Theoretical quantum memory design often involves selectively focusing on certain energy levels to mimic an ideal $\mathrm{\Lambda }$ configuration, a common approach that may unintentionally overlook the impact of neighboring levels or undesired couplings. While this simplification may be justified in certain protocols or platforms, it can significantly distort the achievable memory performance. Through numerical semiclassical analysis, we show that the presence of unwanted energy levels and undesired couplings in an absorptive memory based on a nitrogen-vacancy center can significantly amplify the signal, resulting in memory efficiencies exceeding unity, a clear indication of unwanted noise at the quantum level. Strikingly, this effect occurs even when the apparent noise, i.e., output in the absence of an input field, is negligible. We then generalize our results using semianalytical estimations to analyze this amplification, and propose a strategy to reduce its effect. Our findings extend to memory platforms beyond nitrogen-vacancy centers; as an example, we also analyze a cavity-based rubidium memory that experiences the same issue.

A charge qubit couples to environmental electric field fluctuations through its dipole moment, resulting in fast decoherence. We propose the $p$-orbital ($pO$) qubit, formed by the single-electron, $p$-like valence states of a five-electron Si quantum dot, which couples to charge noise through the quadrupole moment. We demonstrate that the $pO$ qubit offers distinct advantages in quality factor, gate speed, readout, and size. We use a phenomenological, dipole two-level-fluctuator charge noise model to estimate a $T_2^{*}\sim 80\mathrm{ns}$. In conjunction with Rabi frequencies of order 10 GHz, an order of magnitude improvement in qubit quality factor is expected relative to state-of-the-art semiconductor spin qubits. The $pO$ qubit features all-electrical control via modulating the dot’s eccentricity. We also show how to perform two-qubit gates via the $1/r^5$ quadrupole-quadrupole interaction. We find a universal gate set using gradient ascent-based control pulse optimization, subject to 10 GHz maximum allowable bandwidth and 1 ns pulse times.

In a broad class of cosmological models where spacetime is described by a pseudo-Riemannian manifold, photons propagate along null geodesics, and their number is conserved, upcoming gravitational wave (GW) observations can be combined with measurements of the baryon acoustic oscillation (BAO) angular scale to provide model-independent estimates of the sound horizon at the baryon drag epoch. By focusing on the accuracy expected from forthcoming surveys such as the Laser Interferometer Space Antenna GW standard sirens and dark energy spectroscopic instrument (DESI) or Euclid angular BAO measurements, we forecast a relative precision of ${\sigma }_{r_{\mathrm{d}}}/r_{\mathrm{d}}\sim 1.5\%$ within the redshift range $z\lesssim 1$. This approach will offer a unique model-independent measure of a fundamental scale characterizing the early universe, which is competitive with model-dependent values inferred within specific theoretical frameworks. These measurements can serve as a consistency test for $\mathrm{\Lambda }\mathrm{CDM}$, potentially clarifying the nature of the Hubble tension and confirming or ruling out new physics prior to recombination with a statistical significance of $\sim 4\sigma$.

We solve models of $N$ species of fermions in the lowest Landau level with $\mathrm{U}(N)$-invariant interactions in the $N\gg 1$ limit. We find saddles of the second quantized path integral at fixed chemical potential corresponding to fractional Hall states with filling $(p/q)$, where the integers $p$ and $q$ depend on the chemical potential and interactions. On a long torus there are $q$ such states related by translation symmetry, and $\mathrm{SU}(N)$-invariant excitations of fractional charge. Remarkably, these saddles and their filling persist as extrema of the second-quantized action at $N=1$. Our construction gives a first-principles derivation of fractional Hall states from strongly interacting fermions.

