Quantum turbulence spans length scales from the system size $L$ to the healing length $\xi$, making direct numerical simulations (DNS) of the Gross-Pitaevskii (GP) equation computationally expensive when $L\gg \xi$. We present a matrix-product state (MPS) solver for the GP equation that efficiently compresses the wavefunction by truncating weak interlength-scale correlations. This approach reduces memory usage by factors ranging from $10\times$ to over $10000\times$ compared to DNS. We benchmark our approach on nonlinear excitations, namely dark solitons (1D) and quantized vortices (2D, 3D), capturing key dynamics such as Kelvin-wave propagation and vortex-ring emission in the case of vortex-line reconnection. For turbulent states composed of multiple nonlinear excitations, we find that the memory compression of the MPS representation is directly proportional to the soliton or vortex densities. We also accurately reproduce established results from two-point correlation functions and energy spectra, where we recover the incompressible kinetic energy spectrum with little memory overhead. These results demonstrate the representative capabilities of the MPS ansatz for quantum turbulence and pave the way for studying this nonequilibrium state using previously prohibited system sizes. Moreover, the MPS ansatz can be adapted to existing quantum algorithms, providing a framework to implementing our time-evolution method on near-future quantum processing units.

Filtering is commonly used in quantum optics to reject noise photons, and also to enable interference between independent photons. However, filtering the joint spectrum of photon pairs can reduce the inherent coincidence probability or loss-independent heralding efficiency. Here we investigate filtering for multiphoton applications based on entanglement and interference (e.g., quantum teleportation). We multiplex C-band entangled photons and C-band classical communications into the same long-distance fibers, which enables scalable low-loss quantum networking but requires filtering of spontaneous Raman scattering noise from classical light. Using tunable-bandwidth filters, low-jitter detectors, and polarization filters, we distribute wavelength-degenerate time-bin entangled photons in the C band (1536.5 nm) over 25 km/25 km standard fibers (50 km) each carrying 10 Gbit/s C-band classical data signals. Narrow filtering enables milliwatt-level C-band power, which exceeds the power achieved by comparable studies by roughly an order of magnitude and could feasibly support terabit per second classical rates. We evaluate how performance depends on pump and filter bandwidths, multipair emission, filter shapes, loss, phase matching, and how quantum information is measured. We find a trade-off between reducing noise impact and increasing single-mode purity, and discuss mitigation methods toward optimal multiphoton applications. Importantly, these results apply to noise in free space and in quantum devices (sources, frequency converters, switches, detectors, etc.) and provide insight into filter-induced degradation of single-photon purity and rates even in noise-free environments.

Modern mechanical sensors increasingly measure motion with precision sufficient to resolve the fundamental thermal noise floor over a broad band. Compared with traditional sensors—achieving this limit only near resonance—this capability provides massive gains in acquisition rates along with access to otherwise obscured transient signals. However, stronger measurements are naturally accompanied by increased back-action. Here we resolve the broadband thermal noise spectrum in the presence of measurement back-action, revealing back-action-induced correlations in noise from many mechanical modes, even those well separated in frequency. The observed spectra can deviate significantly from predictions using standard single-mode and (uncorrelated) multimode models over the broad band, notably even at the mechanical resonance peaks. This highlights the importance of these correlations in any system exhibiting strong back-action, even when the resonances are spectrally well isolated, and/or when the readout noise is high and the resonance peaks appear consistent with simpler models. These correlations advantageously allow the thermal noise spectrum to reach a minimum—equivalent to that of a single mode—in a band far from the resonance peak, where the mechanical susceptibility is comparatively stable against frequency noise.

Synthetic frequency dimensions offer a powerful approach in the simulation of lattice models and control photon dynamics. However, extending this concept to the quantum regime, particularly at the single-photon level, has remained challenging in photonic platforms. Here, we demonstrate quantum-state initialization and detection of single-photon evolutions within a synthetic frequency lattice by integrating a superconducting qubit with a 16 m aluminum coaxial cable. A tunable superconducting quantum interference device–based modulator is employed to synthesize lattice couplings and artificial gauge fields. We observe single-photon quantum random walks and Bloch oscillations, as well as nonadiabatic unidirectional frequency conversion under rapid temporal modulation of the lattice Hamiltonian, and present band-structure measurements. The lattice connectivity can be readily reconfigured to construct higher-dimensional lattices using a multiplicity of drive tones. Our results establish superconducting quantum circuits as a versatile platform for programmable Hamiltonians and extensible synthetic lattices with flexible single-photon control.

