Applications for noisy intermediate-scale quantum computing devices rely on the efficient entanglement of many qubits to reach a potential quantum advantage. Although entanglement is typically generated using two-qubit gates, direct control of strong multiqubit interactions can improve the efficiency of the process. Here, we investigate a system of three superconducting transmon-type qubits coupled via a single flux-tunable coupler. Tuning the frequency of the coupler by adiabatic flux pulses enables us to control the conditional energy shifts between the qubits and directly realize multiqubit interactions. To accurately adjust the resulting controlled relative phases, we describe a gate protocol involving refocusing pulses and adjustable interaction times. This enables the implementation of the full family of pairwise controlled-phase and controlled-controlled-phase gates. Numerical simulations result in fidelities around 99% and gate times below 300 ns using currently achievable system parameters and decoherence rates.

The maximal speed $v^{\ast }$ for magnetic flux quanta is determined by the energy relaxation of unpaired electrons and is thus essential for superconducting microstrip single-photon detectors (SMSPDs). However, the deduction of $v^{\ast }$ from the current-voltage ($I$-$V$) curves at zero magnetic field is hindered by the unknown number of vortices, $n_v$, as a small number of fast-moving vortices can induce the same voltage as a large number of slow-moving ones. Here, we introduce an approach for the quantitative determination of $n_v$ and $v^{\ast }$. The idea is based on the Aslamazov and Larkin prediction of kinks in the $I$-$V$ curves of wide and short superconducting constrictions when the number of fluxons crossing the constriction is increased by one. We realize such conditions in wide $\mathrm{Mo}\mathrm{Si}$ thin strips with slits milled by a focused ion beam and reveal quantum effects in a macroscopic system. By observing kinks in the $I$-$V$ curves with increase of the transport current, we evidence a crossover from a single- to multifluxon dynamics and deduce $v^{\ast }\simeq 12$ km/s. Our experimental observations are augmented with numerical modeling results, which reveal a transition from a vortex chain over a vortex jet to a vortex river with increase of $n_v$ and $v$. Our findings are essential for the development of one-dimensional and two-dimensional few-fluxon devices and provide a demanded approach for the deduction of maximal vortex velocities at the SMSPD operation conditions.

We study the feedback coupling of thermoacoustic combustion instability from the viewpoint of a complex-systems approach, including the early detection of combustion instability. An upwardly traveling large-scale transverse vortex motion gives rise to large heat release rate fluctuations in the shear layer region between the inner and outer recirculation flows. The directional coupling from flow velocity to heat release rate fluctuations clearly appears near the rolled-up flame front generated by the developed transverse vortical structure. These events are strongly associated with the formation of a strong and local thermoacoustic power source cluster during combustion instability. A methodology combining symbolic dynamics-based analysis and a convolutional neural network enables the detection of a precursor of combustion instability.

Vertical static induction transistors (SITs), with vertically arranged source, porous gate, and drain electrodes, were proposed in 1950s and have recently gained new attention because of their suitability as flexible substrates and for hybrid integration with light-emitting diodes. However, the understanding of them is hindered by Schottky gate leakage and relies on case-by-case simulations. Here, we derive concise expressions for the channel potential and current-voltage characteristics for ideal SITs, including the subthreshold swing, threshold voltage, and above-threshold region. The theory is verified by two-dimensional device simulation and agrees well with the reported experimental results. An ideal SIT can be approximated as a partially gated transistor in parallel with a resistance and needs a sub-500-nm pore diameter to exhibit sharp switching in transfer scanning and good saturation in output scanning. The proposed theories connect the device structure and electrical characteristics of SITs concisely, and conclusions are also applicable to permeable base transistors.

The boundary-cancellation theorem for open systems extends the standard quantum adiabatic theorem: assuming the gap of the Liouvillian does not vanish, the distance between a state prepared by a boundary-cancelling adiabatic protocol and the steady state of the system shrinks as a power of the number of vanishing time derivatives of the Hamiltonian at the end of the preparation. Here we generalize the boundary-cancellation theorem so that it applies also to the case where the Liouvillian gap vanishes, and consider the effect of dynamical freezing of the evolution. We experimentally test the predictions of the boundary-cancellation theorem using quantum annealing hardware, and find qualitative agreement with the predicted error suppression despite using annealing schedules that only approximate the required smooth schedules. Performance is further improved by using quantum annealing correction, and we demonstrate that the boundary-cancellation protocol is significantly more robust to parameter variations than protocols that employ pausing to enhance the probability of finding the ground state.

