In the intermediate magnetic field regime, the photon-atom interaction is strongly modified, which can be used to open forbidden transition channels. Using the master equation, we have modeled the cesium $D_2$ optical pumping under different magnetic fields, light intensities, and interaction times. Experimentally, a vacuum cesium atomic beam was employed, and the results show good agreement with the theoretical calculations. Transitions that were originally accessible only via the $|F=3⟩\to |F^{\prime }=3⟩$ and $|F=3⟩\to |F^{\prime }=4⟩$ channels can now be pumped through $|F=3⟩\to |F^{\prime }=2⟩$ and $|F=3⟩\to |F^{\prime }=5⟩$ as well. Based on this effect, we have realized a magneto-optically pumped cesium-beam atomic clock achieving a short-term stability of $1.9\times {10}^{-12}{\tau }^{-1/2}$. This is approximately twice as good as that obtained without optical pumping, using monochromatic light resonant with the $|F=3⟩\to |F^{\prime }=2⟩$ transition employed for both optical pumping and detection. Moreover, this effect is generally applicable to a wide range of systems involving laser cooling and quantum state preparation.

We demonstrate a practical countermeasure against a well-known class of attacks on quantum key distribution (QKD) systems that exploit detection-efficiency mismatch, where the receiver’s detectors do not exhibit identical responses to incoming photons across all degrees of freedom. This class of quantum hacking strategies is broad and significantly includes the time-shift attack, which targets an arrival-time-dependent side-channel at the receiver. The four-state countermeasure, previously only proven to be secure in theory, is implemented here on a gigahertz-clocked prototype QKD system and evaluated for its security and performance. We show that its presence enables almost complete recovery of the system’s ideal secret key rate. Our results provide strong justification for adopting this countermeasure as a standard component in future scalable and practical QKD systems.

The rotational Doppler effect (RDE), where the frequency shift is proportional to both the orbital angular momentum $\ell$ of light and the rotational speed of the object ($\mathrm{\Delta }f\propto \ell \mathrm{\Omega }$), has proven to be a powerful tool for rotational speed sensing and measurement. However, the current detection technique is mainly based on coherent laser sources. There is scarce mention of using partially coherent light sources, let alone sunlight. We found that under conditions of limited spatial coherence and low light—where background noise exceeds the signal—superimposing multiwavelength rotational Doppler signals significantly boosts both signal strength and signal-to-noise ratio, enabling precise measurement of the object’s rotational speed. Our research not only furnishes a framework for exploring how light spatial coherence affects the RDE but also validates sunlight-enabled RDE detection experimentally, highlighting its potential for passive remote sensing.

Recent studies using terahertz time-domain spectroscopy (THz TDS) with spintronic emitters as a source have revealed distinct signatures of the Rashba effect. This effect, which arises from the breaking of inversion symmetry in low-dimensional materials, has been recently investigated in $\mathrm{Co}\mathrm{Fe}\mathrm{B}/{\mathrm{Pt}\mathrm{Se}}_2/{\mathrm{Mo}\mathrm{Se}}_2/{\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$-based heterostructures [Massabeau et al., Inverse Rashba Edelstein THz emission modulation induced by ferroelectricity in $\mathrm{Co}\mathrm{Fe}\mathrm{B}/{\mathrm{Pt}\mathrm{Se}}_2/{\mathrm{Mo}\mathrm{Se}}_2//{\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$ systems, APL Mater. 13, 041102 (2025)]. The observed phenomena are at the source of the generated THz far-field emission, typically through mechanisms such as spin-to-charge conversion triggered by the absorption of ultrafast optical pulses. In this work, we employ first-principles simulations to quantify the Rashba effect at ${\mathrm{Pt}\mathrm{Se}}_2/{\mathrm{Mo}\mathrm{Se}}_2/{\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$ interfaces, expanding the traditional understanding of spin transport by incorporating the orbital degree of freedom. Moreover, we quantify the degree of control on the THz emission depending on the polarization direction of ${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$. In order to achieve this, we analyze the accumulation of both spin and orbital components using linear response theory, revealing distinct behaviors. These findings are crucial for a deeper understanding of the physical processes governing angular momentum-to-charge conversion and THz emission. Moreover, they may provide broader insights into various experimental outcomes, including those related to spin-orbit torque.

