The sign problem in numerical calculations of the QCD Euclidean space path integral of QCD with a chemical potential vanishes if the chemical potential is imaginary. Moreover, calculations of the partition function with imaginary chemical potentials are equivalent to calculations with Lagrange multipliers enforcing the current density. At zero temperature, Lorentz boosts allow one to deduce properties of systems with both number density and current density from properties of systems with a current density alone; this allows both upper and lower bounds to be determined for the equation of state in the form of energy density as a function of number density.

In a canonical Stokes flow geometry, the Hele-Shaw cell, we show that tunable circulations induced by Lorentz forces in a conducting fluid enable particle control. We reveal that energy-optimal control paths correspond to geodesics of an emergent Riemannian metric defined over the fluid domain, which are time-optimal under a maximum-power constraint. Subject to random boundary forcing, particle paths exhibit metric-governed anisotropic diffusion. Our geometric concepts governing optimal control, though developed explicitly for circulation-driven flows, generalize to generic driven Stokes flows and so elucidate recent observations in a three-dimensional context.

We theoretically investigate the Josephson effect between two proximized Fibonacci quasicrystals. A quasiperiodic modulation of the chemical potential on a superconducting substrate induces topological gaps and edge modes with energies above the superconducting gap. We reveal that these supragap edge modes, which we term Fibonacci-Andreev bound states, acquire a dispersion with the phase difference between superconductors when they localize at the Josephson junction interface. Shifting the quasiperiodic modulation controls the localization of these states, and their contribution to the supercurrent in short junctions can completely dominate over the conventional one from subgap Andreev bound states. Topological edge modes in quasiperiodic systems can thus strongly modify the Josephson effect, offering a route for exploring exotic physics in quasicrystals.

A central puzzle in strongly correlated electronic phases is strange metallic transport, marked by $T$-linear resistivity and $B$-linear magnetoresistance, in sharp contrast with quadratic scalings observed in conventional metals. Here, we demonstrate that proximity to quantum critical points, a recurring motif in the phase diagrams of strange metal candidates, can explain both transport anomalies. We construct and solve a minimal microscopic model by coupling electronic excitations at the Fermi surface to quantum critical bosons via a spatially disordered Yukawa interaction, as well as static pinned domains of density wave order. The resultant transport relaxation rate scales as $k_{B}T/\hslash$ at low magnetic fields, and as an effective Bohr magneton ${\tilde{\mu }}_{B}B/\hslash$ at low temperatures. Further, the magnetoresistance in our model shows a scaling collapse upon rescaling the magnetic field and the resistance by temperature, in agreement with experimental observations.

For decades, superconductivity in high-$T_{\mathrm{c}}$ cuprates has been viewed as a competitor that suppresses charge-density-wave (CDW) order by reducing its amplitude and spatial extent. Here, we show that this picture is incomplete, as superconductivity is accompanied by a systematic enhancement of CDW phase coherence across multiple cuprate families. Using resonant soft x-ray scattering combined with a coherence-sensitive momentum-profile analysis, we uncover a BCS-like growth of phase coherence below $T_{\mathrm{c}}$, which phenomenologically manifests as the absence of CDW peak broadening and near-perfect wave-vector locking. This enhancement remains visible even in a disorder-dominated regime created by long-term crystal aging and follows a common trend when compared with published data on Bi-, Hg-, Y-, and Nd-based cuprates. These results indicate that superconductivity reshapes CDW order in two distinct ways, suppressing its amplitude while strengthening its phase coherence, and reveal an additional phase-level interplay with lattice coupling in high-$T_{\mathrm{c}}$ cuprates.

The emerging $\mathbb{Z}$-classified higher-order topological insulators (HOTIs), featuring multiple topological corner states per site, have attracted extensive interest due to their multipole chiral number (MCN) protection and potential for quantum-inspired device engineering. While 2D HOTIs with $\mathrm{MCN}>1$ have been demonstrated on classical platforms, 3D realizations have remained experimentally elusive primarily due to stringent long-range hopping requirements. Here, we present the first experimental realization of 3D $\mathbb{Z}$-classified HOTIs with large MCNs by implementing a synthetic orbital approach through a 3D Su-Schrieffer-Heeger model incorporating degenerate $p$ orbitals. By explicitly incorporating orbital degrees of freedom into the HOTI design, our work enables multidimensional wave control while circumventing conventional hopping limitations. This demonstration of the orbital-engineering paradigm establishes a versatile platform for developing highly integrated acoustic devices.

In the last decade, it was understood that quantum networks involving several independent sources of entanglement which are distributed and measured by several parties allowed for completely novel forms of nonclassical quantum correlations, when entangled measurements are performed. Here, we experimentally obtain quantum correlations in a triangle network structure and provide solid evidence of its nonlocality. Specifically, we first obtain the Elegant distribution proposed in [Gisin et al., Entanglement 25 years after quantum teleportation: Testing joint measurements in quantum networks, Entropy 21, 325 (2019)] by performing a six-photon experiment. Then, we justify its nonlocality based on machine learning tools to estimate the distance of the experimentally obtained correlation to the local set.

