Optical signals carrying quantum correlations can be used to illuminate objects, enabling, in principle, quantum enhanced sensing of the object or its properties. Here, we demonstrate quantum enhanced temperature sensing of microelectronics using bright quantum optical signals. Relying on lock-in detection of thermoreflectivity, we measure the temperature change of a microwire induced by a current with an accuracy of better than ${0.04}^{\circ }$ averaged over 0.1 s. The results show a nearly 50% improvement in accuracy compared to classical light of the same power and is a demonstration of below-shot-noise thermoreflectivity sensing. With moderate improvements, quantum temperature resolution of sub mK can be achieved at optical powers just below the laser-induced heating threshold, and thus the true quantum advantage of temperature sensing is within reach. Other sensing modalities can be adopted to extend the approach to quantum imaging of heat dissipation in microelectronic and semiconductor devices.

The rapid progress of hole spin qubits in group IV semiconductors has been driven by their potential for scalability. This is due to the compatibility with industrial manufacturing standards, as well as the ease of operation and addressability via all-electric drives. However, owing to a strong spin-orbit interaction, these systems present variability and anisotropy in key qubit control parameters such as the Landé $g$-factor, requiring careful characterization for reliable qubit operation. Here, we experimentally investigate a hole double quantum dot in silicon by carrying out spin readout with gate-based reflectometry. We show that characteristic features in the reflected phase signal arising from magnetospectroscopy convey information on site-dependent $g$-factors in the two dots. Using analytical modeling, we extract the physical parameters of our system and, through numerical calculations, we extend the results to point to the prospect of conveniently extracting information about the local $g$-factors from reflectometry measurements.

In conventional solar cells, photogenerated carriers lose part of their energy before they can be extracted to make electricity. The aim of hot-carrier solar cells is to extract the carriers before this energy loss, thereby turning more energy into electrical power. This requires extracting the carriers in a nonequilibrium (nonthermal) energy distribution. Here, we investigate the performance of hot-carrier solar cells for such nonequilibrium distributions. We propose a quantum transport model in which each energy-loss process (carrier thermalization, relaxation, and recombination) is simulated by a Büttiker probe. We study charge and heat transport to analyze the hot-carrier solar cell’s power output and efficiency, introducing partial efficiencies for different loss processes and the carrier extraction. We show that producing electrical power from a nonequilibrium distribution has the potential to improve the output power and efficiency. Furthermore, in the limit where the distribution is thermal, we prove that a boxcar-shaped transmission for the carrier extraction maximizes the efficiency at any given output power.

Ferrimagnetic materials composed of rare earth (RE) and transition metals (TM) are of great interest for spintronic devices due to their tunable net moments and magnetic transport behaviors. Here we experimentally study the Dzyaloshinskii-Moriya interaction (DMI) in $\mathrm{Co}\text{−}\mathrm{Gd}$ ferrimagnets and find that the DMI strength increases substantially as the temperature approaches its moment compensation point. By subtracting the contribution of Heisenberg exchange coupled $\mathrm{Co}$-$\mathrm{Co}$ moments mediated by $\mathrm{Pt}$ from the total DMI strength, we observe a relationship $D_{\text{Co - Gd}}\sim M_s^{0.2\pm 0.06}$. The lower order indicates the weaker Heisenberg exchange compared with $\mathrm{Co}$-$\mathrm{Co}$ moments in $\mathrm{Co}\text{−}\mathrm{Gd}$ alloys. Our results reveal the intrinsic physics of DMI in RE-TM alloys by separating the different contributions of TM-TM and RE-TM sublattice moments from the total DMI and show the promising prospect for the fabrication of skyrmions in RE-TM ferrimagnets near the compensation point.

We demonstrate extreme laser-induced modification confinement in a stack of dielectric layers, along the optical axis, without the use of tight focusing. Specifically, we show that an aperiodic distribution of layer thicknesses can effectively lead to the formation of subsurface laser-induced modifications, confined in a 100-nm single predefined layer only, without affecting the surrounding material. We argue that this confinement is correlated to a local electric field enhancement phenomenon occurring within a specific layer of the stack and we confirm this hypothesis with simulations. Concurrently, we demonstrate the presence of nanocrystallites in the laser-affected areas.

Hybrid quantum classical optimization using near-term quantum technology is an emerging direction for exploring quantum advantage in high-dimensional systems. However, precise characterization of all experimental parameters is often impractical and challenging. A viable approach is to use algorithms that rely entirely on black-box inference rather than analytical gradients. Here, we combine randomized perturbation gradient estimation with adaptive momentum gradient updates and propose AdamSPSA and AdamRSGF algorithms. We prove the asymptotic convergence of the proposed algorithms in a convex setting and benchmark them against other gradient-based black-box optimization algorithms on nonconvex quantum optimal control tasks. Our results indicate that these algorithms accelerate the optimization rate, lower the optimization loss, and efficiently tune up high-fidelity Hann-window single-qubit gates from trivial initial conditions with up to 80 variables for a transmon qubit.

