Extracting useful signals is key to both classical and quantum technologies. Conventional noise filtering methods rely on different patterns of signal and noise in frequency or time domains, thus limiting their scope of application, especially in quantum sensing. Here, we propose a signal-nature-based (not signal-pattern-based) approach which singles out a quantum signal from its classical noise background by employing the intrinsic quantum nature of the system. We design a novel protocol to extract the quantum correlation signal and use it to single out the signal of a remote nuclear spin from its overwhelming classical noise backgrounds, which is impossible to be accomplished by conventional filter methods. Our Letter demonstrates the quantum or classical nature as a new degree of freedom in quantum sensing. The further generalization of this quantum nature-based method opens a new direction in quantum research.

One of the main quests in quantum metrology is to attain the ultimate precision limit with given resources, where the resources are not only of the number of queries, but more importantly of the allowed strategies. With the same number of queries, the restrictions on the strategies constrain the achievable precision. In this Letter, we establish a systematic framework to identify the ultimate precision limit of different families of strategies, including the parallel, the sequential, and the indefinite-causal-order strategies, and provide an efficient algorithm that determines an optimal strategy within the family of strategies under consideration. With our framework, we show there exists a strict hierarchy of the precision limits for different families of strategies.

Kerr-Schild double copy is shown to extend naturally to all free symmetric gauge fields propagating on $(A)dS$ in any dimension. Similarly to the standard lower-spin case, the higher-spin multicopy comes along with the zeroth, single, and double copies. The masslike term of the Fronsdal spin $s$ field equations fixed by gauge symmetry and the mass of the zeroth copy both appear to be remarkably fine-tuned to fit the multicopy pattern forming a spectrum organized by higher-spin symmetry. On the black hole side this curious observation fills up the list of miraculous properties of the Kerr solution.

The dark photon $A^{\prime }$ and the dark Higgs boson $h^{\prime }$ are hypothetical particles predicted in many dark sector models. We search for the simultaneous production of $A^{\prime }$ and $h^{\prime }$ in the dark Higgsstrahlung process $e^{+}{e}^{-}\to A^{\prime }{h}^{\prime }$ with $A^{\prime }\to {\mu }^{+}{\mu }^{-}$ and $h^{\prime }$ invisible in electron-positron collisions at a center-of-mass energy of 10.58 GeV in data collected by the Belle II experiment in 2019. With an integrated luminosity of $8.34{\mathrm{fb}}^{-1}$, we observe no evidence for signal. We obtain exclusion limits at 90% Bayesian credibility in the range of 1.7–5.0 fb on the cross section and in the range of $1.7\times {10}^{-8}–200\times {10}^{-8}$ on the effective coupling ${ϵ}^2\times {\alpha }_D$ for the $A^{\prime }$ mass in the range of $4.0\mathrm{GeV}/c^2<M_{A^{\prime }}<9.7\mathrm{GeV}/c^2$ and for the $h^{\prime }$ mass $M_{h^{\prime }}<M_{A^{\prime }}$, where $ϵ$ is the mixing strength between the standard model and the dark photon and ${\alpha }_D$ is the coupling of the dark photon to the dark Higgs boson. Our limits are the first in this mass range.

We search for the dark photon dark matter (DPDM) using a cryogenic millimeter-wave receiver. DPDM has a kinetic coupling with electromagnetic fields with a coupling constant of $\chi$ and is converted into ordinary photons at the surface of a metal plate. We search for signal of this conversion in the frequency range 18–26.5 GHz, which corresponds to the mass range $74–110\mathrm{\mu }\mathrm{eV}/c^2$. We observed no significant signal excess, allowing us to set an upper bound of $\chi <(0.3-2.0)\times {10}^{-10}$ at 95% confidence level. This is the most stringent constraint to date and tighter than cosmological constraints. Improvements from previous studies are obtained by employing a cryogenic optical path and a fast spectrometer.

Matter-free lattice gauge theories (LGTs) provide an ideal setting to understand confinement to deconfinement transitions at finite temperatures, which is typically due to the spontaneous breakdown (at large temperatures) of the center symmetry associated with the gauge group. Close to the transition, the relevant degrees of freedom (Polyakov loop) transform under these center symmetries, and the effective theory depends on only the Polyakov loop and its fluctuations. As shown first by Svetitsky and Yaffe, and subsequently verified numerically, for the U(1) LGT in ($2+1$) dimensions, the transition is in the 2D $XY$ universality class, while for the $Z_2$ LGT, it is in the 2D Ising universality class. We extend this classic scenario by adding higher charged matter fields and show that the critical exponents $\gamma$ and $\nu$ can change continuously as a coupling is varied, while their ratio is fixed to the 2D Ising value. While such weak universality is well known for spin models, we demonstrate this for LGTs for the first time. Using an efficient cluster algorithm, we show that the finite temperature phase transition of the U(1) quantum link LGT in the spin $S=\frac{1}{2}$ representation is in the 2D $XY$ universality class, as expected. On the addition of $Q=\pm 2e$ charges distributed thermally, we demonstrate the occurrence of weak universality.

