Activity, which represents the kinetic property of dynamics, plays a central role in obtaining thermodynamic speed limits (TSLs). In this paper, we discuss a unified framework that provides the existing TSLs based on different activities such as dynamical activity and dynamical state mobility. This unification is based on generalized means that include standard means such as the arithmetic, logarithmic, and geometric means, the first two of which respectively correspond to the dynamical activity and the dynamical state mobility. We also derive an infinite variety of TSLs for Markov jump processes and deterministic chemical reaction networks using different activities. The lower bound on the entropy production given by each TSL provides the minimum dissipation achievable by a conservative force. We numerically and analytically discuss the tightness of the lower bounds on the entropy production rate in the various TSLs.

We develop a constructive approach to generate quantum neural networks capable of representing the exact thermal states of all many-body qubit Hamiltonians. The Trotter expansion of the imaginary time propagator is implemented through an exact block encoding by means of a unitary, restricted Boltzmann machine architecture. Marginalization over the hidden-layer neurons (auxiliary qubits) creates the nonunitary action on the visible layer. Then, we introduce a unitary deep Boltzmann machine architecture in which the hidden-layer qubits are allowed to couple laterally to other hidden qubits. We prove that this wave-function Ansatz is closed under the action of the imaginary time propagator and, more generally, can represent the action of a universal set of quantum gate operations. We provide analytic expressions for the coefficients for both architectures, thus enabling exact network representations of thermal states without stochastic optimization of the network parameters. In the limit of large imaginary time, the Ansatz yields the ground state of the system. The number of qubits grows linearly with the number of interactions and total imaginary time for a fixed interaction order. Both networks can be readily implemented on quantum hardware via midcircuit measurements of auxiliary qubits. If only one auxiliary qubit is measured and reset, the circuit depth scales linearly with imaginary time and number of interactions, while the width is constant. Alternatively, one can employ a number of auxiliary qubits linearly proportional to the number of interactions, and circuit depth grows linearly with imaginary time only. Every midcircuit measurement has a postselection success probability, and the overall success probability is equal to the product of the probabilities of the midcircuit measurements.

Semiconductor double quantum dots (DQD) coupled to superconducting microwave resonators offer a promising platform for the detection of single microwave photons. In previous works, the photodetection was studied for a monochromatic source of microwave photons. Here, we theoretically analyze the photodetection of single microwave pulses. The photodetection in this case can be seen as a nonlinear filtering process of an incoming signal, the pulse, to an outgoing one, the photocurrent. This analogy to signal processing motivated the derivation of a Wigner-function formalism which provides a compelling visualization of the time and frequency properties of the photodetector for low intensities. We find a trade-off between detecting the time and the frequency of the incoming photons, in agreement with the time-energy uncertainty relation. As the intensity of the source increases, the photodetection is influenced by coherent Rabi oscillations of the DQD. Our findings give insight into the time-dependent properties of microwave photons interacting with electrons in a DQD-resonator hybrid system and provide guidance for experiments on single microwave pulse detection.

Layered Cu/Fe perovskites with a ${\mathrm{YBaCuFeO}}_5$ structure have attracted significant attention owing to the high thermal stability ($T_S$) of their incommensurate spiral magnetic phase. The intrinsic coupling between spin and ferroelectric orders in these cycloidally ordered multiferroics makes them among the most promising spin-driven magnetoelectric multiferroic candidates. In this system, strong in-plane antiferromagnetic couplings lead to collinearly ordered magnetic planes with spin directions alternating with periodicity ($k_x, k_y$) = (0.5, 0.5), while spin propagation along the perpendicular direction is governed by competing frustrated magnetic couplings of varying signs and strengths. In compounds of this family studied to date, the incommensurate spiral order emerges below $T_S$ due to correlated canting of ferromagnetically coupled spins in bipyramidal layers ($k_z=0.5\to 0.5\pm q_S$). Here, we demonstrate that a spiral magnetic ground state can also arise from a distinct precursor collinear spin configuration, where, above $T_S$, spins in the bipyramids are initially antiferromagnetically coupled ($k_z=0\to \pm q_S$). This newly observed spiral magnetic transition, identified and investigated in ${\mathrm{YBaCu}}_{1-x}{\mathrm{M}}_x{\mathrm{FeO}}_5$ compounds (M: Co, Zn), exists beyond the triple magnetic point, previously considered the critical limit for the ordering of the magnetic spiral in ${\mathrm{YBaCuFeO}}_5$. In the compounds investigated, the new spiral state persists in this region, stabilizing at temperatures up to 365 K.

