We propose and demonstrate a scheme for spatial mapping and direct reading of the nonlinear response of optical materials from the propagation of self-accelerating beam profiles. Through a single evolution measurement, a two-dimensional compact Airy beam is able to directly map the nonlinear response of a medium into spatial profiles. The most efficient mapping takes place along some particular transverse directions rather than the direction of the beam acceleration, depending on both the Airy intensity pattern and the type of nonlinearity. Our work may herald a simple yet effective way for measuring the nonlinear optical response, in contrast to the conventional Z-scan technique.

We analyze electric transport and noise properties at 4.2 K of self-shunted superconductor-normal metal-superconductor (SNS) sandwich-type Josephson junctions, comprising $\mathrm{Nb}$ as the superconductor and $\mathrm{Hf}$-$\mathrm{Ti}$ as the normal conducting material, with lateral dimensions down to approximately $80$ nm. The junctions are fabricated with an optimized multilayer $\mathrm{Nb}$ technology based on nanopatterning by electron-beam lithography and chemical-mechanical polishing. The dependence of transport properties on the junction geometry (lateral size and barrier thickness $d_{\mathrm{Hf}\mathrm{-}\mathrm{Ti}}$) is studied, yielding a characteristic voltage $V_c$ up to approximately $100\mu \mathrm{V}$ for the smallest $d_{\mathrm{Hf}\mathrm{-}\mathrm{Ti}}=17$ nm. The observed small hysteresis in the current-voltage curves of devices with high $V_c$ and large size can be attributed to self-heating of the junctions and fitted with an extended version of the resistively shunted junction model. Measurements of voltage noise of single junctions are consistent with the model including self-heating effects. The potential of our technology for further miniaturization of nanoscale superconducting quantum interference devices and for the improvement of their performance is discussed.

Quantum memory is the core device for the construction of large-scale quantum networks. For scalable and convenient practical applications, integrated optical memories, especially on-chip optical memories, are crucial requirements because they can be easily integrated with other on-chip devices. Here, we report the coherent optical memory based on a type-IV waveguide fabricated on the surface of a rare-earth ion-doped crystal (i.e., $\mathrm{E}{\mathrm{u}}^{3+}$:${\mathrm{Y}}_2\mathrm{Si}{\mathrm{O}}_5$). The properties of the optical transition (${}^7{\mathrm{F}}_0\to {}^5{\mathrm{D}}_0$) of the ${\mathrm{Eu}}^{3+}$ ions inside the surface waveguide are well preserved compared to those of the bulk crystal. Spin-wave atomic frequency comb storage is demonstrated inside the type-IV waveguide. The reliability of this device is confirmed by the high interference visibility of $97\pm 1\mathrm{\%}$ between the retrieval pulse and the reference pulse. The developed on-chip optical memory paves the way towards integrated quantum nodes.

Acoustic vortex beams have great potential for contactless particle manipulation and torque-based biomedical applications. However, focusing acoustic waves through highly aberrating layers such as the human skull at ultrasonic frequencies results in strong phase aberrations, which prevent the generation of sharp acoustic images. In the case of a wavefront containing phase dislocations, skull aberrations can inhibit the focusing of acoustic vortex beams inside the cranial cavity. In this paper, we demonstrate that phase-conjugated acoustic holograms can encode time-reversed fields, allowing compensation of the aberrations of the skull and, simultaneously, the generation of a focused vortex inside an ex vivo human skull. The method is applied to single-element geometrically focused sources and results in a very simple and compact ultrasonic system. This work will pave the way to designing low-cost particle-trapping systems, clot manipulation, and the exertion of acoustic-radiation forces and torques in the brain for biomedical applications.

The Bell basis, a set of maximally entangled biphoton states, is a critical prerequisite towards quantum information processing, and many quantum applications have highlighted the requirement for manipulation of the high-dimensional Bell basis. While Bell states can be created by using ingenious single-photon quantum gates, their implementation complexity in higher dimensions is significantly increased. Here we present an elaborate approach to show that the adaptive pump modulation enables the efficient preparation of the Bell basis in arbitrary-dimensional Hilbert space. A complete set of four-dimensional orbital angular momentum Bell states is experimentally created, yielding high fidelities for certifying the entanglement dimensionality. Our strategy can be simply generalized to prepare more complex forms of quantum states, even exploiting other physical degrees of freedom. Also, it can facilitate the use of high-dimensional entanglement in a variety of quantum protocols, in particular those requiring quantum dense coding.

