Steady-state Phase Diagram Research Articles

Breakdown of steady-state superradiance in extended driven atomic arrays

Recent advances in generating well controlled dense arrangements of individual atoms in free space have generated interest in understanding how the extended nature of these systems influences superradiance phenomena. Here, we provide an in-depth analysis on how space-dependent light shifts and decay rates induced by dipole-dipole interactions modify the steady-state properties of coherently driven arrays of quantum emitters. We characterize the steady-state phase diagram, with particular focus on the radiative properties in the steady state. Interestingly, we find that diverging from the well-established Dicke paradigm of equal all-to-all interactions significantly modifies the emission properties. In particular, the prominent quadratic scaling of the radiated light intensity with particle number in the steady state—a hallmark of steady-state Dicke superradiance—is entirely suppressed, resulting in only linear scaling with particle number. We show that this breakdown of steady-state superradiance occurs due to the emergence of additional dissipation channels that populate not only superradiant states but also subradiant ones. The additional contribution of subradiant dark states in the dynamics leads to a divergence in the time scales needed to achieve steady states. Building on this, we further show that measurements taken at finite times for extended atom ensembles reveal properties closely mirroring the idealized Dicke scenario. Published by the American Physical Society 2024

Signatures of quantum phases in a dissipative system.

Lindbladian formalism, as tuned to dissipative and open systems, has been all-pervasive to interpret non-equilibrium steady states of quantum many-body systems. We study the fate of free fermionic and superconducting phases in a dissipative one-dimensional Kitaev model-where the bath acts both as a source and a sink of fermionic particles with different coupling rates. As a function of these two couplings, we investigate the steady state, its entanglement content, and its approach from varying initial states. Interestingly, we find that the steady state phase diagram retains decipherable signatures of ground state critical physics. We also show that early-time fidelity is a useful marker to find a subclass of phase transitions in such situations. Moreover, we show that the survival of critical signatures at late-times, strongly depend on the thermal nature of the steady state. This connection hints at a correspondence between quantum observables and classical magnetism in the steady state of such systems. Our work uncovers interesting connections between dissipative quantum many-body systems, thermalization of a classical spin and many-body quantum critical phenomena.

Origin of Two Distinct Stress Relaxation Regimes in Shear Jammed Dense Suspensions.

Many dense particulate suspensions show a stress induced transformation from a liquidlike state to a solidlike shear jammed (SJ) state. However, the underlying particle-scale dynamics leading to such striking, reversible transition of the bulk remains unknown. Here, we study transient stress relaxation behaviour of SJ states formed by a well-characterized dense suspension under a step strain perturbation. We observe a strongly nonexponential relaxation that develops a sharp discontinuous stress drop at short time for high enough peak-stress values. High resolution boundary imaging and normal stress measurements confirm that such stress discontinuity originates from the localized plastic events, whereas system spanning dilation controls the slower relaxation process. We also find an intriguing correlation between the nature of transient relaxation and the steady-state shear jamming phase diagram obtained from the Wyart-Cates model.

Self-organization and shape change by active polarization in nematic droplets

Active forces drive critical biological processes such as spontaneous organization and shape change during cell division. Here, we present a minimal hydrodynamic model leading to a unified description of self-organization and division in nematic droplets through active polarity sorting of cytoskeletal filaments by molecular motors. We find that motors self-organize within droplets while structuring filaments into polarized aster defects. At large activity, motors deform droplets leading to multidroplet chains and droplet division, consistent with experiments on actomyosin tactoids. We predict droplet steady-state phase diagrams that inform programmable shape changes in confined soft materials.

Internal, primary and combination resonances of a wind turbine blade with coupled flapwise and edgewise motions

In recent decades blades of wind turbines have been designed longer and longer for better performance of energy harvesting. The growth in structural flexibility has strengthened the effect of geometric nonlinearity and led to complicated nonlinear dynamic behavior of vibration response. In this paper, an investigation on internal, primary and multi-mode combination resonances of a flexible wind turbine blade with coupled flapwise and edgewise motions is studied. Through the Hamilton's principle, the dynamical model is established using the Euler-Bernoulli beam considering the actions of gravitational and unsteady aerodynamic force. The displacement of the blade is expanded into four basic modes based on the Galerkin's method, three in flapwise direction and one in edgewise direction. The governing equations of the four modal coordinates are solved using the method of multiple scales in transient and steady-state. For the transient responses, the internal and multi-mode combination resonances are revealed by the transfer of energy between resonant modes. Unlike the case of primary and internal resonances, the quasi-periodic under the multi-mode combination resonance is discovered through phase diagram of the first edgewise mode. For the steady-state responses, amplitude-frequency curves and phase diagrams of resonance modes under the primary and multi-mode combination resonance are derived. Influence of the combination resonance on the primary resonance is discussed for the steady-state responses with different aerodynamic force and geometric nonlinearity. Finally, parametric analyses are presented to show how steady-state motion of flapwise and edgewise modes vary with detuning parameters and design parameters.

