Quantum technology is playing an increasingly important role due to the intrinsic parallel processing capabilities enabled by quantum superposition, exceeding the upper limits of classical performances in diverse fields. An integrated photonic chip offers an elegant way to construct large-scale quantum systems in a physically scalable fashion; however, nonuniformity of quantum sources prevents all the elements from being connected coherently for exponentially increasing Hilbert space. Here, we experimentally demonstrate 128 identical quantum sources integrated on a single silica chip. By actively controlling the light-matter interaction in femtosecond laser direct writing, we are able to unify the properties of waveguides comprehensively and therefore the spontaneous four-wave mixing process for quantum sources. We verify the indistinguishability of the on-chip sources by a series of heralded two-source Hong-Ou-Mandel interferences, with all the dip visibilities above 90%. In addition, the brightness of the sources is found easily reaching the megahertz level and being applicable to both discrete-variable and continuous-variable platforms, showing either clear antibunching feature or large squeezing parameter under different pumping regimes. The demonstrated scalability and uniformity of the quantum sources, together with integrated photonic network and detection, will enable large-scale all-on-chip quantum processors for real-life applications.

Radiative heat management for personal comfort using photonic engineered textiles has the potential to provide a substantial advantage for an energy-efficient and sustainable society. Here, we propose a Janus-yarn design approach for a dual-mode double-sided thermoregulating fabric: a passive-radiative-management textile using asymmetric yarn composition, leading to dual-emissivity characteristics. The fabric provides both passive cooling and heating functions, achieved by wearing the textile inside out. The very strong emissivity contrast is achieved by utilizing both metallic and dielectric fibers within the yarn, benefiting from the plasmonic gap on the one hand and Fabry-Perot and multipole localized modes on the other. This tailored combination of reflective and absorptive structures leads to a substantial emissivity asymmetry between the two surfaces of the fabric ($\mathrm{\Delta }\epsilon$ = 0.72). Consequently, the fabric provides a very wide ${13.1}^{\circ }\mathrm{C}$ set-point temperature window, with the wearer staying comfortable between 11.3 and ${24.4}^{\circ }\mathrm{C}$.

Impedance mismatch between free space and absorptive materials is a fundamental issue plaguing the pursuit of high-efficiency light absorption. In this work, we design and numerically demonstrate a type of nonresonant impedance-matched optical metasurface exhibiting ultrabroadband reflectionless absorption based on the anomalous Brewster effect, which is denoted as an optical Brewster metasurface here. Interestingly, the Brewster metasurface exhibits a type of extreme angular asymmetry: a transition between perfect transparency and perfect absorption appears when the sign of the incident angle is changed. Such a remarkable phenomenon originates from the coexistence of traditional and anomalous Brewster effects. Guidelines for material selection based on an effective-medium description and strategies such as the integration of a metal back-reflector or a folded metasurface are proposed to improve the absorption performance. Finally, a gradient optical Brewster metasurface exhibiting ultrabroadband and near-omnidirectional reflectionless absorption is demonstrated. Such high-efficiency asymmetric optical metasurfaces may find applications in optoelectrical and thermal devices like photodetectors, thermal emitters, and photovoltaics.

Dictated by the causality constraint, the existence of a minimum absorber thickness has set an almost insurmountable obstacle for the remediation of ultralow-frequency noise in the tens of Hz to 150 Hz regime, owing to the very large absorber thickness required. Here, we show that, by manipulating the boundary condition in a calculated manner on the backside of the absorber, the causal constraint can be circumvented, and broadband near-total absorption of ultralow-frequency acoustic waves may be realized with an absorber thickness that is an order of magnitude less than the causal minimum. Our work delineates a design paradigm for the ultralow-frequency acoustic absorbers.

We show that the lower levels of a large-spin network with a collective antiferromagnetic interaction and collective couplings to three reservoirs may function as a quantum-absorption refrigerator. In appropriate regimes, the steady-state cooling current of this refrigerator scales quadratically with the size of the working medium, i.e., the number of spins. The same scaling is observed for the noise and the entropy production rate.

