In this study, we uncover the intrinsic information processes in non-Hermitian quantum systems and their thermodynamic effects. We demonstrate that these systems can exhibit negative entropy production, making them potential candidates for information engines. We also identify a key informational quantity that can characterize phase transitions beyond the reach of traditional partition functions. This work enhances our understanding of the interplay between information and thermodynamics, providing a new perspective on non-Hermitian quantum systems.

To effectively utilize quantum incompatibility as a resource in quantum information processing, it is crucial to evaluate how incompatible a set of devices is. In this study, we propose an ordering to compare incompatibility and reveal its various properties based on the operational intuition that larger incompatibility can be detected with fewer states. We especially focus on the typical class of incompatibility exhibited by mutually unbiased qubit observables and numerically demonstrate that the ordering yields new classifications among sets of devices. Moreover, the equivalence relation induced by this ordering is proved to uniquely characterize mutually unbiased qubit observables among all pairs of unbiased qubit observables. The operational ordering also has a direct implication for a specific protocol called distributed sampling.

Accurate temperature estimation in the quantum and cryogenic regimes remains a fundamental challenge. Here, we investigate nonequilibrium quantum thermometry using a single-qubit probe coupled to a bosonic bath through noncommuting interaction operators, which unify pure dephasing and dissipative dynamics within a spin-boson model. We show that the interference between these two coupling channels induces strong non-Markovian feedback between populations and coherences, leading to coherence trapping and enhanced thermal sensitivity. Remarkably, by tuning the coupling structure, the probe's temperature sensitivity exhibits a quadratic low-temperature scaling, even under weak coupling. Moreover, while coherence-based measurements are formally suboptimal, they become the most informative in the early nonequilibrium regime, where memory effects dominate. Our findings identify noncommutative system-bath couplings as a practical and tunable resource for achieving high-precision quantum thermometry in realistic open-system architectures.

We uncover features of generalized contextuality by connecting it to the Kirkwood-Dirac (KD) quasiprobability distribution. Quantum states can be represented by KD distributions, which take values in the complex unit disk. Only for “KD-positive” states are the KD distributions joint probability distributions. A KD distribution can be measured by a series of weak and projective measurements. We design such an experiment and show that it is contextual iff the underlying state is not KD positive. We analyze this connection with respect to mixed KD-positive states that cannot be decomposed as convex combinations of pure KD-positive states. Our result is the construction of a noncontextual experiment that enables an experimenter to verify contextuality.

Quantum computing has the potential to solve complex problems faster and more efficiently than classical computing. It can achieve speedups by leveraging quantum phenomena like superposition, entanglement, and tunneling. Quantum walks (QWs) form the foundation for many quantum algorithms. Unlike classical random walks, QWs exhibit quantum interference, leading to unique behaviors such as linear spreading and localization. These properties make QWs valuable for various applications, including universal computation, time series prediction, encryption, and quantum hash functions. One emerging application of QWs is decision-making. Previous research has used QWs to model human decision processes and solve multiarmed bandit problems. This paper extends QWs to collective decision-making, focusing on minimizing decision conflicts, cases where multiple agents choose the same option, leading to inefficiencies like traffic congestion or overloaded servers. Prior research using quantum interference has addressed two-player conflict avoidance but struggled with three-player scenarios. This paper proposes a method using QWs to entirely eliminate decision conflicts in three-player cases, demonstrating its effectiveness in collective decision-making.

Quantum channels often cause information loss of a quantum system, and it is desirable to quantify such loss. Alternatively, one may ask how much information can be preserved by a quantum channel. In this work we introduce a quantifier for information loss of quantum channels via uncertainty of the corresponding Choi states determined by the channel-state duality, reveal its basic properties, derive its ranges for various channels, and identify the extremal channels (which depend crucially on the relation between the input and output system dimensions) with the minimal and maximal information loss. Furthermore, we evaluate this quantifier for some prototypical quantum channels and their corresponding complementary channels. We further compare information loss and irreversibility by illuminating their similarities and differences. These results shed light on channel structures from an information-theoretic perspective.