Chiral perturbation theory and its unitarized versions have played an important role in our understanding of the low-energy strong interaction. Yet, so far, such studies typically deal exclusively with perturbative or nonperturbative channels. In this Letter, we report on the first global study of meson-baryon scattering up to one-loop order. It is shown that covariant baryon chiral perturbation theory, including its unitarization for the negative strangeness sector, can describe meson-baryon scattering data remarkably well. This provides a highly nontrivial check on the validity of this important low-energy effective field theory of QCD. We show that the $\overline{K}N$ related quantities can be better described in comparison with those of lower-order studies, and with reduced uncertainties due to the stringent constraints from the $\pi N$ and $KN$ phase shifts. In particular, we find that the two-pole structure of $\mathrm{\Lambda }(1405)$ persists up to one-loop order reinforcing the existence of two-pole structures in dynamically generated states.

We calculate the equation of state of asymmetric nuclear matter at finite temperature based on chiral effective field theory interactions to next-to-next-to-next-to-leading order. Our results assess the theoretical uncertainties from the many-body calculation and the chiral expansion. Using a Gaussian process emulator for the free energy, we derive the thermodynamic properties of matter through consistent derivatives and use the Gaussian process to access arbitrary proton fraction and temperature. This enables a first nonparametric calculation of the equation of state in beta equilibrium, and of the speed of sound and the symmetry energy at finite temperature. Moreover, our results show that the thermal part of the pressure decreases with increasing densities.

Studying the dynamics of dark states is challenging due to their inability to undergo single-photon emission or absorption. This challenge is made even more difficult for dark autoionizing states owing to their ultrashort lifetime of a few femtoseconds. High-order harmonic spectroscopy recently appeared as a novel method to probe the ultrafast dynamics of a single atomic or molecular state. Here, we demonstrate the emergence of a new type of ultrafast resonance state as a manifestation of coupling between Rydberg and a dark autoionizing state dressed by a laser photon. Through high-order harmonic generation, this resonance results in extreme ultraviolet light emission that is more than one order of magnitude stronger than for the off-resonance case. The induced resonance can be leveraged to study the dynamics of a single dark autoionizing state and the transient changes in the dynamics of real states due to their overlap with the virtual laser-dressed states. In addition, the present results allow the generation of coherent ultrafast extreme ultraviolet light for advanced ultrafast science applications.

Finding a reliable Ising machine for solving nondeterministic polynomial-class problems has attracted great attention in recent years, where an authentic system can be expanded with polynomial-scaled resources to find the ground state Ising Hamiltonian. In this Letter, we propose an extremely low power optomechanical coherent Ising machine based on a new enhanced symmetry breaking mechanism and highly nonlinear mechanical Kerr effect. The mechanical movement of an optomechanical actuator induced by the optical gradient force greatly increases the nonlinearity by a few orders and significantly reduces the power threshold using conventional structures capable of fabrication via photonic integrated circuit platforms. With the simple but strong bifurcation mechanism and remarkably low power requirement, our optomechanical spin model opens a path for chip-scale integration of large-size Ising machine implementations with great stability.

Silicon (Si) exhibits a rich collection of phase transitions under ambient-temperature isothermal and shock compression. This report describes in situ diffraction measurements of ramp-compressed Si between 40 and 389 GPa. Angle-dispersive x-ray scattering reveals that Si assumes an hexagonal close-packed (hcp) structure between 40 and 93 GPa and, at higher pressure, a face-centered cubic structure that persists to at least 389 GPa, the highest pressure for which the crystal structure of Si has been investigated. The range of hcp stability extends to higher pressures and temperatures than predicted by theory.

We survey the phase diagram of high-pressure molecular hydrogen with path integral molecular dynamics using a machine-learned interatomic potential trained with quantum Monte Carlo forces and energies. Besides the HCP and $C2/c\text{−}24$ phases, we find two new stable phases both with molecular centers in the $Fmmm\text{−}4$ structure, separated by a molecular orientation transition with temperature. The high temperature isotropic $Fmmm\text{−}4$ phase has a reentrant melting line with a maximum at higher temperature (1450 K at 150 GPa) than previously estimated and crosses the liquid-liquid transition line around 1200 K and 200 GPa.

