Building on the recent work in [K. L. Tsakmakidis, et al., Nature Communications 16, 5719 (2025)], we analyze the therein introduced Pauli-matrix first-order formulation pertaining to the Engquist-Majda one-way wave problem. We show that the Pauli formulation provides a local doubled matrix factorization whose Hamiltonian is unitarily equivalent to a rotated Weyl Hamiltonian. Because the doubled system contains both longitudinal roots, exact recovery of one scalar one-way branch requires a nonlocal spectral projector. For homogeneous Maxwell fields, the auxiliary branch space should be distinguished from the two-dimensional physical polarization space, leading to a four-component polarization-preserving lift. Numerical snapshots illustrate one-way directional propagation in the selected sector.
ABSTRACT Optimizing each pulse time slice independently can reach high fidelity but, left unchecked, produces high‐energy controls. MAGICARP, a Pontryagin‐inspired shooting method, instead yields smooth, energy‐efficient pulses from few parameters. We extend MAGICARP from driftless to closed systems with constant drift, focusing on two exchange‐coupled spins in a magnetic field. Optimization is staged: dressed drift eigenstates define the target, shooting is done in the rotating‐wave frame, then an exact laboratory‐frame refinement is applied. At matched infidelity versus Krotov and GRAPE, MAGICARP uses the least energy, conserves pulse area, concentrates spectral weight on gate‐relevant transitions, and is most robust to exchange‐coupling noise. GRAPE converges to a similar solution with more parameters, while black‐box Krotov requires about an order of magnitude more energy. A large, unfiltered run survey reveals a weak‐driving quantum speed limit: below a critical gate time, low‐amplitude QFT controls vanish, and the minimum energy diverges as approaches the limit, following , where is the drift‐free time‐optimal area cost and is a pole at the speed limit.
ABSTRACT The physical understanding of biological processes relies on precise measurements of the energy landscapes of small systems, like proteins or RNA and DNA molecules. Non‐equilibrium pulling measurements establish energy landscapes in finite time but introduce a non‐measurable bias due to work dissipated during the measurement. Theory and simulations are used to compare the efficiencies of different feedback protocols for reducing dissipation and improving free energy measurements under the experimentally relevant condition of equal measurement time. While slower processes are less irreversible, reducing dissipation with feedback does not necessarily improve free‐energy estimation. Feedback strategies, defined as correlated sequences of discrete‐ and continuous‐time feedback protocols, are the most efficient at reducing dissipation and measurement bias in single‐molecule pulling experiments.
ABSTRACT Over the course of an extended process, a generational transition took place in Göttingen physics in the years 1914–1920, as the result of which the two chairs of physics held by Woldemar Voigt and Eduard Riecke were eventually replaced by Max Born and James Franck. As part of this process, the Göttingen mathematicians, led by Felix Klein and David Hilbert, prevented Johannes Stark, a Göttingen‐trained experimental physicist, from succeeding Riecke. Stark applied for the position himself with the Prussian Ministry of Culture. A particularly revealing letter dated July 1, 1915—presented here in full and contextualized—reveals his egocentric character, his dismissive attitude toward physicists who conducted mathematics‐based research, and his anti‐Semitic views even at that early stage.
ABSTRACT Altermagnets combine the vanishing net magnetization of antiferromagnets with the nonrelativistic momentum‐space spin splitting of ferromagnets. Achieving efficient and nonvolatile control of their spin textures has become a central challenge in altermagnetic spintronics. While ferroelectric switching has dominated early studies of multiferroic altermagnets, mechanical control through ferroic lattice degrees of freedom provides a complementary route, as it does not rely on spontaneous electric polarization. In this Perspective, we review recent progress in the mechanical control of altermagnetism and organize the emerging mechanisms into three closely related routes: ferroelastic control , where switching between symmetry‐related lattice variants reorients or reconstructs the spin texture; coupled multiferroic control , represented by altriferroic materials combining altermagnetism, ferroelasticity, and ferroelectricity; and hidden staggered structural control , represented by antiferroelastic altermagnets whose staggered distortions reverse the spin splitting without reversing the Néel vector. These concepts are hierarchical and may overlap, with altriferroicity representing a multiferroic extension built on ferroelastic order. We further discuss the key challenges currently facing this field. Overall, these developments show that ferroic lattice control offers a promising route toward structurally reconfigurable altermagnetic spintronics.