Frequency references based on solid-state spins promise simplicity, compactness, robustness, multifunctionality, ease of integration, and high densities of emitters. Nitrogen-vacancy (NV) centers in diamond are a natural candidate, but the electronic zero-field splitting ($D\approx 2.87\mathrm{GHz}$) exhibits a large fractional temperature dependence (around $25\mathrm{ppb}/\mathrm{mK}$), which has precluded its use as a stable clock transition. Here we show that this limitation can be overcome by forming a composite frequency reference that combines measurements of the electronic splitting $D$ with the nuclear quadrupole splitting ($Q\approx 4.94\mathrm{MHz}$) of the ${}^{14}\mathrm{N}$ nuclear spin intrinsic to the NV center. We further benchmark this composite approach against alternative strategies for mitigating temperature sensitivity, including cryogenic operation, temperature compensation, and active stabilization. By implementing a specially designed pulse sequence with an eight-phase control scheme that suppresses pulse imperfections, we interleave measurements of $D$ and $Q$ in a high-density NV ensemble and demonstrate a temperature-compensated composite frequency reference. The stability of this composite diamond clock is characterized over a 10-day period at room temperature through a comparison to a $\mathrm{Rb}$ vapor-cell clock, yielding a fractional instability below $5\times {10}^{-9}$ for an averaging time of $\tau =200\mathrm{s}$ and below $1\times {10}^{-8}$ at $\tau =2\times {10}^5\mathrm{s}$, corresponding to measured improvements by a factor of approximately $4$ and approximately $200$, respectively, over a clock based purely on the single frequency $D$ for the same periods. By characterizing the residual sensitivity to magnetic fields, optical power, and radio-frequency drive amplitudes, we find that temperature is no longer the dominant source of instability. These results establish complementary electron- and nuclear-spin transitions in diamond as a viable route to thermally robust frequency metrology, providing a pathway toward compact, multifunctional solid-state clocks and quantum sensors.

Bifurcation, which alters the number and stability of equilibria in multistable systems, is the primary mechanism governing the formation of elastic sequential snap-through instabilities. However, to date, there is no general understanding of the multistable energy landscape organized by bifurcations underlying snap-through. Here, we conduct a theoretical, numerical, and experimental analysis of serial bistable planar curved beams widely proposed in the recent literature, developing numerical algorithms and experimental schemes to explore the bifurcation structures within the energy landscape. Such systems provide sufficient physical transparency, owing to their low dimension and clear interaction, making them ideal for the analysis of bifurcation structures. Two types of elastic sequential snap-through instability are discovered: competition-induced phase transitions, triggered by limit forces (switching fields) between units, and unit phase transitions, triggered by the equivalent stiffness of system variables within each unit. In our method, we propose a general tunable snap-through path design strategy for use in multistable systems, which can be extended to broader systems with interacting units. Importantly, by tuning stiffness properties and the limit force perturbations, custom-designed saddle-node bifurcation pairs and traverse-stable paths can be achieved, providing universal design rules for elastic sequential transitions.

Fast, high-fidelity, single-shot readout of superconducting qubits in quantum processors demands quantum-limited amplifiers to preserve the optimal signal-to-noise ratio. Typically, quantum-limited amplification is achieved with parametric down-conversion of a strong pump tone, which imposes significant hardware overhead and severely limits scalability. Here, we demonstrate the first dc-powered broadband amplifier operating within 0.2 photons of the quantum limit. Our impedance-engineered inelastic Cooper-pair tunneling amplifier (ICTA)—a voltage-biased superconducting quantum interference device in which Cooper pairs tunnel inelastically by emitting signal-idler photon pairs—operates in reflection, delivering 13 dB of average gain across a 3.5-GHz bandwidth in a single stage. Semiclassical simulations accurately predict the gain and saturation power, enabling further design improvements. By eliminating the pump-tone infrastructure, the broadband ICTA promises to dramatically reduce the hardware complexity of quantum-limited amplification in superconducting quantum processors.

