The efficient preparation of collective eigenstates of subwavelength-spaced optical dipoles is a prerequisite for observing their signature radiative properties and for their applications in quantum information processing. We theoretically investigate the deterministic preparation of super- and subradiant states of two dipole-coupled two-level quantum emitters at deep-subwavelength separation using the Swing-UP of quantum EmitteR population (SUPER) excitation scheme. Utilizing suitable pulse parameters for two red-detuned, time-overlapping Gaussian pulses, the SUPER scheme enables close-to-unity population inversion in the targeted collective eigenstates. Furthermore, a tunable optical phase in the SUPER scheme enables the simultaneous inversions in both pure super- and subradiant states with finite populations, thereby resulting in the preparation of hybrid collective states. These results are possible to realize with or without an optical cavity. Our approach to populating the collective eigenstates in a cavity environment paves the way for the efficient preparation of these states in the presence of environmental decoherence. Our scheme enables single-photon generation, which is measured using the second-order correlation function. We also discuss in detail possible experimental realizations, in particular using solid-state emitters and molecules.

We employed Bohmian mechanics to solve the equations of motion for a charged particle traveling in a free electron gas. Quantum effects are accounted for by including the Bohm quantum-mechanical potential $Q$, which depends on the electronic density, in the typical classical description. Our approach provides a computationally efficient alternative to traditional quantum calculations for determining the electronic stopping force of charged particles in matter. We use this framework to investigate the stopping of fast protons and slow highly charged xenon ions in the free electron gas. For highly charged ions, we predict the stopping force as a function of the projectile charge exchange.

Recent theoretical works predict a hierarchy of long-lived, nonhydrodynamic modes in two-dimensional Fermi liquids arising from the feature—supposedly unique to two dimensions—that relaxation by head-on scattering is not efficient in the presence of Pauli blocking. This leads to a parity-based separation of scattering rates, with odd-parity modes relaxing much more slowly than even-parity ones. In this work, we establish that a similar effect exists in isotropic three-dimensional (3D) Fermi liquids, even though relaxation does not proceed solely by head-on scattering. We show that while the relaxation rates of even and odd modes in 3D share the same leading-order $\sim T^2$ low-temperature scaling typical of Fermi liquids, their magnitudes differ, with odd-parity modes relaxing more slowly than even ones for a broad class of interactions. We find a relative difference between odd-parity and even-parity relaxation rates as large as $40\%$ just by Pauli blocking alone, with a strong additional dependence on the scattering potential, such that the odd-even staggering is further enhanced by interactions that favor large-angle scattering. We identify signatures of these odd-parity relaxation rates in the static transverse conductivity as well as the transverse collective mode structure. Our results establish the unexpected existence of a tomographiclike regime in higher-dimensional Fermi liquids and suggest experimental probes via transport measurements.

Semiconductor nanowires (NWs) with strong Rashba spin-orbit coupling (RSOC), when exposed to a suitably applied Zeeman field, exhibit one-dimensional helical channels with a spin orientation locked to the propagation direction within the magnetic energy gap. Here, by adopting a scattering-matrix approach applied to a tight-binding model of the NW, we demonstrate that the thermoelectric (TE) properties can be widely controlled by tuning the misalignment angle $\varphi$ between the spin-orbit directions of two NW segments. In particular, when the RSOC vectors are antiparallel (Dirac-paradox configuration), we predict a significant violation of the Wiedemann-Franz law, and a strong enhancement of the Seebeck coefficient and the $ZT$ figure of merit. We also show that the Zeeman gap determines the optimal energy window for doping and temperatures. These results suggest that controlling the spin-orbit field direction, which can be achieved with suitably applied wrap gates, is a promising alternative for tuning and optimizing the TE response in quantum-coherent semiconducting NW devices.

Skutterudites are promising materials for thermoelectric and spintronics applications. Here, we explore spin fluctuations in the ${\mathrm{FeSb}}_3$ skutterudite and their effect on its electronic structure using Hubbard-corrected density-functional theory calculations. We identify multiple magnetic- and charge-disproportionated configurations, with an antiferromagnetic metallic ground state. Paramagnetic fluctuations modeled through a special quasirandom spin structure open a 61 meV gap, consistent with experiments. This state features nondegenerate spin channels and band-avoided crossings, resembling a Luttinger-compensated ferrimagnet. Mapping the electronic structure to a Heisenberg Hamiltonian fails to explain the low Néel temperature ($\lesssim 10\mathrm{K}$), suggesting that factors such as stoichiometry and magnetic exchange frustration may play an important role, calling for more detailed experimental investigations.