Nonlinear effects are widely utilized in quantum metrology to enhance measurement precision by leveraging complex dynamical behaviors. Here, we propose a quantum scrambling-integrated scheme that optimizes the selection of initial states and parameter encoding by exploiting the nonlinear dynamical trajectories and their geometric properties in phase space. We consider a two-mode Bose-Einstein condensate as a typical example. Within a certain parameter range, using uncorrelated spin coherent states located at saddle points and separatrices enables the measurement precision to reach the Heisenberg scaling. An analytical expression for the quantum Fisher information under long-time evolution is provided, and our analysis further reveals that the enhancement mechanism is governed by the sensitivity of the energy spectrum to parameter variations. Compared to the criticality-enhanced protocol that requires parameters to approach the critical point, our scheme offers a distinct advantage in its applicability over a broader range of parameters. Moreover, this scheme can also be applied to models that include one- and two-axis countertwisting interactions and chaotic dynamics. This Letter offers a new perspective for advancing the application of nonlinear dynamics to enhance the parameter estimation precision in quantum systems.

Environmentally induced decoherence leads to irreversible energy loss during the active charging and discharging processes of quantum batteries (QBs). To address this issue, we propose a charging protocol utilizing the nonlocal coupling properties of giant atoms (GAs). In this Letter, both the QB and its charger are implemented as superconducting GAs with multiple nonlocal coupling points to a shared microwave waveguide. By engineering these atoms in a braided configuration, where their coupling paths are spatially interleaved, we realize lossless energy transfer dynamics. This is achieved by exploiting destructive interference to suppress waveguide-mediated dissipation while simultaneously preserving coherent interactions between the charger and the QB. The charging properties of separated and nested coupled configurations are also investigated. The results show that these two configurations underperform the braided configuration. Additionally, we propose a long-range chiral charging protocol that facilitates unidirectional energy transfer between the charger and the battery, with the capability to reverse the flow direction by modulating the applied magnetic flux. Our results provide guidelines for implementing a decoherence-resistant charging protocol and remote chiral QBs in circuits with GA engineering.

A longstanding open problem in quantum complexity theory is whether Quantum Merlin-Arthur (QMA), the quantum analog of nondeterministic polynomial time, is equal to ${\mathrm{QMA}}_1$, its one-sided error variant. We show that $\mathrm{QMA}={\mathrm{QMA}}^{\infty }={\mathrm{QMA}}_1^{\infty }$, where ${\mathrm{QMA}}_1^{\infty }$ is like ${\mathrm{QMA}}_1$, but the verifier has an infinite register, as part of their witness system, in which they can efficiently perform a shift (increment) operation. We call this register an “infinite counter,” and compare it to a program counter in a Las Vegas algorithm. The result, $\mathrm{QMA}={\mathrm{QMA}}^{\infty }$ means such an infinite register does not increase the power of QMA, but does imply perfect completeness. By truncating our construction to finite dimensions, we get a QMA-amplifier that only amplifies completeness, not soundness, but does so in significantly less time than previous QMA amplifiers. Our new construction achieves completeness $1-2^{-q}$ using $O(1)$ calls to each of the original verifier and its inverse, and $O(\log q)$ other gates, proving that QMA has completeness doubly exponentially close to 1, i.e., $\mathrm{QMA}=\mathrm{QMA}(1-2^{-2^r},2^{-r})$ for any polynomial $r$.

Initialization of mechanical modes in the quantum ground state is crucial for their use in quantum information and quantum sensing protocols. In quantum processors, impurity of the modes’ initial state affects the infidelity of subsequent quantum algorithms. In quantum sensors, excitations out of the ground state contribute to the noise of the detector, and their prevalence puts a bound on rare events that deposit energy into the mechanical modes. In this Letter, we measure the excited-state populations of GHz-frequency modes in a high-overtone bulk acoustic wave resonator. We find that the population of the first excited state can be as low as $P_p=(1.2\pm 5.5)\times {10}^{-5}$, corresponding to an effective temperature of 25.2 mK, which are upper bounds limited by imperfections in the measurement process. These results compare favorably to the lowest populations measured in superconducting circuits. Finally, we use the measured populations to constrain the amplitude of high-frequency gravitational waves, the kinetic mixing strength of ultralight dark matter, and nonlinear modifications of the Schrödinger equation describing wave function collapse mechanisms. Our Letter establishes high-overtone bulk acoustic wave resonators as a versatile resource for quantum state initialization and studies of fundamental physics.

We prove positivity of a weighted holographic energy for four-dimensional spacetimes with negative cosmological constant whose conformal boundary at infinity is conformally static and admits either spherical sections, or toroidal sections with compatible spin structure.

Gravitational waves (GWs) from compact binaries are excellent probes of gravity in the strong- and dynamical-field regimes. We report a test of general relativity (GR) with the third GW Transient Catalog (GWTC-3) plus a few O4 events using the recently developed neural post-Einsteinian framework, both on individual events and at the population level through hierarchical modeling. We find no significant violation of GR and place a constraint that, for the first time, efficiently covers non-GR theories characterized by not only post-Newtonian deviations but also those beyond under the same theory-agnostic framework.

