We present a quantitative microscopic analysis of the formation of exciton-polaritons, the composite particles possessing light and material components, polariton-polariton interactions, and resonant pumping dynamics in cylindrical semiconductor micropillars. We obtain that, due to the exciton-exciton interaction, the polaritonic states’ populations become redistributed among pumped and pristine states. We discuss how the redistribution effect can be used in devices generating photons with nonzero orbital angular momenta.

We propose a nontrivial two-qubit gate scheme in which Rydberg atoms are subject to designed pulses resulting from geometric evolution processes. By utilizing hybrid robust nonadiabatic and adiabatic geometric operations on the control atom and target atom, respectively, we improve the robustness of the two-qubit Rydberg gate against Rabi control errors as well as blockade errors in comparison with the conventional two-qubit blockade gate. Numerical results with the current state-of-the-art experimental parameters corroborates the above mentioned robustness. We also evaluate the influence induced by the motion-induced dephasing and the dipole-dipole interaction and imperfection-excitation-induced leakage errors, which both could decrease the gate fidelity. Our scheme provides a promising route towards systematic control error (Rabi error) as well as blockade-error-resilient geometric quantum computation on neutral atom system.

Further research on organic molecule crystals with spontaneous polarization as a possible candidate for the bulk photovoltaic effect is urgently needed to meet the requirements for optoelectric devices. We demonstrate the shift current in a type of molecular crystal that acts at high temperatures and contains organic molecules with electron donor-acceptor groups, such as paranitroaniline derivatives. We find an extremely strong multicomponent shift-current response along the parallel and perpendicular to polar molecules of the crystals using density-functional simulations, which is more than 10 times larger than the previously reported value for shift current over a broad spectral range from visible to ultraviolet spectrum. Even more intriguing, the remarkable dependency of the conduction- and valence-band dispersions on the lattice constant along polarization allows the shift current in these organic molecule structures to be tuned under stress and doping. Our findings not only suggest a class of organic compounds for realizing the highly controllable shift-current response, but also open up a channel for the search for solar materials.

The squeeze-film-damping effect is one of the main limits in many precision experiments, especially in the study of short-range interactions, and its physical mechanism is still not very clear. We develop a torsion pendulum to measure the damping effects caused by the thermal motion of residual gas between a cubic test mass and a pair of symmetric movable plates. The measured results are consistent with the model that synthesized the elastic and inelastic collisions by introducing a thermal accommodation coefficient (TAC). In our research, the pressure dependence of the TAC, which can be expressed as an exponential decay function, is also observed. This dependence may imply that the elastic collisions correspond to the simple bouncing of residual gas molecules, while the inelastic collisions correspond to the adsorption and desorption cycle of gas molecules on the surface. The method in this work and the discovered TAC pressure dependence are instructive for the analysis of residual-gas effects in weak-force measurements, as well as the deviation correction of rarefied gas pressure measurements based on the squeeze-film-damping effect.

Photophoretic levitation is a propulsion mechanism by which lightweight objects can be lifted and controlled through their interactions with light. Since photophoretic forces on macroscopic objects are usually maximized at low pressures, they may be tested in a vacuum chamber in close proximity to the chamber floor and walls. We report experimental evidence that the terrain under levitating microflyers, including the chamber floor or the launchpad from which the microflyer lifts off, can greatly increase the photophoretic lift forces relative to their free-space (midair) values. To characterize this so-called “ground effect” during vacuum-chamber tests, we introduce a miniature launchpad composed of three J-shaped (candy-cane-like) wires that minimize the microflyer’s extraneous interactions with the underlying surfaces. We compare our J-shaped-wire launchpad with previously used wire-mesh launchpads for simple levitating Mylar-based disks with diameters of 2, 4, and 8 cm. Importantly, we discover that wire-mesh launchpads increase the photophoretic lift force by up to sixfold. A significant ground effect is also associated with the bottom of the vacuum chamber, particularly when the distance to the bottom surface is less than the diameter of the levitating disk. We provide guidelines to minimize the ground effect in vacuum-chamber experiments, which are necessary to test photophoretic microflyers intended for high-altitude exploration and surveillance on Earth or on Mars.

The ability to perform fast, high-fidelity entangling gates is a requirement for a viable quantum processor. In practice, achieving fast gates often comes with the penalty of strong-drive effects that are not captured by the rotating-wave approximation. These effects can be analyzed in simulations of the gate protocol, but those are computationally costly and often hide the physics at play. Here, we show how to efficiently extract gate parameters by directly solving a Floquet eigenproblem using exact numerics and a perturbative analytical approach. As an example application of this toolkit, we study the space of parametric gates generated between two fixed-frequency transmon qubits connected by a parametrically driven coupler. Our analytical treatment, based on time-dependent Schrieffer-Wolff perturbation theory, yields closed-form expressions for gate frequencies and spurious interactions, and is valid for strong drives. From these calculations, we identify optimal regimes of operation for different types of gates including $i$swap, controlled-Z, and cnot. These analytical results are supplemented by numerical Floquet computations from which we directly extract drive-dependent gate parameters. This approach has a considerable computational advantage over full simulations of time evolutions. More generally, our combined analytical and numerical strategy allows us to characterize two-qubit gates involving parametrically driven interactions, and can be applied to gate optimization and cross-talk mitigation such as the cancelation of unwanted $ZZ$ interactions in multiqubit architectures.

Carrier thermalization in a superlattice solar cell made of polar semiconductors is studied theoretically by considering a minimal model where electron-phonon scattering is the principal channel of carrier energy loss. Of note, the effect of an intrinsic quantum mechanical property, the phonon coherence, on carrier thermalization is investigated, within a semiclassical picture in terms of phonon wave packet. It turns out that coherent longitudinal optical (LO) phonons weaken the effective electron-phonon coupling, thus supposedly lowering the carrier-energy-loss rate in the solar cell. The resulting thermalization power is indeed significantly reduced by the coherent phonons, resulting in an enhanced hot-carrier effect, particularly for thin enough well layer where carrier confinement is also strong. A recent experiment on a superlattice solar-cell prototype is shown to manifest the coherent phonon-driven phenomenon. Our results demonstrate the practical implications of the fundamental quantum coherence property of phonons in semiconductors for improving superlattice solar-cell performance, via hot-carrier effect.

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.