Measurement error mitigation (MEM) is essential for realizing reliable quantum computation. Model-free measurement error mitigation (MF-MEM) is an important class of MEM methods that employs Pauli twirling—typically with a random twirling set—to convert measurement noise into a state-independent scaling factor, thereby enabling error mitigation through simple calibration. However, such methods face prohibitive sampling overhead, limiting their scalability. To address this, we introduce subsystem-balanced Pauli twirling (SB-PT), a twirling method designed for MF-MEM that enforces Pauli operator balance on measuring subsystems to selectively suppress dominant measurement noise. Theoretically, for a weight-$\tau$ Pauli observable, SB-PT removes all independent error components using only $\mathcal{O}\left(4^{\tau }\right)$ random circuits, substantially reducing the sampling overhead over conventional Pauli twirling. This efficiency gain is most significant for sparse observables. To extend such resource-efficient mitigation to arbitrary observables, we generalize and integrate a hardware-efficient measurement transformation framework that converts high-weight Pauli operators into low-weight effective ones via linear-depth circuits. The circuit noise introduced during this transformation is jointly mitigated with native measurement noise using a unified twirling protocol, ensuring robust performance. Extensive numerical simulations demonstrate a greater than 16-fold improvement in sampling efficiency over conventional random twirling, with consistent performance gains across varying system sizes and error regimes. This work provides a resource-frugal and experimentally viable path toward high-fidelity measurement in near-term quantum devices.

Curvature plays a central role in the proper function of many biological processes. With active matter being a standard framework for understanding many aspects of the physics of life, it is natural to ask what effect curvature has on the collective behavior of active matter. In this paper, we use the classical theory of surfaces to explore the active motion of self-propelled agents confined to move on a smooth curved two-dimensional surface embedded in Euclidean space. Even without interactions and alignment, the motion is nontrivially affected by the presence of curvature, leading to effects akin, e.g., to gravitational lensing and tidal forces. Such effects can lead to intermittent trapping of particles and profoundly affect their flocking behavior. We show that these effects are governed by a geometric torque that, in the absence of noise and interactions, compels particles to move along geodesics.

Useful applications of quantum information technologies can be found by identifying tasks in which quantum resources outperform their classical counterparts. In this work, we introduce a two-party communication primitive, random exclusion code (REC), which is a single-shot prepare-and-measure protocol where a sender encodes a random message into a shorter sequence and a receiver attempts to exclude a randomly chosen letter in the original message. We present quantum advantages in RECs in two ways: probability and dimension. We show that RECs with quantum resources achieve higher success probabilities than classical strategies. We verify that, with the additional constraint that successful outcomes occur uniformly and without error, the quantum resources required to describe detection events of RECs have a smaller dimension than classical ones. We also show that a guessing counterpart, random access codes, may not have a dimension advantage over classical resources. Our results elucidate various possibilities of achieving quantum advantages in two-party communication.

We investigate a one-dimensional superconducting lattice that realizes all internal symmetries permitted in non-Hermitian systems, characterized by nonreciprocal hopping, on-site dissipation, and $s$-wave singlet pairing in a Su-Schrieffer-Heeger-type structure. The combined presence of pseudo-Hermiticity and sublattice symmetry imposes constraints on the energy spectra. We identify parameter regimes featuring real spectra, purely imaginary spectra, complex flat bands, and Majorana zero modes, the latter emerging when a uniform transverse magnetic field suppresses the non-Hermitian skin effect. We show that a uniform component of the on-site dissipation is essential for stabilizing the zero modes, whereas a purely staggered dissipation destroys the topological superconductivity. Through Hermitianization, we construct a spectral winding number as a topological invariant and demonstrate its correspondence with the gap-closing conditions and appearance of the Majorana zero modes, allowing us to establish topological phase diagrams. Moreover, we reveal nontrivial correlations between the particle-hole and spin components of left and right eigenstates, enforced by chiral symmetry, pseudo-Hermiticity, and their combination. Our results highlight how non-Hermiticity, sublattice structure, and superconductivity together enrich symmetry properties and give rise to interesting topological phenomena.

Lasers serve as the fundamental workhorses of photonic quantum technologies, with perfectly coherent light fields being essential for many protocols that generate nonclassical light, implement coherent control schemes, and initialize qubits. However, no laser is absolutely ideal and the implications of deviations from perfect coherence in quantum technological tasks remain unclear. In this study, we theoretically and experimentally explore the quantum coherence properties of lasers from a resourcetheory perspective, establishing a significant connection between photonics, quantum optics, and quantum information science. We demonstrate that the maximum achievable quantum coherence for laser light is constrained by spontaneous emission and the purity of the dephased laser field state. As a critical example application in quantum information protocols, we show that the quantum coherence of a laser field with a given mean photon number directly governs the maximum purity attainable when initializing a qubit in a superposition state through resonant driving. Our findings are highly relevant for bridging applied physics and engineering with integrated photonic quantum technologies and resource theories, paving the way for reliable benchmarking of various coherent light sources for applications in photonics and quantum protocols.

