arXiv subjects

Bastien Lapierre

Publications and source records attributed to Bastien Lapierre.

At least 19 recordsLinked to original sources

arXiv2026

Dissipation-enhanced scrambling in the SYK model coupled to a lossy cavity

We study the Yukawa-Sachdev-Ye-Kitaev model, a disordered model of $N$ Majorana fermions and $R=\gamma N$ bosons in which the bosons are linearly coupled to independent realizations of SYK $p$-body interactions, in the presence of dissipation, modeled by a Lindblad master equation. Motivated by recent proposals for implementing SYK models in quantum simulators, we focus on bosonic leakage at rate $\kappa$. Initializing the system in the steady state, we analyze the late-time fermionic relaxation rate and the Lyapunov exponent, solving the large-$N$ theory both numerically and for $p$ large, finding a rich landscape of dynamical behaviors. Most notably, the Lyapunov exponent remains positive for every value of $\kappa$ and, for $p>2$, can even grow as $\kappa$ increases. The QED case $p=2$, which lies between the fully chaotic regime $p>2$ and the integrable case $p=1$, exhibits special features. We also identify a critical value of the boson-to-fermion ratio $\gamma_c \approx 2/p^2$ separating distinct dynamical regimes.

quant-ph↗

arXiv2026

Emergent Self-Similar Quantum Revivals in Spiral Drives

We uncover a distinct form of nonequilibrium temporal order: self-similar quantum revivals in a many-body system driven by quasiperiodic spiral kicks, where the system recurrently returns close to its initial state at a hierarchically nested sequence of times. We demonstrate that both the fidelity and entanglement entropy exhibit this self-similar temporal structure. It originates from an emergent dynamical attractor, which we identify, such that all momentum modes eventually fall into the same closed orbits at self-similar times. We analytically justify this behavior and show that, for special momentum modes, this attractor arises as a consequence of a generalized spin echo process, and more generally we prove its existence using quasiperiodic SU(2) cocycles. Interestingly, the dynamics between consecutive revivals supports either volume- or area-law entanglement scaling, tunable via the driving parameters. In the presence of integrability-breaking perturbations, the system eventually heats up, but a long-lived prethermal regime with algebraically tunable lifetime occurs before heating sets in. Our results establish self-similar quantum revivals as a new paradigm for nonequilibrium quantum matter and provide a realistic route for its observation in current quantum simulators.

quant-ph↗

arXiv2026

Observing conformal Floquet dynamics on a digital quantum processor

Quantum simulations are traditionally confined to exploring dynamics starting from unentangled or low-entanglement states due to severe bottlenecks in protocol design, hardware performance, and classical verification. Here, we report the first experimental observation of non-equilibrium dynamics initiated directly from a many-body critical state. Using a fully-connected trapped-ion processor, we prepare the critical ground state of a transverse-field Ising model via a hardware-tailored, logarithmic-depth quantum circuit based on multi-scale entanglement renormalization. Following this initialization, we apply a deep Floquet drive that maintains emergent conformal symmetry, enabling us to benchmark the lattice dynamics against analytical results from continuum theory. In the resulting conformal heating phase, we extract a central charge consistent with the Ising universality class ($c=1/2$) from the universal decay of the Loschmidt echo and observe spatial energy localization predicted by field theory. Conversely, the non-heating phase exhibits global finite-time revivals. This work establishes a scalable and versatile framework for exploring critical quantum dynamics.

quant-ph↗

arXiv2026

Bootstrapping Symmetries in Quantum Many-Body Systems from the Cross Spectral Form Factor

Symmetries play a central role in quantum many-body physics, yet uncovering them systematically remains challenging. We introduce a bootstrap framework designed to reconstruct the representation theory of hidden finite group symmetries of quantum many-body lattice Hamiltonians, using only a known symmetry subgroup $N$ and spectral correlations between its symmetry sectors. We introduce a novel variant of the spectral form factor, the cross spectral form factor (xSFF), which we compute via exact diagonalization to seed the bootstrap algorithm. By applying the constraints derived from these data alongside the algebraic conditions of the fusion rules, our bootstrap procedure sharply restricts the set of candidate groups $G$. Remarkably, without any prior assumptions regarding the full symmetry group $G$, our method can systematically recover its representation-theoretic data, including the number and dimensions of the irreducible representations, their branching rules with respect to $N$, the fusion algebra, and the full character table. This framework applies equally well to chaotic and integrable many-body systems and accommodates both unitary and anti-unitary symmetries. Through various examples, we demonstrate that the underlying group $G$ can be uniquely identified. In particular, our bootstrap independently recovers the $\mathbb{Z}_4$ symmetry at the self-dual point of the three-state quantum torus chain, detects signatures of projective representations in the effective Hamiltonian of the driven Bose-Hubbard model, and rediscovers the $\eta$-pairing $\mathrm{SO}(4)$ symmetry of the one-dimensional Fermi-Hubbard model. Our framework thus establishes a practical route to identify symmetries directly from dynamical spectral observables.