Optical control of functional properties in ferroic materials is now a highly appealing topic because it may entail different paradigms for future technologies. In ferroelectrics, in particular, controlling the properties with light implies noncontact external control of the material’s functionality, thereby opening a pathway for developing the next generation of photocontrolled devices. Recently, experimental observations have demonstrated that the dielectric permittivity of charged-domain-wall ferroelectrics can be easily modulated by visible light. However, because of the wide band gap of ferroelectric materials, the physical origin of this phenomenon is still controversial. Here, the photoinduced electronic reconstruction mechanism is proposed as the primary light-absorption mechanism in charged domain walls, allowing an understanding of the origin of the visible-light control of dielectric permittivity in ferroelectric materials.

Magnetic-free optomechanically induced nonreciprocity may stimulate a wide range of practical applications in quantum technologies. However, how to suppress the thermal-noise flow from the mechanical reservoir is still a difficulty encountered in achieving optomechanically nonreciprocal effects on a few- and even single-photon level. Here, we show how to realize thermal-noise cancellation by quantum interference for optomechanically induced nonreciprocity in a whispering-gallery-mode (WGM) microresonator. We find that both nonreciprocal transmission and amplification can be achieved in the WGM microresonator when coupled to two coupled mechanical resonators. More interestingly, the thermal noise can be suppressed when the two coupled mechanical resonators couple to a common thermal reservoir. The thermal-noise cancellation is induced by the destructive quantum interference between the two flow paths of the thermal noises from the common reservoir. The scheme of quantum-interference-induced thermal-noise cancellation can be applied in both sideband-resolved and unresolved regimes, even with strong backscattering taken into account. Our work provides an effective way to achieve nonreciprocal effects on a few- or single-photon level without precooling the mechanical mode to the ground state.

A set of ${\mathrm{Pr}}^{3+}$-doped ${\mathrm{KLuS}}_2$ samples with different $\mathrm{Pr}$ concentrations are synthesized in the form of transparent crystalline hexagonal platelets by chemical reaction under a flow of hydrogen sulfide. Their structural, optical, and scintillation properties are investigated thoroughly by means of x-ray powder diffraction, time-resolved luminescence spectroscopy, scintillation light yield, and decay measurements to assess the spectroscopic properties of ${\mathrm{Pr}}^{3+}$ ions in the ${\mathrm{KLuS}}_2$ host. Charge-trapping processes are further investigated by electron paramagnetic resonance. The fundamental absorption band edge of the ${\mathrm{KLuS}}_2$ host is located at 303 nm, the absorption due to the ${\mathrm{Pr}}^{3+}$ 4f → 5d transition is found at 347 nm, the emission maximum is given by the $4f^{1}5d1$ → ${}^3{H}_4$ transition of the ${\mathrm{Pr}}^{3+}$ ion at 380 nm, and the leading photoluminescence and scintillation decay time is around 1 ns at room temperature. The moderate scintillation light yield reaches 7200 ph/MeV. A phenomenological model is fitted to the measured temperature dependences of the photoluminescence emission spectra and photoluminescence decay times to better understand the dynamics of the 5d excited state of the ${\mathrm{Pr}}^{3+}$ center in the ${\mathrm{KLuS}}_2$ host. The number of photons emitted in the first nanosecond of the scintillation response is evaluated and found to be considerably higher (1.6–2.5 times) than that in the commercial $(\mathrm{Lu};\mathrm{Y}{)}_2({\mathrm{SiO}}_4)\mathrm{O}$:$\mathrm{Ce},\mathrm{Ca}$ scintillator, which shows the potential of $\mathrm{Pr}$-doped ${\mathrm{KLuS}}_2$ for fast-timing scintillator applications.

