Superconducting parametric amplifiers (SPAs) have seen great interest in recent years due to their high gain and quantum limited noise performance. Among these amplifiers, resonant SPAs have been widely developed for experiments where ultralow-noise narrow-band amplification is of interest, such as the search for axion dark matter in particle physics and the detection of spectroscopic lines in astrophysics, while also finding applications in quantum computing. This work presents an amplifier based on a complementary split-ring resonator, patterned on a $\mathrm{Nb}\mathrm{Ti}$-coated sapphire substrate embedded within a waveguide, designed to work at a set of four narrow frequency bands throughout the $K$ band (18–27 GHz) using the kinetic inductance of the superconducting film. The $S$-parameters measured at 400 mK, using a sorption cooler, show the four resonances between 23.3 and 26.3 GHz at 1-GHz spacing, with a maximum transmission on resonance of $-1$ dB. Four-wave mixing has been observed with each resonance, and a maximum signal gain of 30 dB has been measured, corresponding to 29 dB of insertion gain. The noise performance of the amplifier has been measured, showing an added noise of 1.2 half-quanta at 400 mK. These results are relevant to high-frequency axion dark matter experiments and help motivate the exploration of higher frequencies in quantum technologies.

Deep frequency modulation interferometry (DFMI) resolves phase ambiguity in absolute distance measurements by jointly estimating two length-encoding parameters: the coarse and unambiguous effective modulation depth ($m$), and the fine but ambiguous interferometric phase ($\varphi$). We establish a comprehensive framework quantifying the fundamental precision limits and practical accuracy constraints of this technique. A Fisher-information analysis defines the intrinsic estimator precision for $m$ and $\varphi$, while the contribution of carrier frequency drift introduces an additional, time-dependent source of random error. Numerical simulations reveal a structured error landscape with previously unrecognized “valleys of robustness,” where systematic biases from common hardware imperfections are suppressed by orders of magnitude. An analytical model based on signal orthogonality explains their origin and predicts their locations. The results yield a consolidated error budget accounting for both random and systematic errors, providing a quantitative design paradigm for absolute length metrology via DFMI.

State transitions during qubit measurements are extremely detrimental to quantum tasks that rely on repeated measurements, such as quantum error correction. These state transitions can occur when excessive measurement power leads to qubit excitations outside its computational space. Alternatively, the qubit state can decay rapidly when the measurement protocol inadvertently couples the qubit to lossy modes such as two-level systems (TLSs). We experimentally verify the impact of these TLSs in qubit readout by measuring the transition errors at different qubit flux bias. Because such state transitions during measurements are often localized in frequency space, we demonstrate the ability to avoid them during a fluxonium readout by exploiting the qubit’s flux tunability. By synchronizing the flux bias with the readout photon dynamics, we reduce the readout error by 48% (49%) in 1-$\text{μ}\mathrm{s}$ (0.5-$\text{μ}\mathrm{s}$) integration time. Our work advances the understanding of state transitions in superconducting circuit measurements and demonstrates the potential of fluxonium qubits to achieve fast high-fidelity readout.

We show that purely lossy defects in one- and two-dimensional non-Hermitian photonic crystals can induce transmission matrix singularities not accessible with lossless defects. These singularities in turn can enable dramatic enhancement of overall system gain not accessible through conventional means. We further show that the underlying mechanism behind the loss-induced gain enhancement is due to the resonances being located specifically at topological branch-cut singularities in the reflection coefficient with nontrivial winding numbers. The resulting resonances can exhibit exceptionally high-quality factors in excess of approximately ${10}^4$. Our work highlights the counterintuitive role of loss in engineering singularities in the gain response in non-Hermitian systems and its connection to topological phenomena in photonic systems.

Directional control of heat remains a central challenge for energy conversion, waste-heat utilization, and thermal management, as existing thermal rectifiers exhibit low efficiency or operate only at cryogenic temperatures. Here we demonstrate giant phonon rectification in solid-state “phonon Tesla valves”, inspired by Nikola Tesla’s fluidic one-way valve but governed by fundamentally different transport physics. Using ab initio Boltzmann transport simulations with full scattering matrices, we show that hydrodynamic phonon transport in graphite coupled with asymmetric valve geometry produces strong forward-backward contrast in phonon relaxation. Single-stage devices achieve rectification ratios of up to approximately 8, while multistage configurations reach ratios of approximately 16, far exceeding those of prior thermal diodes. The rectification mechanism originates from asymmetric relaxation of nonequilibrium phonons at diffusive boundaries, in contrast to inertia-driven fluid Tesla valves. These results examine the performance limits of phonon Tesla valves and establish a platform for directional heat control and highlight the unique potential of hydrodynamic phonons for thermal information processing and energy technologies.

