While atomic frequency standards are improving at a staggering pace, the timing community has relied on the same continuously running atomic clocks for decades: commercial cesium beams and hydrogen masers. Challenges in incorporating the latest technological advancements into operational clocks have resulted in technology lag compared with frequency standards that consequently impacts timing applications, such as system synchronization, positioning and timescales. The first cold-atom clocks to contribute to the free-running international atomic timescale, EAL, are the four rubidium fountains in operation at the US Naval Observatory in Washington, DC, that came online in 2011. With 12 years of uninterrupted data from the International Bureau of Weights and Measures (BIPM) from Modified Julian Date (MJD) 56074 to MJD 60429, we report on the long-term timing performance of these clocks. The highest performing fountain exhibits time deviation of 8 ns at approximately $3$ years and a holdover of the BIPM’s best timescale of $\pm 14$ ns at 12 years.

For quantum computation using photons, performing deterministic quantum gate operations is a challenge due to the probabilistic nature of the photon-photon interaction. Encoding qubits in multiple degrees of freedom of photons and controlling operations between them is one of the promising ways to navigate the probabilistic behavior. Using the single-photon discrete-time quantum walk in combination with polarization and path degrees of freedom, we experimentally demonstrate the realization of a universal set of quantum gates with high fidelity at room temperature. The deterministic realization of quantum gates through the photonic quantum walk are characterized via quantum state tomography. For a three-qubit system using a single photon, the first qubit is encoded using polarization information, and the other two qubits are encoded using path information, closely resembling a Galton-board setup. To generate a six-qubit Greenberger-Horne-Zeilinger state, entangled photon pairs are used to entangle the two three-qubit modules on which gate operations are performed. We also provide insights into the mapping of photonic quantum walk operations to quantum circuit representation and propose method to resourcefully scale. This demonstration marks significant progress towards using quantum walks for quantum computing and provides a framework for using fewer photons in combination with different degrees of freedom of photons to scale the number of qubits.

We have designed an automatic differentiation-based strategy to generate optical trap arrays that change smoothly over time. Instead of repeatedly regenerating the holograms for each time step, we derive the differential form of the phase dynamics that enables the continuous evolution of the trap coordinates. This differential form is derived from the implicit differentiation of the fixed point of the Gerchberg-Saxton algorithm, which is computationally efficient. We carried out numerical and laboratory experiments to demonstrate its effectiveness at improving the phase continuity and reducing the computational burden compared to traditional pure interpolation techniques. By combining the method with the spatial light modulator, the method is promising for the dynamic manipulation of particles in real experiments.

Integrated microring resonators have a broad range of applications in diverse fields with the potential to design compact, robust, energy-efficient devices crucial for quantum applications. Degenerate optical parametric oscillations (DOPOs) realized in dual-pumped microring resonator with third-order optical nonlinearity are of special interest. They demonstrate both bistability of the phase of the excited signal mode and generation of nonclassical light, which can be used for coherent photonic computing. Using coupled mode equations, we perform a comprehensive numerical analysis of DOPO conditions with normal group velocity dispersion and with bichromatic pumping. Through analytical and numerical approaches, we identify optimal setup parameter values that minimize the threshold power, highlighting the importance of considering the full spectrum of mode interactions. Additionally, we show that dispersion engineering, achievable in photonic molecules or photonic crystal microresonators, may provide a targeted frequency shift of specific microresonator modes resulting in pump power threshold reduction.

