arXiv subjects

Catalin-Mihai Halati

Publications and source records attributed to Catalin-Mihai Halati.

At least 19 recordsLinked to original sources

arXiv2026

Zeeman Ladders in Frustrated XYZ Spin Chains

We investigate the nature of the excitations captured by the dynamical response of XYZ triangular spin-1/2 ladders. We complement experimental inelastic neutron scattering results on the compound $\text{Cs}_\text{2}\text{CoBr}_\text{4}$ with numerically exact simulations based on time-dependent matrix product state methods. Our results show that bound states of spinon excitations can arise in XYZ beyond the requirement of strong Ising anisotropies. We analyze the role of the frustrated triangular couplings on the excitations giving rise to the spin dynamical structure factor and show how the features of the bound states manifest themselves in the different polarization channels.

cond-mat.str-el↗

arXiv2026

Controlling charge and spin currents through nonreciprocal dissipative processes

We investigate the generation and control of both charge and spin currents via nonreciprocal dissipative mechanisms in a two-dimensional spinful fermionic atom quantum system with broken inversion and time-reversal symmetries. Within the Gorini-Kossakowski-Sudarshan-Lindblad master equation formalism and using an approach based on the time-dependent generalized Gibbs ensemble, we identify in the weak dissipative coupling regime the minimal set of nonreciprocal jump operators required to induce charge and spin currents and to control both their direction and magnitude. We find that in the presence of finite tunneling, Rashba coupling and magnetic field, the combine application of two jump operators nonreciprocally coupling each spin species to a different spatial direction of motion is sufficient to generate both types of current. Furthermore, by tuning the degree of nonreciprocity of the jump operators we modify the dominant transport mechanism from spin to charge. Finally, we checked that this nonreciprocal current generation mechanism is robust to the application of dephasing noise as even in the presence of this additional dissipative process the steady-state occupation distributions for the quasiparticle modes of the Hamiltonian remains non-trivial, an essential requirement to obtain non-zero currents.

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arXiv2026

Dissipative Generation of Currents by Nonreciprocal Local and Global Environments

We investigate the mechanisms necessary for the stabilization of complex quantum correlations by exploring dissipative couplings to nonreciprocal reservoirs. We analyze the role of locality in the coupling between the environment and the quantum system of interest, as we consider either local couplings throughout the system, or a single global coupling. We contrast the results obtained for the two scenarios in which a chain of strongly interacting hardcore bosonic atoms is coupled directly to Markovian kinetic dissipative processes, or experiences effective dissipation through the mediation of the field of a lossy optical cavity. To investigate the dissipative dynamics of the many-body quantum systems considered we perform numerical simulations employing matrix product states methods. We show that by coupling atomic tunneling terms to the global field of a dissipative cavity we can stabilize at long times both finite currents and current-current correlations throughout the atomic chain. This is in contrast to the setup in which dissipation acts directly via local tunneling processes, where currents arise in a narrow region of the system and the current-current correlations are rapidly decaying.

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arXiv2026

Fluctuation-Induced Bistability in the Dissipative Dynamics of Generic Cavity-Matter Quantum Systems

We demonstrate that fluctuation-induced bistability is a robust and generic phenomenon in strongly interacting many-body systems with strong light-matter coupling. We identify a common microscopic mechanism based on resonances between photonic transitions and many-body energy scales, unifying the emergence of fluctuation-induced bistability across a broad class of models, including interacting spins, fermions, and bosons coupled to cavity modes. We develop complementary methods to study both the steady-state properties of fluctuation-induced bistability and its dynamical formation at finite times. In particular, we introduce the dressed-state rate equation approach, which reveals rich metastable dynamics and enables the investigation of its system-size dependence. By comparing its predictions with numerically-exact tensor-network simulations, we identify signatures of fluctuation-induced bistability already in small systems on finite timescales. Our results establish fluctuation-induced bistability as a universal feature of dissipative cavity-coupled many-body systems and provide a general framework for the investigation of its non-equilibrium dynamics across a wide range of hybrid quantum platforms.

