Optimal Time-Entropy Bounds and Speed Limits for Brownian Thermal Shortcuts.

By controlling the variance of the radiation pressure exerted on an optically trapped microsphere in real time, we engineer temperature protocols that shortcut thermal relaxation when transferring the microsphere from one thermal equilibrium state to another. We identify the entropic footprint of such accelerated transfers and derive optimal temperature protocols that either minimize the production of entropy for a given transfer duration or accelerate the transfer for a given entropic cost as much as possible. Optimizing the trade-off yields time-entropy bounds that put speed limits on thermalization schemes. We further show how optimization expands the possibilities for accelerating Brownian thermalization down to its fundamental limits. Our approach paves the way for the design of optimized, finite-time thermodynamics for Brownian engines. It also offers a platform for investigating fundamental connections between information geometry and finite-time processes.

Reply to "Comment on 'Harvesting information to control nonequilibrium states of active matter' ".

We stress that the limitations on one of the results of our paper [R. Goerlich et al., Phys. Rev. E 106, 054617 (2022)2470-004510.1103/PhysRevE.106.054617], which are mentioned in the preceding Comment [A. Bérut, preceding Comment, Phys. Rev. E 107, 056601 (2023)10.1103/PhysRevE.107.056601], were actually already acknowledged and discussed in the original publication. Although the observed relationship between the released heat and the spectral entropy of the correlated noise is not universal (but limited to one-parameter Lorentzian spectra), the existence of such a clear relationship is a solid experimental finding. It not only gives a convincing explanation for the surprising thermodynamics observed in the transitions between nonequilibrium steady states, but also provides new tools for the analysis of nontrivial baths. In addition, by using different measures of the correlated noise information content, it may be possible to generalize these results to non-Lorentzian spectra.

Harvesting information to control nonequilibrium states of active matter.

We propose to use a correlated noise bath to drive an optically trapped Brownian particle that mimics active biological matter. Due to the flexibility and precision of our setup, we are able to control the different parameters that drive the stochastic motion of the particle with unprecedented accuracy, thus reaching strongly correlated regimes that are not easily accessible with real active matter. In particular, by using the correlation time (i.e., the "color") of the noise as a control parameter, we can trigger transitions between two nonequilibrium steady states with no expended work, but only a calorific cost. Remarkably, the measured heat production is directly proportional to the spectral entropy of the correlated noise, in a fashion that is reminiscent of Landauer's principle. Our procedure can be viewed as a method for harvesting information from the active fluctuations.

Coincidence study of core-ionized adamantane: site-sensitivity within a carbon cage?

We investigate the fragmentation dynamics of adamantane dications produced after core-ionization at the carbon edge followed by Auger decay. The combination of high-resolution electron spectroscopy, energy-resolved electron-ion multi-coincidence spectroscopy and different theoretical models allows us to give a complete characterization of the processes involved after ionization. We show that energy- and site-sensitivity is observed even for a highly-symmetric molecule that lacks any unique atomic site.

Noise and ergodic properties of Brownian motion in an optical tweezer: Looking at regime crossovers in an Ornstein-Uhlenbeck process.

We characterize throughout the spectral range of an optical trap the nature of the noise that drives the Brownian motion of an overdamped trapped single microsphere and its ergodicity, comparing experimental, analytical, and simulated data. We carefully analyze noise and ergodic properties (i) using the Allan variance for characterizing the noise and (ii) exploiting a test of ergodicity tailored for experiments done over finite times. We derive these two estimators in the Ornstein-Uhlenbeck low-frequency trapped-diffusion regime and study analytically their evolution toward the high-frequency Wiener-like free-diffusion regime, in very good agreement with simulated and experimental results. This study is performed comprehensively from the free-diffusion to the trapped-diffusion regimes. It also carefully looks at the specific signatures of the estimators at the crossover between the two regimes. This analysis is important to conduct when exploiting optical traps in a metrology context.

Phase-space methods for the spin dynamics in condensed matter systems.

