. While interspecies interactions are crucial in order to create the strongly entangled impurity states, it can also inhibit correlations depending on the ordering of the impurities and three-body impurity-bath correlations. We show how these drawbacks can be mitigated by manipulating the properties of the bath, namely its size, mass and intraspecies interactions, allowing to create impurity Bell states over a wide range of impurity-impurity interactions.

cond-mat.quant-gas↗

arXiv2024

Quantum soliton-trains of strongly correlated impurities in Bose-Einstein condensates

Strongly correlated impurities immersed in a Bose-Einstein condensate (BEC) can form a periodic structure of tightly localized single atoms due to competing inter- and intra-species interactions, leading to a self-organized pinned state. In this work, we show numerically that the impurities in the self-pinned state form a soliton-train, as a consequence of a BEC-mediated attractive self-interaction and ordering due to the exclusion principle. The dynamics of the impurities possess similar characteristics to bright matter-wave solitons as they appear in attractive BECs, however in the few impurities case, the detailed nature of collisions is determined by their quantum statistics.

cond-mat.quant-gas↗

arXiv2024

Phases and dynamics of few fermionic impurities immersed in two-dimensional boson droplets

We unravel the ground state properties and emergent non-equilibrium dynamics of a mixture consisting of a few spin-polarized fermions embedded in a two-dimensional bosonic quantum droplet. For an increasingly attractive droplet-fermion interaction we find a transition from a spatially delocalized fermion configuration to a state where the fermions are highly localized and isolated. This process is accompanied by the rise of induced fermion-fermion interactions mediated by the droplet. Additionally, for increasing attractive droplet-fermion coupling, undulations in the droplet density occur in the vicinity of the fermions manifesting the back-action of the latter. Following interaction quenches from strong attractive to weaker droplet-fermion couplings reveals the spontaneous nucleation of complex excitation patterns in the fermion density such as ring and cross shaped structures. These stem from the enhanced interference of the fermions that remain trapped within the droplet, which emulates, to a good degree, an effective potential for the fermions. The non-negligible back-action of the droplet manifests itself in the fact that the effective potential predictions are less accurate at the level of the many-body wave function. Our results provide a paradigm for physics beyond the reduced single-component droplet model, unveiling the role of back-action in droplets and the effect of induced mediated interactions.

cond-mat.quant-gas↗

arXiv2024

High fidelity control of a many-body Tonks--Girardeau gas with an effective mean-field approach

Shortcuts to adiabaticity (STA) are powerful tools that can be used to control quantum systems with high fidelity. They work particularly well for single particle and non-interacting systems which can be described exactly and which possess invariant or self-similar dynamics. However, finding an exact STA for strongly correlated many-body systems can be difficult, as their complex dynamics may not be easily described, especially for larger systems that do not possess self-similar solutions. Here, we design STAs for one-dimensional bosonic gas in the Tonks--Girardeau limit by using a mean-field approach that succinctly captures the strong interaction effects through a quintic nonlinear term in the Schrödinger equation. We show that for the case of the harmonic oscillator with a time-dependent trap frequency the mean-field approach works exactly and recovers the well-known STA from literature. To highlight the robustness of our approach we also show that it works effectively for anharmonic potentials, achieving higher fidelities than other typical control techniques.

quant-ph↗