To date, realization of a continuous-wave active atomic clock has been elusive, primarily due to parasitic heating from spontaneous emission while repumping the atoms. Here, we propose a solution to this problem by replacing the random emission with coupling to an auxiliary cavity, making repumping a fully collective process. While it is known that collective two-level models do not possess a generic lasing threshold, we show this restriction is overcome with multilevel atoms, since collective pumping and decay can be performed on distinct transitions. Using relevant atomic parameters, we find this system is capable of producing an $\mathcal{O}(100\mathrm{\mu }\mathrm{Hz})$-linewidth continuous-wave superradiant laser. Our principal result is the potential for an operating regime with cavity length vibration sensitivity below $\mathcal{O}({10}^{-14}/g)$, including a locus of parameter values where it completely vanishes even at steady state.

Stimulated scattering of incoherent excitons into an exciton-polariton mode leads to the buildup of a polariton condensate whose polarization is sensitive to a small seeded population that triggers the stimulated process. We show, within a semiclassical stochastic Gross-Pitaevskii model, that this mechanism enables a robust polarization memory operation: the condensate tends to align its Stokes vector with that of the seed and to maintain it for times far exceeding an individual polariton lifetime. Importantly, this single-photon-seeded regime is modeled as an initial weak excitation of the condensate mode within a semiclassical description and does not imply full quantum-state storage. We quantify the memory performance by a classical polarization-alignment metric and find that the seed polarization can remain well preserved on a nanosecond timescale under realistic parameters.

Elastic disordered interfaces driven through a heterogenpeous landscape respond via intermittent avalanches. In the overdamped limit, avalanche sizes follow a scale-free power-law distribution. Here, we investigate how inertial and dynamical terms beyond the overdamped approximation modify this behavior, focusing on the combined effects of interaction range, dimensionality, and dissipation. Using large-scale numerical simulations, we show that these additional terms robustly generate system-spanning events—so-called kings—responsible for a characteristic bump in the avalanche size distribution, which arise only in the presence of dissipation. We identify two distinct mechanisms underlying this phenomenon. In two-dimensional systems with long-range elasticity, we observe genuine kings, which persist in the thermodynamic limit and are consistent with mean field predictions. In contrast, one-dimensional systems with long-range elasticity and systems with short-range interactions in both 1D and 2D exhibit ghost kings: failed synchronization events producing large, but finite, ballistically spreading avalanches. Our findings clarify the origin of bump features in avalanche statistics and establish the conditions under which true system-spanning events emerge in realistic, dissipative systems.

Quantum transport remains a central yet experimentally challenging problem in condensed matter and quantum physics. Here we report the first complete experimental characterization of the full spectrum of quantum transport behaviors in a one-dimensional Fibonacci chain—the paradigmatic quasicrystalline model—spanning localization, subdiffusion, normal and superdiffusion, and ballistic transport. Using a tunable photonic quantum-walk platform, these regimes are unambiguously resolved through their distinct power-law scalings of the mean square displacement and smooth autocorrelation function, together with pronounced oscillatory dynamical structures. These signatures arise from the intrinsic multifractal spectra and hyperuniform order of the Fibonacci quasicrystal, long predicted but never before experimentally resolved. Beyond mapping a comprehensive transport regime diagram, our highly controllable platform provides a powerful and versatile framework for exploring quasiperiodicity, multifractal criticality, and emergent quantum transport phenomena.

High precision measurements are essential to solve major scientific and technological challenges, from gravitational wave detection to healthcare diagnostics. Quantum sensing delivers greater precision, but an in-depth optimization of measurement procedures has been overlooked. Here, we present a systematic strategy for parameter estimation in the low-data limit that integrates experimental control parameters and natural symmetries. The method is guided by a Bayesian quantifier of precision gain, enabling adaptive optimization tailored to the experiment. We provide general expressions for optimal estimators for any parameter. The strategy’s power is demonstrated in a quantum technology experiment, in which ultracold caesium atoms are confined in a micromachined hole in an optical fiber. We find a fivefold reduction in the fractional variance of the estimated parameter, compared to the standard measurement procedure. Equivalently, our strategy achieves a target precision with a third of the data points previously required. Such enhanced device performance and accelerated data collection will be essential for applications in quantum computing, communication, metrology, and the wider quantum technology sector.

