Nitrogen-vacancy (N-$V$) diamonds have attracted keen interest for nanoscale sensing and spin manipulation. In particular, the nonequilibrium electron spin polarization after optical excitation of single N-$V$ centers has successfully been transferred to nuclear spin baths in the surrounding of defects. However, these experiments need to be extended to N-$V$ ensembles that have promising practical applications in the hyperpolarization of bulk sample volumes for NMR signal enhancement. Here, we use a dense, shallow ensemble of N-$V$ centers to demonstrate polarization transfer to nuclear spins in a well-defined composite diamond sample system. This allows us to address three different types of nuclear spins in different positions with respect to the N-$V$ polarization source: from the close proximity of ${}^{13}\mathrm{C}$ inside the diamond lattice to the self-assembled molecular system consisting of ${}^1\mathrm{H}$ and ${}^{19}\mathrm{F}$ spins outside the diamond and over multiple interfaces. We show that ensemble N-$V$ experiments face problems different from single N-$V$ experiments. In particular, using spinlock pulses, the inhomogeneously broadened electron spin resonance line of the N-$V$ ensemble limits the minimal resonance linewidth with which the transfer protocol can occur. Furthermore, we compare the N-$V$ spin-polarization losses and polarization transfer rates to the different nuclear baths and discuss the role of spin diffusion as detrimentally affecting the direct observation of nuclear polarization buildup within the detection volume of nanoscale N-$V$-NMR experiments.

Most applications of metasurfaces require excitation and control of both electric and magnetic surface currents. For such purposes, the metasurface must have a finite thickness to handle magnetic surface currents. For metasurface sheets of negligible thickness that offer only electric response, coherent illumination can compensate the need to create discontinuities of the tangential electric field component using magnetic surface currents. Most of the known coherent metasurfaces are space uniform and can control only plane-wave absorption and specular reflection. However, it is also known that periodical space-modulated (inhomogeneous) metasurfaces can be used to realize anomalous reflection, refraction, and other useful effects. In this paper, we propose the concept of a coherently illuminated space-modulated metasurface that functions as a coherent asymmetric absorber. We study its behavior under nonideal illumination and suggest applications related to sensing.

Measurement of the absolute value of the applied pressure in high-pressure muon and neutron experiments is a complicated task. It often requires the presence of a calibration material inside the sample volume, and could also cause additional time to obtain the response of the calibrant. Here we describe the use of optical calibrants for precise determination of the pressure value inside the piston-cylinder clamp cells. Utilizing the concept of separate volumes for the sample and the optical media, a setup for conducting in situ pressure measurements is successfully tested. Pressures in both the “sample” and the “optical” volumes are proved to be the same within experimental accuracy. The use of ${\mathrm{Sr}\mathrm{B}}_4{\mathrm{O}}_7:(0.01{\mathrm{Sm}}^{2+},0.03{\mathrm{Eu}}^{2+})$ as a pressure calibrant allows for a high accuracy of pressure determination by considering up to eight fluorescence lines.

Transmission asymmetry in reciprocal systems offers an appealing alternative to bulkier nonreciprocal implementations for certain applications. Common reciprocal routes to transmission asymmetry of linearly polarized light involve a rotation of its polarization. Here, we explore a different route with a linear all-dielectric metagrating that preserves polarization, while lacking inversion symmetry along the surface-normal direction. Our all-angle transmission calculations reveal an abrupt transition from a symmetric to an asymmetric transmission response that traces the Bragg critical wavelength of higher-order beam emergence as a function of the incident angle. By adopting an analogy between scattering from a multiport network and the metagrating paradigm we establish why the only necessary condition for transmission symmetry breaking in this class of systems is the emergence of any higher-order Bragg diffracted beam. We further show how such a transmission symmetry breaking is consistent with reciprocity and also demonstrate the underpinning symmetry-breaking mechanism with a first-principles numerical experiment. Finally, we shed light on some previous misconceptions regarding transmission symmetry breaking related to the role of the substrate or need for change of diffraction order number at each interface. Our proposed metagrating can exhibit a strong transmission asymmetry, with contrast that can be as high as approximately 75%, thus underlining its potential as a blueprint for passive asymmetric or nonlinear self-biasing nonreciprocal metasurfaces relevant to integrated and active photonics.