Electron-hole pairs in organic photovoltaics are known to dissociate efficiently despite a Coulomb binding energy that exceeds thermal energy, a behavior that remains only partially understood. While previous studies have highlighted the role of electron-phonon interactions and nonequilibrium effects, a clear and physically transparent picture of the dissociation mechanism is still lacking. In this work, we investigate this problem using a two-dimensional quantum transport model based on the nonequilibrium Green’s function formalism, treating the donor-acceptor interface as an open system. Rather than aiming at a material-specific description, our approach is designed to identify the key mechanisms governing charge separation. We show that increasing electron-phonon coupling leads to a strong enhancement of the dissociation probability, reaching values close to 90%. This behavior is explained by the broadening of quantum states, which promotes interpolymer chain hybridization and induces a transition from hopping to quasiband transport. Most importantly, we demonstrate that these effects give rise to a ratchetlike mechanism at the interface, combining phonon-assisted transitions and carrier delocalization, which enables directional transport and suppresses recombination. This Markovian mechanism, which arises from the interplay between the Coulomb potential profile and vibrational energies, provides a unified and physically transparent explanation for efficient exciton dissociation, even under equilibrium phonon conditions.

Achieving accurate and rapid sorting of orbital angular momentum (OAM) modes in synthesized acoustic vortex beams plays a pivotal role in OAM-harnessing underwater acoustic communication. However, most existing studies distinguish OAM modes alone and are performed predominantly in airborne environments, while lacking the capability to simultaneously demodulate other dimensions of sound waves, such as frequency. Here we propose the design and experimental realization of a monolayered metademultiplexer with subwavelength thickness for multidimensional demultiplexing across both the OAM domain and the frequency domain of underwater acoustic vortex beams via a binary-amplitude modulation strategy. By imposing a theoretically derived nondispersive binary-amplitude profile, the metademultiplexer comprising only two simple units is imprinted with OAM selectivity and a chromatic aberration characteristic, enabling it to untwist and focus multifrequency and multimode underwater vortex beams into the designated spatially separated detection points within three-dimensional space behind the device. Thanks to this effective mapping between the spatial location and the spectral and OAM modes, the high-capacity OAM and frequency information can be simultaneously demultiplexed in a passive, real-time, and flexible way, while the proposed method remains compatible with conventional demultiplexing techniques harnessing other physical dimensions. The metademultiplexer is implemented with ultrathin acoustically rigid material with high-pressure resistance, and its effectiveness is validated through both numerical simulation and underwater experimental measurement, demonstrating high-accuracy demodulation of spatially and spectrally multiplexed acoustic vortex beams with interchannel crosstalk below −20 dB. We envision that our binary amplitude–coded demultiplexing strategy offers a promising pathway toward the development of advanced OAM-based acoustic information processing devices.

Stochastic resonance (SR) can amplify weak electric field signals in nonlinear systems by means of externally injected noises. Here, we propose and experimentally demonstrate a modified SR method, termed squeezing-induced SR, implemented in a system involving a trapped ion behaving as a Duffing oscillator. We find that squeezing the phase noise of the oscillator results in amplified fluctuations of the corresponding amplitude, which helps achieve the SR. Since no auxiliary noise source is needed, squeezing-induced SR may enhance the signal-to-noise ratio by $4.28\pm 0.39$ dB compared with conventional noise-induced SR under identical conditions of electric field detection. This technique offers a promising approach for developing atomic ion sensors to detect weak electric field signals.