Humans perform adaptive locomotion in diverse environments. To adapt to changes in speed, they switch their gait between walking and running. Many gait parameters suddenly change at gait transitions and the walk-to-run and run-to-walk transition speeds differ (i.e., hysteresis appears). However, the mechanism of this hysteresis remains largely unclear. With the recent momentum toward manned exploration programs, it has become increasingly important to elucidate the effects of low-gravity environments on human locomotion. Low gravity significantly alters gait transitions. In particular, the sudden changes in the gait parameters and hysteresis disappear. The mechanism of these changes in low-gravity environments also remains largely unclear. In this study, we developed a neuromechanical model to reproduce the sudden gait transitions and hysteresis under normal gravity and the smooth gait transitions and disappearance of hysteresis under low gravity, as verified by a comparison with human data. A nonlinear dynamic analysis shows that resonance induces saddle-node bifurcations, which cause the sudden gait transitions and hysteresis, and that low gravity changes the resonance such that it induces a cusp catastrophe, which causes the smooth gait transitions and disappearance of hysteresis. Our results will lead to a better understanding of human adaptation to gravity in terms of motor control, contributing to future human space activities, and provide useful insight into rehabilitation techniques.

Cells actively regulate their size during the cell cycle to maintain volume homeostasis across generations. While various mathematical models of cell size regulation have been proposed to explain how this is achieved, relating these models to experimentally observed cell size distributions has proved challenging. In this paper we present a simple formula for the cell size distribution in lineages as observed in, e.g., a mother machine, and provide a new derivation for the corresponding result in populations, assuming exponential cell growth. Our results are independent of the underlying cell size control mechanism and explain the characteristic shape underlying experimentally observed cell size distributions. We furthermore derive universal moment identities for these distributions and show that our predictions agree well with experimental measurements of E. coli cells, both on the distribution and the moment level.

The brain is able to sustain many different states as shown by the daily natural transitions between wakefulness and sleep. Yet, the underlying complex dynamics of these brain states are essentially in nonequilibrium. Here, we develop a thermodynamical formalism based on the off-equilibrium extension of the fluctuation-dissipation theorem (FDT) together with a whole-brain model. This allows us to investigate the nonequilibrium dynamics of different brain states and more specifically to apply this formalism to wakefulness and deep sleep brain states. We show that the off-equilibrium thermodynamical signatures of brain states are significantly different in terms of the overall level of differential and integral violation of FDT. Furthermore, the framework allows for a detailed understanding of how different brain regions and networks are contributing to the off-equilibrium signatures in different brain states. Overall, this framework shows great promise for characterizing and differentiating brain states in health and disease.

The spread of behavior in collective evasion of mobile animal groups can be predicted by reconstructing quantitative interaction networks. Based on the assumption of time scale separation between a fast contagion process and a slower movement response, the underlying interaction networks have been previously assumed to be static, determined by the spatial structure at the onset of the collective escape response. This idealization does not account for the temporal evolution of the spatial network structure, which may have a major impact on the behavioral contagion dynamics. Here, we propose a spatially explicit, agent-based model for the coupling between behavioral contagion and the network dynamics originating from the spreading movement response. We explore the impact of movement parameters (startle speed, initial directionality, and directional noise) on average cascade size. By conducting numerical simulations for different density levels, we show that increasing escape speed suppresses the cascade size in most cases, that the cascade size depends strongly on the movement direction of the initially startled individual, and that large variability in the direction of individual escape movements (rotational noise) will typically promote the spread of behavioral contagion through spatial groups. Our work highlights the importance of accounting for movement dynamics in behavioral contagion, and facilitates our understanding of rapid coordinated response and collective information processing in animal groups.

Perturbing resonant systems causes shifts in their associated scattering poles in the complex plane. In a previous study [N. Byrnes and M. R. Foreman, arXiv:2408.11360], we demonstrated that these shifts can be calculated numerically by analyzing the residue of a generalized Wigner-Smith operator associated with the perturbation parameter. In this work, we extend this approach by connecting the Wigner-Smith formalism with results from standard electromagnetic perturbation theory applicable to open systems with resonances of arbitrary quality factors. We further demonstrate the utility of the method through several numerical examples, including the inverse design of a multilayered nanoresonator sensor and an analysis of the enhanced sensitivity of scattering zeros to perturbations.

Spin noise spectroscopy (SNS) has become a mainstream approach to probe the dynamics of a spin ensemble in and out of equilibrium. Current models describing spin noise in interacting samples are based on an effective single-particle dynamics in a bath. Here, we report the observation of a strong interaction regime which significantly affects the spin dynamics. Performing SNS in a dense rubidium vapor, we observe anomalous distortions of the usual spin noise spectra, which we attribute to resonant dipole-dipole interaction within the ensemble. As the density of the vapor increases, we observe a dramatic broadening of the usual resonances and the emergence of an unexpected extra low-frequency noise component. We use a simple microscopic two-body numerical model to reproduce and discuss these observations. Our results suggest that the spectra cannot be described by the usual models of single-atom dynamics and arise from the evolution of interacting pairs of atoms. This work opens the way to the study of many-body spin noise or higher-order correlators in atomic vapors using SNS.

