Radio-frequency (rf) reflectometry provides a useful method for sensitive and fast detection of dynamic processes in quantum systems. We use this method to detect excitation of the quantized (Rydberg) states of the vertical motion in a system of surface-bound electrons on liquid helium. The Rydberg transition is detected as a change in the rf reflection from a resonant circuit coupled to microwave-excited electrons. It is found that the observed reflection response drastically differs from an expected state-dependent dispersive shift of the resonant frequency. To elucidate the origin of the observed response, the result is compared with an independent reflection measurement on the same electron system modulated by an electrostatic potential and with a numerical simulation using the Green’s function method. The findings suggest that the observed response to the Rydberg resonance must be attributed to the in-plane motion of the photoexcited many-electron system rather than to the Rydberg transitions of independent electrons. Our work demonstrates that rf reflectometry could be a useful tool to study dynamic processes, such as quantum ac transport and collective excitations, in this system.

High-fidelity two-qubit gates are essential for scalable quantum computing. We present a scheme based on superconducting transmon qubits and a control pulse delivery protocol that enables arbitrary controlled-phase gates modulated solely by an independent arbitrary waveform generator pulse. We combined a tunable coupler design with bipolar flux-pulsing to demonstrate a controlled-phase gate, achieving a peak fidelity of 99.5%. Our gates inherit the advantages of both approaches: minimal residual $ZZ$ coupling, built-in echo-like low-frequency noise protection, and time-scale control pulse reproducibility, while remaining easy to calibrate. We optimize the system’s energy levels to mitigate leakage to the coupler and suppress residual interactions. Numerical simulations of the scheme as three qutrits indicate that an error below $1\times {10}^{-3}$ is achievable. We confirm the scalability potential of the proposed scheme on high-fidelity four-qubit and eight-qubit quantum processors.

We explore the quantum-metrological potential of subwavelength-spaced emitter arrays coupled to a one-dimensional nanophotonic waveguide. In this system, strong dipole-dipole interactions profoundly modify the collective optical response, leading to the emergence of ultranarrow subradiant resonances. Through an eigenmode analysis of the effective non-Hermitian Hamiltonian, we derive the decay rate of the most-subradiant state, which, within the present model and geometry, exhibits an $N^{-3}$ scaling with even-odd oscillatory behavior in the deep-subwavelength regime. This scaling is directly observable in the single-photon scattering spectrum, enabling the detection of minute changes in atomic separation with a figure of merit that scales as $N^3$. The quantum Fisher information scales as $N^6$ and can be closely approached by measuring spectral shifts near the steepest slope of the most-subradiant resonance. These enhancements remain robust under realistic positional disorder, confirming that dipole-dipole-engineered subradiance provides a viable resource for quantum metrology. Our work bridges collective waveguide-QED physics and high-precision sensing, opening a route toward scalable quantum sensors on integrated nanophotonic platforms.

Neutral atom arrays provide a versatile platform to implement coherent quantum annealing as an approach to solving hard combinatorial optimization problems. Here we present and experimentally demonstrate an efficient encoding scheme based on chains of Rydberg-blockaded atoms, which we call quantum wires, to natively embed maximum weighted independent set (MWIS) and quadratic unconstrained binary optimization (QUBO) problems on a neutral atom architecture. For graphs with quasi-unit-disk connectivity, in which only a few long-range edges are required, our approach requires a significantly lower overhead in the number of ancilla qubits than previous proposals, facilitating the implementation on currently available hardware. To demonstrate the approach, we perform annealing of weighted graphs on a programmable atom array using local light shifts to encode problem-specific weights across graphs of varying sizes. This approach successfully identifies the solutions to the original MWIS and QUBO graph instances. Our work expands the operational toolkit of near-term neutral atom arrays, enhancing their potential for scalable quantum optimization.

Heralded multiphoton entanglement generation is a central bottleneck for photonic quantum computing, where resource costs typically skyrocket with target size. We explore efficient methods for generating photon states with tunable entanglement, providing a flexible tool for quantum state engineering. We introduce a theoretical framework that has been numerically validated, demonstrating the capacity to generate GHZ-like states incrementally from nonlogical intermediate states. We demonstrate that in certain scenarios—such as reducing the resource cost for building large maximally entangled GHZ states—these variable-entanglement states can outperform their fixed-entanglement counterparts. By adjusting intermediate states and optimizing interferometer schemes, we improve photon number cost efficiency of GHZ-like states generation. Our findings indicate that while not a universal solution, nonmaximally entangled states offer practical advantages for specific photonic quantum information tasks.