Particle creation and annihilation in a dynamically disordered totally asymmetric simple exclusion process.

We study a single-channel dynamically disordered totally asymmetric simple exclusion process with bulk particle attachment and detachment. The continuum mean-field equations are derived and solved numerically to obtain steady-state phase diagrams and density profiles. The effects of various parameters, namely particle attachment rate, defect binding and unbinding rates, and binding constant, have been investigated. An increase in the attachment rate of particles reduces the number of steady-state phases, whereas a variation in defect binding and unbinding rates shifts the phase boundaries. One of the important consequences of introducing particle nonconserving dynamics is the appearance of shock in the steady state. The shock dynamics have been thoroughly examined and the defect strength is found to have a significant effect on the shock position. The mean-field solutions are validated using extensive Monte Carlo simulations.

Nonuniform phases in the geometrically frustrated dissipative XYZ model

We investigate the steady-state phase diagram of the dissipative spin-1/2 XYZ model on a two-dimensional triangular lattice, in which each site is coupled to a local environment. By means of cluster mean-field approximation, we find that the steady-state phases of the system are rather rich, in particular there exist various types of nonuniform antiferromagnetic phases due to the geometrical frustration. As the short-range correlations included in the analysis, the numerical results show that the oscillatory phase disappears while the triantiferromagnetic and biantiferromagnetic phases remain to exist in the thermodynamic limit. Moreover, the existence of the spin-density-wave phase, which is missed by the single-site mean-field analysis, is also revealed by the spin-structure factor.

Nonequilibrium phases and phase transitions of the XY model

We obtain the steady-state phase diagram of a transverse-field XY spin chain coupled at its ends to magnetic reservoirs held at different magnetic potentials. In the long-time limit, the magnetization bias across the system generates a current-carrying nonequilibrium steady state. We characterize the different nonequilibrium phases as functions of the chain's parameters and magnetic potentials, in terms of their correlation functions and entanglement content. The mixed-order transition, previously observed for the case of a transverse-field Ising chain, is established to emerge as a generic feature of a wider class of out-of-equilibrium problems. The critical exponents associated with this universality class are determined analytically. Results are also contrasted with those obtained in the limit of Markovian reservoirs. Our findings should prove helpful in establishing the properties of nonequilibrium phases and phase transitions of extended open quantum systems.

Feedback induced magnetic phases in binary Bose-Einstein condensates.

Weak measurement in tandem with real-time feedback control is a new route toward engineering novel nonequilibrium quantum matter. Here we develop a theoretical toolbox for quantum feedback control of multicomponent Bose-Einstein condensates (BECs) using backaction-limited weak measurements in conjunction with spatially resolved feedback. Feedback in the form of a single-particle potential can introduce effective interactions that enter into the stochastic equation governing system dynamics. The effective interactions are tunable and can be made analogous to Feshbach resonances-spin independent and spin dependent-but without changing atomic scattering parameters. Feedback cooling prevents runaway heating due to measurement backaction and we present an analytical model to explain its effectiveness. We showcase our toolbox by studying a two-component BEC using a stochastic mean-field theory, where feedback induces a phase transition between easy-axis ferromagnet and spin-disordered paramagnet phases. We present the steady-state phase diagram as a function of intrinsic and effective spin-dependent interaction strengths. Our result demonstrates that closed-loop quantum control of Bose-Einstein condensates is a powerful tool for quantum engineering in cold-atom systems.