The 247-keV state in ${}^{54}\mathrm{Sc}$, populated in the $\beta$ decay of ${}^{54}\mathrm{Ca}$, is reported here as a nanosecond isomer with a half-life of 26.0(22) ns. The state is interpreted as the $1^{+}$ member of the $\pi f_{7/2}\otimes \nu f_{5/2}$ spin-coupled multiplet, which decays to the $3^{+},\pi f_{7/2}\otimes \nu p_{1/2}$ ground state. The new half-life corresponds to a pure $E2$ transition with a strength of 1.93(16) W.u., providing the most precise, unambiguous $B(E2)$ value in the neutron-rich $fp$ region to date for a nucleus with valence protons above $Z=20$. Notably, it is roughly 4 times larger than the $B(E2;1/2^{-}\to 5/2^{-})$ value in ${}^{55}\mathrm{Ca}$. The results, as compared to semiempirical and ab initio shell-model calculations, indicate (1) a weak $N=34$ subshell gap relative to $N=32$, (2) a large $E2$ enhancement in Sc as compared to Ca due to $1p-1h$ proton excitations across $Z=28$, and (3) empirical effective proton and neutron charges $e_{\pi }=1.30(8)e$ and $e_{\nu }=0.452(7)e$, respectively, that are in contrast to reports of $e_{\pi }\approx 1.1–1.15e$ and $e_{\nu }\approx 0.6–0.8e$ for $fp$-shell nuclei near $N=Z$. We demonstrate that these reports are erroneous and that, in fact, a universal set of effective charges can be used across the $sd$ and $fp$ shells.

Quantum low-density parity-check (QLDPC) codes offer a promising path to low-overhead fault-tolerant quantum computation but lack systematic strategies for exploration. In this Letter, we establish a topological framework for studying the bivariate-bicycle codes, a prominent class of QLDPC codes tailored for real-world quantum hardware. Our framework enables the investigation of these codes through universal properties of topological orders. In addition to efficient characterizations using Gröbner bases, we also introduce a novel algebraic-geometric approach based on the Bernstein-Khovanskii-Kushnirenko theorem. This approach allows us to analytically determine how the topological order varies with the generic choices of bivariate-bicycle codes under toric layouts. Novel phenomena are unveiled, including topological frustration, where ground-state degeneracy on a torus deviates from the total anyon number, and quasifractonic mobility, where anyon movement violates energy conservation. We demonstrate their intrinsic link to symmetry-enriched topological orders and derive an efficient method for generating finite-size codes. Furthermore, we extend the connection between anyons and logical operators using Koszul complex theory. Our Letter provides a rigorous theoretical basis for exploring the fault tolerance of QLDPC codes and deepens the interplay among topological order, quantum error correction, and advanced algebraic structures.

The unabating discovery of nanoskyrmions in centrosymmetric magnets challenges the conventional Dzyaloshinskii-Moriya (DM) skyrmion stabilization mechanism. We investigate ${\mathrm{Gd}}_2{\text{PdSi}}_3$ using polarized resonant x-ray scattering and find that the low-field incommensurate modulations are elliptical helices, evolving into spin-density waves at higher fields. Quasi-2D magnetism arises via local DM interactions generated by inversion symmetry breaking around Gd-Gd bonds, which we characterize using atomistic simulations. Our findings suggest a prominent “hidden” role of DM interactions even in centrosymmetric skyrmionic hosts.

We present a least square state estimator regularized by state purity to accomplish the task of quantum state tomography and entanglement verification, and report an experimental validation on a superconducting processor. First, a scalable full-state tomography is achieved with state fidelity 0.8217(1) for the 9-qubit $W$ state and 0.6817(1) for the 17-qubit Greenberger-Horne-Zeilinger state, with the latter reaching 0.7587(1) under a pure-state assumption. Then, the presence of genuine multiqubit entanglement in the majority of generated states is conclusively certified by violating the corresponding entanglement witness. Finally, it is demonstrated that our method can achieve superior tomography accuracy with limited measurement settings and that mitigating error is essential for leveraging noisy quantum systems in quantum processing tasks. Our results pave the way for more accurate full characterization of larger-scale many-body quantum systems.

