In cuprates that exhibit high-temperature superconductivity (HTS), as the doping level $p$ is increased beyond the optimal value, the superfluid density $n_{s0}$ decreases and eventually vanishes, closely tracking the critical temperature $T_c$. This has been interpreted using a dirty-$d$-wave extension of the Bardeen-Cooper-Schrieffer theory, assuming that $T_c$ and $n_{s0}$ decrease with increasing disorder and pair breaking. To test this hypothesis, we tuned the doping level in overdoped ${\mathrm{La}}_{2\text{-x}}{\mathrm{Sr}}_{\mathrm{x}}{\mathrm{CuO}}_{4\text{−}\delta }$ films by electrolyte gating, measured several parameters used to quantify the level of disorder (the residual resistivity ratio $\mathrm{RRR}$, the mean free path $l_0$, and the electron mobility $\mu$), and studied how $T_c$ and $n_{s0}$ scale with these. The experimentally measured dependence turned out to be the opposite of the expected—$T_c$ and $n_{s0}$ increased with increasing disorder. This brings the question of the true origin of the demise of $T_c$ and $n_{s0}$ with overdoping back to the center stage of the quest to decipher the HTS enigma.

Superconducting circuits are arguably taking a leading role in driving the ongoing quantum technological revolution. A detailed knowledge of the microscopic fluctuating electromagnetic properties plays an important role in advancing the circuitry design, testing, and material integration of cutting-edge superconducting quantum electronics. Here, we report scanning nitrogen-vacancy (NV) quantum sensing of local magnetic noise environment of an on-chip superconducting resonator. We find that quasiparticle-induced fluctuating magnetic fields can drive NV spin relaxation, which shows a peak value around the superconducting transition point of niobium at the thermal equilibrium state. External microwave driving at the resonator mode frequency significantly increases the quasiparticle density, leading to enhancement of magnetic noise. We further perform optically detected magnetic resonance measurements to demonstrate quasiparticle magnetic noise mediated off-resonant dipole coupling between the NV center and niobium resonator. Our Letter reports experimental observation of the Hebel-Slichter peak signature by an external sensor outside of a superconductor. The presented study also highlights the advantages of quantum sensors in investigating miniaturized superconducting devices, providing insights into their future performance improvements.

Rupture of the contacts forming a frictional interface governs frictional failure in both natural and engineered systems. Often such failure is governed by brittle fracture, where a small cohesive length $\xi$ regularizes the singular rupture tip. We experimentally study rupture nucleation under conditions where $\xi$ is large, exceeding the interface width. Within $\xi$, initially 2D expanding fronts transition into slow 1D rupture fronts while still establishing $\xi$. Rapid rupture only ensues after $\xi$ is established, at the Griffith length. This cohesive-scale-driven nucleation should be generic when $\xi$ dominates geometrical scales, with ramifications for material failure, friction, and fault-zone dynamics.

We develop a deep variational free energy framework to compute the equation of state of hydrogen in the warm dense matter region. This method parameterizes the variational density matrix of hydrogen nuclei and electrons at finite temperature using three deep generative models: a normalizing flow model for the Boltzmann distribution of the classical nuclei, an autoregressive transformer for the distribution of electrons in excited states, and a permutational equivariant flow model for the unitary backflow transformation of electron coordinates in Hartree-Fock states. By jointly optimizing the three neural networks to minimize the variational free energy, we obtain the equation of state and related thermodynamic properties of dense hydrogen for the temperature range where electrons occupy excited states. We compare our results with other theoretical and experimental results on the deuterium Hugoniot curve, aiming to resolve existing discrepancies. Our results bridge the gap between the results obtained by path-integral Monte Carlo calculations at high temperature and ground-state electronic methods at low temperature, thus providing a valuable benchmark for hydrogen in the warm dense matter region.

The deconfined quantum critical point (DQCP), which separates two distinct symmetry-broken phases, was conjectured to be an example of $(2+1)\mathrm{D}$ criticality beyond the standard Landau-Ginzburg-Wilson paradigm. However, this hypothesis has been met with challenges and remains elusive. Here, we perform a systematic study of a microscopic model realizing the DQCP with a global symmetry tunable from SO(5) to O(4). Through the lens of fuzzy sphere regularization, we uncover the key information on the renormalization group flow of conformal operators. We reveal O(4) primaries decomposed from original SO(5) primaries by tracing conformal operator content and identifying the “avoided level crossing” in the operator flows. In particular, we find that the existence of a scalar operator, in support of the nature of pseudo-criticality, remains relevant, persisting from SO(5) to O(4) DQCP. This Letter not only uncovers the nature of O(4) DQCP but also demonstrates that the fuzzy sphere scheme offers a unique perspective on the renormalization group flow of operators in the study of critical phenomena.