Calculation of steady-state dynamical phase diagram in U-Mo binary system under irradiation

The steady-state dynamical phase diagram of U-Mo system under irradiation is studied by the thermodynamic model and effective free energy model. In the effective free energy model, we consider the irradiation-enhanced diffusion and ballistic mixing caused by recoil implantation and cascade collision. The effective free energy and diffusivity of each phase in U-Mo binary system at different temperatures were calculated. The dynamical phase diagrams of U-Mo alloys under different irradiation intensities were calculated and the differences between the dynamical phase diagram and thermodynamic equilibrium phase diagram was discussed. The calculated results show that, due to the irradiation-induced ballistic mixing, the high-temperature stable γ(U,Mo) phase can be stabilized near room temperature, which agree well with the experimental reports.

Steady-State Dynamic Phase Diagram Calculation of U-Ti and U-V Binary System under Irradiation

In this paper, by considering the irradiation-enhanced diffusion, a combination of effective free energy model and the thermodynamic model was used for studying the phase relationships in the U-Ti and U-V binary system under irradiation. The steady-state dynamical phase diagrams of U-Ti and U-V binary alloys under different irradiation intensities were calculated and compared with the conventional thermodynamic equilibrium phase diagram. The calculated results show that under irradiation the high-temperature stable (βTi, γU) and (γU,V) phases were stabilized at relatively low temperature resulting in invariant reactions at relatively low temperature. In addition, with the increase of the irradiation intensity, the temperature of the invariant reactions increased, and the phase regions of the (βTi, γU) and (γU,V) also increased.

Steady-state phase diagram of a weakly driven chiral-coupled atomic chain

A chiral-coupled atomic chain of two-level quantum emitters allows strong resonant dipole-dipole interactions, which enables significant collective couplings between every other emitters. We numerically obtain the steady-state phase diagram of such system under weak excitations, where interaction-driven states of crystalline orders, edge or hole excitations, and dichotomy of chiral flow are identified. We distinguish these phases by participation ratios and structure factors, and find two critical points which relate to decoherence-free subradiant sectors of the system. We further investigate the transport of excitations and emergence of crystalline orders under spatially-varying excitation detunings, and present non-ergodic butterfly-like system dynamics in the phase of extended hole excitations with a signature of persistent subharmonic oscillations. Our results demonstrate the interaction-induced quantum phases of matter with chiral couplings, and pave the way toward simulations of many-body states in nonreciprocal quantum optical systems.

Two-channel totally asymmetric simple exclusion process with site-wise dynamic disorder

Being inspired by the biological process of gene transcription, we investigate the phenomenology of transport on two-channel TASEP in the presence of dynamical defects under symmetric coupling conditions. The continuum mean-field equations are derived and then solved numerically to obtain steady-state phase diagrams. The role of various parameters namely defect (un-)binding constants, lane-changing rates has been thoroughly examined. The defect (un-)binding rates are found to affect the phase boundaries in the phase plane. The effect of system size on the steady-state dynamics of the system has also been analyzed. The theoretical results are validated by performing extensive Monte Carlo simulations.

Dissipation-Induced Instabilities of a Spinor Bose-Einstein Condensate Inside an Optical Cavity.

We investigate the dynamics of a spinor Bose-Einstein condensate inside an optical cavity, driven transversely by a laser with a controllable polarization angle. We focus on a two-component Dicke model with complex light-matter couplings, in the presence of photon losses. We calculate the steady-state phase diagram and find dynamical instabilities in the form of limit cycles, heralded by the presence of exceptional points and level attraction. We show that the instabilities are induced by dissipative processes that generate nonreciprocal couplings between the two collective spins. Our predictions can be readily tested in state-of-the-art experiments and open up the study of nonreciprocal many-body dynamics out of equilibrium.

Antiferromagnetic single-layer spin-orbit torque oscillators

We show how a charge current through a single antiferromagnetic layer can excite and control self-oscillations. Sustained oscillations with tunable amplitudes and frequencies are possible in a variety of geometries using certain classes of non-centrosymmetric materials that exhibit finite dissipative spin-orbit torque. We compute the steady-state phase diagram as a function of the current and spin-orbit torque magnitude. The anisotropic magnetoresistance causes the conversion of the resulting AF oscillations to a terahertz AC output voltage. These findings provide an attractive and novel route to design terahertz antiferromagnetic spin-orbit torque oscillators in simple single-layer structures.