Almost four decades ago, Bergman and Milton independently showed that the isotropic effective electric permittivity of a two-phase composite material with a given volume fraction is constrained to lie within lens-shaped regions in the complex plane that are bounded by two circular arcs. An implication of particular significance is a set of limits to the maximum and minimum absorption of an isotropic composite material at a given frequency. Here, after giving a short summary of the underlying theory, we show that the bound corresponding to one of the circular arcs is at least almost optimal by introducing a certain class of hierarchical laminates. In regard to the second arc, we show that a tighter bound can be derived using variational methods. This tighter bound is optimal as it corresponds to assemblages of doubly coated spheres, which can be easily approximated by more realistic microstructures. We briefly discuss the implications for related problems, including bounds on the complex polarizability.

The Talbot effect has found profound applications in a wide variety of research fields, facilitating the development of sensing, imaging, and lithography, among others. Taking advantage of the flexibilities offered by the bidimensional Talbot effect, we propose and experimentally demonstrate a 2-bit coding acoustic metasurface lens. It is capable of arranging the far-field wave-energy distribution and thus tailoring the passive amplification of wave pattern at positions away from the source. By simply adjusting two different types of embedded helicoid units and their layout in the metasurface lens to change the coding sequences, the intensity amplification factor and period of the self-image can be manipulated simultaneously within the same imaging plane. The proposed Talbot lens allows flexible far-field sound redistribution and enhancement. Along with the nonresonant nature, it may open possibilities in applications such as acoustic communication, sonography, and signal processing.

Quantum information can be protected from noise and decoherence by encoding it into a decoherence-free subspace of the full Hilbert space. In this approach, it is important to devise implementations of quantum logic gates acting on the encoded logical qubits. Here, we experimentally investigate the implementation of an entangling linear optical controlled-$Z$ gate on two logical qubits encoded into pairs of physical qubits, which protects the quantum information from collective dephasing. This decoherence-resilient two-qubit gate on logical qubits is realized using a suitable four-qubit quantum gate on the physical qubits, which may help to protect the encoded quantum information from systematic errors arising due to imperfect operations on single logical qubits. We characterize the gate operation on input superposition states and demonstrate its ability to protect quantum coherence even under complete collective dephasing.

Plasmonic nanopores are the subject of extensive investigations as a potential platform to enable efficient optical readout in translocation experiments with biomolecules such as DNA and proteins. They allow for the engineering of electromagnetic fields at the nanoscale, which are typically used to enhance the emission efficiency of fluorescent molecules. Their features make them suitable for detection strategies based on the energy transfer between translocating molecules and the nanopore itself. Here, we carry out an optical experiment to show that a handful of diffusing dyes acting as donors can exchange energy via Förster-resonance energy transfer (FRET) with a gold nanopore functionalized with dyes behaving as acceptors. The FRET pair is composed of ATTORho6G (donor) and Alexa610 (acceptor). To perform this proof-of-concept experiment, we use a gold nanopore with a diameter of 80 nm, prepared on a ${\text{Si}}_3{\text{N}}_4$ membrane. We observe that the presence of the acceptors on the walls of the nanopore reduces the lifetime of the diffusing donors. In addition, we observe that the presence of the acceptors reduces the fluorescence signal on the donor detection channel and increases the fluorescence signal on the acceptor detection channel. The combination of these three effects gives us enough evidence to claim that the diffusing donors exchange energy with the functionalized nanopore via FRET, despite the relatively large size of the nanopore. The FRET efficiency of the process is found to be of the order of $30\mathrm{\%}$, which is in fairly good agreement with a theoretical value obtained using a simplified model.

