arXiv subjects

Jayson G. Cosme

Publications and source records attributed to Jayson G. Cosme.

At least 19 recordsLinked to original sources

arXiv2026

Time crystals in cavity-BEC systems

The understanding of light-induced dynamical states continues to be a challenging and fruitful pursuit of science. This pursuit is supported by quantum simulation of dynamical phenomena, e.g., in ultracold atom systems. Typically, ultracold atom dynamics are read out destructively, via time-of-flight imaging, limiting a detailed analysis. However, atom-cavity systems provide a real-time readout of the photonic state via photon emission from the cavity, making the system ideally suited for the simulation of dynamical phenomena. Here, we review three distinct time crystalline states, predicted and realized in a cavity-BEC system. We give an example for each of them, based on minimal few-mode models. We characterize the time crystalline states via correlation functions of the cavity mode, and characteristic momentum modes of the condensate. This supports a clear distinction between these time crystals. More generally, the sequence of studies reviewed here, serves as a blueprint for setting up minimal models and their characterization, for dynamical phenomena.

cond-mat.quant-gas↗

arXiv2026

Universal logic gates for coupled period-doubling systems

We propose a general architecture for universal logic operations using NAND and NOR gates on classical information encoded in period-doubled states of periodically-driven systems. The protocol involves applying a single pulse that simultaneously couple two input nodes with an output node. We show that the states of the nodes can be precisely controlled by tuning the coupling strength and pulse duration, allowing for robust logic gate operation. To highlight the universality of the protocol, we demonstrate its applicability on different systems, such as classical networks of dissi- pative parametric oscillators (DPO), quantum networks of Kerr parametric oscillators (KPO), and the periodically-driven open Dicke lattice model (DLM) emulating discrete time crystals (DTCs). We identify the parameter regimes in which the logic gate architecture is valid, and we showcase its robustness in the presence of fluctuations.

quant-ph↗

arXiv2025

Dynamics and fragmentation of bosons in an optical lattice inside a cavity using Wannier and position bases

The atom-cavity system is a versatile platform for emulating light-matter systems and realizing dissipation-induced phases, such as limit cycles (LCs) and time crystals. Here, we study the dynamics of a Bose-Einstein condensate (BEC) inside an optical cavity with transverse pumping and an additional intracavity optical lattice along the cavity axis. Specifically, we explore the theoretical predictions obtained from expanding the atomic field operators of the second-quantized Hamiltonian in two ways: (i) position basis and (ii) single-band Wannier basis. Both bases agree on the existence of most types of static and dynamical phases. However, the large sea of irregular dynamical phase, captured within the position basis, is absent in the Wannier basis. Moreover, we show that they predict different types of LCs due to the inherent limitation of the single-band Wannier expansion, highlighting the importance of including higher energy bands to correctly capture certain phenomena. Using truncated Wigner approximation, we investigate the fragmentation dynamics of the BEC. We demonstrate that both position and Wannier bases qualitatively agree on the photon-mediated fragmentation dynamics of the BEC in the density-wave phase, despite the absence of interatomic interactions. The presence of interatomic interaction leads to further fragmentation, which can only be observed in larger system sizes. Finally, we predict a sudden increase in the fragmentation behavior for larger pump intensities.

cond-mat.quant-gas↗

arXiv2025

Universality of dissipative discrete time crystal formation

We demonstrate that the Kibble-Zurek mechanism (KZM) holds for open systems transitioning from a disordered phase to a discrete time crystal (DTC). Specifically, we observe the characteristic power-law scaling with quench time of the number of spatial defects and the transition delay measured from the time at which the system crosses the critical point. We show analytically that this universal behavior can be traced back to how systems that can be mapped onto a dissipative linear parametric oscillator (DLPO) satisfy the adiabatic-impulse (AI) approximation, evinced by the divergence of the relaxation time of the DLPO near a critical point. We verify our predictions in both the classical and quantum regimes by considering two systems: the Sine-Gordon model, which is a paradigmatic system for emulating classical DTCs; and the open Dicke lattice model, an array of spin-boson systems subject to quantum fluctuations. We establish a universality class for DTC formation in systems that can be mapped onto a DLPO and show that the classical and quantum models considered here belong to this class.

cond-mat.stat-mech↗

arXiv2025

Controlled bit-flip of period-doubling and discrete time crystalline states in open systems