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arXiv2026

Master Equation for a Quantum Gas of Polarizable Particles in Cavities

Quantum gases of atoms and molecules in optical cavities offer a formidable laboratory for studying the out-of-equilibrium dynamics of open quantum systems with long-range interactions. Long-range interactions are here mediated by multiple scattering of cavity photons and can induce the formation of quantum structures in space and time. Control of these dynamics requires a detailed understanding of all relevant mechanisms at play. Due to the strong correlations induced by light, however, perturbative theoretical models, which reduce the number of degrees of freedom, do not correctly capture the regime where the interplay of photon-mediated long-range forces and quantum fluctuations of light and matter become significant, such as across the transition to self-organization. In this work, we present the derivation of an effective Lindblad master equation for the dynamics of the sole motional variables of polarizable particles, such as atoms or molecules, that dispersively couple to cavity fields. The master equation is valid even for relatively large intracavity photon numbers, and is apt to study both the steady-state regime and the out-of-equilibrium dynamics where quantum fluctuations of the field seed the onset of macroscopic coherences. We validate the theoretical description by showing that it captures the dynamics across a wide temperature interval, from Doppler cooling down to the ultra-cold regime, and from weak to strong cavity-mediated interactions. Our theory provides a powerful framework for the description of cavity-induced dynamics of quantum matter. In doing so, it permits to connect models of statistical mechanics with cavity-QED experimental platforms, thus enabling quantum simulation of long-range interacting matter.

quant-ph↗

arXiv2025

Steady state diagram of interacting fermionic atoms coupled to dissipative cavities

We investigate fermionic atoms subjected to an optical lattice and coupled to a high finesse optical cavity with photon losses. A transverse pump beam introduces a coupling between the atoms and the cavity field. We explore the steady state phase diagram taking fluctuations around the mean-field of the atoms-cavity coupling into account. Our approach allows us to investigate both one- and higher-dimensional atomic systems. The fluctuations beyond mean-field lead to an effective temperature which changes the nature of the self-organization transition. We find a strong dependence of the results on the atomic filling, in particular when contrasting the behavior at low filling and at half filling. At low filling the transition to a self-organized phase takes place at a critical value of the pump strength. In the self-organized phase the cavity field takes a finite expectation value and the atoms show a modulation in the density. Surprisingly, at even larger pump strengths a strongly non-monotonous behavior of the temperature is found and hints towards effects of cavity cooling at many-body resonances. Additionally multiple self-organized stable solutions of the cavity field and the atoms occur, signaling the presence of a fluctuation-induced bistability, with the two solutions having different effective temperatures previously discussed in [Tolle et al., Phys. Rev. Lett. 134, 133602 (2025)]. In contrast, at half filling a bistable region arises at the self-organization transition already neglecting the fluctuations. The presence of the fluctuations induce an effective temperature as at lower filling and change the behavior of the transition and the steady states drastically. We analyze the properties of the occurring steady states of the coupled atoms-cavity system.

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arXiv2025

From Light-Cone to Supersonic Propagation of Correlations by Competing Short- and Long-Range Couplings

We investigate the dynamical spreading of correlations in many-body quantum systems with competing short- and global-range couplings. We monitor the non-equilibrium dynamics of the correlations following a quench, showing that for strong short-range couplings the propagation of correlations is dominated at short and intermediate distances by a causal, light-cone, dynamics, resembling the purely short-range quantum systems. However, the interplay of short- and global-range couplings leads to a crossover between space-time regions in which the light-cone persists to regions where a supersonic, distance-independent, spreading of the correlations occurs. We identify the important ingredients needed for capturing the supersonic spreading and demonstrate our findings in systems of interacting bosonic atoms, in which the global range coupling is realized by a coupling to a cavity light field, or atomic long-range interactions, respectively. We show that our results hold in both one and two dimensions and in the presence of dissipation. Furthermore, we characterize the short time power-law scaling of the distance-independent growth of the density-density correlations.

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arXiv2025

Interaction dependence of the Hall response for the Bose-Hubbard triangular ladder

We explore the behavior of the Hall response of a Bose-Hubbard triangular ladder in a magnetic field as a function of the repulsive on-site atomic interactions. We consider a wide range of interaction strengths, from the weakly interacting limit to the hardcore regime. This is realized by computing the Hall polarization following the quench of a weak linear potential which induces the flow of a current through the system, using time-dependent matrix product state numerical simulations. We complement our understanding in the regime of small magnetic fields by analytical calculations of the equilibrium value of the Hall polarization for non-interacting bosonic atoms, or under a mean-field assumption. The Bose-Hubbard triangular flux ladder exhibits a rich phase diagram, containing Meissner, vortex and biased-chiral superfluid phases. We show that the Hall response can be employed to fingerprint the various chiral state, the frustration effects occurring in the limit of strong interactions, and the phase boundaries of the equilibrium phase diagram.