Fault-tolerant modular quantum computing requires stabilizer measurements across the modules in a quantum network. For this, entangled states of high quality and rate must be distributed. Currently, two main types of entanglement distribution protocols exist, namely emission-based and scattering-based, each with its own advantages and drawbacks. On the one hand, scattering-based protocols with cavities or waveguides are fast but demand stringent hardware such as high-efficiency integrated circulators or strong waveguide coupling. On the other hand, emission-based platforms are experimentally feasible but have so far relied on Bell-pair fusion with extensive use of slow two-qubit memory gates, limiting thresholds to approximately 0.16%. Here, we consider a fully distributed surface code using emission-based entanglement schemes that generate GHZ states in a single shot, i.e., without the need for Bell-pair fusions. We show that our optical setup produces Bell pairs, $W$ states, and GHZ states, enabling both memory-based and optical protocols for distilling high-fidelity GHZ states with significantly improved success rates. Furthermore, we introduce protocols that completely eliminate the need for memory-based two-qubit gates, achieving thresholds of approximately 0.19% with modest hardware enhancements, increasing to above approximately 0.24% with photon-number-resolving detectors. These results show the feasibility of emission-based architectures for scalable fault-tolerant operation.

Quantum metrology promises measurement precision beyond the classical limit by using suitably tailored quantum states and detection strategies. However, scaling up this advantage is experimentally challenging, due to the difficulty of generating high-quality large-scale probes. Here, we build a photonic setup that achieves enhanced precision scaling by manipulating the probe’s dynamics through operations performed in a coherently controlled order. Our setup applies an unknown rotation and a known orbital angular momentum increase in a coherently controlled order, in a way that reproduces a hybrid quantum switch involving gates generated by both discrete and continuous variables. The unknown rotation angle $\theta$ is measured with precision scaling as $1/4ml$ when a photon undergoes a rotation of $2m\theta$ and an angular momentum shift of $2l\hslash$. With a practical enhancement factor as high as 2317, we achieve a normalized precision of approximately equal to ${10}^{-4}$ rad per photon. The precision enhancement consumes only a linearly increasing number of applications of the gates while achieving a nonlinear scaling of the precision. We further indicate that this nonlinear enhancement roots in an in-depth exploration of the Heisenberg uncertainty principle (HUP). The very quantum noncommutativity that imposes fundamental limitations on measurement precision under the HUP is transformed into a valuable quantum resource that enables the observed nonlinear enhancement.

In autonomous quantum error correction, the lifetime of a logical bosonic qubit can be extended beyond its physical constituents without feedback measurements. Leveraging autonomous error correction, we propose a gate-based microwave quantum repeater (GBMQR) with encoded bosonic grid states. Each repeater station comprises a transmon and two bosonic resonators: one resonator serves as a stationary quantum memory utilizing autonomous error correction and the other serves as an information bus for entanglement generation. Entanglement is generated sequentially through the successful absorption of a microwave photon wave packet. This method enables deterministic entanglement generation, in contrast to a probabilistic mixing of two heralding signals on a balanced beam splitter. Furthermore, our GBMQR employs an all-bosonic entanglement swapping Bell-state measurement. This is implemented via a bosonic controlled-$\mathrm{Z}$ gate and two separate $X$-basis projective homodyne measurements on the stationary stored code words. Our approach circumvents mode-mismatch losses associated with routing and interfering heralding modes on a beam splitter and confines losses to those arising from stationary storage. We evaluate the performance of the proposed quantum repeater by calculating its secret key rate under realistic laboratory environments. Moreover, we explicitly demonstrate that at the stationary damping rate of ${\kappa }_{\text{damp}}^{-1}=40\mathrm{ms}$, GBMQR can achieve entanglement generation and swapping success probabilities of approximately 0.75 and 0.58, respectively, surpassing the hallmark success probability of $1/2$ set by ideal linear beam-splitter-based Bell-state measurements. The proposed device can be implemented using currently available superconducting microwave technology and is suited for secure chip-to-chip communication and distributed quantum computing.

Reconfigurable, anisotropic Huygens metasurfaces are limited to an angle beam steering between $30°$ and $40°$. This limitation can be overcome using bianotropy for wide-angle refraction. However, this type of reconfigurability requires a mechanism that allows for the broad tuning of the impedance of the unit cells while minimizing losses to increase the efficiency of refraction. This paper shows a methodology for the design and validation of a reconfigurable unit cell for anisotropic and bianisotropic Huygens metasurfaces. It proposes dual-resonant geometries to achieve reactance tunability of more than $150\mathrm{\Omega }$ and characterizes the reactances of various layers through simulations and waveguide measurements. The work includes interlayer coupling analysis and characterization of supercells that validate the reconfigurability of the unit cell for wide-angle refraction with an efficiency of 86% and phase-gradient applications for beam-tilting angles of $0°$, $15°$, and $30°$.

The double-free-layer magnetic tunnel junction has emerged as a promising structure for high-density memory applications due to its enhanced thermal stability. However, optimizing its multiple design parameters through experimental trial and error is prohibitively time-consuming, while existing numerical tools remain inadequate for solving the coupled transport-magnetization dynamics problem. To achieve accurate and efficient optimization, an integrated coupled model combining the transport process and magnetodynamics is proposed, achieving a validated speed-up factor of 117.1 and enabling device-level parameter optimization, such as ferromagnetic coupling strength and thermal stability. The transport process is modeled based on nonequilibrium Green’s function method, accelerated by two numerical techniques: (a) a mixed sampling strategy for energy integrals involving sharp peak-shaped function and (b) a complex integral approach to bypass singularities in energy-resolved functions. For magnetization dynamics, the variable-step 1(2)-order Runge-Kutta method is employed to compute the time evolution of the free-layer magnetizations. With the coupled model, the design space is systematically explored using both single-objective optimization and Bayesian optimization. A minimum switching time of 0.846 ns is achieved at the optimal parameter setting.