quant-ph↗

arXiv2026

Observing quantum many-body dynamics in emergent curved spacetime using programmable quantum processors

We digitally simulate quantum many-body dynamics in emergent curved backgrounds using 80 superconducting qubits on IBM Heron processors. By engineering spatially varying couplings in the spin-$\frac12$ XXZ chain, consistent with the low-energy description of the model in terms of an inhomogeneous Tomonaga-Luttinger liquid, we realize excitations that follow geodesics of an effective metric inherited from the underlying spatial deformation. Following quenches from N\'eel and few-spin-flip states, we observe curved light-cone propagation, horizon-induced freezing in the local magnetization, and position-dependent oscillation frequencies set by the engineered spatial deformation. Despite strong spatial inhomogeneity, unequal-time correlators reveal ballistic quasiparticle propagation in the spin chain. These results establish large-scale digital quantum processors as a flexible platform for detailed and controlled exploration of many-body dynamics in tunable and synthetic curved spacetimes.

quant-ph↗

arXiv2025

Nonequilibrium Probes of Quantum Geometry in Gapless Systems

Much of our understanding of gapless quantum matter stems from low-energy descriptions using conformal field theory. This is especially true in 1+1 dimensions, where such theories have an infinite-dimensional parameter space induced by their conformal symmetry. We reveal the underlying quantum geometry by considering finite many-body systems driven by time-dependent conformal transformations. For small deformations, perturbation theory predicts absorption rates and linear responses that probe the quantum geometric tensor. For arbitrarily large but adiabatic deformations, we show that periodic drives give rise to nontrivial return amplitudes involving the quantum metric, beyond the familiar leading order that only features a Berry phase. The former is less sensitive to decoherence than the latter, so it can provide robust experimental signatures of our predictions. Our field-theoretic findings are universal, comprising general relations between measurable quantities and quantum geometry that only depend on the emergent effective description. This is supported both by numerical simulations of gapless lattice models, and by exact results for quantum dynamics under certain Floquet drives, probing the full dynamical parameter space.

cond-mat.str-el↗

arXiv2025

Spatially Structured Entanglement from Nonequilibrium Thermal Pure States

We study quantum quench dynamics in (1+1)-dimensional critical systems, starting from thermal pure states called crosscap states, and evolving them under spatially inhomogeneous Hamiltonians. The spatial inhomogeneity is introduced through a deformation of the Hamiltonian, expressed as linear combinations of the generators of the $SL^{(q)}(2,\mathbb{R})$ subalgebra of the Virasoro algebra. We analyze the free massless Dirac fermion theory and holographic conformal field theory as prototypical examples of integrable and non-integrable dynamics. Consistent with general expectations, "M\"obius-type" deformations lead to thermalization in the non-integrable case, and to periodic revivals in the integrable one. In contrast, "sine-square-type" and "displacement-type" deformations prevent both thermalization and scrambling, instead producing late-time, graph-like entanglement patterns. These patterns emerge from the interplay between the deformed Hamiltonian and the crosscap initial state and appear to be universal: they are determined solely by the deformation profile while remaining largely insensitive to microscopic details. Finally, we perform a holographic calculation in three-dimensional gravity using AdS$_3$/CFT$_2$, which reproduces the main features of our (1+1)-dimensional study.

cond-mat.stat-mech↗

arXiv2025

Local-to-Global Entanglement Dynamics by Periodically Driving Impurities

We study the entanglement dynamics of one-dimensional fermionic chains subject to a local Floquet drive of a two-site impurity, and uncover a sharp transition in the entanglement dynamics set by the driving period $T$. For large periods, the entanglement entropy (EE) grows linearly in time, signaling a heating phase with volume-law entanglement; below a critical period $T_\ast$, the EE instead grows subextensively, characteristic of a local quantum quench. We establish this dichotomy in two complementary settings: a gapless nearest-neighbor hopping chain, where a single transition separates logarithmic from volume-law growth, and a gapped Su-Schrieffer-Heeger (SSH) chain, whose two-band structure yields a richer phase diagram with multiple area-to-volume-law transitions. In the noninteracting limit, we trace these transitions analytically to quasienergy folding in the single-particle Floquet spectrum: a single $\pi$-gap closure for the NN chain, and a sequence of foldings at both 0- and $\pi$-gaps for the SSH chain, yielding the alternating pattern of heating and non-heating phases. We further show that the so-called ``average energy" operator furnishes a many-body diagnostic of the transition, remaining local in the non-heating phase but developing non-local couplings in the heating phase. For the gapless chain, using extensive matrix-product-state simulations, we demonstrate that the non-heating phase and its subextensive entanglement growth survive weak interactions over numerically accessible timescales. Our results establish local Floquet engineering as a route to emergent bulk phenomena, offering a new perspective on energy localization and thermalization in driven many-body systems.