Spintronic terahertz (THz) emitters, utilizing ferromagnets/nonferromagnetic metal heterostructures, offer significant potential across imaging, communication, sensing, and material detection. To investigate whether the femtosecond laser-induced spin current and/or orbital current from ferromagnets can emit THz waves through the inverse spin Hall effect or inverse orbital Hall effect in nonferromagnetic metals, we focused on the $\mathrm{Ni}(\mathrm{Co},\mathrm{Co}\mathrm{Fe}\mathrm{B})/\mathrm{Ti}$ heterostructures. These structures exhibit a negligible inverse spin Hall effect but a pronounced inverse orbital Hall effect in the $\mathrm{Ti}$ layers, allowing us to explore the function of ferromagnets as the optimal laser-excited orbital current source. By examining the THz amplitude as a function of $\mathrm{Ti}$ thickness, we determine that the orbital current diffusion length in $\mathrm{Ti}$ is around 57.7 nm. Additionally, we employ the second-harmonic Hall resistance method to derive the thickness-dependent orbital Hall angle in the $\mathrm{Ti}$ layers, based on the conversion of electric charge current to orbital current. Notably, the results from this method are highly consistent with those from THz emission measurements, indicating that the interconversion between orbital current and charge current is equivalent not only on picosecond timescales but also nearly instantaneously. Furthermore, by comparing the substantial THz amplitude emitted from $\mathrm{Ni}/\mathrm{Pt}$ heterostructures, which feature a significant spin Hall effect in $\mathrm{Pt}$ layers, with that of $\mathrm{Ni}/\mathrm{Ti}$, we confirm that $\mathrm{Ni}$ also serves as an effective laser-excited spin-current source. Our findings indicate that utilizing materials with substantial orbital Hall angles and/or spin Hall angles in $\mathrm{Ni}$-based heterostructures could enhance the emission of THz waves.

The presence of quasiparticles typically degrades the performance of superconducting microwave circuits. The readout signal can generate nonequilibrium quasiparticles, which lead to excess microwave loss and decoherence. To understand this effect quantitatively, we measure quasiparticle fluctuations and extract the quasiparticle density across different temperatures, readout powers, and resonator volumes. We find that microwave power generates a higher quasiparticle density as the active resonator volume is reduced and show that this effect sets a sensitivity limit on kinetic inductance detectors. We compare our results with theoretical models of direct microwave photon absorption by quasiparticles and conclude that an unknown, indirect mechanism plays a dominant role in quasiparticle generation. These results provide a route to mitigate quasiparticle generation due to readout power in superconducting devices.

Non-Hermitian dynamics in quantum systems have unveiled novel phenomena, yet the implementation of valid non-Hermitian quantum measurement remains a challenge, because a feasible quantum projective mechanism on the complete but skewed non-Hermitian eigenstates is not explicit in experiments. This limitation hinders the direct acquisition of non-Hermitian observable statistics (e.g., non-Hermitian population dynamics), and also constrains investigations of non-Hermitian quantum measurement properties such as the uncertainty relation. Here we address these challenges by presenting a non-Hermitian projective protocol and investigating the non-Hermitian uncertainty relation. We derive the uncertainty relation for pseudo-Hermitian (PH) observables under the specific non-Hermitian metric. We then investigate the projective measurement properties for general quantum states which are projected onto the complete non-Hermitian eigenvectors, and present a quantum simulation method to apply the valid non-Hermitian projective measurement on a direct-sum dilated space. Subsequently, we experimentally construct a quantum simulator in the quantum optical circuit and realize a proof-of-principle experiment involving three-dimensional non-Hermitian quantum measurement on single-photon qutrits. Using this platform, we explore the uncertainty relation experimentally with different PH metrics. Our non-Hermitian quantum measurement method is state independent and outputs directly the non-Hermitian quantum projective statistics, paving the way for studies of extensive non-Hermitian observables in the quantum domain.

Timing measurement is crucial for ultrafast high-precision position detection and characterization of nonrepetitive physical processes in ultrafast lasers. In this work, we showed that timing jitter measurements at the attosecond level could be achieved by using a time-stretched self-coherent detection (TSSCD) system. A piezoelectric transducer was placed in the signal arm of the detection system and driven with a sinusoidal signal to induce the timing jitter signal to be measured. The modulation-induced fast timing jitter was then characterized by using a chirped swept signal. The TSSCD system had a high-frequency noise floor of about 2 × ${10}^{-13}{\mathrm{fs}}^2$/Hz and an integrated timing jitter noise less than 5 as. The measured timing jitter amplitude determined from integration of the power spectral density varied linearly with the driving voltage with a fitting $R^2$ of 0.99999, and a timing jitter amplitude as low as about 1 as could be measured. The experimental results agree well with the results from numerical simulations. By using ultrafast high-precision measurements, an attosecond-level timing jitter emulated by a random 8-level pulse amplitude modulated sinusoidal signal is successfully measured, indicating its potential for application in optical signal data processing and communications.