In this work, we explore the robustness of a bit-flip operation against thermal and quantum noise for bits represented by the symmetry-broken pairs of the period-doubled (PD) states in a classical parametric oscillator and discrete time crystal (DTC) states in a fully-connected open spin-cavity system, respectively. The bit-flip operation corresponds to switching between the two PD and DTC states induced by a defect in a periodic drive, introduced in a controlled manner by linearly ramping the phase of the modulation of the drive. In the absence of stochastic noise, strong dissipation results in a more robust bit-flip operation in which slight changes to the defect parameters do not significantly lower the success rate of bit-flips. The operation remains robust even in the presence of stochastic noise when the defect duration is sufficiently large. The fluctuations also enhance the success rate of the bit-flip below the critical defect duration needed to induce a switch. By considering parameter regimes in which the DTC states in the spin-cavity system do not directly map to the PD states, we reveal that this robustness is due to the system being quenched by the defect towards a new phase that has enough excitation to suppress the effects of the stochastic noise. This allows for precise control of the bit-flip operations by tuning into the preferred intermediate state that the system will enter during a bit-flip operation. We demonstrate this in a modified protocol based on precise quenches of the driving frequency.

quant-ph↗

arXiv2025

Torus bifurcation of a dissipative time crystal

Using a quantum gas setup consisting of a Bose-Einstein condensate strongly coupled to a high-finesse optical cavity by a transverse pump laser, we experimentally observe an instability of a dissipative continuous time crystal (CTC) towards a time crystalline state exhibiting two prominent oscillation frequencies. Applying a mean-field approximation model and a Floquet analysis, we theoretically confirm that this transition is a manifestation in a many-body system of a torus bifurcation between a limit cycle (LC) and a limit torus (LT). We theoretically illustrate the LC and LT attractors using the minimal model and experimentally reconstruct them using Takens' embedding theorem applied to the non-destructively measured intracavity photon dynamics.

cond-mat.quant-gas↗

arXiv2025

Observation of a zero-energy excitation mode in the open Dicke model

Approaching phase boundaries in many-body systems can give rise to intriguing signatures in their excitation spectra. Here, we explore the excitation spectrum of a Bose-Einstein condensate strongly coupled to an optical cavity and pumped by an optical standing wave, which simulates the famous Dicke-Hepp-Lieb phase transition of the open Dicke model with dissipation arising due to photon leakage from the cavity. For weak dissipation, the excitation spectrum displays two strongly polaritonic modes. Close to the phase boundary, we observe an intriguing regime where the lower-energetic of these modes, instead of showing the expected roton-type mode softening, is found to approach and persist at zero energy, well before the critical pump strength for the Dicke-Hepp-Lieb transition boundary is reached. Hence, a peculiar situation arises, where an excitation is possible at zero energy cost, but nevertheless no instability of the system is created.

cond-mat.quant-gas↗

arXiv2024

Impact of quantum noise on phase transitions in an atom-cavity system with limit cycles

Quantum fluctuations are inherent in open quantum systems and they affect not only the statistical properties of the initial state but also the time evolution of the system. Using a generic minimal model, we show that quantum noise smoothens the transition between a stationary and a dynamical phase corresponding to a limit cycle (LC) in the semiclassical mean-field approximation of a generic open quantum system. Employing truncated Wigner approximation, we show that the inherent quantum noise pushes the system to exhibit signatures of LCs for interaction strengths lower than the critical value predicted by the standard mean-field theory, suggesting a noise-induced emergence of temporal ordering. Our work demonstrates that the apparent crossover-like behavior between stationary phases brought by finite-size effects from quantum fluctuations also apply to transitions involving dynamical phases. To demonstrate this on a specific physical system, we consider a transversely pumped atom-cavity setup, wherein LCs have been observed and identified as continuous time crystals. We compare the oscillation frequencies of the LCs in the one-dimensional (1D) and two-dimensional regimes, and find that the frequencies have larger shot-to-shot fluctuations in 1D. This has an important consequence in the effectiveness of entrainment of LCs for a periodically driven pump intensity or light-matter coupling strength.

