Steady-state coherence in open quantum systems is crucial for quantum technologies, yet its behavior is not fully understood due to the interplay between collective and individual decoherence. While collective decoherence is thought to induce steady-state coherence, experiments often fail to observe this because of individual decoherence. We study a system of two harmonic oscillators coupled to both individual and collective environments, introducing a tunable parameter to adjust the decoherence proportions. By analytically solving the exact dynamical equations, we find that steady-state coherence depends on the initial state under collective decoherence, but not under partial decoherence. Interestingly, non-Markovianity induces rich and complex steady-state coherence behaviors. Our results clarify the role of non-Markovian decoherence in quantum systems and provide a benchmark for assessing approximate methods for modeling quantum processes.

Motivated by recent advances in ultracold atomic gas experiments, we investigate a two-terminal mesoscopic system in which two-body loss occurs locally at the center of a one-dimensional chain. By means of the self-consistent Born approximation in the Keldysh formalism, we uncover mesoscopic current formulas that are experimentally relevant and applicable to the weak dissipation regime. Although these formulas are analogous to those for systems with one-body loss, it turns out that the channel transmittance and loss probability depend on the nonequilibrium occupation at the lossy site. We demonstrate that this occupation dependence leads to a weaker suppression of currents in the presence of two-body loss compared to one-body loss.

By employing the Naimark dilation, we establish a fundamental connection between non-Hermitian quantum sensing and postselected measurements. The sensitivity of non-Hermitian quantum sensors is determined by the effective quantum Fisher information (QFI), which incorporates the success probability of postselection. We demonstrate that non-Hermitian sensors, regardless of the specific form of decoherence or the choice of probe states, cannot outperform their Hermitian counterpart when all information is harnessed, since the total QFI for the extended system constrains the effective QFI of the non-Hermitian subsystem. Moreover, we quantify the efficiency of non-Hermitian sensors with the ratio of the effective QFI to the total QFI, which can be optimized within the framework of postselected measurements with minimal experimental trials. In addition, the performances of non-Hermitian sensors versus different types of technical noises can be judged using our framework. Our work provides a distinctive theoretical framework for investigating non-Hermitian quantum sensing and designing noise-resilient quantum metrological protocols.

We consider a linear array of trapped ions subjected to local parametric modulation of the trapping potential and continuous laser cooling. In our model, the phase of the parametric modulation varies linearly along the array, breaking time-reversal symmetry and inducing nontrivial topological effects. The linear response to an external force is investigated with the Green's function formalism. We predict the appearance of topological amplification regimes in which the trapped ion array behaves as a directional amplifier of vibrational excitations. The emergence of topological phases is determined by a winding number related to non-Hermitian point-gap topology. Beyond its fundamental interests as a topological driven-dissipative system, our setup can be used for quantum sensing of ultraweak forces and electric fields. We consider a scheme in which a trapped ion at one edge of the array acts as a sensor of an ultraweak force, and the vibrational signal gets amplified toward the last trapped ion, which acts as a detector. We consider arrays of 2–30 ${}^{25}\mathrm{Mg}^{+}$ ions, assuming that the detector ion's displacement is measured via fluorescence with a spatial resolution of 200–500 nm, and predict sensitivities as small as $1\mathrm{yN}{\mathrm{Hz}}^{-1/2}$. Our system has the advantage that the detected force frequency can be tuned by adjusting the frequency of the periodic drive.

The excitation energy of ${}^{229m}\mathrm{Th}$ is extremely low at $8.4\mathrm{eV}$; thus, this isotope exhibits changes in its decay modes depending on the chemical state, specifically the outermost electronic states. However, the reported half-lives of the $\gamma$-ray transition are not consistent among the previous experiments. In this study, we investigate the chemical states of ${}^{229m}\mathrm{Th}$ by density functional theory calculations. Based on these results, we evaluate the relationship between the experimental half-life of each sample and the electronic state of $\mathrm{Th}$. The calculation results indicate that ion trap method, ${\mathrm{CaF}}_2$ model, and ${\mathrm{MgF}}_2$ one decay only via the $\gamma$-ray transition, whereas ${\mathrm{LiSrAlF}}_6$ one decays via the $\gamma$-ray transition and has a possibility of decay via internal conversion and electron bridge.

In the quest to unveil the laws of nature, particle detectors produce an ever-increasing amount of data. Large data rates require the use of specialized triggers that promptly reduce the data rate to a manageable level; however, in doing so, unexpected phenomena may escape detection. In this work, we present a methodology based on recent quantum compression techniques that can store exponentially more information than classically available methods. We encode the full neutrino telescope event information using parity observables in an IBM quantum processor using eight qubits to demonstrate this. Then, we show that we can recover the information stored on the quantum computer with a fidelity of 84%. Finally, we illustrate the use of our protocol by performing a classification task that separates electron-neutrino events from muon-neutrino events in a neutrino telescope. We find that this classification method is limited by our ability to find adequately faithful representations of the classical data within the quantum systems, necessitating further investigations into finding these representations.