The ability to precisely control the localization of individual cells or other microscopic biological particles in aqueous suspension inside a microfluidic confinement is essential for the realization of future tools for single-cell studies in basic biology and medicine. We previously demonstrated that thermoacoustic streaming stemming from interactions of an acoustic field with a thermal gradient induced by focused light can produce fast, confined, and modular local flow fields. In this work, we study the buildup and decay of thermoacoustic streaming generated by a focused laser directed into an acoustic half-wavelength standing wave. For a pre-established sound field, we observe the timescale for buildup and decay of the thermoacoustic streaming upon activating the laser, and vice versa. For the system investigated, we find that while the buildup of thermoacoustic streaming takes only 2 ms for sound field-controlled thermoacoustic onset, laser-irradiation-controlled onset is ten times slower. This is explained by the relatively slow thermal diffusion in the system compared to the fast buildup of the acoustic resonance. Furthermore, we demonstrate how the combination of fast timing control by the sound field and the subsound-wavelength spatial control offered by the confined temperature gradient makes it possible to move a single particle a distance of $100\text{μ}\mathrm{m}$ at $350\text{μ}\mathrm{m}/\mathrm{s}$ while leaving the trajectory of another nearby particle, less than $25\text{μ}\mathrm{m}$ away, unaffected.

Block encoding is a key ingredient in the recently developed quantum singular value transformation (QSVT) framework, which provides a unifying description for many quantum algorithms. Although it was initially introduced to simplify and optimize resource utilization in various problems—such as searching, amplitude estimation, and Hamiltonian simulation—it is reasonable to expect that the capabilities of QSVT extend beyond these applications and offer untapped potential for designing new quantum algorithms. In this paper, we affirm this perspective by leveraging block encoding to substantially enhance two previously proposed quantum algorithms: largest eigenvalue estimation and quantum gradient descent. Unlike previous works that rely on sophisticated approaches, our findings demonstrate that even using just elementary operations within the unitary block-encoding framework can eliminate major scaling factors, present in their original counterparts. This results in more efficient quantum algorithms, which are capable of tackling target computational problems with better efficiency. Furthermore, we illustrate how our proposed method can be extended to other contexts, including matrix inversion and multiple eigenvalue estimation, and discuss its potential for a variety of applications toward the stability analysis of physical systems, mechanical vibration, and transport phenomena, as well as molecular geometry optimization.

Modular quantum architectures have emerged as a promising approach for scaling quantum computing systems by connecting multiple quantum processing units. However, this approach introduces significant challenges due to costly intercore operations between chips and quantum state transfers, which contribute to noise and quantum decoherence. This paper presents QARMA, a qubit-mapping approach using attention-based deep reinforcement learning for modular quantum architectures, along with its extension, QARMA-R, which incorporates dynamic qubit reuse. Our approach combines an attention-based mechanism with graph neural networks to learn optimal qubit allocation, routing, and reuse strategies that minimize intercore communication. Our experimental results show significant improvements over state-of-the-art approaches. Compared to highly optimized Qiskit with modular architecture configuration, QARMA-R reduces intercore communication by up to 100% (86% on average), while QARMA maintains 15%–40% improvement for larger circuits without reuse. Against traditional modular qubit mapping, our approach achieves a 97%–100% reduction in intercore operation. The proposed methods advance quantum circuit compilation and enable the execution of larger quantum algorithms on resource-constrained modular quantum systems, thereby contributing to the growing body of research on scalable quantum computing architectures.

Quantum random-number generators (QRNGs) produce true random numbers based on the inherent randomness of quantum theory, rendering them a foundational segment of quantum cryptography. Distinguished from trusted-device QRNGs, whose security depends on characterized devices, semi-device-independent (semi-DI) QRNGs permit partial devices to be defective or even maliciously manipulated, achieving a good trade-off between generation rate and security. In this paper, we propose a semi-DI QRNG that resists general attacks while accounting for finite-size effects. The protocol requires no rigorous characterization of the source and measurement devices other than limiting the energy of the emitted states, significantly reducing the demand on practical QRNG systems. Leveraging the tight Kato’s inequality for correlated variables, we show that our protocol generates more randomness than it consumes. Furthermore, we demonstrate the scheme using a continuous-variable system with ternary inputs of states. Heterodyne detection is employed to enable phase compensation through data postprocessing, alleviating the stringent requirement on system stability. The system operates at 100 MHz, achieving a net random-number generation rate of 1.165 Mbps at $5.3\times {10}^9$ rounds. Our work offers a promising approach to achieving both robust security and a high generation rate with a simple experimental setup.

In this work, we demonstrate a single-mode squeezed light source in a dual-pumped integrated ring microresonator and map the dependence of the noise quadrature on the pump-laser frequency detuning, achieving $1\mathrm{dB}$ of squeezing at the optimal operating point. We further demonstrate that utilizing a common-pass local-oscillator approach by passing the local oscillator through the same optical amplification stages as the pumps reduces its integrated root-mean-square phase noise to ${1.72}^{\circ }$, enabling minute-scale stable noise measurements.