We present a method characterizing thermal noise in an optical cavity independent from quantum noise despite the thermal noise falling below the quantum noise limit. Using this method, we measured the thermal noise contribution from a GaAs/AlGaAs micromirror suspended on a GaAs cantilever microresonator when brought to a cryogenic temperature ($\sim 25\mathrm{K}$) and incorporated into a Fabry-Pérot cavity. An optical spring is formed in this optical cavity. Previously, this setup exploited an optical spring to produce a displacement sensitivity falling 2.8 dB below the free-mass standard quantum limit (SQL), as reported by Cullen et al. [Phys. Rev. Lett. 133, 113602 (2024)]. Here we use a similar setup to measure thermal noise which fell a maximum of 5 dB below the SQL. This measurement, in turn, allowed for an investigation of quantum noise suppression resulting from the optical spring effect, falling a maximum of 10 dB below the SQL, a new benchmark for sub-SQL optomechanical measurements.

Using $(10087\pm 44)\times {10}^{6}J/\psi$ events collected with the BESIII detector, we present a study of resonant structures in the $J/\psi \to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}\gamma$ and $\mathrm{\Lambda }{\overline{\mathrm{\Sigma }}}^0\gamma$ processes, reporting the first observation of the electromagnetic radiative decays of the $\mathrm{\Lambda }(1520)$ and $\mathrm{\Lambda }(1690)$ to $\gamma {\mathrm{\Sigma }}^0$, with a statistical significance of $16.6\sigma$ and $23.2\sigma$, respectively. The ratio of the branching fractions $\{\mathcal{B}[\mathrm{\Lambda }(1520)\to \gamma \mathrm{\Lambda }]/\mathcal{B}[\mathrm{\Lambda }(1520)\to \gamma {\mathrm{\Sigma }}^0]\}$ is determined to be $3.19\pm 0.34(\mathrm{stat})\pm 0.19(\mathrm{syst})$, which is in agreement with flavor SU(3) symmetry within two standard deviations. The branching fraction of $\mathrm{\Lambda }(1520)\to \gamma {\mathrm{\Sigma }}^0$ is measured to be $\mathcal{B}[\mathrm{\Lambda }(1520)\to \gamma {\mathrm{\Sigma }}^0]=[2.66\pm 0.28(\mathrm{stat})\pm 0.50(\mathrm{syst})]\times {10}^{-3}$, corresponding to a partial width of $\mathrm{\Gamma }[\mathrm{\Lambda }(1520)\to \gamma {\mathrm{\Sigma }}^0]=[46.8\pm 6.6(\mathrm{stat})\pm 9.3(\mathrm{syst})]\mathrm{keV}$, which is inconsistent with predictions from the relativized constituent quark model and the Algebraic model. Additionally, we observe a clear resonant structure in the $\gamma {\mathrm{\Sigma }}^0$ mass spectrum near $1.7\mathrm{GeV}/c^2$, attributed to the $\mathrm{\Lambda }(1690)$. The product branching fraction $\mathcal{B}[J/\psi \to \overline{\mathrm{\Lambda }}\mathrm{\Lambda }(1690)+\mathrm{c}.\mathrm{c}.]\times \mathcal{B}[\mathrm{\Lambda }(1690)\to \gamma {\mathrm{\Sigma }}^0]$ is measured for the first time as $[6.05\pm 0.42(\mathrm{stat})\pm 0.39(\mathrm{syst})]\times {10}^{-6}$. However, no corresponding structure is seen in the $\gamma \mathrm{\Lambda }$ mass spectrum, so an upper limit on the product branching fraction $\mathcal{B}[J/\psi \to \overline{\mathrm{\Lambda }}\mathrm{\Lambda }(1690)+\mathrm{c}.\mathrm{c}.]\times \mathcal{B}[\mathrm{\Lambda }(1690)\to \gamma \mathrm{\Lambda }]$ is determined to be $5.08\times {10}^{-7}$ at the 90% confidence level.