In the field of quantum sensing, quantum resources occupy a core position. Besides the two well-known quantum resources—the number N of quantum entangled probes and the coherent evolution time $T$—the spin quantum number $S$ has also been confirmed as another key quantum resource. This paper focuses on high-spin quantum systems in a general Gaussian noise environment under the assumption that the noise factor in the exponential part of the modulus of the off-diagonal elements of the system's density matrix is $\chi \left(\tau \right)=\alpha {\tau }^{\beta }$ (where $\alpha >0$ and incorporates relevant noise parameters, and $\beta$ is a positive number whose specific value is determined by the detailed characteristics of the noise) and systematically investigates the estimation problem of the noise parameter $\xi$ using the spin quantum number $S$ as the quantum resource. Surprisingly, as $\beta$ increases gradually, the scaling behaviors of the estimation errors of parameters $\omega$ and $\xi$ with respect to $S$ show distinctly opposite trends. Specifically, the estimation precision of parameter $\omega$ satisfies $\delta \omega \propto 1/S^{1-1/\beta }$, while the estimation precision of parameter $\xi$ follows $\delta \xi \propto 1/S^{1/\beta }$. Furthermore, regardless of the value of $\beta$, the estimation precisions of parameters $\omega$ and $\xi$ always exhibit a complementary relationship, i.e., $\delta \omega \delta \xi \propto 1/S$. Subsequently, taking Ornstein-Uhlenbeck noise as a specific example, we further estimate the noise parameters $b$ (noise amplitude), ${\tau }_c$ (noise memory time), and parameter $\omega$; the final conclusions are completely consistent with the estimation conclusions of $\xi$ and $\omega$ in the general Gaussian noise environment.

Optical clocks have garnered widespread attention due to their unparalleled precision in the fields of time-frequency standards, geodetic measurements, and fundamental physics research. Among recent advances, highly charged ion (HCI)-based optical clocks have attracted significant scientific interest owing to their remarkable insensitivity to electromagnetic perturbations and enhanced sensitivity to potential variations of the fine-structure constant $\left(\alpha \right)$. Although the recent successful demonstration of an ${\mathrm{Ar}}^{13+}$ optical clock has validated the feasibility of HCI-based systems, ${\mathrm{Ni}}^{12+}$ (featuring an ultranarrow clock transition linewidth) stands out as a superior candidate for achieving HCI optical clocks with ${10}^{-19}$ level uncertainty and stability. In this work, we report the Coulomb crystallization of highly charged nickel ions (Ni-HCIs). Through a precise deceleration and sympathetic cooling protocol in a room-temperature linear Paul trap, high-energy Ni-HCI bunches were sympathetically cooled from megakelvin energies down to the hundred-millikelvin range using laser-cooled ${\mathrm{Be}}^{+}$ ions. This work represents a pivotal step toward the realization of an optical clock based on ${\mathrm{Ni}}^{12+}$ ion.

In high-order harmonic generation (HHG), nondipole effects become increasingly significant at long driving wavelengths, as the magnetic field leads to a lateral drift of the continuum electron, which disrupts the electron recollision and inhibits the harmonic emission. To address this problem, we revisit the dynamics of the continuum electrons under electromagnetic fields in the HHG process and show that the magnetic effect on the drift includes a fundamental-frequency and a double-frequency component. By adding an additional field to counteract the double-frequency effect caused by the magnetic field, we construct an effective linearly polarized field that recovers the recollision of all returning electrons to the parent ion. Consequently, the harmonic yield is restored and becomes the same as the result within the dipole approximation across the broad spectral range. This work provides a scheme that completely suppresses the nondipole drift effect and fully compensates for the harmonic yield reduction, paving the way to efficiently generate coherent radiation in the range from extreme ultraviolet to soft x-ray and ultrashort pulses based on HHG.