We present the first constraints on primordial magnetic fields from the Lyman-$\alpha$ forest using full cosmological hydrodynamic simulations. At the scales and redshifts probed by the data, the flux power spectrum is extremely sensitive to the extra power induced by primordial magnetic fields in the linear matter power spectrum, at a scale that we parametrize with $k_{\mathrm{peak}}$. We rely on a set of more than a quarter million flux models obtained by varying thermal and reionization histories and cosmological parameters. We find a hint of extra power that is well fitted by the primordial magnetic field model with $B\sim 0.2\mathrm{nG}$, corresponding to $k_{\mathrm{peak}}\sim 20{\mathrm{Mpc}}^{-1}$. However, when applying very conservative assumptions on the modeling of the noise, we obtain a $3\sigma$ C.L. lower limit $k_{\mathrm{peak}}>30{\mathrm{Mpc}}^{-1}$, which translates into the tightest bounds on the strength of primordial intergalactic magnetic fields: $B<0.30\mathrm{nG}$ (for a fixed, nearly scale-invariant $n_{\mathrm{B}}=-2.9$).

We report on a search for sub-GeV dark matter (DM) particles interacting with electrons using the DAMIC-M prototype detector at the Modane Underground Laboratory. The data feature a significantly lower detector single $e^{-}$ rate (factor 50) compared to our previous search, while also accumulating a 10 times larger exposure of $\sim 1.3\mathrm{kg}\text{−}\mathrm{day}$. DM interactions in the skipper charge-coupled devices (CCDs) are searched for as groups of two or three adjacent pixels with a total charge between 2 and $4e^{-}$. We find 144 candidates of $2e^{-}$ and 1 candidate of $4e^{-}$, where 141.5 and 0.071, respectively, are expected from background. With no evidence of a DM signal, we place stringent constraints on DM particles with masses between 1 and $1000\mathrm{MeV}/c^2$ interacting with electrons through an ultralight or heavy mediator. For large ranges of DM masses below $1\mathrm{GeV}/c^2$, we exclude theoretically motivated benchmark scenarios where hidden-sector particles are produced as a major component of DM in the Universe through the freeze-in or freeze-out mechanisms.

Charged hadron elliptic anisotropies ($v_2$) are presented over a wide transverse momentum ($p_{\mathrm{T}}$) range for proton-lead ($p\mathrm{Pb}$) and lead-lead (PbPb) collisions at nucleon-nucleon center-of-mass energies of 8.16 and 5.02 TeV, respectively. The data were recorded by the CMS experiment and correspond to integrated luminosities of 186 and $0.607{\mathrm{nb}}^{-1}$ for the $p\mathrm{Pb}$ and PbPb systems, respectively. A four-particle cumulant analysis is performed using subevents separated in pseudorapidity to effectively suppress noncollective effects. At high $p_{\mathrm{T}}$ ($p_{\mathrm{T}}>8\mathrm{GeV}$), significant positive $v_2$ values that are similar between $p\mathrm{Pb}$ and PbPb collisions at comparable charged particle multiplicities are observed. This observation suggests a common origin for the multiparticle collectivity for high-$p_{\mathrm{T}}$ particles in the two systems.

We determine the low-energy constants $f_0$, $L_4^r$ and $L_5^r$ of SU(3) chiral perturbation theory from a lattice QCD calculation of the scalar form factors of the pion with fully controlled systematics. Lattice results are computed on a large set of $N_f=2+1$ gauge ensembles covering four lattice spacings $a\in [0.049,0.086]\mathrm{fm}$, pion masses $M_{\pi }\in [130,350]\mathrm{MeV}$, and various large physical volumes. By determining the notorious quark-disconnected contributions with unprecedented precision and using a large range of source-sink separations $t_{\mathrm{sep}}\in [1.0,3.25]\mathrm{fm}$, we are able for the first time to obtain the scalar radii from a $z$-expansion parametrization of the form factors rather than a simple linear approximation at small momentum transfer. The low-energy constants are obtained from the physical extrapolation of the radii using next-to-leading-order SU(3) next-to-leading-order chiral perturbation theory to parametrize the quark mass dependence. Systematic uncertainties are estimated via model averages based on the Akaike information criterion. Our determination of $L_4^r$ is the first lattice determination to obtain a result not compatible with zero.