Despite quantum networking concepts, designs, and hardware becoming increasingly mature, there is no consensus on the optimal wavelength for free-space systems. We present an in-depth analysis of a daytime free-space quantum channel as a function of wavelength and atmospheric spatial coherence (the Fried coherence length). We choose decoy-state quantum key distribution bit yield as a performance metric in order to reveal the ideal wavelength choice for an actual qubit-based protocol under realistic atmospheric conditions. Our analysis represents a rigorous framework to analyze requirements for spatial, spectral, and temporal filtering. These results will help guide the development of free-space quantum communication and networking systems. In particular, our results suggest that shorter wavelengths in the optical band should be considered for free-space quantum communication systems. Our results are also interpreted in the context of atmospheric compensation by higher-order adaptive optics.

A noiseless, photon-counting detector, which resolves the energy of each photon, could radically change astronomy, biophysics, and quantum optics. Superconducting detectors promise an intrinsic resolving power at visible wavelengths of $R=E/\delta E\approx 100$ due to their low excitation energy. We study superconducting energy-resolving microwave kinetic inductance detectors (MKIDs), which hold particular promise for larger cameras. A visible and near-infrared photon absorbed in the superconductor creates a few thousand quasiparticles through several stages of electron-phonon interaction. Here we demonstrate experimentally that the resolving power of MKIDs at visible to near-infrared wavelengths is limited by the loss of hot phonons during this process. We measure the resolving power of our aluminum-based detector as a function of photon energy using four lasers with wavelengths between $1545$–$402\mathrm{nm}$. For detectors on thick $\mathrm{Si}\mathrm{N}$/$\mathrm{Si}$ and sapphire substrates the resolving power is limited to $10$–$21$ for the respective wavelengths, consistent with the loss of hot phonons. When we suspend the sensitive part of the detector on a 110-nm-thick $\mathrm{Si}\mathrm{N}$ membrane, the measured resolving power improves to $19$–$52$, respectively. The improvement is equivalent to a factor $8\pm 2$ stronger phonon trapping on the membrane, which is consistent with a geometrical phonon propagation model for these hot phonons. We discuss a route towards the Fano limit by phonon engineering.

The utility of local fields formed around a biased conductive scanning nanoscale tip is demonstrated for the trapping, tracking, and displacement of magnetic textures hosted by a substrate. The method operates at a low energy cost, is noninvasive, and is highly controllable. Detailed results are presented for the dynamic of a magnetic vortex in the sample beneath the tip. It is shown that the near-field-assisted tracking does not suffer from the usually undesirable transversal motion of magnetic vortices or skyrmions due to the topological Hall effect. Tuning the near field of the tip allows for the generation of packaged skyrmions with different topological charges. The results endorse the potential of near-field engineering for information storage and processing based on topological magnetic structure.

Owing to ever increasing gate fidelities and to a potential transferability to industrial CMOS technology, silicon spin qubits have become a compelling option in the strive for quantum computation. In a scalable architecture, each spin qubit will have to be finely tuned and its operating conditions accurately determined. In view of this, spectroscopic tools compatible with a scalable device layout are of primary importance. Here we report a two-tone spectroscopy technique providing access to the spin-dependent energy-level spectrum of a hole double quantum dot defined in a split-gate silicon device. A first gigahertz-frequency tone drives electric dipole spin resonance enabled by the valence-band spin-orbit coupling. A second lower-frequency tone (approximately $500\mathrm{MHz}$) allows for dispersive readout via rf-gate reflectometry. We compare the measured dispersive response to the linear response calculated in an extended Jaynes-Cummings model and we obtain characteristic parameters such as $g$ factors and tunnel and spin-orbit couplings for both even and odd occupation.