Ultracold multicomponent fermions (atoms or molecules) loaded in optical lattices provide an ideal platform for simulating $\mathrm{SU}\left(N\right)$ Hubbard models that host unconventional many-body quantum states beyond SU(2). A prime example is the attractive three-color Hubbard model, in which trion states emerge at strong coupling. Nevertheless, much of its trion ordering on two-dimensional lattices remains uncertain. Here, we employ the determinant quantum Monte Carlo method to simulate the attractive three-color Hubbard model on a $\pi$-flux square lattice at half filling. We show that color-dependent attractive interaction can induce the coexisting charge density wave (CDW) and Néel-ordered states in the three-color $\pi$-flux Hubbard model. In particular, enhanced charge fluctuations (cf. honeycomb lattice) cause much stronger Néel ordering on the $\pi$-flux square lattice. The coexisting charge and Néel orders survive up to a melting temperature, at which they vanish simultaneously. The Ginzburg-Landau (GL) analysis on the coexistence of CDW and Néel orders demonstrates how color-dependent Hubbard interactions stabilize coexisting orders from the perspective of GL free energy principle.

Plasmonic nanocavities, known for their ability to enhance light-matter interactions, are further advanced in this study through the design of a nested plasmonic nanocavity. By replacing the conventional flat metal substrate with a silver (Ag) coated nanosphere array, the nested plasmonic nanocavity achieves significant enhancements in both electric-field intensity and its spatial gradient effect under excitation of a linearly polarized beam. This plasmonic nanocavity breaks the dipole selection rule, enabling the visualization of forbidden quadrupole-Raman scattering modes in the 4-thiobenzonitrile molecules. Additionally, the strong localized electric field induces a measurable Stark effect in the dipole-Raman spectra. The nested plasmonic nanocavity thus serves as a powerful platform for probing weak molecular processes, leveraging its dual enhancement of electric-field and gradient effects to unlock new spectroscopic capabilities.

In this work, we present a field-theoretic model of strongly coupled photonic molecules composed of interacting dielectric cavities in a closed, perfect-electric-conductor domain. Within this setting, we treat the resulting intermode couplings nonperturbatively. We demonstrate the predictive power of this framework by showing that supermode eigenfrequencies, field profiles, and mode volumes can be obtained directly from the isolated-cavity modes and dielectric environment, without electromagnetic simulations of the composite structure or numerical fitting. While our model affirms the phenomenological approach of modeling coupled cavity modes as simple coordinate-coupled oscillators in the weak coupling regime, we show that this intuition remarkably breaks down for strong coupling. Instead, we demonstrate that strongly coupled cavity modes are analogous to harmonic oscillators we term as doubly coupled, with interactions via electric and magnetic fields appearing as independent coordinate-coordinate and momentum-momentum couplings, respectively. We show that this distinction is not merely cosmetic, but gives rise to observable properties while providing deep insights into the physical mechanism behind previously observed phenomena, such as coupling induced frequency shifts. Finally, we illustrate that the complex interplay of these dual couplings suggests the possibility to realize exotic phenomena that typically only occur in the ultrastrong coupling regime, here predicted to emerge for comparably modest mode splittings within a regime we term pseudo-ultrastrong coupling.

We propose a scheme to generate the generalized two-mode Schrödinger cat state for two optical fields coupled to a three-level atom. The scheme is based on the competition between the unitary dynamics induced by a classical driving and the field-atom coupling. Under the condition of strong ground-state coupling, the two-mode displaced Schrödinger's cat state can be successfully prepared by adjusting the coupling strength between the classical laser and the atom to be much larger than that between the two fields and the atom. Furthermore, by choosing different initial states, it is also possible to prepare a maximally three-dimensional entangled state through strong ground-state coupling. To rigorously assess its feasibility, we have also analyzed the scheme's robustness against dissipation, confirming its practicality under realistic noise and identifying a broad, experimentally accessible parameter “sweet spot.” Our proposal provides insights into the area of multimode Schrödinger cat states.

We present a neural network-based computational method for investigating strong-field-induced electron-positron pair creation from the quantum vacuum. In computational quantum field theory (CQFT), the fermionic vacuum is modeled as the set of all negative-energy eigenstates of the Dirac equation. To compute the dynamical evolution of electronic and positronic observables, each of these Dirac sea states must be evolved in time. Traditionally, this is done by solving the time-dependent Dirac equation separately for each state—a computationally intensive task. As a first step toward addressing the runtime challenges, especially in higher-dimensional spatial calculations, we explore an alternative solution method based on neural networks. In this approach, the neural network is trained to leverage information from the time evolution of the first state, thereby significantly reducing the CPU time required to compute the time evolution of the remaining states.

