Common belief is that the large band shifts observed in incommensurate misfit compounds, e.g., ${(\text{LaSe})}_{1.14}({\mathrm{NbSe}}_2{)}_2$, are due to interlayer charge transfer. By contrast, our analysis, based on both angle-resolved photoemission spectroscopy (ARPES) measurements and a specialized ab initio framework employing only quantities well defined in incommensurate materials, demonstrates that the large band shifts instead reflect changes in valence band hybridization and interlayer bonding. The strong alignment of our ab initio predictions and ARPES measurements confirms our understanding of the incommensurate electronic structure and charge transfer.

Multiferroic materials, combining ferroelectricity and ferromagnetism, can host complex band phenomena. Using density functional theory and symmetry analysis, we identify the multiferroic EuO as a prototypical system exhibiting a giant, switchable nonreciprocal band structure effect, that is an asymmetry in electronic bands at special points in the Brillouin zone, enabled by spin-orbit coupling. In particular, our results highlight the crucial role of magnetic symmetries—beyond inversion and time-reversal breaking. Ultimately, the predicted effect leads to a colossal bulk photovoltaic response, with injection currents far exceeding those in known oxides, enabling new cross-functionalities.

Quantum Monte Carlo (QMC) methods are essential for the numerical study of large-scale quantum many-body systems, yet their utility has been significantly hampered by the difficulty in computing key quantities such as off-diagonal operators and entanglement. This Letter introduces Bell-QMC, a novel QMC framework leveraging Bell sampling, a two-copy measurement protocol in the transversal Bell basis. We demonstrate that Bell-QMC enables an efficient and unbiased estimation of both challenging classes of observables, offering a significant advantage over previous QMC approaches. Notably, the entanglement across all system partitions can be computed in a single Bell-QMC simulation. We implement this method within the stochastic series expansion, where we design an efficient update scheme for sampling the configurations in the Bell basis. We demonstrate our algorithm in the one-dimensional transverse-field Ising model and the two-dimensional ${\mathbb{Z}}_2$ lattice gauge theory, extracting universal quantum features using only simple diagonal measurements. This Letter establishes Bell-QMC as a powerful framework that significantly expands the accessible quantum properties in QMC simulations, providing a substantial advantage over conventional QMC.

Computing inner products of the form $\mathrm{tr}(AB)$, where $A$ is a $d$-dimensional density matrix [with $\mathrm{tr}(A)=1$, $A\ge 0$] and $B$ is a bounded-norm observable [Hermitian with $\mathrm{tr}(B^2)\le O[\mathrm{poly}(\log d)]$ and $\mathrm{tr}(B)$ known], is fundamental across quantum science and artificial intelligence. Classically, both computing and storing such inner products require $O(d^2)$ resources, which rapidly becomes prohibitive as $d$ grows exponentially. In this Letter, we introduce a quantum approach based on qudit classical shadow tomography, significantly reducing computational complexity from $O(d^2)$ down to $O[\mathrm{poly}(\log d)]$ in typical cases and at least to $O[d\mathrm{poly}(\log d)]$ in the worst case. Specifically, for $n$-qubit systems (with $n$ being the number of qubit and $d=2^n$), our method guarantees efficient estimation of $\mathrm{tr}(\rho O)$ for any known stabilizer state $\rho$ and arbitrary bounded-norm observable $O$, using polynomial computational resources. Crucially, it ensures constant-time classical postprocessing per measurement and supports qubit and qudit platforms. Moreover, classical storage complexity of $A$ reduces from $O(d^2)$ to $O(m\log d)$, where the sample complexity $m$ is typically exponentially smaller than $d^2$. Our results establish a practical and modular quantum subroutine, enabling scalable quantum advantages in tasks involving high-dimensional data analysis and processing.

High-fidelity, meter-scale microwave interconnects between superconducting quantum processor modules are a key technology for extending the system size beyond constraints imposed by device manufacturing equipment, yield, and signal delivery. Although tomographic experiments have been used in previous demonstrations for benchmarking remote state transfer between modules, they do not reliably separate state preparation and measurement (SPAM) error from the error per state transfer. Recent developments based on randomized benchmarking provide a compatible theory for separating these two errors. In this Letter, we present a module-to-module interconnect based on tunable-coupling qubits and benchmark, in a SPAM-error-tolerant manner enabled by a frame-tracking technique, a remote state transfer fidelity of 98.8% across a 60 cm-long coplanar waveguide (CPW). The state transfer is implemented via a superadiabatic transitionless driving method, which suppresses intermediate excitation in the internal modes of the CPW. We further propose and construct a remote cnot gate between modules, composed of local controlled-Z (CZ) gates in each module and remote state transfers, and report a gate fidelity of 93.3% using the randomized benchmarking method. The remote cnot construction and benchmarking we present provide a way to fully characterize the module-to-module link operation and standardize reporting fidelity, analogous to randomized benchmarking protocols for other quantum gates.