Single-body diffusion and two-body dispersion are fundamental processes in classical turbulence, governing particle mixing and transport. However, their behaviors in superfluid turbulence remain largely unexplored. In this study, we numerically investigate the diffusion and relative dispersion of both quantized vortices and superfluid parcels in the 0 K limit in two distinct turbulence regimes: ultraquantum turbulence, characterized by a randomized vortex tangle, and quasiclassical turbulence, in which locally polarized vortices create large-scale flows resembling classical turbulence. Our results reveal that while vortex segments exhibit similar superdiffusion behavior at short times in both regimes, superfluid parcels behave differently—following the same superdiffusion scaling in ultraquantum turbulence but deviating significantly in quasiclassical turbulence. This contrast provides a key clue to the origin of short-time superdiffusion, a puzzle since its recent discovery. Additionally, we show that two-body dispersion of both vortex segments and superfluid parcels exhibits distinct scaling behaviors in ultraquantum and quasiclassical turbulence, highlighting fundamental differences in these two turbulence regimes. Our findings bridge a critical gap in superfluid turbulence research, offering useful insights into turbulent transport in inviscid quantum fluids.

In a quantum many-body system, such as atoms, molecules, and atomic nuclei, interparticle interactions generate a complex quantum level scheme that can be analyzed progressively: from the simplest picture of independent quasiparticles moving in a self-consistent mean field to more complete descriptions that include residual interactions and the opening of decay channels above some excitation thresholds. Residual interactions lead to two seemingly contrasting phenomena: the emergence of collective modes (such as rotational and vibrational excitations) associated with specific symmetries, and internal thermalization, which gives rise to features of quantum chaos and causes these collective modes to damp. The picture becomes more intricate once decay channels become energetically accessible, allowing the system to decay irreversibly by means such as particle emission and thus transition to an open quantum regime. In this work, we investigate the competition between internal many-body dynamics and explicit, irreversible decay. These processes can occur on comparable timescales, leading to an initial stage of rapid dynamics followed by equilibration. We show that the decay of the faster components drives the system into an exponentially decaying regime, characterized by a noisy decay current. For this study, we adopt a general, albeit simplified, model of a collective mode embedded in a chaotic background and coupled to open decay channels. The interplay of timescales revealed in this framework appears to reflect universal features of open quantum systems.

The relativistic quantum-mechanical description of a charged Laguerre-Gauss beam accelerated in a uniform electric field has been fulfilled. Stationary wave eigenfunctions are rigorously derived. The evolution of the beam parameters during acceleration is considered in detail. The practically important effect of extraordinary suppression of transverse spreading of the beam is discovered, carefully analyzed, and properly explained. Our results provide direct evidence that vortex particle beams can be accelerated without destroying their intrinsic vortex properties, paving the way for high-energy vortex beam applications.

Chiral active matter is a variant of active matter systems in which the motion of the constituent particles violates mirror symmetry. In this article, we simulate two-dimensional chiral Active Brownian Particles, the simplest chiral model in which each particle undergoes circular motion, and show that the system crystallizes at low densities well below the melting point of the equilibrium counterpart. Crystallization is only possible if the orbital radius is long enough to align the circulating particles, but short enough for neighboring particles to avoid collisions. Of course, the system must be driven sufficiently far from equilibrium, since chirality cannot affect thermodynamic properties in classical equilibrium systems. The fluid-crystal phase diagram shows a re-entrant melting transition as a function of the radius of the circles. We show that at least one of the two transitions follows the same two-step melting scenario as in equilibrium systems.

Detailed knowledge of particle-beam properties is of great importance to understand and push the performance of existing and next-generation particle accelerators. We recently proposed a phase-space tomography method to reconstruct the five-dimensional (5D) phase space, i.e., the charge density distribution in all three spatial directions and the two transverse momenta. Here, we present the first experimental demonstration of the method at the FLASHForward facility at DESY. This includes the reconstruction of the 5D phase-space distribution of a GeV-class electron bunch, the use of this measured phase space to create a particle distribution for simulations, and the extraction of the transverse 4D slice emittance.

Bacteria possess diverse mechanisms to regulate their motility in response to environmental and physiological signals, enabling them to navigate complex habitats and adapt their behavior. Some of these mechanisms are species specific and enable cells to modulate their movement based on the ecological identity of neighboring species. Here, we introduce a model in which bacteria interact via local signals that either enhance or suppress the motility of neighboring cells depending on species type. Through large-scale simulations and a coarse-grained stochastic model, we demonstrate the emergence of a sharp transition driven by nucleation processes: increasing the density of motility-suppressing interactions drives the system from a fully mixed, motile phase to a state characterized by large, stationary bacterial clusters. Remarkably, in systems with a large number of interacting species, this transition can be triggered solely by altering the structure of the motility-regulation interaction matrix while maintaining species and interaction densities constant. In particular, we find that heterogeneous and modular interactions promote the transition more readily than homogeneous random ones. These findings add a dimension to the theory of motility-induced phase separation and contribute to the ongoing effort to understand microbial interactions, suggesting that structured, nonrandom ones may be key to reproducing commonly observed spatial patterns in microbial communities.