We introduce a reversible theory of exact entanglement manipulation by establishing a necessary and sufficient condition for state transfer under trace-preserving transformations that completely preserve the positivity of partial transpose (PPT). Under these free transformations, we show that logarithmic negativity emerges as the pivotal entanglement measure for determining entangled states' transformations, analogous to the role of entropy in the second law of thermodynamics. Previous results proved that entanglement is irreversible under quantum operations that completely preserve PPT and under all nonentangling transformations. In this work, we find that going beyond the complete positivity constraint imposed by standard quantum mechanics enables a reversible theory of exact entanglement manipulation, which may suggest a potential incompatibility between the reversibility of entanglement and the fundamental principles of quantum mechanics.

In paraxial approximation, the electromagnetic eigenmodes inside an optical microresonator can be derived from a Schrödinger-type eigenvalue problem. In this framework, tilting the cavity mirrors introduces a linear term to the potential energy of the system. In our paper, we apply solution strategies for inverse problems to precisely determine and control the relative orientation of two mirrors forming an optical microcavity. Our approach employs the inversion of the Schrödinger equation to reconstruct the effective potential landscape, and thus mirror tilts, from observed mode patterns. We investigate regularization techniques to address the ill-posed nature of inverse problems and to improve the stability of solutions. Our method consistently achieves an angle resolution of order 100 nanoradians per measurement. We consider our method applicable to a wide variety of optical resonators and driving schemes.

In strong-field ionization of molecules, intense light pulses are thought to have a negligible direct influence on atomic nuclei. Molecular dissociation is thus expected to be determined by the geometrical configuration of the molecular ion at the ionization instant. Contrary to this picture, we observe a counterintuitive electron-proton angular correlation and the formation of proton vortices following strong-field ionization of ${\mathrm{H}}_2$ molecules by bicircularly polarized two-color laser fields. We explain this phenomenon by the pathway interference and localization of the residual ${\mathrm{H}}_2{}^{+}$ electron in different angular-momentum states formed in the tail of the driving laser pulse. We validate this interpretation by combining a quantum-mechanical numerical simulation of the field-driven coupled electronic-nuclear dynamics and a semiclassical-trajectory model for the phase accumulation of the laser-driven electronic-nuclear wave packet. Our joint experimental and theoretical study reveals a general picture of vortex electron localization which can be used for controlling molecular-bond breaking with circularly polarized laser fields.

Magnetic field generation in ultraintense laser-solid interactions is studied over a range of laser intensities relevant to next-generation laser facilities $(a_0=50–500)$ using two-dimensional (2D) particle-in-cell simulations including strong-field quantum electrodynamic effects. It is found that fields $O\left(0.1\right)$ MT (1 GG) may be generated by relativistic electrons traveling along the surface of the target. However, a significant fraction of the energy budget is converted to high-energy photons, approximately $38\%$ at $a_0=500$, greatly reducing the available energy for field generation. A model for the evolution of the target-surface fields is created and the scaling of the field strength with $a_0$ is extracted from a set of 2D simulations. The simulated scaling allows for the estimation of field strengths and the model gives insight into the evolution of the fields on the next generation of laser facilities, a necessary component to the proposal of any future magnetized experiment.

After rainfall, pine needles often float on the surface of small puddles. As the water evaporates, they self-assemble into distinct clusters. Motivated by this natural phenomenon, we experimentally investigate the dynamic evolution of synthetic particles as the liquid surface shrinks in area. Our experiments demonstrate the tendency of particles to aggregate, forming distinct clusters as the liquid boundary shrinks. We systematically examine the emergence of these clusters and explore how their sizes and numbers evolve with changes in the packing fraction. We also analyze particle rotation during the process and discuss the formation of the final configuration comprising clusters of various orientations. Complementary numerical simulations demonstrate qualitative agreement with our experimental findings. This study sheds additional light on the self-assembly of macroscopic particles in a dynamically evolving medium.

Continuous superradiance using a narrow optical transition has the potential to improve the short-term stability of state-of-the-art optical clocks. Even though pulsed superradiant emission on a $\mathrm{mHz}$ linewidth clock transition has been shown, true continuous operation, without Fourier limitation, has turned out to be extremely challenging. The trade-off between maintaining a high atomic flux while minimizing decoherence effects presents a significant obstacle. Here, we discuss the design of a machine that could overcome this problem by combining a high-flux continuous beam of ultracold strontium atoms with a bowtie cavity for the generation of superradiant lasing. To evaluate the feasibility of our design, we present simulation results for continuous high-efficiency cooling, loading, and pumping to the upper lasing state inside the bowtie cavity. We then present two different models for simulating the generated superradiant field by taking into account position-dependent shifts, collisional decoherence, light shifts, and atom loss. Finally, we estimate a laser linewidth of less than $100\mathrm{mHz}$, limited by atom number fluctuations, resulting in an output power of hundreds of $\mathrm{fW}$.