As a cornerstone of advanced quantum techniques, parameter estimation is fundamental to precision measurement in physics. Although quantum-enhanced estimation of single parameter has been demonstrated in various two-level systems, measurable parameters remain highly limited. While multilevel quantum systems are capable of measuring diverse parameters, achieving this under general quantum dynamics remains a daunting challenge. Here, we propose a versatile framework for parameter estimation in multilevel systems under general quantum dynamics. Furthermore, we experimentally demonstrate quantum-enhanced measurement of relative values between multiple parameters using a superconducting qutrit sensor. In our experiments, two resonant microwave drives with distinct phases and amplitudes are used to coherently encode parameters into the qutrit. We achieve quantum-enhanced measurement of the ratio of two Rabi frequencies, the phase sum, and the phase difference between the microwave fields, demonstrating precision approaching the Heisenberg limit. Our Letter advances the frontier of quantum metrology and offers new possibilities for high-precision, resource-efficient measurements, with broad applications across science and technology.

Developing a dark matter detector with wide mass tunability is an immensely desirable property, yet, it is challenging due to maintaining strong sensitivity. Resonant cavities for dark matter detection have traditionally employed mechanical tuning, moving parts around to change electromagnetic boundary conditions. However, these cavities have proven challenging to operate in sub-Kelvin cryogenic environments due to differential thermal contraction, low heat capacities, and low thermal conductivities. Instead, we develop an electronically tunable cavity architecture by coupling a superconducting 3D microwave cavity with a dc flux tunable superconducting quantum interference device. With a flux delivery system engineered to maintain high coherence in the cavity, we perform a hidden-photon dark matter search below the quantum-limited threshold. A microwave photon counting technique is employed through repeated quantum nondemolition measurements using a transmon qubit. With this device, we perform a hidden-photon search and constrain the kinetic mixing angle to $ϵ<8.2\times {10}^{-15}$ in a tunable band from 5.672 to 5.694 GHz. By coupling multimode tunable cavities to the transmon, wider hidden-photon searching ranges are possible.

We discover a surprising relationship between exceptional effective field theories (EFTs) in de Sitter space and a notion of generalized energy conservation (GEC) of an $S$ matrix defined in an extended Poincaré patch of four-dimensional de Sitter. By demanding that such an $S$ matrix has support only when the total energies of in and out states are equal, we constrain the coupling constants in theories of self-interacting scalars living in the exceptional series of de Sitter representations. We rediscover the theories of Dirac-Born-Infeld (DBI) and special Galileon, and when increasing the conformal dimension, we find evidence for new exceptional theories where the four-point scalar self-interactions are uniquely fixed in terms of a single coupling constant. We conjecture that for each integer conformal dimension $\mathrm{\Delta }\ge 4$, there is at least one exceptional EFT that can be entirely fixed by GEC.

In this Letter, we observe a novel resonant mechanism, namely, the modulation-induced Feshbach resonance. By applying a far-detuned laser to the cesium $D_2$ transition with intensity modulation, we periodically modulate the energy levels of atomic collisional states. This periodic modulation connects the free-scattering states to shallow molecular states. At specific frequencies, significant atom loss is observed, which corresponds to the resonant coupling between these two types of states. This precisely corresponds to a form of Feshbach resonance, yet in the frequency domain rather than the magnetic-field domain. Using this method, we can directly scan the energy spectrum of molecular bound states without synthesizing any molecules. In addition to these bound states, we can also probe the molecular states embedded in the continuum, which are typically very difficult to detect by the conventional methods based on molecular synthesis. Moreover, by using a far-detuned laser instead of a magnetic field, it enables spatially dependent control over atomic interactions, coupling multiple levels simultaneously and inducing new Feshbach resonances for those atoms that do not have conventional magnetic resonances. Therefore, we believe that this new resonant mechanism offers new opportunities for controlling atomic and molecular interactions in quantum simulations.

Scalable atom-based quantum platforms for simulation, computing, and metrology require fast high-fidelity, low-loss imaging of individual atoms. Standard fluorescence detection methods rely on continuous cooling, limiting the detection range to one atom and imposing long imaging times that constrain the experimental cycle and midcircuit conditional operations. Here, we demonstrate fast and low-loss single-atom imaging in optical tweezers without active cooling, enabled by the favorable properties of ytterbium. Collecting fluorescence over microsecond timescales, we reach single-atom discrimination fidelities above 99.9% and single-shot survival probabilities above 99.5%. Through interleaved recooling pulses, as short as a few hundred microseconds for atoms in magic traps, we perform tens of consecutive detections with constant atom-retention probability per image—an essential step toward fast atom reuse in tweezer-based processors and clocks. Our scheme does not induce parity projection in multiply occupied traps, enabling number-resolved single-shot detection of several atoms per site. This allows us to study the near-deterministic preparation of single atoms in tweezers driven by blue-detuned light-assisted collisions. Moreover, the near-diffraction-limited spatial resolution of our low-loss imaging enables number-resolved microscopy in dense arrays, opening the way to direct site-occupancy readout in optical lattices for density fluctuation and correlation measurements in quantum simulators.

