We investigate the nonequilibrium dynamics of a kinetic slush state realized via facilitated excitations in a two-dimensional dissipative Rydberg atom array. Utilizing kinetic Monte Carlo simulations in the strong dephasing regime, we show that tuning the laser detuning to compensate for nearest-neighbor interactions enables facilitated dynamics, while residual next-nearest-neighbor interactions induce kinetic frustration. This competition gives rise to an emergent slush phase characterized by pronounced dynamical heterogeneity and the coexistence of liquid- and solid-like configurations. By probing its nonequilibrium real-time evolution, we uncover a dynamical crossover from isotropic spreading to one-dimensional constrained growth, which can be continuously tuned by the frustration strength. Within this crossover regime, the slush dynamics generate fractal cluster geometries and generalized Ornstein-Zernike spatial correlations. Finite-size scaling analysis supports the system's proximity to criticality. Our findings establish driven-dissipative Rydberg systems as a highly controllable platform for engineering complex nonequilibrium soft-matter phenomena.
AI Summary
Can facilitated Rydberg excitation produce slush-like spatial structure and heterogeneous dynamics when coherence is suppressed? This paper studies a square Rydberg array with strong dephasing, using adiabatic elimination to obtain classical spin-flip rates and kinetic Monte Carlo simulations. Detuning compensates one nearest-neighbor interaction, while next-nearest-neighbor interactions suppress branching. The main model imposes a hard single-neighbor facilitation constraint and tunes frustration through $\eta=2V_{\mathrm{NNN}}/\gamma$.
Starting from one excitation, strong finite frustration produces early, approximately one-dimensional chain growth followed by delayed two-dimensional branching. At $\eta=100$, fitted density-growth exponents are $0.48$ and $1.36$ in successive time intervals. A fixed-axis model of the infinite-frustration limit gives diffusive growth, $\rho\propto\tau^{1/2}$, and stationary density $1/(2L)$. Within density-plateau observation windows, ramified configurations exhibit heterogeneous activity and slowly decaying autocorrelations: on a $64\times64$ lattice, the fraction of sites recording no flips over $T=10^5$ increases from $3.47\%$ at $\eta=0$ to $61.02\%$ at $\eta=100$.
Spatial correlations fit $C(r)\propto r^{-\alpha}e^{-r/\xi}$, with $\alpha\simeq0.48$ at strong frustration. At $\eta=707$, simulations through $L=256$ show approximately constant $\xi/L\simeq0.5$ and intermediate-distance scaling collapse, interpreted as proximity to criticality. Cluster mass versus chemical distance yields exponent $1.808\pm0.005$.
These are finite-time kinetic signatures, not established distinct equilibrium phases. Tests including off-resonant flips, third-neighbor interactions, and weak spontaneous decay retain slush-like features over observation windows; stronger decay fragments clusters and reduces activity contrast. Experimental observation requires formation and measurement before decay becomes significant.
Little sign of AI-generated textIncrementalStrong assumptionsOverclaims
Central claim may not hold: For all finite frustration strengths, the hard-constrained model has the same uniform stationary distribution within the seed-accessible component, so its reported frustration-dependent steady-state spatial correlations and morphologies require an unresolved finite-time interpretation.
The stated drive and dephasing parameters convert the simulated weak-decay rates to 1–10 Hz rather than the quoted 0.1–1 kHz, placing the proposed physical rates outside the demonstrated weak-decay regime.
With the stated frequency convention, the simulated observation interval corresponds to 10–30 ms, which is not short compared with the proposed physical decay times of 1–10 ms.
Written by gpt-6.1-sol from the paper's full text. Automated: it can be wrong.
We investigate the nonequilibrium dynamics of a kinetic slush state realized via facilitated excitations in a two-dimensional dissipative Rydberg atom array. Utilizing kinetic Monte Carlo simulations in the strong dephasing regime, we show that tuning the laser detuning to compensate for nearest-neighbor interactions enables facilitated dynamics, while residual next-nearest-neighbor interactions induce kinetic frustration. This competition gives rise to an emergent slush phase characterized by pronounced dynamical heterogeneity and the coexistence of liquid- and solid-like configurations. By probing its nonequilibrium real-time evolution, we uncover a dynamical crossover from isotropic spreading to one-dimensional constrained growth, which can be continuously tuned by the frustration strength. Within this crossover regime, the slush dynamics generate fractal cluster geometries and generalized Ornstein-Zernike spatial correlations. Finite-size scaling analysis supports the system's proximity to criticality. Our findings establish driven-dissipative Rydberg systems as a highly controllable platform for engineering complex nonequilibrium soft-matter phenomena.