This paper presents an end-to-end design method for the synthesis of dielectric metasurfaces with modulated thickness that are able to realize desired radiation patterns in the far field with high precision. The method relies on integral equations and the method of moments to calculate the induced surface and volumetric current densities throughout the metasurface upon a given incident illumination. By avoiding homogenization of the dielectric layer and calculating directly the scattered fields through the method of moments, the near-field and far-field response of the metasurface can be accurately predicted and optimized. In particular, a design example of a modulated dielectric metasurface, fed by a single embedded line source, is presented for the realization of a Chebyshev array pattern with $-20$-$\mathrm{dB}$ sidelobe level. Moreover, an externally fed dielectric metasurface performing beam splitting of a normally incident plane wave is designed, three-dimensionally printed and measured, showing two reflected beams at $\pm {30}^{\circ }$, high suppression of specular reflections ($>14\mathrm{dB}$), and satisfactory agreement with the simulated and desired radiation patterns. The proposed design method for beamforming with dielectric metasurfaces can find application in higher frequencies where the use of copper may be problematic due to higher Ohmic losses and fabrication challenges.

In recent years, high-resolution additive manufacturing has enabled a diverse range of low-cost methods for ultrasonic wave-front shaping. Acoustic holograms, in particular, allow for the generation of arbitrary diffraction-limited acoustic fields at megahertz frequencies from single-element transducers. These are phase plates that function as direct acoustic analogs to thin optical holograms. In this work, it is shown that, by using multiple polymer three-dimensional (3D) printing, two-material (binary) acoustic analogs to “thick” or volume optical holograms can also be generated. First, an analytic approach for designing a volume hologram that diffracts a set of input fields onto a desired set of output fields is briefly summarized. Next, a greedy-optimization approach based on random downhill binary search able to account for the constraints imposed by the chosen fabrication method is introduced. Finally, an experimental test case designed to diffract the field generated by a 2.54-cm planar lead zirconate titanate (PZT) transducer onto eight distinct patterns dependent on the direction of the incident field is used to validate the approach and the design method. Field scans of the eight target fields demonstrate that acoustic analogs of optical volume holograms can be generated using multipolymer printing and that these allow the multiplexing of distinct fields onto different incident field directions.

Single-flux-quantum (SFQ) digital circuitry has great potential in building a scalable control system of superconducting qubits. In this work, we describe a practical SFQ-based two-qubit gate for transmon qubits. The controlled-$Z$ (CZ) gate is activated by near-resonant SFQ-pulse trains near the target transition involving the second excited state. Numerical simulations show that the fidelity of a SFQ-activated CZ gate in excess of 99.9% is achievable within 100-ns gate time. We evaluate the CZ gate error caused by leakage and SFQ-pulse width. Combined with the proposed feasible expansion methods, this work is a supplement to the scalable and integratable superconducting-qubit control system based on SFQ digital logic.

We present an experimental “pattern-distortion” (PD) technique which connects the shape of a liquid lens to its magnification. We demonstrate how to optimize the technique for arbitrary droplet sizes and optical configurations, and demonstrate its widespread utility in three distinct situations. Firstly, we consider multiple sessile droplets. Although ubiquitous in nature, understanding of their complex interactions is limited, partly due to experimental limitations in determining individual droplet volumes for arbitrary configurations. We use the PD technique to overcome these limitations, and we find excellent agreement between our experimental data and three recent theoretical models. Secondly, we show how our technique can be used to inform the design of liquid lenses. Thirdly, we extend the method to composite droplets systems, using it to extract the size of an air bubble trapped inside a liquid droplet.

Erbium-doped solids are prime candidates for quantum memories in optical quantum networks given their telecom-compatible photon emission. An electron spin of erbium with millisecond coherence time is desirable for generating remote entanglement between adjacent quantum network nodes. Here we report GHz-range electron-spin transitions of ${}^{167}{\mathrm{Er}}^{3+}$ in a yttrium oxide (${\mathrm{Y}}_2{\mathrm{O}}_3$) matrix with coherence times that are consistently longer than a millisecond. By polarizing paramagnetic impurity spins we achieve a spin $T_2$ up to 1.46 ms, and up to 7.1 ms after dynamical decoupling. These coherence lifetimes are among the longest found for erbium in crystalline matrices despite the presence of host nuclear spins. We further enhance the coherence time beyond conventional dynamical decoupling, using customized sequences to simultaneously mitigate spectral diffusion and dipolar interactions. Our study not only establishes ${}^{167}{\mathrm{Er}}^{3+}$: ${\mathrm{Y}}_2{\mathrm{O}}_3$ as a significant quantum memory platform but also provides a guideline for engineering long-lived erbium spins in a variety of host materials for quantum technologies.