The magnetic field is one of the most fundamental control parameters in materials science. A pulsed magnetic-field apparatus can generate high magnetic fields that are inaccessible by conventional dc-field magnets. One important issue is that measurement techniques compatible with pulsed fields are rather limited due to short pulse duration and large electromagnetic or mechanical noise originating from field pulses. The magneto-optical Kerr effect (MOKE), the change in the state of light polarization upon reflection from magnetic materials, has the potential to become a powerful tool for investigation of magnetic properties of a wide range of materials including nontransparent materials or thin films in pulsed fields. Nevertheless, since the MOKE response is typically very small, MOKE measurements under pulsed fields are quite challenging. Here, we present a method to measure polar MOKE under high pulsed magnetic fields of 2-ms pulse width. The keys of this technique are a ferrule-based compact sample-fiber fixture and a phase-resolved numerical lock-in analysis, combined with the high-resolution optical apparatus based on an all-fiber loopless Sagnac interferometer. We succeeded in measuring MOKE signals from various ferromagnetic or ferrimagnetic samples above 40 T and down to 77 K, significantly extending the limits of previously reported pulse-field MOKE measurements. Our apparatus is simple enough to be compatible with larger-scale experiments in pulse-field facilities, thus becoming a promising tool to optically investigate material properties in pulsed fields.

We propose an efficient scheme for generating a stable spin-squeezed state in a hybrid magnon-nitrogen-vacancy (NV) centers system via magnon-Floquet driving. The system consists of a yttrium iron garnet (YIG) film directly coupled to NV centers that are equidistant from the film surface, and at the same time the YIG film is driven by a Floquet field. The magnon dissipation is exploited to distribute the NV centers into the dark state, manifesting as the stable spin-squeezed state. We show that the system exhibits the low- or high-energy dark state, which is determined by whether the lowering or the raising spin operator plays the dominant role in evolution. Furthermore, we also show that the spin squeezing is robust against thermal effects and decoherence, and it is possible to detect the change in $N$ at the single-spin level, since it exhibits a distinct odd-even effect. This scheme provides a feasible way for experimental implementation and thus has potential applications in quantum information processing, quantum simulation, and precision metrology.

Time-reversal (TR) symmetry is crucial for understanding a wide range of physical phenomena, and plays a key role in constraining fundamental particle interactions and in classifying phases of quantum matter. In this work, we introduce an ensemble of random quantum circuits that are representative of the dynamics of generic TR-invariant many-body quantum systems. We derive a general statistical mechanics model describing entanglement, many-body quantum chaos, and quantum information dynamics in such TR-invariant circuits. As an example of application of our formalism, we study the universal properties of measurement-induced phase transitions in monitored TR-invariant systems, with measurements performed in a TR-invariant basis. We find that TR invariance of the unitary part of the dynamics does not affect the universality class, unless measurement outcomes are postselected to satisfy the global TR invariance of each quantum trajectory. We confirm these predictions numerically and find, for both generic and Clifford-based evolutions, critical exponents in the case of “strong,” i.e., global TR invariance where each quantum trajectory is TR invariant.

Carrier transport in quantum networks is governed by a variety of factors, including network dimensionality and connectivity, on-site energies, couplings between sites and whether they are short or long range, leakage processes, and environmental effects. In this work, we identify classes of quasi-one-dimensional chains with energy profiles that optimize carrier transport under such influences. Specifically, we optimize on-site energies using Optax’s optimistic gradient descent and AdaMax algorithms, enabled by the JAX automatic differentiation framework. Focusing on nonequilibrium steady-state transport, we study the system’s behavior under combined unitary and nonunitary (dephasing and dissipative) effects using the Lindblad quantum master equation. After validating our optimization scheme on short chains, we extend the study to larger systems where we identify systematic patterns in energy profiles. Our analysis reveals that different types of energy landscapes enhance transport, depending on whether intersite tunneling couplings in the chain are short or long range, the existence of environmental interactions, and the temperature of the environment. Our classification and insights of optimal energy landscapes offer guidance for designing efficient transport systems for electronic, photovoltaic, and quantum communication applications.

We reveal the noncyclic Pancharatnam phase—arising from the coherent system-meter interaction—as a fundamental criterion that governs the optimal performance of quantum compression channels in postselected metrology. This phase embodies a geometric connection that enables precise control over the parallel evolution of the meter state, thereby maximizing the quantum Fisher information per trial and achieving lossless compression channels. Remarkably, fine-tuning the postselection parameter just below this optimal phase incurs substantial information loss, whereas tuning it just above fully suppresses undesired parallel evolution, enhancing information retention beyond that achievable in postselected protocols lacking Pancharatnam phase effects. We further reveal that leveraging qudit-meter states can unlock a substantial additional enhancement. These findings establish the Pancharatnam phase as a geometric benchmark, guiding the design of high-precision quantum parameter estimation protocols.

Diffusive approximations of Markov jump processes often fail to accurately capture large fluctuations. This is confounding, as the rare events triggered by these large fluctuations, such as the failure of electronic memories, are often the object of interest. In this paper, we present an improved diffusive approximation, extending a method previously limited to equilibrium systems. Using recently developed tools from stochastic thermodynamics, we prove its validity to linear order in departures from equilibrium and demonstrate its superior accuracy over the Kramers-Moyal expansion in predicting both steady state and transient properties, including the error rate of a nonequilibrium electronic memory.