quant-ph↗

arXiv2025

Entanglement transitions in structured and random nonunitary Gaussian circuits

We study measurement-induced phase transitions in quantum circuits consisting of kicked Ising models with postselected weak measurements, whose dynamics can be mapped onto a classical dynamical system. For a periodic (Floquet) non-unitary evolution, such circuits are exactly tractable and admit volume-to-area law transitions. We show that breaking time-translation symmetry down to a quasiperiodic (Fibonacci) time evolution leads to the emergence of a critical phase with tunable effective central charge and with a fractal origin. Furthermore, for some classes of random non-unitary circuits, we demonstrate the robustness of the volume-to-area law phase transition for arbitrary random realizations, thanks to the emergent compactness of the classical map encoding the circuit's dynamics.

quant-ph↗

arXiv2025

Driven Non-Unitary Dynamics of Quantum Critical Systems

We investigate the interplay between unitary and non-unitary driven many-body dynamics in (1+1)-dimensional quantum critical systems described by conformal field theory (CFT). By formulating a coherent state approach, we demonstrate that the growth of entanglement entropy and energy can be found analytically for a class of non-unitary driven CFTs, where the evolution alternates between real and imaginary time evolution, the latter corresponding to postselected weak measurements. We find that non-unitary evolution leads to the emergence of steady states at infinite times for the cases of periodic, quasiperiodic, and random drives. In a special class of drives, for mixed initial states, we uncover purification phase transitions that arise as a result of the competition between unitary evolution and weak measurements. We compare the CFT evolution with the corresponding non-unitary dynamics of critical lattice models, finding remarkable agreement.

cond-mat.str-el↗

arXiv2025

Chiral Instabilities in Driven-Dissipative Quantum Liquids

We investigate the nonequilibrium dynamics of periodically driven Tomonaga-Luttinger liquids (TLLs) coupled to a thermal bath using a Floquet-Lindblad approach. When the coupling to the bath satisfies detailed balance, we obtain a condition for parametric instabilities to be suppressed, symmetrically for both chiralities. Remarkably, by designing a purely chiral coupling to the bath, instead of instability suppression, we uncover a driven-dissipative phase transition between the former symmetric parametric instability and a new chiral parametric instability. In the latter, a single chirality of bosonic quasiparticles gets exponentially amplified, leading to a dynamical chiral imbalance within the TLL, reminiscent of the non-Hermitian skin effect.

cond-mat.stat-mech↗

arXiv2024

Quantum Hall edges beyond the plasma analogy

We demonstrate that the widely used plasma analogy is unreliable at predicting edge properties of quantum Hall states. This discrepancy arises from a fundamental difference between quantum Hall droplets and plasmas (Coulomb gases): the former are incompressible liquids subject to area-preserving deformations, while the latter are governed by electrostatics and thus involve conformal transformations. Consequently, the plasma analogy fails at the edge, except in fine-tuned geometries, as it does not account for the emergent local edge velocity. We quantitatively show how the analogy's failure affects physical quantities, such as fluctuations of local observables and absorption rates in microwave spectroscopy, measurable in both solid-state experiments and quantum simulators.

cond-mat.mes-hall↗

arXiv2024

Topology of ultra-localized insulators and superconductors

The topology of an insulator can be defined even when all eigenstates of the system are localized - an extreme case of Anderson insulators that we call ultra-localized. We derive the classification of such ultra-localized insulators in all symmetry classes and dimensions. We clarify their bulk-boundary correspondence and show that ultra-localized systems are in many instances phases of matter not described by the known classification of topological insulators and superconductors. As a consequence, we clarify which conventional topological phases are Wannierizable, and which topological phases cannot exist without delocalized states.