Steady-state phase diagram of quantum gases in a lattice coupled to a membrane

In a recent experiment [Vochezer {\it et al.,} Phys. Rev. Lett. \textbf{120}, 073602 (2018)], a novel kind of hybrid atom-opto-mechanical system has been realized by coupling atoms in a lattice to a membrane. While such system promises a viable contender in the competitive field of simulating non-equilibrium many-body physics, its complete steady-state phase diagram is still lacking. Here we study the phase diagram of this hybrid system based on an atomic Bose-Hubbard model coupled to a quantum harmonic oscillator. We take both the expectation value of the bosonic operator and the mechanical motion of the membrane as order parameters, and thereby identify four different quantum phases. Importantly, we find the atomic gas in the steady state of such non-equilibrium setting undergoes a superfluid-Mott-insulator transition when the atom-membrane coupling is tuned to increase. Such steady-state phase transition can be seen as the non-equilibrium counterpart of the conventional superfluid-Mott-insulator transition in the ground state of Bose-Hubbard model. Further, no matter which phase the quantum gas is in, the mechanic motion of the membrane exhibits a transition from an incoherent vibration to a coherent one when the atom-membrane coupling increases, agreeing with the experimental observations. Our present study provides a simple way to study non-equilibrium many-body physics that is complementary to ongoing experiments on the hybrid atomic and opto-mechanical systems.

Dynamical transitions in a driven diffusive model with interactions

We study the dynamics of an asymmetric simple exclusion process with open boundaries and local interactions using a pair approximation which generalizes the 2-node cluster mean field theory and the Markov chain approach to kinetics and shares with these approaches the property of reproducing exact results for the bulk current-density relation and the steady-state phase diagrams. We find that the relaxation rate exhibits a dynamical transition, with no static counterpart, analogous to that found without interactions. Remarkably, for some values of the model's parameters, we find 2 dynamical transitions in the same low-density phase. We study the dynamics of relaxation to the steady state on both sides of these transitions and make an attempt at providing a physical interpretation for this phenomenon. Results from numerical approaches and a modified Domain Wall Theory confirm the picture provided by the pair approximation.

Magnetic order in a Fermi gas induced by cavity-field fluctuations

We study magnetic orders of fermions under cavity-assisted Raman couplings in a one-dimensional lattice at half filling. The cavity-enhanced atom-photon coupling introduces a dynamic long-range interaction between the fermions, which competes with the short-range on-site interaction and leads to a variety of magnetic orders. Adopting a numerical density-matrix-renormalization-group method, we investigate the various magnetic orders and map out the steady-state phase diagram. Interestingly, as all the phase transitions take place outside the superradiant regime, the magnetic orders are associated with cavity-field fluctuations with a vanishing number of photons on the mean-field level.

Effect of interactions for one-dimensional asymmetric exclusion processes under periodic and bath-adapted coupling environment

Stimulated by the effect of the nearest neighbor interactions in vehicular traffic and motor proteins, we study a 1D driven lattice gas model, in which the nearest neighbor particle interactions are taken in accordance with the thermodynamic concepts. The non-equilibrium steady-state properties of the system are analyzed under both open and periodic boundary conditions using a combination of cluster mean-field analysis and Monte Carlo simulations. Interestingly, the fundamental diagram of current versus density shows a complex behavior with a unimodal dependence for attractions and weak repulsions that turns into the bimodal behavior for stronger repulsive interactions. Specific details of system-reservoir coupling for the open system have a strong effect on the stationary phases. We produce the steady-state phase diagrams for the bulk-adapted coupling to the reservoir using the minimum and maximum current principles. The strength and nature of interaction energy has a striking influence on the number of stationary phases. We observe that interactions lead to correlations having a strong impact on the system dynamical properties. The correlation between any two sites decays exponentially as the distance between the sites increases. Moreover, they are found to be short-range for repulsions and long-range for attractions. Our results also suggest that repulsions and attractions asymmetrically modify the dynamics of interacting particles in exclusion processes.

Miscible–immiscible transition and nonequilibrium scaling in two-component driven open condensate wires

We investigate the steady state phase diagram of two-component driven open condensates (DOCs) in one dimension. We identify a miscible–immiscible transition which is predominantly driven by gapped density fluctuations and occurs upon increasing the inter-component dissipative coupling. Below the transition in the miscible phase, we find the effective long wavelength dynamics to be described by a two-component Kardar–Parisi–Zhang (KPZ) equation that belongs to the nonequilibrium universality class of the one-dimensional single-component KPZ equation at generic choices of parameters. Our results are relevant for different experimental realizations for two-component DOCs in exciton–polariton systems.