We build a parametric amplifier with a Josephson field-effect transistor (JoFET) as the active element. The resonant frequency of the device is field-effect tunable over a range of $2\mathrm{GHz}$. The JoFET amplifier has $20\mathrm{dB}$ of gain, $4\mathrm{MHz}$ of instantaneous bandwidth, and a 1-dB compression point of $-125.5\mathrm{dBm}$ when operated at a fixed resonance frequency.

In this work, we experimentally demonstrate the concept of space-time wave localization using programmable defects. The dynamic properties of the local resonators of an electromechanical metamaterial, comprising piezoelectric elements connected to synthetic impedance circuits, are digitally controlled to modulate a trivial point defect in space and time. The experimental results show that the vibration energy is gradually transferred and localized over subsequent unit cells according to the defect position. The practical realization of space-time wave localization using programmable defects in elastic metamaterials may enable innovative solutions for information transmission, multiplexing and demultiplexing, sensing, and coding.

Fast and efficient switching of nanomagnets is one of the main challenges in the development of future magnetic memories. We numerically investigate the evolution of static and dynamic spin-wave (SW) magnetization in short (50–400 nm in length and 120 nm in diameter) cylindrical ferromagnetic nanowires, where competing magnetization configurations of a single vortex (SV) and a Bloch-point vortex domain wall (BP-DW) can be formed. For a limited nanowire length range (between 150 and 300 nm), we demonstrate reversible transitions induced by a microwave field (forwards) and by opposite spin currents (backwards) between topologically different SV and BP-DW states. By tuning the nanowire length, the excitation frequency, the microwave pulse duration, and the spin-current value, we show that the optimum (low-power) manipulation of the BP-DW can be achieved with a microwave excitation tuned to the main SW mode for nanowire lengths around 230–250 nm, where single-vortex domain-wall magnetization reversal via nucleation and propagation of a SV-DW transition takes place. An analytical model of the dynamics of the Bloch point provides an estimate of the gyrotropic mode frequency close to that obtained via micromagnetic simulations. A practical implementation of the method in a device is proposed, involving microwave excitation and the generation of opposite spin currents via the spin-orbit torque. Our findings open up an alternative pathway for the creation of topological magnetic memories.

The efficacy of a physical reservoir computer model based on traveling spin waves in a spin-wave delay-line active-ring resonator was demonstrated recently. In the present work, we investigate how this neuromorphic device can be adapted for sensing applications. In this “reservoir computing for sensing” framework, we exploit strong coupling of the physical reservoir to its environment to utilize the reservoir as a sensing element. The dynamics of traveling spin waves in delay-line active rings are strongly dependent on the magnetic field and carrier frequency of those spin waves. Treating the spin-wave frequency as an environmental variable, we excite the active ring into different dynamical states by modulating the carrier frequency of a drive signal of microwave pulses injected into the ring. Training a linear regression on the time-multiplexed output from the ring allows the periodic amplitude patterns of the spin waves to be mapped reproducibly onto two-dimensional trajectories, representing periodic “behavioral” targets. Our work demonstrates the versatility of a magnonic resonator as a multipurpose computing and sensing device.

Realizing a quantum network will require long-lived quantum memories with optical interfaces incorporated into a scalable architecture. Color-center quantum emitters in diamond have emerged as a promising memory modality due to their optical properties and compatibility with scalable integration. However, developing a scalable color-center emitter module requires significant advances in the areas of heterogeneous integration and cryogenically compatible packaging. Here we report on a cryogenically stable and network compatible quantum emitter module for memory use. This quantum emitter module is a significant development towards advanced quantum networking applications such as distributed sensing and processing.

We assess the continuous-wave and dynamic performance of a photonic laser cavity consisting of a silicon-rich-nitride-on-insulator disk resonator overlaid with a transition-metal dichalcogenide (TMD) bilayer heterostructure (${\mathrm{WSe}}_2/{\mathrm{Mo}\mathrm{S}}_2$) acting as the gain medium. The optically pumped TMD heterostructure fosters an interlayer exciton with long radiative recombination lifetime, providing light emission in the near-infrared ($\sim 1130$ nm). Following a meticulous design process, we propose a silicon-on-insulator-compatible, monolithically integrated optical source capable of emitting milliwatt power inside an integrated waveguide, featuring a low pump-power threshold of $\sim 16{\mathrm{kW}/\mathrm{cm}}^2$, and exhibiting an estimated total quantum efficiency of approximately 1.7%. The proposed laser cavity is analyzed and designed using a rigorous theoretical framework based on perturbation theory and temporal coupled-mode theory, capable of treating nanophotonic cavities of any geometry and material composition comprising both bulk and/or sheet gain media. The framework is built upon fundamental electromagnetic and semiclassical gain equations, rendering it general and adaptable to different cavity configurations and gain-media descriptions. It constitutes a powerful tool for the efficient analysis of contemporary micro- and nanophotonic semiconductor lasers, since it is capable of predicting fundamental laser characteristics, providing design directives, deriving continuous-wave design metrics, and evaluating the dynamic response of realistic laser cavities.