Many computational problems are intractable through classical computing and, as Moore’s law is drawing to a halt, demand for finding alternative methods in tackling these problems is growing. Here, we realize a liquid light machine for the NP-hard max-3-cut problem based on a network of synchronized exciton-polariton condensates. We overcome the binary limitation of the decision variables in Ising machines using the continuous-phase degrees of freedom of a coherent network of polariton condensates. The condensate network dynamical transients provide optically fast annealing of the $XY$ Hamiltonian. We apply the Goemans and Williamson random hyperplane technique, discretizing the $XY$ ground-state spin configuration to serve as ternary decision variables for an approximate optimal solution to the max-3-cut problem. Applications of the presented coherent network are investigated in image-segmentation tasks and in circuit design.

Multipartite entanglement is one of the core concepts in quantum information science with broad applications that span from condensed matter physics to quantum physics foundation tests. Although its most studied and tested forms encompass two-dimensional systems, current quantum platforms technically allow the manipulation of additional quantum levels. We report the experimental demonstration and certification of a high-dimensional multipartite entangled state in a superconducting quantum processor. We generate the three-qutrit Greenberger-Horne-Zeilinger state by designing the necessary pulses to perform high-dimensional quantum operations. We obtain the fidelity of $76\mathrm{\%}\pm 1\mathrm{\%}$, proving the generation of a genuine three-partite and three-dimensional entangled state. To this date, only photonic devices have been able to create and certify the entanglement of these high-dimensional states. Our work demonstrates that another platform, superconducting systems, is ready to exploit genuine high-dimensional entanglement and that a programmable quantum device accessed on the cloud can be used to design and execute experiments beyond binary quantum computation.

The high performance of hybrid perovskite-based devices is attributed to its excellent bulk transport properties. However, carrier dynamics, especially at the metal-perovskite interface, and their influence on device operation are not widely understood. This work presents the dominant transport mechanisms in methylammonium lead iodide (MA${\mathrm{Pb}\mathrm{I}}_3$) perovskite-based asymmetric metal electrode lateral devices. The device operation is studied with interelectrode lengths varying from 4 µm to 120 µm. Device characteristics indicate distinct ohmic and space-charge-limited current regimes that are controlled by the interelectrode length and applied bias. The electric-potential mapping using Kelvin-probe microscopy across the device indicates minimal ion-screening effects and the presence of a transport barrier at the metal-MA${\mathrm{Pb}\mathrm{I}}_3$ junction. Furthermore, photocurrent imaging of the channel using near-field excitation-scanning microscopy reveals dominant recombination and charge-separation zones. These lateral devices exhibit photodetector characteristics with a responsivity of about 51 mA/W in self-powered mode and 5.2 A/W at 5 V bias in short-channel devices (4 µm). The low device capacitance enables a fast light-switching response of approximately 12 ns.

Metagratings are periodic arrays of subwavelength scatterers, or atoms, engineered to refract or reflect waves toward anomalous directions with unit efficiency. Here, we design and build a metagrating to control the reflection direction of waterborne ultrasound waves impinging on a rigid or free surface. The grating and its atoms are designed to cancel the specular reflection and to redirect acoustic power toward a negative-reflection direction, through the first-negative-order Floquet mode. Despite a simple design, based on C-shaped brass particles acting as Helmholtz resonators, the grating is efficient ($>90\mathrm{\%}$) over a relatively broad range of frequencies (74–103 kHz) for a broad range of incidence angles (${14}^{\circ }$–${54}^{\circ }$). This good performance is obtained by tuning the distance between the atoms and the reflective surface. A multiple-scattering analytical model is presented to explain the phenomenon and a finite-element model is developed to further investigate the performance of the proposed design. Predictions from the model are confirmed experimentally in a water tank. The simplicity, reconfigurability, and scalability of the design, as well as its high efficiency, broadband behavior, and robustness to the incidence angle are all features that make the grating potentially useful for various applications in underwater acoustics, such as telemetry, communication, or noise mitigation.