With the development of alternative computing schemes working at cryogenic temperatures, superconducting memory elements have gained interest. In this context, superconducting quantum interference devices (SQUIDs) are promising candidates, as they may trap different discrete amounts of magnetic flux. We demonstrate that a field-assisted writing scheme allows such a device to operate as a multilevel memory by the readout of eight distinct vorticity states at zero magnetic field. We present an alternative mechanism based on single phase slips, which allows the vorticity state to be switched while preserving superconductivity. This mechanism provides a possibly deterministic channel for flux control in SQUID-based memories, under the condition that the field-dependent energy of different vorticity states are nearby.

In non-line-of-sight (NLOS) imaging, the spatial information of hidden targets is reconstructed from the time-of-light (TOF) of the multiple bounced signal photons. The need for NLOS imagers to perform extensive scanning in the transverse spatial dimensions constrains the imaging speed and reconstruction quality while limiting their applications on static scenes. Utilizing a photon TOF histogram with picosecond temporal resolution, we develop compressive non-line-of-sight imaging enabled by deep learning. Two-dimensional images ($32\times 32$ pixels) of the NLOS targets can be reconstructed with superior reconstruction quality via a convolutional neural network (CNN), using significantly downscaled data ($8\times 8$ scanning points) at a downsampling ratio of $6.25\mathrm{\%}$ compared to the traditional methods. The CNN is end-to-end trained purely using simulated data but robust for image reconstruction with experiment data. Our results suggest that deep learning is effective for reducing the scanning points and total capture time towards scanningless NLOS imaging and videography.

Physical quantum systems are commonly composed of more than two levels and offer the capacity to encode information in higher-dimensional spaces beyond the qubit, starting with the three-level qutrit. Here, we encode neutral-atom qutrits in an ensemble of ultracold ${}^{87}\mathrm{Rb}$ and demonstrate arbitrary single-qutrit SU(3) gates. We generate a full set of gates using only two resonant microwave tones, including synthesizing a gate that effects a direct coupling between the two disconnected levels in the three-level $\mathrm{\Lambda }$-scheme. Using two different gate sets, we implement and characterize the Walsh-Hadamard Fourier transform, and find similar final-state fidelity and purity from both approaches. This work establishes the ultracold neutral-atom qutrit as a promising platform for qutrit-based quantum information processing, extensions to $d$-dimensional qudits, and explorations in multilevel quantum state manipulations with nontrivial geometric phases.

Compensated ferrimagnets (FIMs) made of rare-earth transition-metal compounds have stimulated increasing interest for enabling fast spin dynamics. Taking $\mathrm{Fe}$-$\mathrm{Tb}$ compounds as an example, substantial efforts have been made on the study of compensated magnetism and its potential spintronic applications. Current-induced spin-orbit torque (SOT) switching and its evolution with compensated ferrimagnetism in these compounds, however, remain to be systematically explored, which motivates the present study. By combining magnetometry and anomalous Hall effect measurements, a compositional magnetization compensation point ($x_c$ = 0.25) is determined for ${\mathrm{Fe}}_{1-x}{\mathrm{Tb}}_x$ films of a fixed thickness of 6.5 nm. The antiferromagnetic coupling between $\mathrm{Fe}$ and $\mathrm{Tb}$ sublattices is directly revealed by conducting element-specific x-ray magnetic circular dichroism measurements. The evolution of SOT switching as a function of $\mathrm{Tb}$ concentration (x) in $\mathrm{Pt}/{\mathrm{Fe}}_{1-x}{\mathrm{Tb}}_x/\mathrm{Ta}$ multilayers is subsequently investigated. An enhanced SOT efficiency (approximately 3 times) is obtained at $x_c$ = 0.25. By conducting an endurance test, reliable SOT switching is revealed for over ${10}^4$ cycles. Our work suggests that compensated FIMs of composition ${\mathrm{Fe}}_{1-x}{\mathrm{Tb}}_x$ could be implemented for realizing efficient and stable spin-orbitronic performances.

The nonlinear coupling between on-chip confined optical modes and free-space continuum modes is investigated. The radiation of second-harmonic wave due to the pump fields in integrated lithium niobate microcavities is experimentally observed. The mechanism of nonlinear optical radiation (NOR) is further verified by demonstrating the reversal process of NOR, i.e., the difference frequency generation between a free-space input and an on-chip pump field. The revealed mechanism of NOR is universal for all dielectric photonic integrated devices, which indicates unavoidable extra energy leakage channels of optical micro- and nanostructures, and also enables an alternative approach for spatial engineering of optical fields and light sources. For example, benefited from the phase-matching-free nature of NOR, an integrated atomic gas sensor for the absorption spectroscopy of Rb atoms is built.