In many biological systems, from sinuses to airways, ciliary arrays are essential for transporting particles and bacteria. Challenging long-held assumptions, we show that the classical Eulerian view of cilia-induced flow overlooks a key feature of time-averaged transport. Using theoretical modeling and numerical simulations, we demonstrate that the drift generated by ciliary motion is not uniform, as previously predicted, but varies with distance from the ciliary surface in unexpected ways. This variation reveals drift stagnation points, offering a potential means to distinguish healthy from impaired ciliary beating and refines our understanding of fluid-driven transport.

We express the dynamics of the two probability amplitudes in the elementary Landau-Zener problem in terms of the solution of the corresponding Riccati differential equation and identify three key features: (i) The solution of the Riccati equation provides the bridge between the two probability amplitudes. (ii) Neglecting the nonlinearity in the Riccati equation is equivalent to the Markov approximation which yields the exact asymptotic expression for one of the probability amplitudes. (iii) The Riccati equation identifies the origin of the failure of the Markov approximation not being able to provide us, in general, with the correct asymptotic expression of the other probability amplitude. Our approach relies on approximate yet analytical solutions of the Riccati equation in different time regimes, highlighting the impact of its nonlinear nature on the time evolution of the system.

The intertwining of electron-hole correlation and nontrivial topology is known to give rise to exotic topological excitonic insulators. Here, we show that the involvement of quantum geometry can characterize more exotic excitonic phases exhibiting physical properties that are not influenced by their topology but by geometry. Starting from a topological band insulator and gradually reducing the band gap, many-body interaction can initially generate a $p+ip$-wave and then an $s$-wave excitonic insulator. Interestingly, they bear the same Chern number but exhibit completely different spin textures and magneto-optical Kerr responses, reflecting the intricate geometric distinctions in their wave functions. We also propose to enhance the correlation effect via Floquet engineering, which provides a systematic way to realize these topological excitonic insulators and their phase transitions in the nonequilibrium steady states. Our results demonstrate correlated phenomena characterized by quantum geometry, beyond the conventional topological classifications.

Charge density wave (CDW) resulting from a periodic distortion in the lattice creates orders beyond the original lattice. In $2{H\text{−}\mathrm{NbSe}}_2$, one of the layered transition metal dichalcogenides, the $3\times 3$ charge order appears in two-dimensional (2D) layers. Although CDW can be observed by different techniques, the spatial distribution within a 2D layer has never been systematically visualized. Here, by using scanning tunneling microscopy and density functional theory, we monitored the evolution of CDW along the $c$ axis and found a strong relation with the orbital charges. The results show that the appearance of the CDW varies while tuning the tunneling current and undergoes a transition from Se orbital charges to Nb orbital charges. The calculation of orbital charge distributions shows that both CDW intensity modulation and the transition are strongly intertwined with the distribution of Se $4p$ orbitals and Nb $4d$ orbitals.

Bacteria evolve in volatile environments and complex spatial structures. Migration, fluctuations, and environmental variability therefore have a significant impact on the evolution of microbial populations. Here, we consider a class of spatially explicit metapopulation models arranged as regular (circulation) graphs where wild-type and mutant cells compete in a time-fluctuating environment in which demes (subpopulations) are connected by slow cell migration. The carrying capacity is the same at each deme and endlessly switches between two values associated with harsh and mild environmental conditions. It is known that environmental variability can lead to population bottlenecks, following which the population is prone to fluctuation-induced extinction. Here, we analyze how slow migration, spatial structure, and fluctuations affect the phenomena of fixation and extinction on clique, cycle, and square lattice metapopulations. When the carrying capacity remains large, bottlenecks are weak and deme extinction can be ignored. The dynamics is thus captured by a coarse-grained description within which the probability and mean time of fixation are obtained analytically. This allows us to show that, in contrast to what happens in static environments, the mutant fixation probability depends on the rate of migration. We also show that the fixation probability and mean fixation time can exhibit a nonmonotonic dependence on the switching rate. When the carrying capacity is small under harsh conditions, bottlenecks are strong, and the metapopulation evolution is shaped by the coupling of deme extinction and strain competition. This yields rich dynamical scenarios, among which we identify the best conditions to eradicate mutants without dooming the metapopulation to extinction. We offer an interpretation of these findings in the context of an idealized treatment strategy and discuss possible generalizations of our models.