Diffusion wake accompanying a Mach cone is a unique feature of the medium response to projectiles traveling at a speed faster than the velocity of sound. This is also the case for jet-medium interaction inside the quark-gluon plasma in high-energy heavy-ion collisions. It leads to a depletion of soft hadrons in the opposite direction of the propagating jet and, recently, has been observed in $Z$-jet events of $\mathrm{Pb}+\mathrm{Pb}$ collisions at LHC. In dijet events, however, the diffusion wake of one jet usually overlaps with the medium-induced hadron enhancement of the other jet without a clear signal except a reduction of the hadron enhancement, unless there is a large rapidity gap between the two jets. We propose to use the rapidity asymmetry of jet-hadron correlations in dijets with a finite rapidity gap relative to that without, as a robust and background-free signal of the diffusion wake. The asymmetry emerges because the diffusion wake of one jet is shifted to a finite rapidity relative to the other jet. Consequently, a depletion of soft hadrons appears in the shifted rapidity region of the diffusion wake and an enhancement in the rapidity region of the other jet whose soft hadron enhancement is no longer or less reduced by the diffusion wake as in dijets without a rapidity gap. We predict the rapidity asymmetry using both theoretical and mixed-event background subtraction for different values of the rapidity gap within the CoLBT-hydro model. Future measurements of this rapidity asymmetry with high statistics data on dijets should provide more precise insights into the jet-induced diffusion wake and properties of the quark-gluon plasma.

The ability to slow down light at the single-photon level has applications in quantum information processing and other quantum technologies. We demonstrate two methods, both using just a single artificial atom, enabling dynamic control over microwave light velocities in waveguide quantum electrodynamics (QED). Our methods are based on two distinct mechanisms harnessing the balance between radiative decay and nonradiative decoherence rates of a superconducting artificial atom in front of a mirror. In the first method, we tune the radiative decay of the atom using interference effects due to the mirror; in the second method, we pump the atom to effectively control its nonradiative decoherence. When the half of the radiative decay rate exceeds the nonradiative decoherence rate, we observe positive group delay; conversely, dominance of the nonradiative decoherence results in negative group delay. Our results advance signal-processing capabilities in waveguide QED.

We experimentally investigate a system composed of two levitating nanospheres whose motions are indirectly coupled via coherent scattering in a single optical cavity mode. The nanospheres are loaded into a double longitudinal tweezer created with two lasers at different wavelengths, where chromatic aberration leads to the formation of two separate trapping sites. We achieve strong coupling between each pair of modes in the transverse plane of the tweezer, and we show the emergence of dark modes in the overall coupled motion. The observed features are ubiquitous in a variety of classical and quantum systems. As such, our experiment will allow us to explore the classical analog of typically quantum dynamics, and in further developments to investigate the transition to the quantum domain.

Gaining a fundamental understanding of turbulent flows of dilute polymer solutions has been a challenging and outstanding problem for a long time. In this Letter, we examine homogeneous, isotropic polymeric turbulence at large Reynolds and Deborah numbers through direct numerical simulations. While at the largest scales at which the flow inertial turbulence exists, we find that the flow is fundamentally altered from Newtonian turbulence below the Kolmogorov scale. We demonstrate that “elastic turbulence” exists at the smallest scales of polymeric turbulence by quantifying multiple statistical properties of the flow—energy spectrum and flux in Fourier space as well as the spatial statistics of the velocity field—the structure functions and kurtosis, and energy dissipation. Our results show the coexistence of two fundamentally distinct types of turbulence in polymeric fluids and point to the ubiquity of elastic turbulence, which was hitherto only known to exist for negligible inertia.

