We propose a squeezed-light source meeting the stringent requirements of continuous-variable quantum sampling. Using the time-dependent effective second-order nonlinear interaction induced by a strong driving beam in the presence of the ${\chi }_3$ response in a microresonator, our approach is compatible with established nanophotonic platforms. With typical realistic parameters, squeezed states with a mean photon number of 10 or higher can be generated in a single consistent temporal mode at repetition rates of over 100 MHz. Over 15 dB of squeezing is expected in existing ultralow-loss platforms.

Transparent conducting oxides (TCOs) and graphene have been extensively investigated as promising materials for electro-optic modulation applications due to their dynamically configurable near-infrared properties. In this study, a detailed comparison between modulators comprising either a TCO film or a graphene-insulator-graphene structure is presented, considering a conventional silicon photonic waveguide as the underlying physical system. Both in-line and resonant configurations are investigated, integrating an electro-optic switching mechanism that changes the free-carrier concentration in the configurable material by means of electrical gating. The carrier-concentration change effect is rigorously modeled using solid-state physics principles, providing a physically consistent and straightforward comparison between the investigated material platforms. The performance of the designed modulators is thoroughly evaluated in terms of the extinction ratio, insertion loss, energy consumption, and bandwidth in both TE and TM operation. On the whole, both technologies support high-performance optical modulation, with TCO designs exhibiting an up to $40\mathrm{\%}$ smaller footprint, with their graphene counterparts standing out for their subpicojoule-per-bit performance on a physical system as simple as the employed silicon-wire waveguide. The low insertion losses as well as the impressive over-100-GHz switching speeds suggest both TCOs and graphene as very promising material candidates for future on-chip modulation applications.

In the gate model of quantum computing, a program is typically decomposed into a sequence of 1- and 2-qubit gates that are realized as control pulses acting on the system. A key requirement for a scalable control system is that the qubits are addressable—that control pulses act only on the targeted qubits. The presence of control crosstalk makes this addressability requirement difficult to meet. To provide metrics that can drive the requirements for decreasing crosstalk, we present three measurements that directly quantify the dc and ac flux crosstalk present between tunable transmons, with sensitivities as fine as 0.001%. We develop the theory to connect ac-flux-crosstalk measures to the infidelity of a parametrically activated two-qubit gate. We use quantum process tomography in the presence of crosstalk to provide an empirical study of the effects of crosstalk on two-qubit-gate fidelity.

Detection of biomolecules and biological nanoparticles by means of induced aggregation of larger nanoparticles using light scattering as readout was first accomplished in the middle of the last century. Since then, technical advances together with novel nanomaterials have enabled more sophisticated readout schemes, paving the way for methods exploiting dual-probe hybridization for biomolecular or nonoparticle recognition that today can compete with established bioanalytical methods. Herein, we present a quantitative assay, with single-nanoparticle readout, utilizing receptor-containing cell-membrane mimics in the shape of approximately 100-nm lipid liposomes rather than conventional antibody-modified nanoparticles to enable detection of virus particles in solution. Specifically, the method is based on virus-mediated aggregation of differently fluorescent-labeled liposomes that contain the ganglioside GM1 receptor for the Simian Virus 40 (SV40). The aggregation kinetics of the differently colored liposomes is studied by monitoring the spatial colocalization level of the liposomes and a theoretical model that successfully represents aggregation kinetics versus virus concentration is proposed. The limits of detection are identified experimentally for our current setup and theoretically in a more general context. The consistency between theory and experiments suggests that the approach will be generically applicable for similar biosensing applications or for the study of related systems where natural interactions with cell-membrane components can be used to induce liposome aggregation.

Attenuating low-frequency waves over a broad bandwidth is essential for earthquake protection or energy harvesting, yet it is very difficult due to the weak dissipation of materials and long wavelengths. This task is more challenging for elastic waves of complex modes. Here, we show that energy attenuation can be more efficient by trapping broadband low-frequency elastic waves in an omnidirectional concentrator designed by a transformation method. A prototype of 20 cm in diameter is fabricated for experimental demonstration, which consists of inhomogeneous honeycomb cells. Experimental results agree very well with simulation results and demonstrate that it can absorb complex elastic waves efficiently in the range of 10–800 Hz.