In this work, ultrastrong photon-to-magnon coupling is demonstrated for on-chip multilayered superconductor-ferromagnet-insulator hybrid thin-film structures reaching a coupling strength above 6 GHz, coupling ratio about 0.6, single-spin coupling strength about 350 Hz, and cooperativity about ${10}^4$. Strong characteristics of coupling are achieved owing to a radical suppression of the photon phase velocity in an electromagnetic resonator. With achieved coupling, the spectrum reveals the inapplicability of the Dicke quantum model, and evidences a contribution of the diamagnetic $A^2$ interaction term in the Hamiltonian of the system, which satisfies the Thomas-Reiche-Kuhn sum rule. The contribution of the $A^2$ term denotes the validity of the Hopfield quantum model and manifests observation of a different hybrid polariton quasiparticle, namely the plasmon-magnon polariton.

Quantum machine learning is expected to be one of the first practical applications of near-term quantum devices. Pioneer theoretical works suggest that quantum generative adversarial networks (GANs) may exhibit a potential exponential advantage over classical GANs, thus attracting widespread attention. However, it remains elusive whether quantum GANs implemented on near-term quantum devices can actually solve real-world learning tasks. Here, we devise a flexible quantum GAN scheme to narrow this knowledge gap. In principle, this scheme has the ability to complete image generation with high-dimensional features and could harness quantum superposition to train multiple examples in parallel. We experimentally achieve the learning and generating of real-world handwritten digit images on a superconducting quantum processor. Moreover, we utilize a gray-scale bar dataset to exhibit competitive performance between quantum GANs and the classical GANs based on multilayer perceptron and convolutional neural network architectures, respectively, benchmarked by the Fréchet distance score. Our work provides guidance for developing advanced quantum generative models on near-term quantum devices and opens up an avenue for exploring quantum advantages in various GAN-related learning tasks.

Spin-torque nano-oscillators (STNOs) are nanoscale devices with wide-band-frequency tunability. Their multifunctional rf properties are well suited to define schemes for wireless communications that use basic protocols for data transmission, such as amplitude-, frequency-, and phase-shift keying (ASK, FSK, and PSK, respectively). ASK and FSK are demonstrated for STNOs, but the implementation of PSK is more challenging because the STNO phase suffers from large fluctuations. Here, we introduce a special PSK technique for STNOs by combining their modulation and injection-locking functionality. The concept is validated using magnetic-tunnel-junction-based vortex STNOs for injection locking at 2f and f/2, showing phase shifts up to $0.70\pi \mathrm{rad}$ and data-transmission rates up to 4 Mbit/s. Quadrature phase-shift keying and analog phase modulation are also implemented, where the latter is employed for voice transmission over a distance of 10 m. This demonstrates that the STNO’s phase noise and output power meet the requested performances for operations in existing communication schemes.

Spins in ${\mathrm{Si}}_x$${\mathrm{Ge}}_{1-x}$ quantum dots are promising candidates for quantum bits but are also challenging due to the valley degeneracy and weak spin-orbital coupling. In this work, we demonstrate that valley states can serve as an asset that enables full two-axis control of a singlet-triplet qubit formed in a double quantum dot. We measure the valley spectrum in each dot using magnetic field spectroscopy of Zeeman split triplet states. We find a finite probability of valley states to flip during interdot transitions, which in turn provides a $g$-factor difference $\mathrm{\Delta }g$ between two dots. This $\mathrm{\Delta }g$ serves as an effective magnetic field gradient and allows for qubit rotations with a rate that increases linearly with an external magnetic field. We measure several interdot transitions and find that this valley-introduced $\mathrm{\Delta }g$ is universal and electrically tunable. This could potentially simplify the scaling up of quantum information processing in the ${\mathrm{Si}}_x$${\mathrm{Ge}}_{1-x}$ platform by removing the requirement for magnetic field gradients, which are difficult to engineer.