We investigate the quantum dynamics of an ultrarelativistic electron interacting with intense counterpropagating laser beams. In contrast to the resonance regime where the stimulated Compton scattering occurs, we focus on a scenario where, in the electron's rest frame, the frequency of the counterpropagating wave significantly exceeds that of the copropagating wave. Leveraging a recently developed approximation for the classical dynamics in this configuration, we solve the Klein-Gordon and Dirac equations using a quasiclassical Wentzel-Kramers-Brillouin (WKB) approach. The resulting spin expectation value reproduces the numerical solution of the Bergmann-Michel-Telegdi (BMT) equation, while the spin-averaged momentum agrees with its classical counterpart, as expected. Crucially, we demonstrate that, under certain conditions, the wave function's sensitivity to the electron's momentum causes the normalized acceleration $\chi$ of a quantum wave packet to deviate significantly from the classical value. This finding implies that emission processes cannot be accurately described by classical theory, even in the low-$\chi$ regime. The derived wave functions provide a foundation for calculating probabilities of nonlinear QED processes in this common field configuration.

The quantum geometric tensor (QGT) fundamentally encodes the geometry and topology of quantum states in both Hermitian and non-Hermitian regimes. While adiabatic perturbation theory links its real part (quantum metric) and imaginary part (Berry curvature) to energy fluctuations and generalized forces, respectively, in Hermitian systems, direct measurement of the QGT, which is defined using both left and right eigenstates of a non-Hermitian Hamiltonian, remains challenging. Here we develop two quantum simulation schemes to directly extract all components of the QGT in pseudo-Hermitian systems with real spectra. Each scheme independently determines the complete QGT using generalized expectation values of either the energy fluctuation operator or the generalized force operator with respect to two time-evolved states prepared through distinct nonadiabatic evolutions, thereby establishing two self-contained measurement protocols. We illustrate the validity of these schemes on two $q$-deformed two-band models: one with nontrivial topology and the other with a nonvanishing off-diagonal quantum metric. Numerical simulations demonstrate that, for suitably chosen nonadiabatic ramp velocities, both schemes achieve high-fidelity agreement with theoretical predictions for measuring the QGT in both models and successfully capture the topological phase transition of the first model using Chern numbers calculated from Berry curvatures. For larger velocities, the generalized force scheme yields greater accuracy for the real part of the QGT, while the energy fluctuation scheme better captures its imaginary part. This work establishes a framework for extending dynamical measurement schemes from Hermitian to pseudo-Hermitian systems with real spectra.

We focus on a dissipative three-level system as a case study to analytically demonstrate that strong system-bath coupling separates the relaxation dynamics of this dissipative quantum system into two distinct regimes: a short-time dynamics that, as expected, accelerates with increasing coupling to the environment, and a slow dynamics that, counterintuitively, becomes prolonged at sufficiently strong coupling. Using the reaction-coordinate polaron-transform mapping, we uncover the general mechanism behind this effect and derive accurate expressions for both relaxation timescales. Numerical simulations confirm our analytical predictions. From a practical perspective, our results suggest that strong coupling to a dissipative bath can autonomously generate and sustain long-lived quantum coherences, offering a promising strategy for bath-engineered quantum state preparation.

Floquet code is a dynamical quantum memory with a periodically evolving logical space. As a defining feature, the code exhibits an anyon automorphism after each period, giving rise to a nontrivial evolution of each logical state. In this paper, we study the Floquet code under local decoherence and perfect measurements and demonstrate that, below the decoherence threshold, the code is in a robust phase characterized by the anyon automorphism. We first derive the three-dimensional (3D) statistical mechanics model for the maximum likelihood decoder of the two-dimensional (2D) Floquet code under local Pauli decoherence. We identify a class of two-qubit Pauli channels under which the 3D statistical mechanics model becomes decoupled 2D models and obtain the threshold for such decoherence channels. We then propose a diagnostic of the anyon automorphism in the presence of local decoherence. We analytically show that this diagnostic distinguishes the Floquet code from the toric code under repeated syndrome measurements and undergoes a phase transition at the threshold.