We propose a new consistency condition for the compatibility of a gravitational effective field theory in AdS with a dual holographic description in terms of a family of large-$N$ CFTs. Using large-$N$ factorization of correlation functions combined with a properly defined notion of single- and multiparticle operators, we argue that the cubic scalar bulk couplings for fields dual to operators with extremal arrangements of the conformal dimensions should vanish. We apply this criterion to the 4d $\mathcal{N}=1$ effective supergravity theory describing the simplest DGKT ${\mathrm{AdS}}_4$ vacua in type IIA string theory and show that it is nontrivially satisfied. In addition, we calculate explicitly all nonvanishing three-point correlation functions of low-lying scalar operators in the putative 3D CFTs dual to these ${\mathrm{AdS}}_4$ string theory backgrounds.

We present a symbol-level bootstrap construction of the planar, two-loop six-gluon scattering amplitude for the $--++++$ helicity configuration in quantum chromodynamics (QCD), focusing on the maximal weight pieces—the “most complicated terms” in the sense of Lipatov et al. Building on recent advances in the understanding of the relevant function space, we incorporate as a crucial new ingredient the complete set of leading singularities, obtained from an analysis of on-shell diagrams. The resulting expressions are manifestly conformally invariant and clarify the structure of previous five-particle results. Combining this with the symbol bootstrap, we show that constraints from physical limits are sufficient to determine the answer. We thus obtain the first concrete characterization of two-loop six-gluon amplitudes at symbol level and at highest weight. Remarkably, we find that the effective function space involves only 137 symbol letters—significantly fewer than the full set of 167 possible letters, suggesting a yet-unexplained underlying structure akin to that seen in maximally supersymmetric Yang-Mills theory. From the novel amplitude results we extract previously unknown symbol-level results describing two-loop triple collinear and double soft limits.

A measurement of parity violation in the hyperfine structure of ${}^{138}\mathrm{Ba}{}^{19}\mathrm{F}$ [E. Altuntaş et al. Phys. Rev. Lett. 120, 142501 (2018)] is reinterpreted with electronic structure calculations in terms of beyond standard model vector boson mediated electron-nucleus interactions. Our results set constraints on previously unexplored, new boson mediated axial vector-vector nucleus-electron interactions. Similar bounds are obtained by analyzing the atomic parity violation experiment with ${}^{133}\mathrm{Cs}$. Moreover, we show that future experiments with cold heavy diatomic molecules like ${}^{137}\mathrm{BaF}$ or ${}^{225}\mathrm{RaF}$ can improve the present sensitivity to axial vector-vector nucleus-electron and nucleon-nucleus interactions by at least 2 orders of magnitude for large boson masses.

We derive a formulation of relativistic spin hydrodynamics with totally antisymmetric spin tensors that satisfy the Frenkel-Mathisson-Pirani condition. In our proposed spin hydrodynamics, the second law of thermodynamics is fulfilled by the spin-induced corrections in the heat flow, the viscous tensor, and the antisymmetric part of the energy-momentum tensor. These corrections are interpreted as the inverse spin Hall effect and the anomalous Hall effect in the nonrelativistic limit. We show that our evolution equation for the spin density is interpreted as an extension of the Bargmann-Michel-Telegdi equation known in relativistic many-body systems, including the Thomas precession term, the spin-rotation term, and new coupling terms between spin and hydrodynamic variables.

Airy wave functions are associated with one of the simplest scenarios in wave mechanics: a quantum bouncing ball. In other words, they are the eigenstates of the time-independent Schrödinger equation with a linear potential. In the domain of optics, laser beams that are spatially shaped as Airy functions (“Airy beams”) have been shown to exhibit a prominent lobe that follows a curved path, rather than propagating in a straight line, and which has self-healing properties in the presence of obstacles. Here, we observe the presence of Airy resonances in two-dimensional photonic crystals composed of a lattice of holes in a silicon slab. Analogously to electrons in a linear potential, these Airy resonances arise due to a linear spatial variation in the lattice constant of the holes. We map the electromagnetic description of the photonic crystal onto a 2D non-Hermitian Schrödinger equation with a linear potential, which we call a “superpotential.” The non-Hermiticity appears in the form of a complex effective mass due to out-of-plane radiation and fundamentally alters the collective optical response of the Airy resonances.

In a tokamak plasma, we measure nonlinear coupling between harmonics comprising a saturated edge oscillation, as predicted by nonlinear magnetohydrodynamic simulations. The coherent structure formed by this coupling suppresses bursty edge-localized modes that cause energy and particle loss. We also measure nonlinear coupling of the edge harmonic oscillation to core-resonant magnetic tearing modes. When tearing modes are present, the edge oscillation harmonics decouple, and edge-localized modes return. We conclude that nonlinear interaction with tearing modes interrupts the formation of the edge harmonic oscillation.