Understanding and suppressing sources of decoherence is a leading challenge in building practical quantum computers. In superconducting qubits, low-frequency charge noise is a well-known decoherence mechanism that is effectively suppressed in the transmon qubit. Devices with multiple charge-sensitive modes can exhibit more complex behaviors, which can be exploited to study charge fluctuations in superconducting qubits. Here we characterize charge sensitivity in a superconducting qubit with two transmonlike modes, each of which is sensitive to multiple charge-parity configurations and charge-offset biases. Using Ramsey interferometry, we observe sensitivity to four charge-parity configurations and track two independent charge-offset drifts over hour time-scales. We provide a predictive theory for charge sensitivity in such multimode qubits which agrees with our results. Finally, we demonstrate the utility of a multimode qubit as a charge detector by spatially tracking local-charge drift.

Symmetry considerations are key to our understanding of the fundamental laws of nature. The presence of a symmetry implies that a physical system is invariant under specific transformations, and this invariance may have deep consequences. For instance, symmetry arguments state that a system will remain in its initial state if incentives to actions are equally balanced. Here, we apply this principle to a chain of qubits and show that it is possible to engineer the symmetries of its Hamiltonian in order to keep quantum information intrinsically protected from both relaxation and decoherence. We show that the coherence properties of this system are strongly enhanced relative to those of its individual components. Such a qubit chain can be realized using a simple architecture consisting of a relatively small number of superconducting Josephson junctions.

Information processing and storage by the same physical system is emerging as a promising alternative to traditional computing platforms. In turn, this requires the realization of elementary units the memory content of which can be easily tuned and controlled. Here, we introduce a polariton-based quantum memristor where the memristive nature arises from the intercavity polariton exchange and is controlled by a time-varying atom-cavity detuning. A dynamical hysteresis is characterized by the fluctuations in the instantaneous polariton number, where the history information is encoded into a dynamical phase. Using a Lindblad master-equation approach, we find that features of the quantum memristor dynamics, such as the area and circulation of the hysteresis loop, showcase a kind of “plasticity” controlled by quantum state initialization. This makes this quantum memristor very versatile for a wide range of applications.

High-energy photons can be generated via inverse Compton scattering (ICS) in the collision between energetic electrons and an intense laser pulse. The development of laser plasma accelerators promises compact and all-optical gamma-ray sources by colliding the electrons from laser wakefield accelerators with high-power driving pulses reflected by a plasma mirror. However, the law of optical focusing hinders realization of both high photon yield and monochromatic spectra in this scenario. We propose an azimuthal spatial-temporal convertor that decouples the focal field strength from laser spot size using helical parabolic geometry. It decomposes the driving laser beam into a pulse train of almost identical divergence angle and focal depth, creating synchronized ICS in the optimized linear regime. The scheme resolves the dilemma between high efficiency and narrow energy spread, facilitating the generation of monochromatic gamma rays using high power lasers beyond relativistic field strengths.

Weyl-like magnon excitations in ordered magnets have attracted significant recent attention. Despite the tantalizing physics and application prospects, the experimental observation of Weyl magnons is still challenging owing to their extraordinarily high frequency that is not accessible to the microstrip antenna technique. Here we predict gigahertz Weyl excitations in the collective dynamics of dipolar-coupled magnetic vortices arranged in a three-dimensional stacked honeycomb lattice. It is found that inversion symmetry breaking leads to the emergence of the type-II Weyl semimetal (WSM) state with tilted dispersion. We derive the full phase diagram of the vortex arrays that support WSMs with both single and double pairs of Weyl nodes, and the topological insulator phase. We observe robust arc surface states in a dual-segment fashion due to the tilted nature of type-II WSMs. Our findings uncover the low-frequency WSM phase in magnetic-texture-based crystals that are indispensable for future Weyltronic applications.