The mass of the lightest hadron in nature, the pion, is one seventh of that of the nucleon and one tenth of the mass of its first excited state, the $\pi (1300)$. This enormous energy difference opens an interesting window into the confinement of quarks and the structure of the lightest hadrons. In this Letter, we provide the first calculation of resonance parameters of the $\pi (1300)$ from lattice quantum chromodynamics (QCD). For this purpose, recently derived state-of-the-art tools are adapted and applied both in the construction of three-hadron operators and for mapping finite-volume spectra to infinite-volume amplitudes, subsequently analytically continuing these to complex energies. For our heavy pion mass ensembles, we find a clear signal of the resonance. Making a simple assumption of vanishing pion mass dependence for the three-body force, but incorporating constraints from Chiral Perturbation Theory for all the two-body channels, enables a robust extrapolation to the physical point. Applying model averaging, we extract a pole position of $M_{\pi (1300)}=(1169\pm 46)-i({62}_{-62}^{+168})\mathrm{MeV}$ supporting values from phenomenology.

Based on the $(2712.4\pm 14.4)\times {10}^6\psi (3686)$ events collected with the BESIII detector, we present a high-precision study of the ${\pi }^{+}{\pi }^{-}$ mass spectrum in $\psi (3686)\to {\pi }^{+}{\pi }^{-}J/\psi$ decays. A clear resonancelike structure is observed near the ${\pi }^{+}{\pi }^{-}$ mass threshold for the first time. A fit with a Breit-Wigner function yields a mass of $285.6\pm 2.5\mathrm{MeV}/c^2$ and a width of $16.3\pm 0.9\mathrm{MeV}$ with a statistical significance exceeding $10\sigma$. To interpret the data, we incorporate final-state interactions (FSI) within two theoretical frameworks: chiral perturbation theory (ChPT) and QCD multipole expansion (QCDME). ChPT describes the spectrum above $0.3\mathrm{GeV}/c^2$ but fails to reproduce the threshold enhancement. In contrast, the QCDME model—assuming the $\psi (3686)$ is an admixture of S- and D-wave charmonium—reproduces the data well. The pronounced dip near $0.3\mathrm{GeV}/c^2$ offers new insight into the interplay between chiral dynamics and low-energy QCD.

Breaking time-reversal symmetry in integrated photonics without magnetic fields remains a fundamental challenge. We demonstrate phonon-induced nonreciprocity through direct lifting of forward-backward mode degeneracy in microring resonators. Coherent acousto-optic coupling generates differential AC Stark shifts between counterpropagating fundamental optical modes, eliminating the need for intermodal conversion or complex photonic structures. Simple microwave excitation of integrated piezoelectric transducers provides dynamic control of nonreciprocal response, with experimentally demonstrated mode splitting exceeding twice the optical linewidth. The linear relationship between the splitting and acoustic power enables real-time reconfigurability across a wide range of optical wavelengths. This mechanism requires only simple microring resonators and fundamental optical modes, transforming nonreciprocity from a specialized technique requiring careful modal engineering to a universal, electrically controlled functionality. Our approach establishes a new paradigm for magnetic-free optical isolation and dynamic topological photonics.

The Josephson diode effect—an asymmetry of critical currents at opposite polarities—has attracted much attention recently. One of its simplest realizations is an asymmetric SQUID with multiple Josephson harmonics tuned away from half-integer flux (in units of the superconducting flux quantum). Here we predict a dual version of this effect in a gate-tunable Cooper pair transistor placed in series with a highly resistive environment. The dual “Bloch diode effect” manifests itself as an asymmetry of critical voltages at opposite polarities when the Cooper pair transistor is tuned away from half-integer gate charge (in units of the Cooper pair charge). It arises from an asymmetry in the dispersion of the transistor’s Bloch bands. A highly resistive environment can be realized with a Josephson junction array, suggesting that such a Bloch diode could be implemented using conventional superconducting quantum circuits.