Using the phase-space formulation of quantum mechanics, we derive a four-component Wigner equation for a system composed of spin-[Formula: see text] fermions (typically, electrons) including the Zeeman effect and the spin-orbit coupling. This Wigner equation is coupled to the appropriate Maxwell equations to form a self-consistent mean-field model. A set of semiclassical Vlasov equations with spin effects is obtained by expanding the full quantum model to first order in the Planck constant. The corresponding hydrodynamic equations are derived by taking velocity moments of the phase-space distribution function. A simple closure relation is proposed to obtain a closed set of hydrodynamic equations.This article is part of the themed issue 'Theoretical and computational studies of non-equilibrium and non-statistical dynamics in the gas phase, in the condensed phase and at interfaces'.

M3C: A Computational Approach To Describe Statistical Fragmentation of Excited Molecules and Clusters.

The Microcanonical Metropolis Monte Carlo method, based on a random sampling of the density of states, is revisited for the study of molecular fragmentation in the gas phase (isolated molecules, atomic and molecular clusters, complex biomolecules, etc.). A random walk or uniform random sampling in the configurational space (atomic positions) and a uniform random sampling of the relative orientation, vibrational energy, and chemical composition of the fragments is used to estimate the density of states of the system, which is continuously updated as the random sampling populates individual states. The validity and usefulness of the method is demonstrated by applying it to evaluate the caloric curve of a weakly bound rare gas cluster (Ar13), to interpret the fragmentation of highly excited small neutral and singly positively charged carbon clusters (Cn, n = 5,7,9 and Cn+, n = 4,5) and to simulate the mass spectrum of the acetylene molecule (C2H2).

Quantum-relativistic hydrodynamic model for a spin-polarized electron gas interacting with light.

We develop a semirelativistic quantum fluid theory based on the expansion of the Dirac Hamiltonian to second order in 1/c. By making use of the Madelung representation of the wave function, we derive a set of hydrodynamic equations that comprises a continuity equation, an Euler equation for the mean velocity, and an evolution equation for the electron spin density. This hydrodynamic model is then applied to study the dynamics of a dense and weakly relativistic electron plasma. In particular, we investigate the impact of the quantum-relativistic spin effects on the Faraday rotation in a one-dimensional plasma slab irradiated by an x-ray laser source.

Adiabatic cooling of trapped non-neutral plasmas.

Non-neutral plasmas can be trapped for long times by means of combined electric and magnetic fields. Adiabatic cooling is achieved by slowly decreasing the trapping frequency and letting the plasma occupy a larger volume. We develop a fully kinetic time-dependent theory of adiabatic cooling for plasmas trapped in a one-dimensional well. This approach is further extended to three dimensions and applied to the cooling of antiproton plasmas, showing excellent agreement with recent experiments [Gabrielse et al., Phys. Rev. Lett. 106, 073002 (2011)].

Nonlinear absorption of ultrashort laser pulses in thin metal films.

Self-consistent simulations of the ultrafast electron dynamics in thin metal films were performed. A regime of nonlinear oscillations was observed that corresponds to ballistic electrons bouncing back and forth against the films' surfaces. When an oscillatory laser field is applied to the film, the field energy is partially absorbed by the electron gas. Maximum absorption occurs when the period of the external field matches the period of the nonlinear oscillations, which, for sodium films, lies in the infrared range. Possible experimental implementations are discussed.

Differential and total (e,2e) cross sections of simple polyatomic molecules.

In this paper, we present a theoretical approach to calculate differential and total ionization cross sections of polyatomic molecules by fast electron impact. More exactly, we have studied the ionization of ammonia (NH(3)) and methane (CH(4)) molecules, and previous results concerning the H(2)O molecule ionization are reported for comparison. The calculations are performed in the distorted wave Born approximation without exchange by employing the independent electron model. The molecular target wave functions are described by linear combinations of atomic orbitals. To describe the interaction between the inactive target electrons and the slow ejected electron, we have introduced a distortion via an effective potential calculated for each molecular orbital. The present theoretical calculations agree well with a large set of existing experimental data in terms of multiple differential and total cross sections.