Photons experience mirror asymmetry of macroscopic chiral media, as in circular dichroism and polarization rotation, since left- and right-handed circular polarizations differently couple with matter handedness. Conversely, free relativistic electrons with vanishing orbital angular momentum have no handedness so the question arises whether they can sense chirality of geometrically symmetric macroscopic samples. In this paper, we show that matter chirality breaks mirror symmetry of the scattered electrons’ quantum decoherence, even when the incident electron wave function and the sample shape have a common reflection symmetry plane. This is physically possible since the wave-function transverse smearing triggers electron sensitivity to the spatial asymmetry of the electromagnetic interaction with the sample, as results from our nonperturbative analysis of the scattered electron reduced density matrix, in the framework of macroscopic quantum electrodynamics. Furthermore, we prove that mirror asymmetry also shows up in the distribution of the electron lateral momentum, orthogonal to the geometric symmetry plane, whose nonvanishing mean value reveals that the electron experiences a lateral mechanical interaction entirely produced by matter chirality.

A half-mirror that divides a spin-polarized electron into two parallel copropagating spin-resolved quantum Hall edge channels one half each is presented in this study. The partition process is coherent, as confirmed by observing the Aharonov-Bohm oscillation at high visibility of up to 85% in a Mach-Zehnder interferometer, which comprises two such half-mirrors. The coherence length of the interferometer exceeds $200\text{μ}\mathrm{m}$, which reflects the robust nature of the copropagating channels against the decoherence caused by the coupling to the environment. In addition, the device characteristics are highly stable, making the device promising in the application of quantum information processing. The beam-splitting process is theoretically modeled, and the numerical simulation successfully reproduces the experimental observation. The partition of the electron accompanied by the spin rotation is explained by the angular momentum transfer from the orbital to the spin via spin-orbit interactions.

Wavefronts modulated by a discrete-phase-sampling lens, such as a spatial light modulator or a digital micromirror device, can be brought into focus after propagating through a random medium. Such techniques are a cornerstone for wave manipulations in multiple scattering environments. In this work, we examine prevailing focusing protocols, including matched filtering and inverse filtering, from the perspective of focus quality, which is defined as the contrast between the energy delivered to the focal peak and the total transmitted energy. Our results show that conventional protocols have limitations in achieving the best focus quality. Based on these analyses, we present an improved wavefront-shaping protocol that directly prioritizes focus quality. The influence of phase sampling resolutions is also analyzed in conjunction with these focusing protocols. Our results can merit the future design and implementation of intelligent lenses, which may potentially benefit various disciplines such as energy delivery, imaging, and communication.

The unique material property of silicon carbide ($\mathrm{Si}\mathrm{C}$) and the recent demonstration of low-loss $\mathrm{Si}\mathrm{C}$-on-insulator integrated photonics platform have attracted considerable research interests for chip-scale photonic and quantum applications. Despite the impressive progresses made in $\mathrm{Si}\mathrm{C}$ photonics, some of its beneficial photonic properties are yet to be fully explored. Here, we carry out a thorough investigation of the Kerr nonlinearity among $4H$-$\mathrm{Si}\mathrm{C}$ wafers from several major wafer manufacturers, and reveal that their Kerr nonlinear refractive index can be significantly different. By eliminating various measurement uncertainties in the four-wave mixing experiment, the best Kerr nonlinear refractive index of $4H$-$\mathrm{Si}\mathrm{C}$ wafers is estimated to be approximately 4 times, instead of the prior estimate of 2 to 3 times, of that of stoichiometric silicon nitride in the telecommunication band. In addition, experimental evidence is developed that the Kerr nonlinearity in $4H$-$\mathrm{Si}\mathrm{C}$ wafers can be stronger along the $c$ axis than that in the orthogonal direction. Our examination of the Kerr nonlinear refractive index also compels a useful correction to the existing model in high-index-contrast waveguides; otherwise, considerable errors can be introduced.