cond-mat.mes-hall↗

arXiv2024

Anisotropic Quantum Hall Droplets

We study two-dimensional (2D) droplets of noninteracting electrons in a strong magnetic field, placed in a confining potential with arbitrary shape. Using semiclassical methods adapted to the lowest Landau level, we obtain near-Gaussian energy eigenstates that are localized on level curves of the potential and have a position-dependent height. This one-particle insight allows us to deduce explicit formulas for expectation values of local many-body observables, such as density and current, in the thermodynamic limit. In particular, correlations along the edge are long-ranged and inhomogeneous. As we show, this is consistent with the system's universal low-energy description as a free 1D chiral conformal field theory of edge modes, known from earlier works in simple geometries. A delicate interplay between radial and angular dependencies of eigenfunctions ultimately ensures that the theory is homogeneous in terms of the canonical angle variable of the potential, despite its apparent inhomogeneity in terms of more naïve angular coordinates. Finally, we propose a scheme to measure the anisotropy by subjecting the droplet to microwave radiation; we compute the corresponding absorption rate and show that it depends on the droplet's shape and the waves' polarization. These results, both local and global, are likely to be observable in solid-state systems or quantum simulators of 2D electron gases with a high degree of control on the confining potential.

cond-mat.mes-hall↗

arXiv2024

Floquet engineered inhomogeneous quantum chaos in critical systems

We study universal chaotic dynamics of a large class of periodically driven critical systems described by spatially inhomogeneous conformal field theories. By employing an effective curved spacetime approach, we show that the onset of quantum chaotic correlations, captured by the Lyapunov exponent of out-of-time-order correlators (OTOCs), is set by the Hawking temperature of emergent Floquet horizons. Furthermore, scrambling of quantum information is shown to be strongly inhomogeneous, leading to transitions from chaotic to non-chaotic regimes by tuning driving parameters. We finally use our framework to propose a concrete protocol to simulate and measure OTOCs in quantum simulators, by designing an efficient stroboscopic backward time evolution.

cond-mat.str-el↗

arXiv2023

Probing Chern number by opacity and topological phase transition by a nonlocal Chern marker

In 2D semiconductors and insulators, the Chern number of the valence band Bloch state is an important quantity that has been linked to various material properties, such as the topological order. We elaborate that the opacity of 2D materials to circularly polarized light over a wide range of frequencies, measured in units of the fine structure constant, can be used to extract a spectral function that frequency-integrates to the Chern number, offering a simple optical experiment to measure it. This method is subsequently generalized to finite temperature and locally on every lattice site by a linear response theory, which helps to extract the Chern marker that maps the Chern number to lattice sites. The long range response in our theory corresponds to a Chern correlator that acts like the internal fluctuation of the Chern marker, and is found to be enhanced in the topologically nontrivial phase. Finally, from the Fourier transform of the valence band Berry curvature, a nonlocal Chern marker is further introduced, whose decay length diverges at topological phase transitions and therefore serves as a faithful indicator of the transitions, and moreover can be interpreted as a Wannier state correlation function. The concepts discussed in this work explore multi-faceted aspects of topology and should help address the impact of system inhomogeneities.

cond-mat.str-el↗

arXiv2023

Marginal quenches and drives in Tomonaga-Luttinger liquids

We study Tomonaga-Luttinger liquids thrown out of equilibrium by marginal deformations in the form of interaction modulations. This is modeled by quenching or periodically driving the Luttinger parameter or, equivalently, the compactification radius of the free boson conformal field theory between two different values. We obtain exact analytical results for the evolution of the Loschmidt echo and observables such as the particle and energy densities. Starting from generic initial states, the quench dynamics are shown to exhibit revivals and temporal orthogonalities. For the periodic drive, we show stability or instability of time-evolved physical quantities dependent on the drive parameters. We also compare the corresponding marginally deformed thermal density matrices by non-perturbatively evaluating their Rényi divergence as a Euclidean quench. All the dynamics are shown to be crucially dependent on the ratio of the Luttinger parameters, which corresponds to the Zamolodchikov distance in the space of marginal deformations. Our setup is equivalently interpreted as the dynamics of the bosonic string upon instantaneous changes of the target-space radius.

cond-mat.stat-mech↗

arXiv2022

Thermal and dissipative effects on the heating transition in a driven critical system

We study the dissipative dynamics of a periodically driven inhomogeneous critical lattice model in one dimension. The closed system dynamics starting from pure initial states is well-described by a driven Conformal Field Theory (CFT), which predicts the existence of both heating and non-heating phases in such systems. Heating is inhomogeneous and is manifested via the emergence of black-hole like horizons in the system. The robustness of this CFT phenomenology when considering thermal initial states and open systems remains elusive. First, we present analytical results for the Floquet CFT time evolution for thermal initial states. Moreover, using exact calculations of the time evolution of the lattice density matrix, we demonstrate that for short and intermediate times, the closed system phase diagram comprising heating and non-heating phases, persists for thermal initial states on the lattice. Secondly, in the fully open system with boundary dissipators, we show that the nontrivial spatial structure of the heating phase survives particle-conserving and non-conserving dissipations through clear signatures in mutual information and energy density evolution.

cond-mat.str-el↗