Quantum Hall bilayers are a uniquely tunable platform that can realize continuous transitions between distinct topological phases of matter. One prominent example is the transition between the Halperin state and the Moore-Read Pfaffian, long predicted to host a critical theory of Majorana fermions but so far not verified in unbiased microscopic simulations. Using the fuzzy-sphere regularization, we identify the low-energy spectrum at this transition with the 3D gauged Majorana conformal field theory. We show that the transition is driven by the closing of the neutral fermion gap, and we directly extract the operator content in both integer and half-integer spin sectors. Our results resolve the long-standing question of the nature of a topological phase transition in a setting relevant to quantum Hall experiments, while also providing a realization of emergent fermionic fields on the fuzzy sphere, previously limited to bosonic fields.

We present a theory for nonlinear, resonant excitation of dynamical axions by counterpropagating electromagnetic waves in materials that break both $\mathcal{P}$ and $\mathcal{T}$ symmetries. We show that dynamical axions can mediate an exponential growth in the amplitude of the lower frequency (Stokes) beam. We also discuss spontaneous generation of a counterpropagating Stokes mode, enabled by resonant amplification of quantum and thermal fluctuations in the presence of a single pump laser. Remarkably, the amplification can be orders of magnitude larger than that obtained via stimulated Brillouin and Raman scattering processes, and can be modulated with the application of external magnetic fields, making stimulated axion scattering promising for optoelectronics applications.

We introduce harmonization, an ensembling method that combines several “noisy” decoders to generate highly accurate decoding predictions. Harmonized ensembles of minimum weight perfect matching-based decoders achieve lower logical error rates than their individual counterparts on repetition and surface code benchmarks, approaching maximum-likelihood accuracy at large ensemble sizes. We can use the degree of consensus among the ensemble as a confidence measure for a layered decoding scheme, in which a small ensemble flags high-risk cases to be checked by a larger, more accurate ensemble. This layered scheme can realize the accuracy improvements of large ensembles with a relatively small constant factor of computational overhead. We conclude that harmonization provides a viable path toward highly accurate real-time decoding.

Dark matter remains one of the most profound and unresolved mysteries in modern physics. To unravel its nature, numerous haloscope experiments have been implemented across various mass ranges. However, very few haloscope experiments have been conducted within the millimeter-wave frequency range, which is in the favored mass region for well-motivated dark matter candidates. Here we designed and constructed a millimeter-wave dielectric haloscope featuring a dark matter detector composed of dielectric disks and a mirror. Using this setup, we conducted a search for randomly polarized dark photon dark matter and found no evidence for its existence. Our results established new constraints on the kinetic mixing parameter in the mass range from 387.72 to $391.03\mathrm{\mu }\mathrm{eV}$, improving the existing limits by 2 orders of magnitude. With future enhancements, our system has the potential to explore new parameter space for dark photons as well as axion dark matter within the millimeter-wave frequency range.

We examine a hypersurface model for the classical dynamics of spinning black holes. Under specific, rigid geometric constraints, it reveals an intriguing solution resembling expectations for the Kerr Black hole three-point amplitude. We explore various generalizations of this formalism and outline potential avenues for applying it to analyze the attraction of spinning black holes.

We present a joint experimental and theoretical investigation of nondipole effects in strong-field double ionization of xenon atoms driven by circularly polarized 800 nm laser fields. We observe that the ${\mathrm{Xe}}^{2+}$ ion momentum distribution in the laser polarization plane is Gaussian. The correlated two-electron momentum distribution along a specific direction in the polarization plane reveals a distinct four-lobe structure. We also measure the photoelectron momentum shift of double ionization along the laser propagation direction, which is associated with the nondipole effect. We find that the nondipole effect shows a remarkable enhancement in momentum shift for low-energy electrons, which deviates from the expectation within the picture of sequential double ionization. We develop a nondipole-corrected two-electron classical trajectory Monte Carlo (CTMC) model that reproduces the experimental observations. The abnormal momentum shift of low-energy electrons originates from recollision-induced linear momentum redistribution. Furthermore, the sensitivity of the nondipole effect to the recollision allows us to resolve distinct angular emission patterns between sequential and nonsequential double ionization. These results indicate that the nondipole effect plays a prominent role in electron correlation, and they offer new insights into many-body linear momentum transfer in intense laser-matter interactions.