$G{e}_{1-x}{\mathrm{Sn}}_x$ quantum wells can be incorporated into $\mathrm{Si}\text{−}\mathrm{Ge}$–based structures with low-carrier effective masses, high mobilities, and the possibility of direct band-gap devices with x ∼ 0.1. However, the electrical properties of p-type $G{e}_{1-x}{\mathrm{Sn}}_x$ devices are dominated by a thermally activated mobility and metallic behavior. At 30 mK the transport measurements indicate localization with a mobility of $380{\mathrm{cm}}^2$/Vs, which is thermally activated with a temperature-independent carrier density of 4 × ${10}^{11}{\mathrm{cm}}^{-2}$. This weakly disordered system with conductivity, σ ∼ $e^2$/h, where e is the fundamental charge and h is Planck’s constant, is a result of negatively charged “Sn-vacancy” complex states in the barrier layers that act as hole traps. A measured hole effective mass of 0.090 ± $0.005m_e$ from the Shubnikov-de Haas effect, where $m_e$ is the free electron mass shows that the valence band is heavy hole dominated and is similar to p-type $\mathrm{Ge}$ with the compressive strain playing the role of quenching the spin-orbit coupling and shifting the unoccupied light-hole states to higher hole energies. The $G{e}_{1-x}{\mathrm{Sn}}_x$ devices have a high quantum mobility of approximately 36 000 ${\mathrm{cm}}^2$/Vs that is not thermally activated. The ratio of transport-to-quantum mobility of approximately 0.01 in $G{e}_{1-x}{\mathrm{Sn}}_x$ devices is unusual and points to several competing scattering mechanisms in the different experimental regimes.

We experimentally demonstrate a previously unforeseen nonlinear effect in optical fibers: up-conversion luminescence generation excited by multiphoton absorption of femtosecond infrared pulses. We directly estimate the average number of photons involved in the up-conversion process, by varying the wavelength of the pump source. We highlight the role of nonbridging oxygen hole centers and oxygen-deficient center defects and directly compare the intensity of side-scattered luminescence with numerical simulations of pulse propagation.

Quantum computation with quantum gates induced by geometric phases is regarded as a promising strategy in fault-tolerant quantum computation, owing to its robustness against operational noise. However, because of the parametric restrictions in previous schemes, the main robust advantage of holonomic quantum gates is reduced. Here, we experimentally demonstrate a solution scheme, obtaining nonadiabatic holonomic single-qubit quantum gates with optimal control in a trapped ${}^{171}{\mathrm{Yb}}^{+}$ ion based on a three-level system with resonant driving, which also has the advantages of rapid evolution and convenient implementation. Compared with previous geometric gates and conventional dynamical gates, the superiority of our scheme is that it is more robust against control amplitude errors, which is confirmed by the gate infidelity as measured by both quantum-process tomography and random benchmarking methods. In addition, we outline how nontrivial two-qubit holonomic gates can also be realized using currently available experimental technology. Thus, our experiment confirms the feasibility of this robust and fast holonomic quantum-computation strategy.

Unidirectional wave propagation in nonreciprocal structures enables exciting opportunities to control and enhance wave-matter interactions in extreme ways. Within this context, here we investigate the possibility of using terminated unidirectional plasmonic waveguides to enhance typically weak nonlinear effects by orders of magnitude. We theoretically demonstrate remarkable levels of electric field enhancement and confinement (field hot spots) when the unidirectional waveguiding structure is terminated with a suitable boundary that fully stops the one-way mode. Such a large field enhancement, originating from a nonresonant effect, is fundamentally different from the narrow-band field concentration effects in resonant plasmonic structures. Instead, it is analogous to the broadband response of plasmonic tapers, but without the need for any adiabatic impedance matching. We show that this effect can indeed lead to a substantial boosting of nonlinear light-matter interactions, exemplified by an improvement of several orders of magnitude in the third-harmonic-generation efficiency, which is of large significance for several applications. More broadly, our findings show the potential of extreme nonreciprocal configurations for enhanced wave-matter interactions.

We investigate the demonstration and quantification of the strong coupling between excitons and guided photons in a $\mathrm{Ga}\mathrm{N}$ slab waveguide. The dispersions of waveguide polaritons are measured from $T=6$ to 300 K through gratings. They are carefully analyzed within four models based on different assumptions, in order to assess the strong-coupling regime. We prove that the guided photons and excitons are strongly coupled at all investigated temperatures, with a small $(11\mathrm{\%})$ dependence on the temperature. However, the values of the Rabi splitting strongly vary among the four models: the “coupled oscillator” model overestimates the coupling; the analytical “Elliott-Tanguy” model precisely describes the dielectric susceptibility of $\mathrm{Ga}\mathrm{N}$ near the excitonic transition, leading to a Rabi splitting equal to $82\pm 10$ meV for fundamental transverse-electric mode; the experimental ellipsometry-based model leads to smaller values of $55\pm 6$ meV. We evidence that, for waveguides including active layers with large oscillator strengths, as required for room-temperature polaritonic devices, a strong bending of the modes’ dispersion is not necessarily the signature of the strong coupling, which requires for its reliable assessment a precise analysis of the material dielectric susceptibility.