Quantum communication between remote chips is essential for realizing large-scale superconducting quantum computers. For such communication, itinerant microwave photons propagating through transmission lines offer a promising approach. However, demonstrations to date have relied on frequency-tunable circuit elements to compensate for fabrication-related parameter variations between sender and receiver devices, introducing control complexity and limiting scalability. In this work, we demonstrate deterministic quantum state transfer and remote entanglement generation between fixed-frequency superconducting qubits on separate chips. To compensate for the sender-receiver mismatch, we employ a frequency-tunable photon-generation technique, which enables us to adjust the photon frequency without modifying circuit parameters. To enhance the frequency tunability, we implement broadband transfer resonators composed of two coupled coplanar-waveguide resonators, achieving a bandwidth of more than 100 MHz. This broadband design enables successful quantum communication across a 30-MHz range of photon frequencies between the remote qubits. Quantum process tomography reveals state transfer fidelities of around 79% and Bell-state fidelities of around 73% across the full frequency range. Our approach avoids the complexity of the control lines and noise channels, providing a flexible pathway toward scalable quantum networks.

Exploiting quantum interference of charge carriers, epitaxial graphene grown on silicon carbide emerges as a game-changing platform for ultrasensitive bolometric sensing, featuring an intrinsic resistive thermometer response unmatched by any other graphene variant. By achieving low and uniform carrier densities, we have accessed a regime of strong charge localization that dramatically reduces thermal conductance, significantly enhancing bolometer performance. Here we present scalable graphene-based bolometers engineered for detecting gigahertz-range photons, a frequency domain essential for superconducting quantum processors. Our devices deliver a state-of-the-art noise equivalent power of 40 $\mathrm{zW}/\sqrt{\mathrm{Hz}}$ at $T=40$ mK, enabled by the steep temperature dependence of thermal conductance, $G_{\mathrm{th}}\sim T^4$ for $T<100\mathrm{mK}$. These results establish epitaxial graphene bolometers as versatile and low-backaction detectors, unlocking new possibilities for next-generation quantum processors and pioneering investigations into the thermodynamics and thermalization pathways of strongly entangled quantum systems.

Fusion power systems can in principle be used to make significant amounts of fissile material. To do so, an operator would have to introduce fertile material, such as uranium-238, in a suitable region of the reactor where it is exposed to an intense neutron flux. The possibility of using a fusion reactor for this purpose has raised the question of how these facilities can be monitored to ensure their peaceful use. This study examines whether covert production of fissile material in a declared fusion plant could be detected with an onsite antineutrino detector. We find that even a relatively small detector should be able to confirm production rates of a few kilograms of plutonium over 30 days, despite the cosmogenic background and the antineutrino emissions associated with neutron activation of reactor components.

Quantum gravity-gradient sensing technology exhibits unique advantages and significant application potential in geophysical research and practical scenarios. We present a free-fall vertical gravity gradiometer based on cold-atom interferometry. Phase-difference extraction employs an elliptical-fitting method that is simple to implement and responds rapidly to gravitational variations. A detailed analysis is conducted on the noise associated with this method and corresponding optimizations are carried out. The device achieves a performance with a sensitivity of 52.9 $\mathrm{E}/\sqrt{\mathrm{Hz}}$ and a stability better than 0.5 E over $7\times {10}^4$ s ($1\mathrm{E}=1\times {10}^{-9}{\mathrm{s}}^{-2}$). Based on this performance, we initially completed the application simulation of resource exploration scenarios in the laboratory and evaluated its accuracy and sensitivity in the exploration field. This research work provides support for future geophysical research and applications.