We report the realization of a blue-detuned magneto-optical trap (BDM) of BaF molecules. The ($1+1$) type BDM and ($1+2$) type conveyor-belt MOT (CB-MOT) are explored. While the ($1+1$) BDM provides only a weak trapping force, the CB-MOT significantly compresses the molecular cloud, achieving a Gaussian rms width of $316\mathrm{\mu }\mathrm{m}$, a temperature of $240\mathrm{\mu }\mathrm{K}$, and a peak number density of $2.4\times {10}^7{\mathrm{cm}}^{-3}$. This performance marks two orders of magnitude improvement over red-detuned MOTs. More importantly, we demonstrate the efficient direct loading of the CB-MOT from a slowed molecular beam, surpassing the loading efficiency of the standard dual-frequency MOT. This surprising result is attributed to the dipole-force-dominated trapping mechanism, wherein the capture velocity increases continuously with laser power, unimpeded by the saturation limit of photon scattering. This method is particularly advantageous for laser cooling and trapping challenging molecular species with large mass, small photon recoil, and narrow linewidths.

It is long established that overdoped cuprate superconductors experience a loss of superfluid density (SFD) with increasing doping, $p$, along with the decline in $T_c$. Such behavior is unconventional and suggests a depletion of the condensate by increasing pairbreaking or the growth of a second nonpairing channel. This led to a recent suggestion that the condensate arises from an incoherent charge channel, which progressively gives way with overdoping to a second, coherent nonpairing channel. Contra these ideas, we report analysis of the field-dependent electronic specific heat of several cuprates from which we find no apparent loss of SFD with overdoping. The SFD per ${\mathrm{CuO}}_2$ plaquette is found to rise progressively with overdoping from $p$ toward ($1+p$), undiminished and much the same as the Hall number, thus implying that all available carriers contribute to the condensate. We suggest this could be the underlying intrinsic behavior for all cuprates. Our samples include $(\mathrm{Y},\mathrm{Ca}){\text{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$, ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$, ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$, and ${\mathrm{Tl}}_2{\mathrm{Ba}}_2{\mathrm{CuO}}_6$, with the latter being the only exception. Our results signal a possible return to a more conventional picture.

We reveal an instantaneous optical valley selection rule that illuminates the coupling between the instantaneous optical chirality of the driving laser field and the chirality of valley systems. Building on this principle, we propose and demonstrate that a single chirality-separated optical field, in which oppositely signed instantaneous optical chiralities are separated within an optical cycle, enables independent manipulation of currents from $K$ and $K^{\prime }$ valleys. Based on this scheme, we highlight two key example applications: (1) complete separation of currents from different valleys, yielding 100%-purity valley-polarized currents, and (2) generation of pure valley current with zero net charge flow. Our Letter offers a robust and highly controllable all-optical strategy for ultrafast engineering valley currents in the optical cycle timescale, paving a new avenue for valleytronics and quantum information technologies.

A fundamental problem in experiments with open quantum systems is to ensure steady-state convergence within a given operational time window. Here, we devise a general state preparation recipe to control relaxation timescales and achieve steady-state convergence within experimental run times. We do so by constructing a unitary operation that cancels multiple relaxation modes. We provide an example in a few-body interacting system (long-range qubit chain), taking into account limitations of experimentally accessible unitary operations in quantum simulators.

Relaxation in open quantum systems is fundamental to quantum science and technologies. Yet, the influence of the initial state on relaxation remains a central, largely unanswered question. Here, by systematically characterizing the relaxation behavior of generic initial states, we uncover a typicality phenomenon in high-dimensional open quantum systems: relaxation becomes nearly initial-state independent as system size increases under verifiable conditions. Crucially, we prove this typicality for many thermalization processes above a size-independent temperature. Our findings extend the typicality to transient open quantum dynamics, in turn identifying a class of systems where two widely used quantities—the Liouvillian gap and the maximal relaxation time—merit re-examination. We formalize this with two new concepts: the “typical strong Mpemba effect” and the “typical relaxation time.” Beyond these conceptual advances, our results provide practical implications: a scalable route to accelerating relaxation and a typical mixing-time benchmark that complements conventional worst-case metrics for quantum simulations and state preparation.

In the present Letter, we introduce, develop, and investigate a connection between multiphoton quantum interference, a core element of emerging photonic quantum technologies, and Hopfield-like Hamiltonians of classical neural networks, the paradigmatic models for associative memory and machine learning in systems of artificial intelligence. Specifically, we show that combining a system composed of $N_{\mathrm{ph}}$ indistinguishable photons in superposition over $M$ field modes, a controlled array of $M$ binary phase shifters, and a linear-optical interferometer, yields output photon statistics described by means of a $p$-body Hopfield Hamiltonian of $M$ Ising-like neurons $\pm 1$, with $p=2N_{\mathrm{ph}}$. We investigate in detail the generalized four-body Hopfield model obtained through this procedure, undergoing a transition from a memory retrieval to a memory black-out regime, i.e., a spin-glass phase, as the amount of stored memory increases. The mapping enables novel routes to the realization and investigation of disordered and complex classical systems via efficient photonic quantum simulators and describes aspects of structured photonic systems in terms of classical spin Hamiltonians.