Nitrogen-vacancy (N-$V$) centers in diamond have shown promise as inherently localized electric field sensors, capable of detecting individual charges with nanometer resolution. Working with N-$V$ ensembles, we demonstrate that a detailed understanding of the internal electric field environment enables enhanced sensitivity in the detection of external electric fields. We follow this logic along two complementary paths. First, using excitation tuned near the N-$V$’s zero-phonon line, we perform optically detected magnetic resonance (ODMR) spectroscopy at cryogenic temperatures in order to precisely measure the N-$V$ center’s excited-state susceptibility to electric fields. In doing so, we demonstrate that the characteristically observed contrast inversion arises from an interplay between spin-selective optical pumping and the N-$V$ centers’ local charge distribution. Second, motivated by this understanding, we propose and analyze a method for optically enhanced electric field sensing using N-$V$ ensembles; we estimate that our approach should enable order-of-magnitude improvements in the dc electric field sensitivity.

Previous demonstrations of free-space quantum communication in daylight have been touted as significant for the development of global-scale quantum networks. Until now, no one has carefully tuned their atmospheric channel to reproduce the daytime sky radiance and slant-path turbulence conditions as they exist between space and Earth. In this article we report a quantum communication field experiment under conditions representative of daytime downlinks from space. Higher-order adaptive optics increased quantum channel efficiencies far beyond those possible with tip-tilt correction alone while spatial filtering at the diffraction limit rejected optical noise without the need for an ultranarrow spectral filter. High signal-to-noise probabilities and low quantum-bit-error rates are demonstrated over a wide range of channel radiances and turbulence conditions associated with slant-path propagation in daytime. The benefits to satellite-based quantum key distribution are quantified and discussed.

We present a general framework for the homogenization theory of space-time metamaterials. By mapping to a frame comoving with the space-time modulation, we derive analytical formulas for the effective material parameters for traveling-wave modulations in the low-frequency limit: electric permittivity, magnetic permeability, and magnetoelectric coupling. In doing so, we provide a recipe for the calculation of effective parameters of space–time-modulated media where the parameters follow a traveling-wave form of any shape and we show how synthetic motion can result in giant bianisotropy. This allows us to deepen the understanding of how nonreciprocity can be achieved in the long-wavelength limit and to completely characterize the different nonreciprocal behaviors available in space–time-modulated media. In particular, we show how the modulation speed, which can be subluminal or superluminal, together with the relative phase between electric and magnetic modulations, provide tuning knobs for the nonreciprocal response of these systems. Furthermore, we apply the theory to derive exact formulas for the Fresnel drag experienced by light traveling through traveling-wave modulations of electromagnetic media, providing insight into the differences and similarities between synthetic motion and moving matter. Since we exploit a series of Galilean coordinate transformations, the theory may be generalized to other kinds of waves.

We present a complete design scheme, from theoretical formulation to experimental validation, exploiting the versatility of metagratings (MGs) for designing a rectangular waveguide (RWG) ${\mathrm{TE}}_{10}$-${\mathrm{TE}}_{20}$ mode converter (MC). MG devices, formed by sparse periodically positioned polarizable particles (meta-atoms), were mostly used to date for beam manipulation applications. In this paper, we show that the appealing diffraction engineering features of the MGs in such typical free-space periodic scenarios can be utilized to efficiently mould fields inside WGs. In particular, we derive an analytical model allowing harnessing of the MG concept for realization of perfect mode conversion in RWGs. Conveniently, the formalism considers a printed-circuit-board MG terminating the RWG, operating as a reflect-mode MC. Following the typical MG synthesis approach, the model directly ties the meta-atom position and geometry with the modal reflection coefficients, enabling resolution of the detailed fabrication-ready design by enforcement of the functionality constraints: elimination of the fundamental ${\mathrm{TE}}_{10}$ reflection and power conservation (passive lossless MG). This reliable semianalytical scheme, verified via full-wave simulations and laboratory measurements, establishes a simple and efficient alternative to common RWG MCs, typically requiring challenging deformation of the WG designed through time-consuming full-wave optimization. In addition, it highlights the immense potential MGs encompass for a wide variety of applications beyond beam manipulation.