cond-mat.quant-gas↗

arXiv2024

Apparent delay of the Kibble-Zurek mechanism in quenched open systems

We report a new intermediate regime in the quench time, $τ_{q}$, separating the usual validity of the Kibble-Zurek mechanism (KZM) and its breakdown for rapid quenches in open systems under finite quench protocols. It manifests in the power-law scaling of the transition time with $τ_{q}$ as the system appears to enter the adiabatic regime, even though the ramp is already terminated and the final quench value is held constant. This intermediate regime, which we dub as the delayed KZM, emerges due to the dissipation preventing the system from freezing in the impulse regime. This results in a large delay between the actual time the system undergoes a phase transition and the time inferred from a threshold-based criterion for the order parameter, as done in most experiments. We demonstrate using the open Dicke model and its one-dimensional lattice version that this phenomenon is a generic feature of open systems that can be mapped onto an effective coupled oscillator model. We also show that the phenomenon becomes more prominent near criticality, and its effects on the transition time measurement can be further exacerbated by large threshold values for an order parameter. Due to this, we propose an alternative method for threshold-based criterion which uses the spatio-temporal information, such as the system's defect number, for identifying the transition time.

cond-mat.stat-mech↗

arXiv2024

Observation of a phase transition from a continuous to a discrete time crystal

Discrete (DTCs) and continuous time crystals (CTCs) are novel dynamical many-body states, that are characterized by robust self-sustained oscillations, emerging via spontaneous breaking of discrete or continuous time translation symmetry. DTCs are periodically driven systems that oscillate with a subharmonic of the external drive, while CTCs are continuously driven and oscillate with a frequency intrinsic to the system. Here, we explore a phase transition from a continuous time crystal to a discrete time crystal. A CTC with a characteristic oscillation frequency $ω_\mathrm{CTC}$ is prepared in a continuously pumped atom-cavity system. Modulating the pump intensity of the CTC with a frequency $ω_{\mathrm{dr}}$ close to $2\,ω_\mathrm{CTC}$ leads to robust locking of $ω_\mathrm{CTC}$ to $ω_{\mathrm{dr}}/2$, and hence a DTC arises. This phase transition in a quantum many-body system is related to subharmonic injection locking of non-linear mechanical and electronic oscillators or lasers.

quant-ph↗

arXiv2024

Realizing limit cycles in dissipative bosonic systems

We propose a general mechanism for generating limit cycle (LC) oscillations by coupling a linear bosonic mode to a dissipative nonlinear bosonic mode. By analyzing the stability matrix, we show that LCs arise due to a supercritical Hopf bifurcation. We find that the existence of LCs is independent of the sign of the effective nonlinear interaction. The LC phase can be classified as a continuous time crystal (CTC), if it emerges in a many-body system. The bosonic model can be realised in three-level systems interacting with a quantised light mode as realised in atom-cavity systems. Using such a platform, we experimentally observe LCs for the first time in an atom-cavity system with attractive optical pump lattice, thereby confirming our theoretical predictions.

cond-mat.quant-gas↗

arXiv2024

Theory of parametric resonance for discrete time crystals in fully-connected spin-cavity systems

We pinpoint the conditions necessary for discrete time crystal (DTC) formation in fully connected spin-cavity systems from the perspective of parametric resonance by mapping these systems onto oscillator like models. We elucidate the role of nonlinearity and dissipation by mapping the periodically driven open Dicke model onto effective linear and nonlinear oscillator models, while we analyze the effect of global symmetry breaking using the Lipkin-Meshkov-Glick model with tunable anisotropy. We show that the system's nonlinearity restrains the dynamics from becoming unbounded when driven resonantly. On the other hand, dissipation keeps the oscillation amplitude of the period-doubling instability fixed, which is a key feature of DTCs. The presence of global symmetry breaking in the absence of driving is found to be crucial in the parametric resonant activation of period-doubling response. We provide analytic predictions for the resonant frequencies and amplitudes leading to DTC formation for both systems using their respective oscillator models.

quant-ph↗

arXiv2023

Dissipationless counterflow currents above T_c in bilayer superconductors

We report the existence of dissipationless currents in bilayer superconductors above the critical temperature $T_c$, assuming that the superconducting phase transition is dominated by phase fluctuations. Using a semiclassical $U(1)$ lattice gauge theory, we show that thermal fluctuations cause a transition from the superconducting state at low temperature to a resistive state above $T_c$, accompanied by the proliferation of unbound vortices. Remarkably, while the proliferation of vortex excitations causes dissipation of homogeneous in-plane currents, we find that counterflow currents, flowing in opposite direction within a bilayer, remain dissipationless. The presence of a dissipationless current channel above $T_c$ is attributed to the inhibition of vortex motion by local superconducting coherence within a single bilayer, in the presence of counterflow currents. Our theory presents a possible scenario for the pseudogap phase in bilayer cuprates.