Magnonics is a promising platform for integrated radio-frequency (rf) devices, leveraging its inherent nonreciprocity and reconfigurability. However, the efficiency of spin-wave transducers driven by rf currents remains a major challenge. In this study, we systematically investigate a spin-wave transducer composed of micrometer-sized rf antennas on yttrium iron garnet films of different thickness—an ideal testbed for integrated magnonic devices. Using propagating spin-wave spectroscopy, we analyze spin-wave transmission, identifying key loss mechanisms and improving device efficiency by reducing ohmic resistance. The resulting improvements enable the reduction of insertion loss to below 10 dB in microscaled spin-wave transducers. At the same time large nonreciprocity can be exploited to achieve significant isolation on the microscale.

The sharp optical resonances of $\mathrm{N}\text{−}{V}^{-}$ centers in diamond at cryogenic temperatures offer powerful new capabilities for material characterization, but extracting the most detailed information typically requires careful calibration of individual sensors, limiting scalability. In this work, we use resonant photoluminescence excitation imaging to optically resolve and monitor hundreds of individual nitrogen vacancies (N-Vs) across large fields of view, enabling a statistical analysis of their spatial distribution with subdiffraction resolution. This multiplexed, nondestructive approach allows quantum sensors to characterize the material platform they inhabit. Focusing on CVD-grown diamond, we uncover significant deviations from random distributions, including an unexpectedly high occurrence of closely spaced clusters comprising two or more N-Vs. These findings suggest non-Poissonian formation dynamics and point to spatially correlated defect generation mechanisms. Beyond offering insight into diamond growth and N-V center formation, our approach enables the scalable identification of naturally occurring N-V clusters, configurations that are promising for entanglement-assisted quantum information protocols and correlated sensing, and establishes a path toward structural and electronic defect analysis in various material hosts at the single-emitter level.

Magnetic resonance force microscopy (MRFM) enables three-dimensional imaging of nuclear spin densities in nanoscale objects. On the basis of numerical simulations, we evaluate the performance of strained $\mathrm{SiN}$ resonators as force sensors and show that their out-of-plane oscillation direction improves the quality of the reconstructed sample. We further introduce a multislice, compressed-sensing scan protocol that maximizes the information obtained for a given measurement time. Our simulations predict that these scanning protocols and optimized algorithms can shorten the total acquisition time by up to 2 orders of magnitude while maintaining the reconstruction fidelity. Our results demonstrate that combining advanced scanning protocols with state-of-the-art resonators is a promising path toward high-resolution MRFM for volumetric imaging of biological nanostructures.

Spaceborne gravitational wave observatories, exemplified by the Laser Interferometer Space Antenna (LISA) mission, are designed to remove laser noise and clock noise from interferometric phase measurements in postprocessing. The planned observatories will utilize electro-optic modulators (EOMs) to encode the onboard clock timing onto the beam phase. Recent research has demonstrated the advantage of introducing an optical frequency comb (OFC) in the metrology system with the modified framework of time-delay interferometry (TDI): the removal of the EOM and the simultaneous suppression of the stochastic jitter of the laser and the clock in the observation band. In this paper, we explore an alternative approach with the OFC-based metrology system. We report that, after proper treatment, it is possible to use the measured carrier-carrier heterodyne frequencies to monitor the time derivative of the pseudoranges, which represent the physical light travel time and the clock difference. This approach does not require changing the existing TDI framework, as previous OFC-based efforts did. Furthermore, this approach naturally captures not only stochastic jitter but also clock offsets and slow drifts. We also present the experimental demonstration of our scheme using two separate systems to model two spacecraft. Using this novel approach, we synchronize the two independent phase measurement systems with an accuracy better than 0.47 ns, while the stochastic jitter in the observation band is suppressed down to the setup sensitivity around the LISA performance levels at 15 pm/$\sqrt{Hz}$.

We demonstrate $4\pi$-steradian vector magnetic field sensing using an ensemble of nitrogen-vacancy ($\mathrm{N}$-$V$) centers in a single-crystal diamond coupled to a microwave (MW) cavity. The MW cavity enhances the spin-photon coupling, which enables efficient, high-contrast spin-state readout via MW interrogation and removes the need for bulky optical collection components. A slowly varying sinusoidal bias magnetic field lifts the zero-field degeneracy of the four crystallographic $\mathrm{N}$-$V$ orientations, allowing each orientation to be individually addressed and used for vector reconstruction of the magnetic field. The resulting magnetometer has a 36% contrast (20 times higher than typical for optical spin-ensemble readout) and achieves a single-axis sensitivity of 250 $\mathrm{pT}/\sqrt{\mathrm{Hz}}$ that is flat from direct current to 1 kHz. Noise models of the composite spin-cavity system establish MW amplitude noise as the dominant noise source and predict a thermal-noise limit of 2 $\mathrm{pT}/\sqrt{\mathrm{Hz}}$.