As we are approaching actual application of quantum technology, it is essential to exploit the current quantum resources in the best possible way. With this in mind, it might not be beneficial to use the usual standard gate sets, inspired by classical logic gates, while compiling quantum algorithms when other less standardized gates currently perform better. We, therefore, consider a promising native gate, which occurs naturally in superconducting circuits, known as the diamond gate. We show how the diamond gate can be decomposed into standard gates and, using single-qubit gates, can work as a controlled-not swap (cns) gate. We then show how this cns gate can create a controlled-phase gate. Controlled-phase gates are the backbone of the quantum Fourier-transform algorithm and we, therefore, show how to use the diamond gate to perform this algorithm. We also show how to use the diamond gate in quantum machine learning; namely, we use it to approximate nonlinear functions and classify two-dimensional data.

The search for hardware-compatible strategies for solving nondeterministic polynomial time (NP)-hard combinatorial optimization problems (COPs) is an important challenge of today’s computing research because of their wide range of applications in real-world optimization problems. Here, we introduce an unconventional scalable approach to face maximum-satisfiability (MAX-SAT) problems that combines probabilistic computing with p-bits, parallel tempering, and the concept of invertible logic gates. We theoretically show the spintronic implementation of this approach based on a coupled set of Landau-Lifshitz-Gilbert equations, showing a potential path for energy efficient and very fast (p-bits exhibiting nanosecond timescale switching) architecture for the solution of COPs. The algorithm is benchmarked with hard MAX-SAT instances from the 2016 MAX-SAT competition (e.g., “HG-4SAT-V150-C1350-1.cnf,” which can be described with 2851 p-bits), including weighted MAX-SAT and maximum-cut problems.

Multicolor attosecond electron bunches with tens of megaelectronvolts energy are extremely useful for wide applications, such as multicolor x-ray generation. Here we propose a scheme to generate such electron bunches with a laser wakefield accelerator driven by a millijoule few-cycle laser pulse via carrier-envelope-phase (CEP)-controlled ionization injection. It is found that the rapid CEP shift of the driving pulse in plasma due to plasma dispersion and Gouy phase shift enables the inner shell electrons of background high-$Z$ ions to be ionized periodically. These electrons are then subsequently injected into the wakefield, where each injection lasts for a distance of a few micrometers only, leading to the generation of multicolor electron bunches with narrow peaks in the energy spectrum and a subfemtosecond duration. With typical laser parameters available currently, simulations show that electron bunches with central energy of about $30\mathrm{MeV}$, energy spread of about $2\mathrm{\%}$, and duration of $460$ attoseconds can be obtained. Such electron sources can be driven by current laser systems operating at kilohertz repetition rates, making them attractive for wide applications.

In optical sensing, it is a fundamental principle that retrieving a certain quantity of spatial information requires a commensurate number of photons to be detected. However, on the issue of imaging moving objects under low photon flux, when the detectable photon flow is insufficient to recover the information flow formed by both motion and structural images of the object, photon crisis is induced and a more photon-efficient sensing method is urgently expected. Here we implement a simultaneous tracking and imaging method. The motion information and spatial information of a moving object are encoded by sequentially projecting the laterally shifting patterns and recording the results via a photomultiplier. Then both the trajectory and the image of the moving object are reconstructed gradually along with its evolution. As a photon-efficient encoding-decoding method is achieved, our method realizes capturing moving object with angular velocity larger than 45 mrad/s, and works well with the average number of detected photons even down to about 2.4 photons/speckle under single-laser-pulse illumination.