Can facilitated Rydberg excitation produce slush-like spatial structure and heterogeneous dynamics when coherence is suppressed? This paper studies a square Rydberg array with strong dephasing, using adiabatic elimination to obtain classical spin-flip rates and kinetic Monte Carlo simulations. Detuning compensates one nearest-neighbor interaction, while next-nearest-neighbor interactions suppress branching. The main model imposes a hard single-neighbor facilitation constraint and tunes frustration through η=2VNNN/γ.
Starting from one excitation, strong finite frustration produces early, approximately one-dimensional chain growth followed by delayed two-dimensional branching. At η=100, fitted density-growth exponents are 0.48 and 1.36 in successive time intervals. A fixed-axis model of the infinite-frustration limit gives diffusive growth, ρ∝τ1/2, and stationary density 1/(2L). Within density-plateau observation windows, ramified configurations exhibit heterogeneous activity and slowly decaying autocorrelations: on a 64×64 lattice, the fraction of sites recording no flips over T=105 increases from 3.47% at η=0 to 61.02% at η=100.
Spatial correlations fit C(r)∝r−αe−r/ξ, with α≃0.48 at strong frustration. At η=707, simulations through L=256 show approximately constant ξ/L≃0.5 and intermediate-distance scaling collapse, interpreted as proximity to criticality. Cluster mass versus chemical distance yields exponent 1.808±0.005.
These are finite-time kinetic signatures, not established distinct equilibrium phases. Tests including off-resonant flips, third-neighbor interactions, and weak spontaneous decay retain slush-like features over observation windows; stronger decay fragments clusters and reduces activity contrast. Experimental observation requires formation and measurement before decay becomes significant.
We show that the dynamics of a laser driven Rydberg gas in the limit of strong dephasing is described by a master equation with manifest kinetic constraints. The equilibrium state of the system is uncorrelated but the constraints in the dynamics lead to spatially correlated collective relaxation reminiscent of glasses. We study and quantify the evolution towards equilibrium in one and two dimensions, and analyze how the degree of glassiness and the relaxation time are controlled by the interaction strength between Rydberg atoms. We also find that spontaneous decay of Rydberg excitations leads to an interruption of glassy relaxation that takes the system to a highly correlated nonequilibrium stationary state. The results presented here, which are in principle also applicable to other systems such as polar molecules and atoms with large magnetic dipole moments, show that the collective behavior of cold atomic and molecular ensembles can be similar to that found in soft condensed-matter systems.
In this Letter, we propose an exotic quantum state that does not order at zero temperature in a Rydberg atom array with antiblockade mechanism. By performing an unbiased large-scale quantum Monte Carlo simulation, we investigate a minimal model with facilitated excitation in a disorder-free system. At zero temperature, this model exhibits a heterogeneous structure of liquid and glass mixture. This state, dubbed quantum slush state, features a quasi-long-range order with an algebraic decay for its correlation function, and is different from most well-established quantum phases of matter.
Due to the variety of tools available to control atomic, molecular, and optical (AMO) systems, they provide a versatile platform for studying many-body physics, quantum simulation, and quantum computation. Although extensive efforts are employed to reduce coupling between the system and the environment, the effects of the environment can never fully be avoided, so it is important to develop a comprehensive understanding of open quantum systems. The system-environment coupling often leads to loss via dissipation, which can be countered by a coherent drive. Open quantum systems subject to dissipation and drive are known as driven-dissipative systems, and they provide an excellent platform for studying many-body nonequilibrium physics. The first part of this dissertation will focus on driven-dissipative phase transitions. Despite the nonequilibrium nature of these systems, the corresponding phase transitions tend to exhibit emergent equilibrium behavior. However, we will show that in the vicinity of a multicritical point where multiple phase transitions intersect, genuinely nonequilibrium criticality can emerge, even though the individual phase transitions on their own exhibit equilibrium criticality. These nonequilibrium multicritical points can exhibit a variety of exotic phenomena not possible for their equilibrium counterparts, including the emergence of complex critical exponents, which lead to discrete scale invariance and spiraling phase boundaries. Furthermore, the Liouvillian gap can take on complex values, and the fluctuation-dissipation theorem is violated, corresponding to an effective temperature which gets "hotter" and "hotter" at longer and longer wavelengths. The second part of this dissertation will focus on Rydberg atoms. In particular, we study how the spontaneous generation of contaminant Rydberg states drastically modifies the behavior of a driven-dissipative Rydberg system due to the resultant dipole-dipole interactions. These interactions lead to a complicated competition of both blockade and anti-blockade effects, leading to strongly enhanced Rydberg populations for far-detuned drive and reduced Rydberg populations for resonant drive.