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arXiv2025

Fluctuation-Induced Bistability of Fermionic Atoms Coupled to a Dissipative Cavity

We investigate the steady state phase diagram of fermionic atoms subjected to an optical lattice and coupled to a high finesse optical cavity with photon losses. The coupling between the atoms and the cavity field is induced by a transverse pump beam. Taking fluctuations around the mean-field solutions into account, we find that a transition to a self-organized phase takes place at a critical value of the pump strength. In the self-organized phase the cavity field takes a finite expectation value and the atoms show a modulation in the density. Surprisingly, at even larger pump strengths two self-organized stable solutions of the cavity field and the atoms occur, signaling the presence of a bistability. We show that the bistable behavior is induced by the atoms-cavity fluctuations and is not captured by the mean-field approach.

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arXiv2025

Controlling the dynamics of atomic correlations via the coupling to a dissipative cavity

We analyze the relaxation dynamics in an open system, composed by a quantum gas of bosons in a lattice interacting via both contact and global interactions. We report the onset of periodic oscillations of the atomic coherences exhibiting hallmarks of synchronization after a quantum quench. The dynamical behavior exhibits the many-body collapse and revival of atomic coherences and emerges from the interplay of the quantum dissipative nature of the cavity field and the presence of a (approximate) strong symmetry in the dissipative system. We further show that the approximate symmetry can dynamically self-organize. We argue that the approximate symmetry can be tailored to obtain long-lived coherences. These insights provide a general recipe to engineer the dynamics of globally-interacting systems.

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arXiv2025

Exploring Frustration Effects of Strongly Interacting Bosons via the Hall Response

We investigate the Hall response of hardcore bosonic atoms on a triangular ladder in a magnetic field. To access the dynamical properties of this many-body quantum system, we employ matrix product states numerical methods. We show that the behavior of the Hall polarization, both in its saturation value and in the short-time dynamics, correlates with the features of the underlying phase diagram, which stem from the interplay of interactions and geometric frustration. This paves the way to employ the Hall response as a sensitive probe of many-body chiral quantum phases in strongly correlated materials.

cond-mat.quant-gas↗

arXiv2024

Experimental observation of repulsively bound magnons

Stable composite objects, such as hadrons, nuclei, atoms, molecules and superconducting pairs, formed by attractive forces are ubiquitous in nature. By contrast, composite objects stabilized by means of repulsive forces were long thought to be theoretical constructions owing to their fragility in naturally occurring systems. Surprisingly, the formation of bound atom pairs by strong repulsive interactions has been demonstrated experimentally in optical lattices. Despite this success, repulsively bound particle pairs were believed to have no analogue in condensed matter owing to strong decay channels. Here we present spectroscopic signatures of repulsively bound three-magnon states and bound magnon pairs in the Ising-like chain antiferromagnet BaCo$_2$V$_2$O$_8$. In large transverse fields, below the quantum critical point, we identify repulsively bound magnon states by comparing terahertz spectroscopy measurements to theoretical results for the Heisenberg-Ising chain antiferromagnet, a paradigmatic quantum many-body model. Our experimental results show that these high-energy repulsively bound magnon states are well separated from continua, exhibit significant dynamical responses and, despite dissipation, are sufficiently long-lived to be identified. As the transport properties in spin chains can be altered by magnon bound states, we envision such states could serve as resources for magnonics based quantum information processing technologies.

cond-mat.str-el↗

arXiv2024

Repulsively bound magnon excitations of a spin-1/2 XXZ chain in a staggered transverse field

We study the excitation spectrum of the one-dimensional spin-1/2 XXZ chain with antiferromagnetic Ising anisotropy across a magnetic quantum phase transition induced by the application of a site-dependent transverse magnetic field. Motivated by the chain antiferromagnet BaCo$_2$V$_2$O$_8$, we consider a situation where the transverse magnetic field has a strong uniform component and a weaker staggered part. To determine the nature of the excitations giving rise to the spin dynamical structure factor, we use a combination of analytical approaches and the numerically exact time-dependent matrix product state method. We identify below the quantum phase transition high-energy many-body two-magnon and three-magnon repulsively bound states which are clearly visible due to the staggered component of the magnetic field. At high magnetic fields and low temperature, single magnons dominate the dynamics. Our theory results are in very good agreement with terahertz spectroscopy experimental results presented in [Wang et al., Nature 631, 760 (2024)].