State-of-the-art single-qubit gates on superconducting transmon qubits can achieve the fidelities required for error-corrected computations; however, parameter fluctuations due to qubit instabilities, environmental changes, and control inaccuracies make it difficult to maintain this performance. To mitigate the effects of these parameter variations, we numerically derive gates that are robust to amplitude and frequency errors using gradient-ascent pulse engineering. We analyze how fluctuations in qubit frequency, drive amplitude, and coherence affect gate performance over time. The robust pulses suppress coherent errors from drive-amplitude drifts over 15 times more than a Gaussian pulse with derivative removal by adiabatic gate (DRAG) corrections. Furthermore, the robust gates, originally designed to compensate for quasistatic errors, also demonstrate resilience to stochastic, time-dependent noise, which is reflected in the dephasing time. They suppress added errors during increases in dephasing by up to 1.7 times more than DRAG.

Stochastic methods offer an effective way to suppress coherent errors in quantum simulation. In particular, the randomized compilation protocol may reduce circuit depth by randomly sampling Hamiltonian terms rather than following the deterministic Trotter-Suzuki sequence. However, its fixed sampling distribution does not adapt to the dynamics of the system, limiting its accuracy. In this work, we propose a fluctuation-guided adaptive algorithm that adaptively updates sampling probabilities based on fluctuations of Hamiltonian terms to achieve higher simulation fidelity. Remarkably, the protocol renders an intuitive physical understanding: Hamiltonian terms with greater sensitivity to the state evolution should be prioritized during sampling. The overhead of measuring fluctuations necessary for updating the sampling probability is affordable, and can be further largely reduced by classical shadows. We demonstrate the effectiveness of the method with numeral simulations across discrete-variable, continuous-variable, and hybrid-variable systems.

Measurement of mutual gravitation on laboratory scales is an outstanding challenge and a prerequisite to probing theories of quantum gravity. A leading technology in tabletop gravity experiments is the torsion balance, with limitations due to thermal decoherence. Recent demonstrations of lithographically defined suspensions in thin-film silicon nitride with macroscale test masses suggest a path forward, as torsion pendulums dominated by gravitational stiffness may achieve higher mechanical quality factors through dilution of material losses. Here, we demonstrate a $250\text{μ}\mathrm{m}\times 5\mathrm{mm}\times 1.8\text{μ}\mathrm{m}$ torsion fiber supporting 87 g and forming a Cavendish-style torsion pendulum with tungsten test masses that is the largest thin-film silicon-nitride-based oscillator to date. Torsion pendulums with thin-film nanofabricated suspensions provide a test bed for near-term tabletop experiments probing classical and quantum gravitational interaction between oscillators.

Measurement-device-independent quantum key distribution (MDI-QKD) eliminates all detector-side vulnerabilities. Compared to weak coherent pulses, heralded single-photon sources (HSPSs) signal the presence of photons, thereby extending the achievable distance of MDI-QKD and enabling advanced protocols such as passive decoy-state implementations and quantum-memory-assisted configurations. In practice, however, spectral correlations between photon pairs in HSPS degrade Hong-Ou-Mandel (HOM) interference visibility. Although narrowband filtering can suppress this effect, it relies on dedicated hardware and lacks flexibility. Here, we propose an MDI-QKD scheme based on a time-domain postprocessing filtering technique that requires no additional hardware, significantly improving both the key rate and the maximum transmission distance. By optimizing the filter width, this method flexibly adapts to variations in the source or channel. Furthermore, it can be readily extended to other protocols relying on HOM interference, including quantum teleportation and entanglement swapping.

Photonic Ising machines represent an emerging computational paradigm for solving combinatorial optimization problems, characterized by ultralow power consumption and accelerated processing capabilities. Spatial photonic Ising machines (SPIMs), in particular, have attracted substantial research interest due to their native architectural scalability and parallel processing topology. However, existing spatial photonic Ising machines employing simulated annealing (SA) face challenges in attaining optimal or near-optimal solutions for large-scale problems due to the complexity of the energy landscape for the Ising models. This paper proposes a Dammann grating–enabled spatial-temporal photonic Ising machine for gradient-inspired parallel simulated annealing with tunable spin-cluster size. Using this novel architecture, we experimentally generated a near-optimal solution for the Max-Cut problem on a 1600-node weighted random graph. Compared with an SA-based SPIM, our codesigned photonic framework achieves a 20-fold acceleration in convergence speed and a 2.6-fold improvement in cut value after 400 iterations. Our proposed system effectively unleashes the scalability and parallel processing capabilities of spatial optical computing, enabling accelerated optimization and improved solution quality, thus demonstrating the potential for superior efficiency for large-scale combinatorial optimization problems.