Metallic antiferromagnets with broken inversion symmetry on the two sublattices, strong spin-orbit coupling, and high Néel temperatures offer alternative opportunities for applications in spintronics. Especially ${\mathrm{Mn}}_2\mathrm{Au}$, with a high Néel temperature and high conductivity, is particularly interesting for real-world applications. Here, manipulation of the orientation of the staggered magnetization, (i.e., the Néel vector) by current pulses was recently demonstrated, with the readout limited to studies of anisotropic magnetoresistance or x-ray magnetic linear dichroism. Here we report on the in-plane reflectivity anisotropy of ${\mathrm{Mn}}_2\mathrm{Au}$(001) films, which are Néel vector aligned in pulsed magnetic fields. In the near-infrared region, the anisotropy is approximately 0.6%, with higher reflectivity for the light polarized along the Néel vector. The observed magnetic linear dichroism is about 4 times larger than the anisotropic magnetoresistance. This suggests the dichroism in ${\mathrm{Mn}}_2\mathrm{Au}$ is a result of the strong spin-orbit interactions giving rise to anisotropy of interband optical transitions, which is in line with recent studies of electronic band structure. The considerable magnetic linear dichroism in the near-infrared region could be used for ultrafast optical readout of the Néel vector in ${\mathrm{Mn}}_2\mathrm{Au}$.

The interaction of charge carriers with hydrogen-related defects plays a key role in modern semiconductor applications. Particularly in the field of micro- and nanoelectronics, where silicon together with amorphous gate oxides is still the technology of choice, $\mathrm{Si}$—H bonds participate in a rich variety of phenomena. For example, the passivating nature of H and its influence on surface reconstruction are fundamentally useful features for modern technologies and emerging research fields alike. However, the dissociation of $\mathrm{Si}$—H bonds results in electrically active defects and is associated with a number of device reliability issues. In this work we develop a general quantum kinetic formulation to describe the dynamics of bond excitation and breaking. The wealth of experimental and theoretical studies on $\mathrm{Si}$—H bond breaking induced by energetic carriers enables us to extract the most useful excitation pathways. Based on the open-system density-matrix theory we develop a model that accounts for all relevant system-bath interactions: vibrational relaxation and dipole scattering as well as resonance-induced excitation. In contrast to existing theoretical studies, our model is coupled to a Boltzmann transport equation solver, which is required for the correct consideration of nonequilibrium carrier energy distribution functions occuring in an electronic device. Finally, we apply our framework to model $\mathrm{Si}$—H bond breakage at the ${\mathrm{Si/SiO}}_2$ interface and validate our approach against different experimental data sets. The results provide a fundamental understanding of $\mathrm{Si}$—H dissociation mechanisms and allow for an accurate microscopic description of hot-carrier-induced damage at the device level. Due to the model formulation being free of empirical parameters, the approach can be easily applied to future technologies and materials systems.

We present a lab-on-chip experiment to accurately measure losses of superconducting microstrip lines at microwave and submillimeter wavelengths. The microstrips are fabricated from $\mathrm{Nb}\text{−}\mathrm{Ti}\text{−}\mathrm{N}$, which is deposited using reactive magnetron sputtering, and amorphous silicon which is deposited using plasma-enhanced chemical vapor deposition (PECVD). Submillimeter wave losses are measured using on-chip Fabry-Perot resonators (FPRs) operating around 350 GHz. Microwave losses are measured using shunted half-wave resonators with an identical geometry and fabricated on the same chip. We measure a loss tangent of the amorphous silicon at single-photon energies of $\tan \delta =3.7\pm 0.5\times {10}^{-5}$ at approximately $6\mathrm{GHz}$ and $\tan \delta =2.1\pm 0.1\times {10}^{-4}$ at 350 GHz. These results represent very low losses for deposited dielectrics, but the submillimeter wave losses are significantly higher than the microwave losses, which cannot be understood using the standard two-level system loss model.