cond-mat.supr-con↗

arXiv2023

Bridging closed and dissipative discrete time crystals in spin systems with infinite-range interactions

We elucidate the role that the dissipation in a bosonic channel plays in the prevalence and stability of time crystals (TCs) in a periodically driven spin-boson system described by the Dicke model. Here, the bosons are represented by photons, and they mediate the infinite-range interactions between the spin systems. For strong dissipation, we study the dynamics using an effective atom-only description and the closed Lipkin-Meshkov-Glick model. By mapping out the phase diagrams for varying dissipation strengths, ranging from zero to infinitely strong, we demonstrate that the area in the phase diagram, where a TC exists, grows with the dissipation strength but only up to an optimal point, beyond which most of the TCs become unstable. We find TCs in both closed-system and dissipative regimes, but dissipative TCs are shown to be more robust against random noise in the drive, and are only weakly affected by the choice of initial state. We present the finite-sized behaviour and the scaling of the lifetime of the TCs with respect to the number of spins and the interaction strength within a fully quantum mechanical description.

quant-ph↗

arXiv2023

Condensate formation in a dark state of a driven atom-cavity system

We demonstrate condensate formation in a dark state in an ultracold quantum gas coupled to a high-finesse cavity and pumped by a shaken optical lattice. We show experimentally and theoretically that the atoms in the dark state display a strong suppression of the coupling to the cavity. On the theory side, this is supported by solving the dynamics of a minimal three-level model and of the full atom-cavity system. The symmetry of the condensate wave function is anti-symmetric with respect to the potential minima of the pump lattice, and displays a staggered sign along the cavity direction. This symmetry decouples the dark state from the cavity, and is preserved when the pump intensity is switched off.

cond-mat.quant-gas↗

arXiv2023

Quantum rotation sensor with real-time readout based on an atom-cavity system

Using an atom-cavity platform, we propose to combine the effective gauge phase of rotated neutral atoms and the superradiant phase transition to build a highly sensitive and fast quantum rotation sensor. The atoms in a well-controlled array of Bose-Einstein condensates are coupled to a single light mode of an optical cavity. The photon emission from the cavity indicates changes in the rotation frequency in real time, which is crucial for inertial navigation. We derive an analytical expression for the phase boundaries and use a semi-classical method to map out the phase diagram numerically, which provides the dependence of the photon emission on the rotation. We further suggest to operate the sensor with a bias rotation, and to enlarge the enclosed area, to enhance the sensitivity of the sensor.

quant-ph↗

arXiv2022

Parametric control of Meissner screening in light-driven superconductors

We investigate the Meissner effect in a parametrically driven superconductor using a semiclassical $U(1)$ lattice gauge theory. Specifically, we periodically drive the $z$-axis tunneling, which leads to an enhancement of the imaginary part of the $z$-axis conductivity at low frequencies if the driving frequency is blue-detuned from the plasma frequency. This has been proposed as a possible mechanism for light-enhanced interlayer transport in YBa$_2$C$_3$O$_{7-δ}$ (YBCO). In contrast to this enhancement of the conductivity, we find that the screening of magnetic fields is less effective than in equilibrium for blue-detuned driving, while it displays a tendency to be enhanced for red-detuned driving.

cond-mat.supr-con↗

arXiv2022

Observation of a continuous time crystal

Time crystals are classified as discrete or continuous depending on whether they spontaneously break discrete or continuous time translation symmetry. While discrete time crystals have been extensively studied in periodically driven systems since their recent discovery, the experimental realization of a continuous time crystal is still pending. Here, we report the observation of a limit cycle phase in a continuously pumped dissipative atom-cavity system, which is characterized by emergent oscillations in the intracavity photon number. We observe that the phase of this oscillation is random for different realizations, and hence this dynamical many-body state breaks continuous time translation symmetry spontaneously. The observed robustness of the limit cycles against temporal perturbations confirms the realization of a continuous time crystal.

cond-mat.quant-gas↗