Inevitably present in many current experiments with ultracold Rydberg atoms, dissipative effects such as dephasing and decay modify the dynamics of the examined system. In this thesis, the dynamics of many-body Rydberg systems in the incoherent regime is studied numerically. Specifically, a wave function Monte Carlo (MCWF) technique is integrated into a coherent two-level many-body Rydberg model, allowing a numerical simulation of dissipative dynamics. This model is used to benchmark a steady-state rate equation model and assess its range of validity. In addition, incoherent, off-resonant excitation dynamics is studied in a one-dimensional disordered geometry. We find that our simulation results can essentially be explained by the equilibration time scale as well as — for positive laser detuning — resonant excitations arising when the laser detuning compensates the Rydberg interaction. Eventually, we employ a rate equation model to investigate excitation spectra for an experimental trap geometry, which we benchmark using the MCWF technique. Based on numerical data, we deduce that in the considered parameter regime the dominant excitation mechanism can be characterized as sequential growth of aggregates of Rydberg excitations around an initial seed. Our simulation results highlight the impact of incoherent effects on observables such as Rydberg population, excitation number fluctuation and pair correlation function.
This thesis presents several experiments investigating the regimes of behaviour of a proto-typical open quantum many-body system far away from equilibrium. The experimental platform is based on ultracold atoms laser-excited to Rydberg states, which we engineer to emulate a strongly interacting, driven-dissipative quantum spin system. The high degree of control over the relevant microscopic processes and their parameters, as well as the ability to widely tune interaction and driving strengths provides the means to address fundamental questions on how different regimes of dynamical behaviour emerge in complex open quantum systems and how they can be characterised. \n \nIn the first part, we discuss how control over the relevant properties of Rydberg spin systems, like temperature, density, long evolution times, strong interactions, tunable driving, and dissipation can be achieved. We introduce the new experimental apparatus developed during this thesis, which combines both single-photon and two-photon Rydberg excitation schemes with high atom densities and long excitation times using an optical dipole trap. Additionally, we investigate theoretically how long coherence times exceeding motional timescales combined with strong many-body interactions can be achieved in such a system. We identify an optimal parameter regime for two-photon excitation where such conditions can be generated with coherence times and interaction strengths comparable to what is achievable for single-photon excitation. \n \nIn the second part we explore the macroscopic non-equilibrium behaviour of our system and devise suitable observables for characterising different regimes of behaviour. We discover that the slow atom loss inherent to our system provides a convenient observable for the many-body state of the system. Focussing on evolution times where the effect of the atom loss on the evolution is small, we discover that the rate of atom loss exhibits powerlaw scaling with the driving strength over several orders of magnitude. The measured scaling exponents reveal the non-equilibrium phase structure of the many-body system and allow us to distinguish dissipation-dominated, paramagnetic and critical regimes, as well as an instability. In the observed critical regime, collectively enhanced driving dominates over dissipation, leading to scaling associated to the critical point of the non-dissipative equilibrium Rydberg spin system. Based on the known microscopic processes of our system, we perform classical many-body rate equation simulations, which agree well with the observed phase structure as well as the position and associated scaling exponents of the individual regimes. These findings open up new means to study and classify out of equilibrium systems based on slow particle loss and powerlaw scaling. \n \nIn the last part of this thesis we reveal a second type of criticality in our system, which is genuinely non-equilibrium in character and arises from an absorbing state phase transition. The critical state of this phase transition dominates the system evolution at late times where particle loss is no longer negligible. We identify self-organisation as the mechanism driving the system to this critical state, which we observe through powerlaw scaling of the non-equilibrium steady-state. These experiments establish Rydberg atoms as a well controlled platform for implementing and exploring models of absorbing state phase transitions and self-organised criticality with unprecedented access to the underlying microscopic properties of the system.
We study the dynamics of dissipative spin lattices with power-law interactions, realized via few-level atoms driven by coherent laser-coupling and decoherence processes. Using Monte Carlo simulations, we determine the phase diagram in the steady state and analyze its generation dynamics. As opposed to mean-field predictions and nearest-neighbor models, there is no transition to long-range-ordered phases for realistic interactions and resonant driving. However, for finite laser detunings, we demonstrate the emergence of crystalline order. Although the static and dynamical critical exponents of the revealed dissipative phase transition fall into the two-dimensional Ising universality class, the found steady states differ considerably from those of an equilibrium Ising magnet. Two complementary schemes for an experimental implementation with cold Rydberg atoms are discussed.