Dirac fermion systems form a unique Landau level at the Fermi level—the so-called zero mode—whose observation itself will provide strong evidence of the presence of Dirac dispersions. Here, we report the study of semimetallic black phosphorus under pressure by ${}^{31}\mathrm{P}$-nuclear magnetic resonance measurements in a wide range of magnetic field up to 24.0 T. We have found a field-induced giant enhancement of $1/T_{1}T$, where $1/T_1$ is the nuclear spin lattice relaxation rate: $1/T_{1}T$ at 24.0 T reaches more than 20 times larger than that at 2.0 T. The increase in $1/T_{1}T$ above 6.5 T is approximately proportional to the squared field, implying a linear relationship between the density of states and the field. We also found that, while $1/T_{1}T$ at a constant field is independent of temperature in the low-temperature region, it steeply increases with temperature above 100 K. All these phenomena are well explained by considering the effect of Landau quantization on three-dimensional Dirac fermions. The present study demonstrates that $1/T_1$ is an excellent quantity to probe the zero-mode Landau level and to identify the dimensionality of the Dirac fermion system.

We consider short-range Ising spin glasses in equilibrium at infinite system size, and prove that, for fixed bond realization and a given Gibbs state drawn from a suitable metastate, each translation and locally invariant function (for example, self-overlaps) of a single pure state in the decomposition of the Gibbs state takes the same value for all the pure states in that Gibbs state. We describe several significant applications to spin glasses.

Adsorption of carbon monoxide (CO) on transition-metal surfaces is a prototypical process in surface sciences and catalysis. Despite its simplicity, it has posed great challenges to theoretical modeling. Pretty much all existing density functionals fail to accurately describe surface energies and CO adsorption site preference as well as adsorption energies simultaneously. Although the random phase approximation (RPA) cures these density functional theory failures, its large computational cost makes it prohibitive to study the CO adsorption for any but the simplest ordered cases. Here, we address these challenges by developing a machine-learned force field (MLFF) with near RPA accuracy for the prediction of coverage-dependent adsorption of CO on the Rh(111) surface through an efficient on-the-fly active learning procedure and a $\mathrm{\Delta }$-machine learning approach. We show that the RPA-derived MLFF is capable to accurately predict the Rh(111) surface energy and CO adsorption site preference as well as adsorption energies at different coverages that are all in good agreement with experiments. Moreover, the coverage-dependent ground-state adsorption patterns and adsorption saturation coverage are identified.

Topological defects usually emerge and vary during the phase transition of ordered systems. Their roles in thermodynamic order evolution keep being the frontier of modern condensed matter physics. Here, we study the generations of topological defects and their guidance on the order evolution during the phase transition of liquid crystals (LCs). With a given preset photopatterned alignment, two different types of topological defects are achieved depending on the thermodynamic process. Because of the memory effect of LC director field across the Nematic-Smectic ($N\text{−}S$) phase transition, a stable array of toric focal conic domains (TFCDs) and a frustrated one are generated in $S$ phase, respectively. The frustrated one transfers to a metastable TFCD array with a smaller lattice constant, and further changes to a crossed-walls type $N$ state due to the inheritance of orientational order. A free energy on temperature diagram and corresponding textures vividly describe the phase transition process and the roles of topological defects in the order evolution across the $N\text{−}S$ phase transition. This Letter reveals the behaviors and mechanisms of topological defects on order evolution during phase transitions. It paves a way for investigating topological defect guided order evolution which is ubiquitous in soft matter and other ordered systems.

We report an axion dark matter search at Dine-Fischler-Srednicki-Zhitnitskii sensitivity with the CAPP-12TB haloscope, assuming axions contribute 100% of the local dark matter density. The search excluded the axion-photon coupling $g_{a\gamma \gamma }$ down to about $6.2\times {10}^{-16}{\mathrm{GeV}}^{-1}$ over the axion mass range between 4.51 and $4.59\mathrm{\mu }\mathrm{eV}$ at a 90% confidence level. The achieved experimental sensitivity can also exclude Kim-Shifman-Vainshtein-Zakharov axion dark matter that makes up just 13% of the local dark matter density. The CAPP-12TB haloscope will continue the search over a wide range of axion masses.

We study coupled unitary Virasoro minimal models in the large rank ($m\to \infty$) limit. In large $m$ perturbation theory, we find two nontrivial IR fixed points which exhibit irrational coefficients in several anomalous dimensions and the central charge. For $N>4$ copies, we show that the IR theory breaks all possible currents that would otherwise enhance the Virasoro algebra, up to spin 10. This provides strong evidence that the IR fixed points are examples of compact, unitary, irrational conformal field theories with the minimal amount of chiral symmetry. We also analyze anomalous dimension matrices for a family of degenerate operators with increasing spin. These display further evidence of irrationality and begin to reveal the form of the leading quantum Regge trajectory.