One-dimensional bosonic systems, such as helium confined to nanopores, exhibit Luttinger liquid behavior characterized by density waves as collective excitations. We investigate the impact of a scattering potential on a low-dimensional quantum liquid. We consider a microscopic model of ${}^4\mathrm{He}$ inside a perturbed nanopore with a localized constriction and employ quantum Monte Carlo simulations to analyze the density of the core within an effective low-energy framework. Our results reveal the emergence of Friedel oscillations in a bosonic quantum liquid without a Fermi surface. Furthermore, we utilize the Luttinger liquid model to predict experimentally observable signatures of this pinning phenomenon in elastic scattering and via the temperature and pressure dependence of mass transport through the deformed nanopore.

We investigate resonant acoustic phonon scattering in the magnetoresistivity of an ultrahigh-mobility two-dimensional electron gas system subject to DC current in the temperature range 10 mK to 3.9 K. For a DC current density of $\sim 1.1\mathrm{A}/\mathrm{m}$, the induced carrier drift velocity $v_{\mathrm{drift}}$ becomes equal to the speed of sound $s\sim 3\mathrm{km}/\mathrm{s}$. When $v_{\mathrm{drift}}\gtrsim s$ very strong resonant features with only weak temperature dependence are observed and identified as phonon-induced resistance oscillations at and above the “sound barrier.” Their behavior contrasts with that in the subsonic regime ($v_{\mathrm{drift}}<s$) where resonant acoustic phonon scattering is strongly suppressed when the temperature is reduced unless amplified with quasielastic inter-Landau-level scattering. Our observations are compared to recent theoretical predictions from which we can extract a dimensionless electron-phonon coupling constant of $g^2=0.0016$ for the strong nonlinear transport regime. We find evidence for a predicted oscillation phase change effect on traversing the “sound barrier.” Crossing the “sound barrier” fundamentally alters the resulting phonon emission processes, and the applied magnetic field results in pronounced and sharp resonant phonon emission due to Landau level quantization.

Quantum sensing with individual spin defects has emerged as a versatile platform to probe microscopic properties of condensed matter systems. Here we demonstrate that quantum relaxometry with nitrogen-vacancy (NV) centers in diamond can reveal the anisotropic spin dynamics of altermagnetic insulators together with their characteristic spin polarised bands. We show that the distance and orientation dependent relaxation rate of a nearby quantum impurity encodes signatures of momentum space anisotropy in the spin diffusion response, a hallmark of altermagnetic order. This directional sensitivity is unprecedented in the landscape of quantum materials sensing, and it enables the distinction of altermagnets from conventional antiferromagnets via local, noninvasive measurements. Our results could spark new NV-sensing experiments on spin transport and symmetry breaking in altermagnets, and highlight the role of NV orientation to probe anisotropic phenomena in condensed matter systems.

The exploration of many-body problems stands at the vanguard of modern physics, presenting profound challenges alongside compelling opportunities. Recently, the non-Hermiticity featured with complex spectra has significantly expanded the landscape of many-body phenomena beyond the Hermitian paradigm. Most existing studies focus on the interplay between non-Hermiticity and many-body interactions, with the latter being Hermitian in isolation. Here, by integrating nonreciprocity, a key mechanism inducing non-Hermiticity, into two-body interactions, we analytically demonstrate how such interactions govern correlated pair and experimentally confirm our prediction in a phononic crystal simulator. Resulting phenomena, including the non-Hermitian inverse skin effect where the particles undergo synchronous motion as a bound pair and accumulate opposite to the dominant hopping direction, as well as the time cluster effect where two initially separate particles tend to cluster and last as a bound pair in the time domain, are unambiguously captured in airborne sound measurements. These findings experimentally unveil the unique phenomena driven by nonreciprocal many-body interactions, opening new pathways for controlled engineering in correlated systems.