We develop an ab initio framework that captures the impact of electron-electron and electron-hole interactions on phonon properties. This enables the inclusion of excitonic effects in the optical phonon dispersions and lifetimes of graphene, both near the center ($\mathrm{\Gamma }$) and at the border ($K$) of the Brillouin zone, at phonon-momenta relevant for Raman scattering and for the onset of the intrinsic electrical resistivity. Near $K$, we find a phonon redshift of $\sim 150{\mathrm{cm}}^{-1}$ and a $10\times$ enhancement of the group velocity, together with a $5\times$ increase in linewidths due to a $26\times$ increase of the electron-phonon matrix elements. These effects persist for doping $2E_F<\hslash {\omega }_{\mathrm{ph}}$ and are quenched at higher dopings. Near $\mathrm{\Gamma }$, the excitonic effects are minor because of the gauge field nature of the electron-phonon coupling at small phonon momentum.

Quasi-one-dimensional magnets can host an ordered longitudinal spin-density wave state (LSDW) in magnetic field at low temperature, when longitudinal correlations are strengthened by Ising anisotropies. In the $S=1/2$ Heisenberg antiferromagnet ${\mathrm{YbAlO}}_3$ this happens via Ising-like interchain interactions. Here, we report the first experimental observation of magnetization plateaux at $1/5$ and $1/3$ of the saturation value via thermal transport and magnetostriction measurements in ${\mathrm{YbAlO}}_3$. We present a phenomenological theory of the plateau states that describes them as islands of commensurability within an otherwise incommensurate LSDW phase and explains their relative positions within the LSDW phase and their relative extent in a magnetic field. Notably, the plateaux are stabilized by ferromagnetic interchain interactions in ${\mathrm{YbAlO}}_3$ and consistently are absent in other quasi-1D magnets such as ${\text{BaCo}}_2{\mathrm{V}}_2{\mathrm{O}}_8$ with antiferromagnetic interchain interactions. We also report a small, steplike increase of the magnetostriction coefficient, indicating a weak phase transition of unknown origin in the high-field phase just below the saturation.

$d$-wave altermagnets have magnetic octupoles as their order parameters [S. Bhowal and N. A. Spaldin, Ferroically ordered magnetic octupoles in $d$-wave altermagnets, Phys. Rev. X 14, 011019 (2024)]. We theoretically show that magnetic octupoles injected from outside generate torque on the $d$-wave altermagnets. The injection can be achieved by the magnetic octupole Hall effect in an adjacent layer. We calculate the magnetic octupole Hall conductivity of the heavy metal $\alpha \text{−}\mathrm{W}$ and find a sizable value comparable to its spin Hall conductivity. Our work generalizes the spin Hall phenomenology (generation by heavy metals and detection by torque in ferromagnets) to the magnetic octupole Hall phenomenology (generation by heavy metals and detection by torque in altermagnets), which can be utilized to electrically control magnetic configurations of altermagnets.

In the gravitational-wave analysis of pulsar-timing-array datasets, parameter estimation is usually performed using Markov chain Monte Carlo methods to explore posterior probability densities. We introduce an alternative procedure that instead relies on stochastic gradient-descent Bayesian variational inference, whereby we obtain the weights of a neural-network-based approximation of the posterior by minimizing the Kullback–Leibler divergence of the approximation from the exact posterior. This technique is distinct from simulation-based inference with normalizing flows since we train the network for a single dataset, rather than the population of all possible datasets, and we require the computation of the data likelihood and its gradient. Unlike Markov chain methods, our technique can trivially exploit highly parallel computing platforms. This makes it extremely fast on modern graphical processing units, on which it can analyze the NANOGrav 15-yr dataset in a few tens of minutes, depending on the probabilistic model, compared to hours or days with the analysis codes used so far. We expect that this speed will unlock new astrophysical and cosmological explorations of pulsar-timing-array datasets with statistical models that are currently too computationally expensive. Furthermore, this kind of variational inference is viable in other contexts of gravitational-wave data analysis, as long as differentiable and parallelizable likelihoods are available.