cond-mat.str-el↗

arXiv2024

Dynamical Instabilities of Strongly Interacting Ultracold Fermions in an Optical Cavity

Recent quench experiments on ultra cold fermions in optical cavities provide a clean platform for studying how long-range interactions between fermions structure their dynamics. Motivated by these experiments, we provide a theoretical analysis of the dynamical instabilities that lead to the formation of superradiance as the hybrid system is driven across the self-organization transition. We compute the rate at which order forms and quantify the fluctuations of the pre-quench state which seed the instability. Our results quantitatively match existing experiments on free fermions and make predictions for quench experiments involving near unitary fermi gases coupled to an optical cavity. Our work suggests that the non-local nature of the photon-mediated interactions between fermions generates ordering dynamics that are qualitatively different than those observed in short-range interacting systems.

cond-mat.quant-gas↗

arXiv2024

Non-equilibrium dynamics of long-range interacting Fermions

A fundamental problem of out-of-equilibrium physics is the speed at which the order parameter grows upon crossing a phase transition. Here, we investigate the dynamics of ordering in a Fermi gas undergoing a density-wave phase transition induced by quenching of long-range, cavity-mediated interactions. We observe in real-time the exponential rise of the order parameter and track its growth over several orders of magnitude. Remarkably, the growth rate is insensitive to the contact interaction strength from the ideal gas up to the unitary limit and can exceed the Fermi energy by an order of magnitude, in quantitative agreement with a linearized instability analysis. We then generalize our results to linear interaction ramps, where deviations from the adiabatic behaviour are captured by a simple dynamical ansatz. Our study offers a paradigmatic example of the interplay between non-locality and non-equilibrium dynamics, where universal scaling behaviour emerges despite strong interactions at the microscopic level.

cond-mat.quant-gas↗

arXiv2023

Bose-Hubbard triangular ladder in an artificial gauge field

We consider interacting bosonic particles on a two-leg triangular ladder in the presence of an artificial gauge field. We employ density matrix renormalization group numerical simulations and analytical bosonization calculations to study the rich phase diagram of this system. We show that the interplay between the frustration induced by the triangular lattice geometry and the interactions gives rise to multiple chiral quantum phases. Phase transition between superfluid to Mott-insulating states occur, which can have Meissner or vortex character. Furthermore, a state that explicitly breaks the symmetry between the two legs of the ladder, the biased chiral superfluid, is found for values of the flux close to $π$. In the regime of hardcore bosons, we show that the extension of the bond order insulator beyond the case of the fully frustrated ladder exhibits Meissner-type chiral currents. We discuss the consequences of our findings for experiments in cold atomic systems.

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arXiv2022

Level statistics of the one-dimensional ionic Hubbard model

In this work we analyze the spectral level statistics of the one-dimensional ionic Hubbard model, the Hubbard model with an alternating on-site potential. In particular, we focus on the statistics of the gap ratios between consecutive energy levels. This quantity is often used in order to signal whether a many-body system is integrable or chaotic. A chaotic system has typically the statistics of a Gaussian ensemble of random matrices while the spectral properties of the integrable system follow a Poisson statistics. We find that whereas the Hubbard model without alternating potential is known to be integrable and its spectral properties follow a Poissonian statistics, the presence of an alternating potential causes a drastic change in the spectral properties which resemble the one of a Gaussian ensemble of random matrices. However, to uncover this behavior one has to separately consider the blocks of all symmetries of the ionic Hubbard model.

cond-mat.quant-gas↗

arXiv2022

Breaking strong symmetries in dissipative quantum systems: Bosonic atoms coupled to a cavity

In dissipative quantum systems, strong symmetries can lead to the existence of conservation laws and multiple steady states. In this work we investigate a strong symmetry for bosonic atoms coupled to an optical cavity, an experimentally relevant system, generalizing the adiabatic elimination techniques and using numerically exact matrix product state methods. We show that for ideal bosons coupled to the cavity multiple steady states exist and in each symmetry sector a dissipative phase transition occurs at a different critical point. This implies that phases of very different nature can coexist. We find that the introduction of a slight breaking of the strong symmetry by a small interaction term leads to a direct transition from multiple steady states to a unique steady state. We point out the phenomenon of dissipative freezing, the breaking of the conservation law at the level of individual realizations in the presence of the strong symmetry. For a small breaking of the strong symmetry we see that the behavior of the individual trajectories still shows some signs of this dissipative freezing before it fades out for a larger symmetry breaking terms.

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