Fully harnessing the vast design space enabled by metamaterials to control electromagnetic (EM) fields remains an open problem for researchers. Inverse-design techniques have shown to best exploit the degrees of freedom available in design, resulting in high-performing systems for wireless communications, sensing, and analog signal processing. Nonetheless, fundamental yet powerful properties of metamaterials are still to be revealed. In this paper, we introduce the concept of perfectly matched metamaterials (PMMs). PMMs are passive, inhomogeneous media that perform purely refractive field transformations under different excitations. Their advantage lies in their simplicity, reflectionless behavior, and suitability for both analytical and numerical design methods. Unlike transformation optics, PMM-based designs are devoid of coordinate transformations. Anisotropic unit cells are configured to control EM fields in a true-time delay manner. Simple analytical designs are reported, which demonstrate the broadband capability of PMM devices. Proposed PMMs may find application in wideband beamforming and analog computing, realizing functionalities such as spatial filtering and signal preprocessing.

We show that by embedding a liquid-filled acoustofluidic cavity in a metamaterial, the quality factor of the cavity at selected acoustic resonance modes can be enhanced by 2–3 orders of magnitude relative to a comparable conventional cavity by matching the coarse-grained elastic moduli of the metamaterial to the acoustic properties of the liquid. The corresponding decrease in dissipation in the cavities is caused by the synchronized motion of the metamaterial and the liquid, which strongly suppresses the resulting acoustic streaming. The weak streaming combined with the enhanced quality factor enables fast acoustophoretic focusing of submicron particles in the cavity.

Precise mapping of the geomagnetic field is essential for understanding Earth’s geodynamics, space weather interactions, and navigation applications. Traditional magnetometers face limitations in sensitivity for a wide dynamic range, and compactness. To address these challenges, the OSCAR-QUBE quantum magnetometer based on nitrogen-vacancy centers in diamond was developed, providing a sensitive and compact solution for space-based magnetic-field measurements. Our system employs optically detected magnetic resonance to measure magnetic fields utilizing the quantum properties of nitrogen-vacancy centers in a miniaturized design. The form factor of the final device was 1U ($10\times 10\times 10{\mathrm{cm}}^3$), weighing 420 g, and had a power consumption of 5 W. Deployed aboard the International Space Station, our magnetometer measured high-resolution magnetic-field maps, achieving a sensitivity of $<300\mathrm{nT}/\sqrt{\mathrm{Hz}}$ and successfully demonstrating in situ vector magnetic-field mapping under low-Earth-orbit conditions. These results validate the flight-proven application of diamond quantum sensing in space, demonstrating the feasibility of solid-state quantum magnetometry for next-generation remote sensing and Earth observation missions. This work lays the foundation for future compact, multisensor quantum payloads for both scientific and commercial space applications.

Artificial transmission lines (ATLs) built with lumped-element inductors and capacitors form the backbone of broadband, nearly quantum-limited traveling-wave parametric amplifiers (TWPAs). When tailoring these transmission lines for parametric processes, nonlinear elements are added, typically nonlinear inductances in superconducting circuits, and energy and momentum conservation between interacting tones must be enforced through careful design of the ATL dispersion relation. However, a unified theoretical framework describing achievable dispersion relations is lacking. Here, I develop such a framework, borrowing from periodic structure theory and passive network synthesis. These complementary approaches divide the design space: periodic loading synthesis employs spatial modulation of frequency-independent components, while filter synthesis employs frequency-dependent responses in spatially uniform components. The framework reveals fundamental constraints and enables the discovery of novel TWPA architectures. In particular, I design a kinetic inductance TWPA with an alternative phase-matching architecture, and a backward-pumped Josephson TWPA exploiting an ambidextrous (i.e., right-left-handed) transmission line.