High-efficiency energy harvesting of ultrasonic elastic waves is crucial for powering electric gadgets in many emerging technologies such as wearable devices, wireless sensing, and biomedical implants. Although topological phononic metamaterials have recently been demonstrated as a promising paradigm for confining and guiding elastic waves through robust bound states, achieving ultrahigh-Q topological resonance with enhanced energy conversion efficiency remains a challenge. In this work, we propose a synthetic-dimensional higher-order topological insulator by engineering the flexural bands of elastic metamaterials, featuring highly localized topological hinge states in the bulk bands. This topological hinge mode stems from the nonzero combination of the bulk polarization and the Chern number in the synthetic-dimensional band structure, thus giving rise to a strong elastic-to-electric energy conversion at the corner of the phononic plate. Through numerical simulations and experimental validations, straightforward evidence of the localized modes with robust protection and consequent abilities in activating the light-emitting diodes (LEDs) array has been demonstrated. Our findings open an avenue for topological-physics-enabled ultrasonic devices and present promising prospects for applications in weak-signal detection and self-powered sensors.

We demonstrate a highly linear superconducting quantum interference device (SQUID) interferometer based on a double-loop (Bi-SQUID) architecture incorporating three superconductor-normal metal-superconductor ($S$-$N$-$S$) junctions. Fabricated using niobium-gold technology, the device exhibits robust operation at liquid helium temperatures, with a superconducting transition temperature of 8.5 K. The dc flux-to-voltage transfer function demonstrates sharp, symmetric, and highly linear behavior at temperatures up to 5 K. Bi-SQUIDs featuring our single-element $S$-$N$-$S$ design represent an interesting and original approach to this field, as they exhibit a numerically estimated spurious-free dynamic range linearity exceeding 60 dB, achieved in a single element, simplifying the requirements in terms of arrays containing hundreds of junctions. These results highlight the potential of proximity-based Bi-SQUIDs for compact and highly linear cryogenic interferometric devices, motivating future investigations of their dynamic and noise performance for applied implementations such as quantum sensing, magnetometry, and biomedical diagnostics.

The $\mathrm{Pt}/\mathrm{Ti}/{\mathrm{Si}\mathrm{O}}_2/\mathrm{Si}$ stack is the most widely adopted substrate for integrating piezoelectric oxide thin films with silicon-based devices. In this work, we demonstrate that lead-free potassium sodium niobate (KNN) piezoelectric thin films fabricated by chemical solution deposition (CSD) exhibit markedly different structural and functional responses when subjected to varying $\mathrm{Ti}$ concentrations, arising from both unintentional $\mathrm{Ti}$ diffusion and intentional $\mathrm{Ti}$ doping. It was found that ${\mathrm{Ti}}^{4+}$ ions incorporated into the KNN lattice substitute ${\mathrm{Nb}}^{5+}$ at B site, acting as acceptor defects to compensate donor-type oxygen vacancies, forming the defect complexes $[\mathrm{T}{{\mathrm{i}}^{\mathrm{\prime }}}_{\mathrm{Nb}}-V_{\mathrm{O}}^{..}{]}^{.}$ and $[\mathrm{T}{{\mathrm{i}}^{\mathrm{\prime }}}_{\mathrm{Nb}}-V_{\mathrm{O}}^{..}-\mathrm{T}{{\mathrm{i}}^{\mathrm{\prime }}}_{\mathrm{Nb}}]$. These defect complexes reduced the dielectric constant, suppressed dielectric loss, and enhanced electric-field induced strain. At 1 mol % $\mathrm{Ti}$ doping, multiphase coexistence was observed, enabling polarization rotation. The coexistence of defects and multiphases yield a remarkably large effective piezoelectric coefficient $d_{33}^{e\mathrm{ff}}$ equivalent to 272 pm/V at 1.5 kHz. These findings establish a pathway for defect and phase engineering in perovskite oxides and highlight the significance of $\mathrm{Ti}$ control for reliable integration of high-performance, lead-free piezoelectric films with silicon-based devices.

The realization of superconducting diodes that operate without external magnetic fields and allow electrical control of polarity is a key goal for the integration of nonreciprocal elements into cryogenic and quantum technologies. Here, we demonstrate a universal and scalable approach to achieving such field-free and electrically reconfigurable Josephson diode functionality. Our method relies on long Josephson junctions with ferromagnetic barriers and asymmetric current injection: a configuration that inherently breaks both time-reversal and inversion symmetries. We show that the diode polarity is set by an applied bias current and can be reversed using short current pulses, without the need for magnetic fields or thermal cycling. The effect is robust, material-agnostic, and compatible with standard established fabrication processes. Our results provide a practical platform for integrating low-dissipation, programmable diodes into superconducting and quantum electronic circuits.