Piezoacoustic drop-on-demand (DOD) inkjet printing is widely applied in high-end digital printing due to its unprecedented precision and reproducibility. Micron-sized droplets of a wide range of chemical compositions can be deposited; however, the stability of piezoacoustic DOD inkjet printing can sometimes be compromised through the stochastic entrainment of bubbles within the ink channel. Here, bubble nucleation, translation, and growth are studied in an experimental silicon-based printhead with a glass nozzle plate using high-speed imaging that is triggered by changes in the ink-channel acoustics. It is found that impurities in the ink can trigger bubble nucleation upon their interaction with the oscillating meniscus. Cavitation inception on a dirt particle during the rarefaction pressure wave is identified as a second mechanism for bubble formation. The acoustic driving pressure within the ink channel, and its change upon bubble nucleation, are obtained from a fit of a Rayleigh-Plesset-type bubble-dynamics equation to the measured time-resolved radial dynamics of the bubble. The measured decrease in channel resonance frequency after bubble entrainment results in a 24% increased ink-jet length. The nucleated bubbles translate toward the ink-channel walls due to acoustic radiation forces and ink streaming. The convective ink flow is characterized using high-speed particle-tracking velocimetry. The vortical flow near the oscillating meniscus is shown to trap the impurities, thereby increasing the particle-to-meniscus interaction probability and, correspondingly, the bubble-entrainment probability.

The thermoradiative diode is a novel heat engine that converts athermal radiative emission from a hot converter to a colder environment into work. This stands in contrast to essentially all radiative heat engines realized to date, where an external hot reservoir radiates toward a converter that resides at (and can be reversibly coupled to) a cold reservoir. We derive the fundamental bounds on conversion efficiency and power production for generalized far-field hot-side heat engines with radiative exchange that can be black body (thermal) or, more generally, athermal. This is followed by the corresponding derivation for the rich landscape of performance bounds for the specific case of thermoradiative diodes, including why the Landsberg-efficiency limit associated with heat engines that include radiative exchange can be surpassed, and how the ultimate Carnot-efficiency limit could be approached.

We report on the fabrication and characterization of flux-tunable, low-loss, superconducting-quantum-interference-device- (SQUID) based transmission lines whose impedance is close to $50\mathrm{\Omega }$. The fabrication process relies on the deposition of a thin dielectric layer (few tens of nanometers) by atomic layer deposition on top of a SQUID array. The whole structure is covered by a nonsuperconducting metallic top-ground plane. We present experimental results from five different samples. We systematically characterize their microscopic parameters by measuring the propagating phase in these structures. We also investigate losses and discriminate conductor losses from dielectric losses. This fabrication method offers several advantages. First, the SQUID-array fabrication relies not on a niobium-trilayer process but on a simpler, double-angle evaporation technique. Second, atomic layer deposition provides a high-quality dielectric, leading to low-loss devices. Furthermore, the SQUID-array fabrication is based on a standard, all-aluminum process, allowing direct integration with superconducting qubits. Moreover, our devices are in situ flux tunable, allowing mitigation of uncertainty inherent in any fabrication process. Finally, because the unit cell is a single SQUID (no extra ground capacitance is needed), it is straightforward to modulate the size of the unit cell periodically, allowing band engineering. This fabrication process can be directly applied to traveling-wave parametric amplifiers.

The coherent perfect absorber (CPA) and laser are a pair of inversely worked wave structures that satisfy the time-reversal relation. We point out that, if the wave energy absorbed by the CPA can be recovered and then be reemitted by its corresponding laser, the combination of CPA and laser will be a wave-controlling device that can “move” the wave energy from one place to another. By extending the concepts of the CPA and laser from previously studied one-dimensional non-Hermitian systems to the two-dimensional ones, this understanding is used to simplify the design of the metasurface in this paper. As examples, an angular-asymmetric transmitting metasurface and wave splitter, which act as a perfect transmitter and retroreflector for waves coming from two oppositely tilted angles and splitting an incident wave into two directions with arbitrary amplitude ratio and phase difference, respectively, are constructed by combining two pieces of the separately designed CPAs. The idea not only greatly simplifies the design of a metasurface, but also bridges between research into the metasurface and a non-Hermitian system.

We present a pump-probe technique for monitoring ultrafast polarizability changes. In particular, we use it to measure the plasma density created at the temporal focus of a self-compressing higher-order pump soliton in a gas-filled hollow-core photonic crystal fiber. This is done by monitoring the wavelength of the dispersive wave emission from a counterpropagating probe soliton. By varying the relative delay between pump and probe, the plasma density distribution along the fiber can be mapped out. Compared with recently introduced interferometric side probing for monitoring the plasma density, our technique is relatively immune to instabilities caused by air turbulence and mechanical vibration. The results of two experiments on argon- and krypton-filled fiber are presented and compared to numerical simulations. The technique provides an important tool for probing photoionization in many different gases and gas mixtures, as well as ultrafast changes in dispersion in many other contexts.