A limiting factor to the exploitation of continuous variables in quantum computing, in particular in the field of quantum machine learning, has been the hindrances of computing the derivatives of a model. The constraint occurs when applying the parameter-shift rule to a photonic circuit, and the number of non-Gaussian gates exceeds a logarithmic trend with respect to the length of the circuit. This condition occurs when dealing with most nonlinear functions. Indeed, it hampers subroutines, such as backpropagation, which are paramount for machine learning and, most significantly, the computation of the derivatives of the model itself. To overcome this hurdle, we propose a method to compute derivatives of functions, implemented by continuous variable circuits, directly through photonic quantum circuits. Unlike the parameter-shift rule, this method does not fail when the number of non-Gaussian gates scales more than logarithmically against the depth of the circuit. We exploit the fact that computing the derivative of a wave function is equivalent to applying the momentum operator, which in the position basis acts as its derivative. The action of this operator is physically embodied by photon-added coherent states. We prove that, up to the second order of derivation, the number of operations does not scale with the depth of the circuit, but only with the order of derivation. We showcase numerical examples of derivatives of elementary functions parametrized on simulated photonic quantum circuits. Thanks to this method, we unleash an embodiment of quantum neural networks on photonic quantum computing platforms.

Efficient sound absorption at low frequencies remains a major challenge, as most architectured materials rely on resonant mechanisms that limit their bandwidth. Here, we demonstrate a nonresonant approach based on resistive materials coupled to soft acoustic boundaries and show its effectiveness in different setups. In a reflection configuration, a critically coupled wire-mesh layer combined with a foam yields a high and broadband absorption over the investigated frequency range 10–6400 Hz. When considering a transmission configuration, placing a side hole near the wire-mesh layer breaks the mirror symmetry and results in a low-frequency and broadband one-sided absorption. This work opens new opportunities for acoustic materials by leveraging the potential of resistive materials for low-frequency and broadband wave manipulation.

Neutrino detection for reactor monitoring using scintillator (NEREUS) is a proposed mobile freight container-style neutrino detector for reactor monitoring. The detection of unshieldable reactor antineutrinos is a unique probe for reactor monitoring due to its noncontact, continuous, and near-real-time capability. It is an attractive safeguard method for nonproliferation applications and complements current monitoring methods, especially for advanced reactors with high-temperature and high-radiation environments, where traditional methods are difficult to apply. In this work, the design of the NEREUS detector is studied and optimized based on extensive Monte Carlo simulations. Its capabilities for reactor monitoring are assessed, alongside its physics potential for applications including sterile neutrino searches.

We demonstrate a minimally destructive in situ technique for measuring and stabilizing slowly drifting magnetic fields in ultracold-atom experiments. While conventional magnetic-field sensors such as Hall, giant magnetoresistive, or fluxgate-based devices are broadly used, their accuracy, precision, and dynamic range can be limited. In addition, these sensors are typically positioned at least several centimeters away from the in-vacuum atomic system, as their operation creates perturbing magnetic fields, and their placement is limited by geometric constraints imposed by the vacuum system. We overcome these issues by using the atomic system itself as a built-in magnetometer. To that end, we employ a pair of weak measurements to determine the Zeeman splitting—and thereby the magnetic field—of a magnetically sensitive atomic transition. We provide closed-form expressions quantifying the trade-offs among measurement noise, dynamic range, and atom loss. This procedure is demonstrated with ultracold ${}^{87}\mathrm{Rb}$, weakly measured using partial-transfer absorption imaging. We then incorporate a Kalman filter to stabilize the magnetic field; this eliminated long-term drift in the ambient field (as high as approximately 70 nT/hr) in exchange for a modest increase in shot-to-shot variability from 1.8(2) to 2.0(2) nT.

The conventional impedance matching based on Fabry-Perot resonance has been widely used to overcome impedance mismatch. However, the phase of transmitted wave in impedance matching system is fixed to certain value. This constraint in phase limits the applications of wave manipulation, which requires spatial phase distribution. In this paper, we find out that Willis metamaterials composed of geometrically asymmetric unit cell can achieve impedance matching with tunable phase over a geometry-dependent range. By exploiting the complex-valued impedance arising from Willis coupling, we fundamentally alter the classical Fabry-Perot resonance conditions to achieve full transmission. This mechanism enables independent control of the phase of transmitted waves. We validate these theoretical predictions through numerical simulations and experimental demonstrations with continuum aluminum structures. Our findings establish a new platform using Willis metamaterials for versatile wave manipulation devices, overcoming long-standing design constraints.