Quantum optical microcombs in integrated ring resonators generate entangled photon pairs over many spectral modes, and allow the preparation of high-dimensional qudit states. Ideally, those sources should be programmable and have a high generation rate, with comb lines tightly spaced for the implementation of efficient qudit gates based on electro-optic frequency mixing. While these requirements cannot all be satisfied by a single resonator device, for which there is a trade-off between the high generation rate and tight bin spacing, a promising strategy is the use of multiple resonators, each generating photon pairs in specific frequency bins via spontaneous four-wave mixing. Based on this approach we present a programmable silicon photonics device for the generation of frequency-bin-entangled qudits, in which bin spacing, qudit dimension, and the bipartite quantum state can be reconfigured on chip. Using resonators with a radius of $22\text{μ}\mathrm{m}$, we achieve a high brightness [about $\mathrm{MHz}/(\mathrm{mW}{)}^2$] per comb line with a bin spacing of 15 GHz, and fidelities above 85% with maximally entangled Bell states up to a Hilbert space dimension of 16. By individually addressing each spectral mode, we realize states that cannot be generated on chip using a single resonator. We measure the correlation matrices of maximally entangled two-qubit and two-qutrit states on a set of mutually unbiased bases, finding fidelities exceeding 98%, and indicating that the source can find application in high-dimensional secure communication protocols.

We propose a new phase detection technique based on a flux-switchable superconducting circuit, the Josephson digital phase detector (JDPD), which is capable of discriminating between two phase values of a coherent input tone. When properly excited by an external flux, the JDPD is able to switch from a single-minimum to a double-minima potential and, consequently, relax in one of the two stable configurations depending on the phase sign of the input tone. The result of this operation is digitally encoded in the occupation probability of a phase particle in either of the two JDPD wells. In this work, we demonstrate the working principle of the JDPD up to a frequency of 400 MHz with a remarkable agreement with theoretical expectations. As a future scenario, we discuss the implementation of this technique to superconducting qubit readout. We also examine the JDPD compatibility with the single-flux-quantum architecture, employed to fast-drive and measure the device state.

Processing quantum information using quantum three-level systems or qutrits as the fundamental unit is an alternative to contemporary qubit-based architectures with the potential to provide significant computational advantages. We demonstrate a fully programmable two-qutrit quantum processor by utilizing the third energy eigenstates of two transmons. We develop a parametric coupler to achieve excellent connectivity in the nine-dimensional Hilbert space enabling efficient implementations of two-qutrit gates. We characterize our processor by realizing several algorithms like Deutsch-Jozsa, Bernstein-Vazirani, and Grover’s search. Our hardware-efficient protocols allow us to show that two stages of Grover’s amplification can improve the success rates of an unstructured search with quantum advantage. Our results pave the way for building fully programmable ternary quantum processors using transmons as building blocks for a universal quantum computer.

In this article, we analyze the photovoltaic effect while assuming a fixed ambient temperature and a varying system temperature rather than using the standard fixed system temperature–based approaches. We do so by complementing the photon rate balance equation (detailed balance, circuit model) with the power balance equation of the system. As a result, a simple approach capable of treating any photovoltaic system emerges. Accordingly, we study the potential-dependent current and temperature of solar cells and thermoradiative power generators. We show that the optimal band gap of a solar cell depends on its heat-transfer coefficient and that its efficiency may rise or fall as solar concentration increases, depending on its ability to dissipate heat. We also identify where the cell’s efficiency and temperature turn from a conductive and/or convective-dominated cooling regime to a radiative-dominated one. For the thermoradiative case, we show that its power decreases when heat intake is suppressed and study the degrading effect of nonradiative recombination on this power production scheme. The proposed model converges to the known fixed system temperature–based approaches when an infinite ability to transfer heat is considered.