Topological one-way edge states promise robust information transport through the notion of photonic crystals. For further applications of edge-state circuits and devices, a high gap Chern number, ${\mathcal{C}}_g$, is required. Contrary to previous realizations using gyrotropic photonic crystals, we show how $|{\mathcal{C}}_g|>1$ can be obtained by gapping multiple Dirac cones, which can surprisingly occur in a reciprocal continuous medium with limited degrees of freedom. A maximum of four one-way edge states is allowed on a single interface between two reciprocal continuous media. One-way signal combiners and splitters are designed with exact control on the branching and transmission efficiencies as immediate applications. Our theoretical investigations will be useful for constructing edge-state devices with multiplexing and demultiplexing capability.

Quantum computation requires the precise control of the evolution of a quantum system, typically through application of discrete quantum-logic gates on a set of qubits. Here, we use the cross-resonance interaction to implement a gate between two superconducting transmon qubits with a direct static dispersive coupling. We demonstrate a practical calibration procedure for the optimization of the gate, combining continuous and repeated-gate Hamiltonian tomography with stepwise reduction of dominant two-qubit coherent errors through mapping to microwave control parameters. We show experimentally that this procedure can enable a ${\widehat{ZX}}_{-\pi /2}$ gate with a fidelity $F=97.0(7)\mathrm{\%}$, measured with interleaved randomized benchmarking. We show this in an architecture with out-of-plane control and readout that is readily extensible to larger-scale quantum circuits.

The complexity of charge trapping in semiconductor devices, such as high-$\kappa$ MOSFETs, is increasing as the devices themselves become more complicated. To facilitate research into such charge-trapping issues, here we propose an optimized simulation framework that is composed of density-functional theory (DFT) for electronic structure calculation and Marcus theory for the calculation of charge-trapping rates. The DFT simulations are either carried out or corrected by using the Heyd-Scuseria-Ernzerhof hybrid functional. Using this framework, the hole-trapping characteristics along multiple paths in $\mathrm{Si}/{\mathrm{Si}\mathrm{O}}_2/{\mathrm{Hf}\mathrm{O}}_2$ stacks are investigated, and the relative importance of each path is revealed by calculating its exact hole-trapping rate. Besides the study on crystalline stacks, we also create an amorphous stack, which is more realistic compared with experiments and real devices, to reveal more active trapping centers and to study the statistical feature of charge trapping induced by structural disorder. In addition, to seek effective measures for relieving these charge-trapping problems, the effects of hydrogen and fluorine passivations are discussed, and physical insights for improving the performance of high-$\kappa$ MOSFETs are provided.

Plasma-based electron or positron wakefield acceleration has made great strides in the past decade. Currently, one major challenge for its applications to coherent light sources and colliders is the relatively large energy spread (few-percent level) of the accelerated beams. This energy spread is usually dominated by a longitudinally correlated energy chirp induced by the wakefield. It is highly desirable to have a systematic method for reducing this spread to $\lesssim 0.1\mathrm{\%}$ and, at the same time, maintaining the beam emittance. Here, a near-ideal dechirper based on a low-density hollow channel plasma is proposed and tested through large-scale three-dimensional particle-in-cell simulations. The theoretical analyses and simulations confirm that the positively correlated energy spread (chirp) of the electron or positron beam from a plasma accelerator can be significantly reduced by its self-wake in the hollow plasma channel from a few percent down to $\lesssim 0.1\mathrm{\%}$ without noticeable beam emittance growth. Such a near-ideal dechirper may significantly improve the beam quality of plasma-based accelerators; thus paving the way for their applications to future compact free-electron lasers and colliders.

The usual Hanle-effect magnetometers allow the measurement of two components of a very-low magnetic field using three orthogonal light beams. Here we present a scheme based on atomic alignment that requires only a single optical access for both a pump beam and a probe beam with a small angle between them. The results of experimental tests of this configuration are in close agreement with the theoretical predictions. We show that measurements of the third component should be possible by instrumentation of a partial depolarization of the pump beam. Such compact architectures open interesting perspectives for magnetometer arrays for medical imaging.