A fiber-optic molecular dispersion spectrometer using code-division multiplexing to make simultaneous phase measurements of a hydrogen cyanide (${\mathrm{H}}^{13}{\mathrm{C}}^{14}\mathrm{N}$) $2{\nu }_3$-band P10 rovibrational transition at multiple optical frequencies is demonstrated. A second-derivative anomalous dispersion response is digitally synthesized from sets of these concurrent measurements. The synthesized measurement demonstrates 3 orders of magnitude noise suppression relative to individual measurements, has intrinsic wavelength tuning linearization, and a spectroscopic detection limit of $146\mathrm{ppb}\mathrm{m}/\sqrt{\mathrm{Hz}}$.

The coexistence of quantum and classical signals over the same optical fiber with minimal degradation of the transmitted quantum information is critical for operating large-scale quantum networks over the existing communications infrastructure. Here, we systematically characterize the quantum channel that results from simultaneously distributing approximate single-photon polarization-encoded qubits and classical light of varying intensities through fiber-optic channels of up to 15 km. Using spectrally resolved quantum process tomography with a Bayesian reconstruction method that we develop, we estimate the full quantum channel from experimental photon counting data, both with and without classical background. Furthermore, although we find the exact channel description to be a weak function of the pump polarization, we nevertheless show that the coexistent fiber-based quantum channel has high process fidelity with an ideal depolarizing channel when the noise is dominated by Raman scattering. These results provide a basis for the future development of quantum repeater designs and quantum error-correcting codes for real-world channels and inform models used in the analysis and simulation of quantum networks.

The traditional Fourier single-pixel imaging (FSI) utilizes cosinusoidal (grayscale) illumination patterns to reconstruct the image of an object. In this paper, we propose a universal mechanism in which FSI can be implemented via arbitrary periodic structured illumination not merely cosinusoidal illumination patterns. The proposed theory is verified by numerical simulations and optical experiments. In the experiment, we demonstrate the result of FSI with phase-shifting sawtooth (trapezoid, square) structured illumination modulated by a light projector. Moreover, in order to underline the high efficiency of the proposed mechanism, we perform FSI utilizing binary (square) illumination patterns generated directly by the digital micromirror devices (DMDs). Therefore, this mechanism can promote the high-performance and extensive applications of FSI in various scenarios.

Asymmetric superconducting tunnel junctions with gaps ${\mathrm{\Delta }}_1>{\mathrm{\Delta }}_2$ have been proven to show a peculiar nonlinear bipolar thermoelectric effect. This arises due to the spontaneous breaking of electron-hole symmetry in the system, and it is maximized at the matching-peak bias $|V|=V_p=({\mathrm{\Delta }}_1-{\mathrm{\Delta }}_2)/e$. In this paper, we investigate the interplay of photon-assisted tunneling (PAT) and bipolar thermoelectric generation. In particular, we show how thermoelectricity, at the matching peak, is supported by photon absorption and emission processes at the frequency-shifted sidebands $V=\pm V_p+n\hslash \omega$, $n\in \mathbb{Z}$. This represents a sort of microwave-assisted thermoelectricity. We show the existence of multiple stable solutions, being associated with different photon sidebands, when a load is connected to the junction. Finally, we discuss how the nonlinear cooling effects are modified by the PAT. The proposed device can detect millimeter-wavelength signals by converting a temperature gradient into a thermoelectric current or voltage.

Information reconciliation significantly impacts the performance of the practical continuous-variable quantum key distribution (CV QKD) system. Fixed-rate error-correction codes limit the potential applications of the CV QKD because they lead to reduced reconciliation efficiency when the signal-to-noise ratio of the quantum channel changes, further deteriorating the system’s performance. Therefore, we propose a rate-adaptive polar-coding-based reconciliation scheme for practical CV QKD systems with the time-variant quantum channel. Experimental results verify that the proposed scheme can successfully extract secret keys within the range of signal-to-noise ratios from $-0.5$ to $-4.5$ dB, and the minimum frame-error rate can be less than ${10}^{-3}$. Moreover, the proposed scheme can promote the application of the CV QKD system in a realistic environment.

Measurement-device-independent quantum key distribution (MDI QKD) is a promising method for remote key sharing that can eliminate all detector side-channel attacks. However, current security proofs often overlook the potential information leakages from the legitimate users’ devices. In a quantum version of Trojan-horse attack (THA), a malicious eavesdropper can inject bright light into the sources of a MDI QKD system and then analyze the back-reflected light to obtain their setting choices, thereby compromising the final security. Here, we derive the finite-key security bounds of decoy-state MDI QKD in the presence of THA, which significantly outperform previous analyses in terms of the secret-key rate and transmission distance. Specifically, we analyze a symmetric three-intensity decoy-state MDI QKD protocol and an efficient four-intensity decoy-state MDI QKD protocol. Our results represent a fundamental step in guaranteeing the implementation security of quantum communication systems.