In precision measurement and quantum metrology, the $2\pi$ periodicity inherent to any interferometric signal sets a fundamental limit in the simultaneous achievement of both high measurement sensitivity and range. Here, based on the extended period of the Lissajous curve, we develop a method to break this sensitivity–maximum-range limit completely. In the measurement of magnetic field using an electronic spin in diamond under ambient conditions, we extend the maximum range by 2 orders of magnitude without sacrificing detection sensitivity and bandwidth for sufficiently long measurement time. Furthermore, we achieve precise detection of a time-varying periodic waveform, where a large measurement range can induce high accuracy and demonstrate a Heisenberg-like scaling within the coherent regime. This Lissajous-curve-based range extension method can be directly applied to any other modulo-limited quantum interferometers, which makes a useful and indispensable stepping stone toward practical interferometric quantum metrology.

We demonstrate the sensitivity enhancement of measurement of microwave electric fields by use of the full information of the complex atomic susceptibility. The transfer characteristics of both the microwave electric fields and the noise relevant to atoms, which are mapped to two quadrature components of the probe light, are systematically measured with use of a Mach-Zehnder interferometer. On the basis of the readout of the full complex atomic susceptibility, a sensitivity enhancement of 12 dB is achieved when the probe light has red detuning of 6 MHz. The results shed light on increasing the sensitivity of atomic sensors of microwave electric fields that is beyond the capability of the traditional antenna.

Emerging applications in the field of finite-frequency mesoscopic physics require accurate modeling tools for the evaluation of carrier-transport dynamics, modulation bandwidth, and frequency conversion effects in nanodevices. With foundations in advanced concepts of many-body and quantum field theories, the nonequilibrium Green’s function technique is widely adopted in the calculation of steady-state carrier-transport properties of nanostrucures, while the evaluation of the frequency response is so far largely unexplored by genuine quantum models. Guided by the connection with drift-diffusion solvers within a local description of carrier-phonon scattering, we propose an accurate, yet computationally efficient nonequilibrium Green’s function model of dissipative carrier transport to study the small-signal properties of semiconductor nanostructures. From the numerical evaluation of steady-state Green’s functions and their functional derivatives, we compute spectrally resolved observables expressed in terms of familiar microscopic quantities germane to the drift-diffusion framework, the most prevalent tool in semiclassical device simulation. Besides drastically improving the convergence properties, the exact Jacobian, complemented with the contribution of the displacement current, gives access to the small-signal admittance. Current-conserving boundary conditions suitable for small-signal analysis provide the correct physical behavior near the contacts. Numerical examples show the accuracy and flexibility of the proposed model.

We experimentally implement a one-directional virtual geometric periodicity in an elastic metamaterial. First, unwanted boundary reflections at the domain ends are cancelled through the iterative injection of the polarity-reversed reflected wave field. The resulting boundless experimental state allows for a much better analysis of the influence of metamaterials on the propagating wave field. Subsequently, the propagating wave field exiting on one end of the structure is reintroduced at the opposite end, creating a virtual geometric periodicity in one propagation direction. We find that the experimentally observed band gap converges to the analytical solution through the introduction of the virtual periodicity. The established work flow introduces an approach to the experimental investigation and validation of metamaterial prototypes in the presence of strongly dispersive wave propagation and internal scattering. The fully data-driven ad hoc treatment of boundary conditions in metamaterial experimentation with arbitrary mechanical properties enables reflection suppression, virtual periodicity, and the introduction of more general fictitious boundaries.

Spintronic nano-oscillators and diodes with reduced nonlinearity benefit from low phase noise and improved device properties. Moreover, they could offer key advantages for realizing neuromorphic applications, such as spike-based neurons and frequency multiplexing in neural networks. Here, we experimentally demonstrate the reduction in nonlinearity of a spin Hall nano-oscillator (SHNO) by compensation of its effective magnetic anisotropy. The study involves optimization of $\mathrm{Co}/\mathrm{Ni}$ multilayer growth to achieve the compensation, followed by spin-diode measurements on patterned microstrips to quantify their anisotropy. The relationship between the second- $(H_{k_2}=0.47\mathrm{mT})$ and first-order $(H_{k_1}^{\mathrm{eff}}=-0.8\mathrm{mT})$ anisotropy fields reveals the existence of an easy cone, thereby validating the presence of compensation. Furthermore, we demonstrate a compensated spin diode that has a fixed frequency when the input power is varied. We then study the current-induced auto-oscillation properties of SHNOs on compensated films by patterning nanoconstrictions of 200 and 100 nm wide. The invariance of the resonance frequency and linewidth of the compensated SHNO with applied dc current indicates the absence of nonlinearity. This independence is maintained irrespective of the applied external fields and their orientations. The compensated SHNO obtained has a linewidth of 1.1 MHz and a peak output power of up to 1 pW/MHz.

