arXiv subjects

Steven Blaber

Publications and source records attributed to Steven Blaber.

9 recordsLinked to original sources

arXiv2026

Delta-Function Kicks are Optimal for Rapidly Driven Inertial Stochastic Systems

Optimal control helps guide our understanding of stochastic thermodynamics, leading to universal properties and geometric formulations. Among the initially surprising properties of optimal control, not only discrete jumps but delta function kicks have been shown to be necessary to minimize dissipation in specific example systems. Using a short-time approximation, I show that delta-function kicks are universally optimal for minimizing dissipation in inertial stochastic systems, including active and quantum dynamics under general constraints. Fundamentally stemming from basic kinematics, delta-function kicks are required to achieve linear scaling of work with short protocol durations compared to the quadratic scaling without the kicks. This implies a diverging (infinite) ratio of saved work in the short-time limit.

cond-mat.stat-mech↗

arXiv2026

Mechanical loss in amorphous solids: spatial correlations, interacting transitions, and annealed thermodynamic pathways

The disordered and defect-rich structure of amorphous solids forms heterogeneous, high-dimensional energy landscapes. Such an energy landscape can be described by a discrete-state network of transitions between stable energy minima. Under low-frequency mechanical oscillations, defect-mediated, thermally activated transitions provide a microscopic mechanism for mechanical dissipation that are the dominant cause of mechanical loss in the mirror coatings of ground based gravitational waves detectors. Using molecular simulations, we find spatially correlated and strongly interacting transitions that require a general network description instead of a superposition of independent two-level systems as traditionally assumed. An annealing study combined with an analysis of dominant relaxation paths in the energy landscape reveals novel mechanisms for reducing room temperature mechanical loss.

cond-mat.mtrl-sci↗

arXiv2024

Connected Network Model for the Mechanical Loss of Amorphous Materials

Dissipation in amorphous solids at low frequencies is commonly attributed to activated transitions of isolated two-level systems (TLS) that come in resonance with elastic or electric fields. Materials with low mechanical or dielectric loss are urgently needed for applications in gravitational wave detection, high precision sensors, and quantum computing. Using atomistic modeling, we explore the energy landscape of amorphous silicon and titanium dioxide, and find that the pairs of energy minima that constitute single TLS form a sparsely connected network with complex topologies. Motivated by this observation, we develop an analytically tractable theory for mechanical loss of the full network from a nonequilibrium thermodynamic perspective. We demonstrate that the connectivity of the network introduces new mechanisms that can both reduce low frequency dissipation through additional low energy relaxation pathways, and increase dissipation through a broad distribution of energy minima. As a result, the connected network model predicts mechanical loss with distinct frequency profiles compared to the isolated TLS model. This not only calls into question the validity of the TLS model, but also gives us many new avenues and properties to analyze for the targeted design of low mechanical loss materials.

cond-mat.mtrl-sci↗

arXiv2022

Optimal Control in Stochastic Thermodynamics

We review recent progress in optimal control in stochastic thermodynamics. Theoretical advances provide in-depth insight into minimum-dissipation control with either full or limited (parametric) control, and spanning the limits from slow to fast driving and from weak to strong driving. Known exact solutions give a window into the properties of minimum-dissipation control, which are reproduced by approximate methods in the relevant limits. Connections between optimal-transport theory and minimum-dissipation protocols under full control give deep insight into the properties of optimal control and place bounds on the dissipation of thermodynamic processes. Since minimum-dissipation protocols are relatively well understood and advanced approximation methods and numerical techniques for estimating minimum-dissipation protocols have been developed, now is an opportune time for application to chemical and biological systems.

cond-mat.stat-mech↗

arXiv2022

Optimal control with a strong harmonic trap

Quadratic trapping potentials are widely used to experimentally probe biopolymers and molecular machines and drive transitions in steered molecular-dynamics simulations. Approximating energy landscapes as locally quadratic, we design multidimensional trapping protocols that minimize dissipation. The designed protocols are easily solvable and applicable to a wide range of systems. The approximation does not rely on either fast or slow limits and is valid for any duration provided the trapping potential is sufficiently strong. We demonstrate the utility of the designed protocols with a simple model of a periodically driven rotary motor. Our results elucidate principles of effective single-molecule manipulation and efficient nonequilibrium free-energy estimation.

cond-mat.stat-mech↗

arXiv2022

Efficient two-dimensional control of barrier crossing

Driven barrier crossings are pervasive in optical-trapping experiments and steered molecular-dynamics simulations. Despite the high fidelity of control, the freedom in the choice of driving protocol is rarely exploited to improve efficiency. We design protocols that reduce dissipation for rapidly driven barrier crossing under two-dimensional control of a harmonic trapping potential, controlling both trap center and stiffness. For fast driving, the minimum-dissipation protocol jumps halfway between the control-parameter endpoints. For slow driving, the minimum-dissipation protocol generically slows down and tightens the trap as it crosses the barrier, resulting in both significant energy savings and increased flux compared to naive and one-dimensional protocols (that only change trap center). Combining fast and slow results, we design protocols that improve performance at all speeds.

cond-mat.stat-mech↗

arXiv2021

Steps minimize dissipation in rapidly driven stochastic systems

Micro- and nano-scale systems driven by rapid changes in control parameters (control protocols) dissipate significant energy. In the fast-protocol limit, we find that protocols that minimize dissipation at fixed duration are universally given by a two-step process, jumping to and from a point that balances jump size with fast relaxation. Jump protocols could be exploited by molecular machines or thermodynamic computing to improve energetic efficiency, and implemented in nonequilibrium free-energy estimation to improve accuracy.

cond-mat.stat-mech↗

arXiv2021

Skewed Thermodynamic Geometry and Optimal Free Energy Estimation

Free energy differences are a central quantity of interest in physics, chemistry, and biology. We develop design principles that improve the precision and accuracy of free energy estimators, which has potential applications to screening for targeted drug discovery. Specifically, by exploiting the connection between the work statistics of time-reversed protocol pairs, we develop near-equilibrium approximations for moments of the excess work and analyze the dominant contributions to the precision and accuracy of standard nonequilibrium free-energy estimators. Within linear response, minimum-dissipation protocols follow geodesics of the Riemannian metric induced by the Stokes' friction tensor. We find the next-order contribution arises from the rank-3 supra-Stokes' tensor that skews the geometric structure such that minimum-dissipation protocols follow geodesics of a generalized cubic Finsler metric. Thus, near equilibrium the supra-Stokes' tensor determines the leading-order contribution to the bias of bidirectional free-energy estimators.

cond-mat.stat-mech↗

arXiv2020

Optimal control of protein copy number

Cell-cell communication is often achieved by secreted signaling molecules that bind membrane-bound receptors. A common class of such receptors are G-protein coupled receptors, where extracellular binding induces changes on the membrane affinity near the receptor for certain cytosolic proteins, effectively altering their chemical potential. We analyze the minimum-dissipation schedules for dynamically changing chemical potential to induce steady-state changes in protein copy-number distributions, and illustrate with analytic solutions for linear chemical reaction networks. Protocols that change chemical potential on biologically relevant timescales are experimentally accessible using optogenetic manipulations, and our framework provides non-trivial predictions about functional dynamical cell-cell interactions.

q-bio.SC↗