The phase delay problem of invisibility cloaks designed by optical conformal mapping is referred to the optical path difference between the waves in upper and lower Riemann sheets. As the frequency changes, the phase delay varies accordingly (here, we call it geometrical dispersion), which restricts the cloaks to working only at some discrete frequencies. Here, we solve the phase-delay problem by placing an optically null medium in the lower Riemann sheet. The conformal cloaks designed by using our method have many advantages, such as a continuous working band (no geometrical dispersion), omnidirectionality, robustness under frequency shifts, and no need for any complex materials that are both anisotropic and inhomogeneous. We also design metallic microchannels to realize our cloaks.

Full-waveform inversion (FWI) can produce previously unobtainable levels of accuracy and is revolutionizing the field of wave imaging. The basic principle is that a numerically produced data set is matched to the measured waveforms, enabling a high-resolution image to be produced since the model being inverted fully captures the physical behavior without approximation. This is achieved by gradually updating the numerical model using optimization algorithms. Currently, most FWI methods aim to recover material properties of a medium containing penetrable scatterers; however, there are many applications that, instead, require the boundary shapes of impenetrable objects to be reconstructed. Conventional velocity-style FWI will be trapped in local minima, with such problems being due to the extremely sharp contrast at the boundary. We propose a FWI procedure to directly recover the geometrical parameters of impenetrable obstacles via shape optimizations. The geometry is reconstructed by iteratively deforming the boundary of the target, following the negative direction of the geometrical boundary gradient. The boundary gradient is calculated from the shape derivatives of mass and stiffness matrices of a finite-element (FE) representation, when distorting the elements attached at the boundary. In addition, multiple-scattering events, which are more likely to occur between impenetrable obstacles, can be utilized automatically to provide substantial information for the inversion. Numerical and experimental results are shown to demonstrate the accuracy of the procedure for an example taken from the field of nondestructive evaluation, giving sizing within fractions of a wavelength for the tested cases; this step change in accuracy could be critical in sizing defects, enabling significantly more reliable decisions to be made about whether it is safe to continue using a component. Mathematical derivations and physical reasons for the success of our approach are illustrated.

The orbital angular momentum (OAM) of light has attracted a great amount of interest in recent times, due to the wide variety of applications it has made possible. Generally, the OAM spectrum is produced by coaxial superposition of several vortex beams, which might increase the complexity of the system. Here, we propose and experimentally demonstrate a simple way to produce a state of light with a controllable OAM spectrum using a binary array of pinholes. More specifically, we show that a spiral structure can convert a plane wave into a beam with a wide OAM spectrum, which can be easily tuned to pure or multiple OAM modes by adapting the structure of the pinhole plate. Furthermore, we show that a simple pinhole plate can produce structured beams with particular OAM states, such as photonic gears (superposition of OAM modes with opposite topological charges ±ℓ) and OAM combs (an optical mode formed by a series of discrete and equally spaced OAM modes, akin to an optical frequency comb). It is worth noting that we demonstrate the OAM comb experimentally. This study provides an avenue for the flexible generation of OAM spectra and the simplicity of the setup could make this approach convenient for many applications, such as optical communications and quantum information.

We consider an approach to fault tolerant quantum computing based on a simple error-detecting code operating as the substrate for a conventional surface code. We anticipate that the approach will be efficient when the noise in the hardware is skewed towards one channel (e.g., phase), or alternatively when the hardware is modular in such a fashion that the local error-detect operations have higher fidelity. We employ a customized decoder where information about the likely location of errors, obtained from the error-detection code, is translated into an advanced variant of the minimum-weight perfect-matching algorithm. A threshold gate-level error rate of 1.42% is found for the concatenated code given highly asymmetric noise. This is superior to the standard surface code and remains so as we introduce a significant component of depolarizing noise; specifically, until the latter is 70% the strength of the former. Moreover, given the asymmetric noise case, the threshold rises to 6.24% if we additionally assume that local operations have 20 times higher fidelity than long-range gates. Thus, for systems that are both modular and prone to asymmetric noise our code structure can be very advantageous.

Nitrogen-vacancy centers (NVCs) in diamond show promise for quantum computing, communication, and sensing. However, the best current method for entangling two NVCs requires that each one is in a separate cryostat, which is not scalable. We show that single NVCs can be laser written 6–15-µm deep inside of a diamond with spin coherence times that are an order of magnitude longer than previous laser-written NVCs and at least as long as naturally occurring NVCs. This depth is suitable for integration with solid immersion lenses or optical cavities and we present depth-dependent ${\mathrm{T}}_2$ measurements. 200 000 of these NVCs would fit into one diamond.