Twin-field quantum key distribution (TFQKD) enables two distant parties to establish a shared secret key, by interfering weak coherent pulses (WCPs) in an intermediate measuring station. This allows TFQKD to reach greater distances than traditional QKD schemes and makes it the only scheme capable of beating the repeaterless bound on the bipartite private capacity. Here, we generalize TFQKD to the multipartite scenario. Specifically, we propose a practical conference key agreement protocol that only uses WCPs and linear optics and prove its security with a multiparty decoy-state method. Our protocol allows an arbitrary number of parties to establish a secret conference key by single-photon interference, enabling it to overcome recent bounds on the rate at which conference keys can be established in quantum networks without a repeater.

An efficient mass sensor based on exceptional points (EPs), engineered under a synthetic magnetism requirement, is proposed. The benchmark system consists of an electromechanical (optomechanical) system where an electric (optical) field is driving two mechanical resonators that are mechanically coupled through a phase-dependent phonon hopping. This phase induces a series of EPs once it matches the condition of $\pi /2(2n+1)$. For any perturbation of the system, the phase-matched condition is no longer satisfied, and this lifts the EP degeneracies, leading to a frequency splitting that scales as the square root of the perturbation strength, resulting in a giant sensitivity-factor enhancement. Owing to the set of EPs, our proposal allows a multiple-sensing scheme and performs better than its anti-$PT$-symmetric sensor counterpart. This work sheds light on platforms that can be used for mass-sensing purposes, opening up new opportunities in nanoparticle or pollutant detection and in water treatment.

Preshared entanglement can significantly boost communication rates in the high thermal-noise and low-brightness transmitter regime. In this regime, for a lossy bosonic channel with additive thermal noise, the ratio between the entanglement-assisted capacity and the Holevo capacity—the maximum reliable communication rate permitted by quantum mechanics without any preshared entanglement—scales as $\log (1/{\overline{N}}_S)$, where the mean transmitted photon number per mode, ${\overline{N}}_S\ll 1$. Thus, preshared entanglement, e.g., distributed by the quantum internet or a satellite-assisted quantum link, promises to significantly improve low-power radio-frequency communications. In this paper, we propose a pair of structured quantum transceiver designs that leverage continuous-variable preshared entanglement (generated, e.g., from a down-conversion source), binary phase modulation, and non-Gaussian joint detection over a codeword block, to achieve this scaling law of capacity enhancement. Furthermore, we describe a modification to the aforesaid receiver using a frontend that uses sum-frequency generation sandwiched with dynamically programmable in-line two-mode squeezers, and a receiver backend that takes full advantage of the output of the receiver’s frontend by employing a nondestructive multimode vacuum-or-not measurement to achieve the entanglement-assisted classical communication capacity.

On-chip mode division (de)multiplexing plays a significant role in integrated devices to greatly improve communication capacity. One of the goals of mode division (de)multiplexing is to realize devices with larger bandwidth and better fabrication tolerance. However, integrated broadband mode division (de)multiplexing devices have rarely been reported up to now. In this work, we experimentally realize a broadband mode division demultiplexing device with a high degree of fabrication tolerance based on a lithium niobate-on-insulator waveguide array. By taking advantage of the fact that different modes in the waveguide array have different group velocities, we experimentally confirm that different modes in the waveguide array have different transverse displacements. The implementation of the integrated broadband mode division demultiplexer may have future applications in information processing technology, quantum communication, and quantum computing.

The removal of undesired beam nonlinear energy chirp (time-energy correlation) or linearization of the beam longitudinal phase space (LPS) is crucial for high-brightness linac-based scientific applications, such as x-ray free-electron lasers. In this paper, we propose that a low-density hollow channel plasma can be used as a near-ideal passive linearizer to significantly linearize the beam LPS and, at the same time, preserve the beam emittance. Physically, the passage of the beam through the hollow plasma channel excites a strong quasicosinoidal longitudinal wakefield that acts to mitigate the beam nonlinear energy chirp by superimposing a reverse chirp on the beam. The theoretical analyses and large-scale three-dimensional start-to-end simulations confirm that the beam longitudinal phase space can be almost completely linearized without noticeable beam emittance growth. Application of such a near-ideal linearizer may significantly improve the performance of numerous accelerator-based applications.