Quantum fluctuation plays a key role in parametric down-conversion in the Langevin regime. In this Letter, we report the experimental realization of optical parametric down-conversion in the Langevin regime on a chip. By precisely controlling the loss inherently tied to fluctuation, we observe the asymmetric Hong-Ou-Mandel dip—a hallmark of quantum fluctuation in the fluctuation-driven parametric down-conversion (PDC)—and the fluctuation-induced compression of single photons by nearly one order of magnitude. These findings pave the way for the manipulation of quantum fluctuation, quantum states, and system-reservoir interaction.

Any amplifier requires coupling to its internal degrees of freedom for energy gain. This coupling introduces extra quantum noise to the output. On the other hand, if the internal degree of the amplifier can be accessed and manipulated, we can manage and even reduce the quantum noise of the amplifier’s output. In this Letter, we present an experiment to reduce the quantum noise of a Raman amplifier by preparing the atomic medium in a correlated state with the Stokes light field. We report an observation of quantum noise reduction of more than 3.5 dB in the atomic Raman amplification process. From another perspective, the Raman amplifier at high gain in turn serves as a measurement tool for the quantum correlation between the atom and light. Furthermore, such a scheme, when viewed as a whole, also forms a quantum-entangled atom-light hybrid interferometer that can lead to quantum-enhanced sensors.

We introduce a driven-dissipative Bose-Hubbard chain describing coupled lossy photonic modes, in which time-reversal symmetry is broken by a coherent drive with a uniform phase gradient. We investigate this model by means of a Gaussian variational ansatz and numerically prove that the steady-state solution is stabilized by an inhomogeneous profile of the driving amplitude, which damps out boundary effects. Our calculations unveil a nonequilibrium phase diagram showing low- and high-density phases for photons separated by a phase coexistence region in which the system exhibits the phenomenon of topological amplification and is characterized by a finite non-Hermitian winding number. Our Letter shows the emergence of non-Hermitian topological phases in an interacting model that can be naturally implemented with superconducting circuits.

Nonlinear magnonics has emerged as a prominent area of research, with a particular focus on on-chip Kerr nonlinearity. This effect is valuable both for its potential to manipulate magnon states and for its role in addressing the scalability challenges that magnonic devices face. In this Letter, we experimentally investigate a Kerr nonlinear magnomechanical system in a yttrium iron garnet thin-film device that supports magnon resonance coupled with multiple high-overtone bulk acoustic wave resonance modes. Notably, the enhanced Kerr nonlinearity resulting from the small mode volume enables clear bistability in the magnon mode at low excitation power. Additionally, we demonstrate the excitation of a magnon-phonon hybrid frequency comb using a single microwave tone and illustrate Kerr-induced synchronization of the frequency comb through externally injected reference microwaves, achieving over 130 comb teeth. Our findings provide a robust platform for the exploration of nonlinear magnonics and represent an advance in the development of on-chip frequency combs.

We observed highly efficient manipulation of the 530 MeV positron beam at Mainz Microtron via bent crystals. The low beam divergence revealed a fine structure in the angular distribution of channeled particles. A compact analytical model, supported by Monte Carlo methods including multiple scattering, accounts for the measurements. We established a criterion for designing a crystal with reduced angular spread of channeled particles for beam manipulation at any energy. This finding is particularly useful in view of applications of channeling to the highest energies.

Ferroelastic materials (materials with switchable spontaneous strain) can be centrosymmetric, but their domain walls are always polar, as their internal strain gradients cause flexoelectricity. This flexoelectric polarization of the walls is not switchable by voltage, because reversing their polarity would require switching the spontaneous strain of the adjacent domains, annihilating the domain wall in the process. However, polarization can also arise from biquadratic coupling between polar and nonpolar order parameters (e.g., octahedral tilts in perovskites). Being quadratic, such coupling is independent of the sign of the polarization and thus allows switching between $+P$ and $-P$. In this Letter, we seek to answer the question of whether the polarization of domain walls in an archetypal ferroelastic perovskite (${\mathrm{CaTiO}}_3$) is switchable, as per biquadratic coupling, or nonswitchable due to unipolar flexoelectricity. Using molecular dynamics calculations, we find that high electric fields gradually suppress tilts, broaden the ferroelastic domain walls, and eventually enable the onset of switchable polarization. Such switching can happen also in the bulk of the crystal, but the critical field is markedly lower in the domain walls, which are thus independently switchable. We also find that the polarization switching is antiferroelectric-like, with a double hysteresis loop. The analysis suggests that double-hysteresis switching can also occur in other ferroelastic perovskites.