The integration, scale-up, and multiplexing arrays of superconducting qubits in quantum circuits are the main challenges of superconducting quantum technology. Here we experimentally investigate the solid-state qubit multiplexing readout scheme, containing coplanar quarter-wavelength resonators coupled with a planar Xmon-type qubit, connected to a common coplanar transmission line. We find that the qubit energy spectrum is modified in the presence of an additional exciting signal at the fundamental frequency of the neighboring resonators. We attribute the origin of this effect to the electromagnetic field propagating through the common ground plane, which changes the qubit’s characteristics. Our finding may be useful for the development of scalable superconducting quantum integrated circuits with arrays of multiplexed or coupled qubits for applications in superconducting quantum processing and computing.

Exploring controllable interactions lies at the heart of quantum science. Neutral Rydberg atoms provide a versatile route toward flexible interactions between single quanta. Previous efforts mainly focused on the excitation annihilation (EA) effect of the Rydberg blockade due to its robustness against interaction fluctuation. We study another effect of the Rydberg blockade, namely transition slow-down (TSD). In TSD, a ground-Rydberg cycling in one atom slows down a Rydberg-involved state transition of a nearby atom, which is in contrast to EA that annihilates a presumed state transition. TSD can lead to an accurate controlled-not (cnot) gate with a submicrosecond duration of about $2\pi /\mathrm{\Omega }+ϵ$ by two pulses, where $ϵ$ is a negligible transient time to implement a phase change in the pulse and $\mathrm{\Omega }$ is the Rydberg Rabi frequency. The speedy and accurate TSD-based cnot gate makes neutral atoms comparable (superior) to superconducting (ion-trap) systems.

Effective quantum information processing is tantamount in part to minimization of the quantum resources needed by quantum logic gates. Here, we propose an optimization of an $n$-controlled-qubit Fredkin gate with a maximum of $2n+1$ two-qubit gates and $2n$ single-qudit gates by exploiting auxiliary Hilbert spaces. The number of logic gates required improves on earlier results on simulating arbitrary $n$-qubit Fredkin gates. In particular, the optimal result for a one-controlled-qubit Fredkin gate (which requires three qutrit-qubit partial-swap gates) breaks the theoretical nonconstructive lower bound of five two-qubit gates. Furthermore, using an additional spatial-mode degree of freedom, we design a possible architecture to implement a polarization-encoded Fredkin gate with linear optical elements.

We report a large enhancement of the spin-orbit-torque (SOT) efficiency achieved by inserting an ultrathin $\mathrm{Co}$ layer between a single-crystal $\mathrm{Pt}$ layer and an epitaxial ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ layer. We attribute this to the strong interfacial orbital hybridization between $\mathrm{Pt}$ and $\mathrm{Co}$. Another effect of this hybridization is the spin-rotation effect based on the out-of-plane component of the magnetic moment, which explains the observation of out-of-plane torques. Our results offer an effective approach to engineer the SOT in a conventional ferromagnet-heavy metal system, which might provide opportunities for spintronic application.

Mirror-symmetric acoustic metascreens producing perfect absorption independently of the incidence side are theoretically and experimentally reported in this work. The mirror-symmetric resonant building blocks of the metascreen support symmetric and antisymmetric resonances that can be tuned to be at the same frequency (degenerate resonances). The geometry of the building blocks is optimized to critically couple both the symmetric and the antisymmetric resonances at the same frequency, allowing perfect absorption of sound from both sides of the metascreen. A hybrid analytical model based on the transfer-matrix method and the modal decomposition of the exterior acoustic field is developed to analyze the scattering properties of the metascreen. The resulting geometry is three-dimensionally printed and experimentally tested in an impedance tube. The experimental results agree well with the theoretical predictions, proving the efficiency of these metascreens for the perfect absorption of sound in ventilation problems.

We present a method relying on shortcuts to adiabaticity to achieve quantum detection of high-frequency signals at the nanoscale in a robust manner. More specifically, our protocol delivers tailored amplitudes and frequencies for control fields that, firstly, enable the coupling of the sensor with high-frequency signals and, secondly, minimize errors that would otherwise spoil the detection process. To exemplify the method, we particularize to detection of signals emitted by fast-rotating nuclear spins with nitrogen-vacancy-center quantum sensors. However, our protocol is straightforwardly applicable to other quantum devices such as silicon-vacancy centers, germanium-vacancy centers, or divacancies in silicon carbide.