In space-based gravitational wave detection missions, the residual acceleration requirement for inertial sensors reaches the femtometer per second squared square root hertz level, which drives the strict requirement for temperature stability of several microkelvins per square root hertz. This necessitates a slight variation of power dissipation for surrounding heat sources, which presents a significant challenge, particularly within the low-frequency band, and highlights the need for thermal-insulation design. Despite the critical role of multilayer insulation (MLI) assemblies in passive thermal insulation, the transfer function remains unexplored, making thermal-insulation design problematic in the frequency domain. In this paper, we introduce the concept of temperature waves to derive precise transfer functions for temperature fluctuations in the MLI, which can efficiently and accurately guide thermal-insulation design in the frequency domain. Considering the geometric constraint between the optical bench and the vacuum chamber in the TianQin gravitational wave detector, bulk insulation materials such as polyimide foam cannot be accommodated, making the use of MLI necessary. On the basis of this precise MLI model, we propose a feasible thermal-insulation design for the inertial sensors, where MLI loosely clads the surrounding area. This design successfully eases the power dissipation variation requirements for the diode and the other heat sources by at least 20 times at 0.1 mHz, significantly enhancing the mission’s feasibility. Furthermore, the precise MLI model and the thermal-insulation design process in this article can be applied to other space missions requiring stringent temperature stability.

Demonstrating that logical qubits outperform their physical counterparts represents a milestone in achieving reliable quantum computation. Here, we propose to protect logical qubits with a dynamical decoupling scheme that implements iswap gates on nearest-neighbor physical qubits, and we experimentally demonstrate this scheme on superconducting transmon qubits. In our scheme, each logical qubit requires only two physical qubits. A universal set of quantum gates on the logical qubits can be achieved such that each logical gate comprises only one or two physical gates. Our experiments reveal that the coherence time of a logical qubit is extended by up to 357% compared to the better-performing physical qubit. Moreover, we demonstrate—to the best of our knowledge, for the first time—that multiple logical qubits can outperform their physical superconducting counterparts. We illustrate a set of universal gates through a logical Ramsey experiment and the creation of a logical Bell state. Given its scalable nature, our scheme holds promise as a component for future reliable quantum computation.

We propose a method for generating optical cat states in propagating pulses based on cavity quantum electrodynamics (QED). This scheme uses multiple four-level systems (FLSs) inside an optical cavity as a light source. Time-modulating driving stimulates it to produce a superposition of coherent states entangled with the FLSs. The postselection of an appropriate state of the FLSs leads to a multicomponent cat state in a propagating pulse. Taking atomic decay and cavity loss into account, we optimize the cavity external coupling rate to maximize the fidelity. We find that its optimum value is formulated similarly to those of other generation methods for propagating states, suggesting a universal property of cavity-QED systems interacting with fields outside the cavity.

Partially gated two-dimensional electron systems (2DESs) represent the basic building block of prospective optoelectronic devices, including electromagnetic detectors and sources; however, the electrodynamic properties of such structures have been addressed only with numerical simulations. Here, we provide an exact solution of the electromagnetic scattering problem at a partially gated 2DES using the Wiener-Hopf technique. We find that the incident $p$-polarized field is enhanced in the immediate vicinity of the gate edge. The edge acts as a plasmonic coupler that launches bidirectional (gated and ungated) plasmons in a weakly dissipative 2DES with an inductive-type impedance. The electric fields in these waves markedly exceed the incident field, especially in the limit of small gate-2DES separation. The amplitude of the ungated wave exceeds that of the gated for a 2DES reactance above the free-space impedance. Both amplitudes are maximized for a 2DES reactance of the order of the free-space impedance multiplied by the ratio of the free-space wavelength and the gate-2DES separation.

Two-dimensional semiconductors are promising candidates for next-generation electronics due to their exceptional electrical, optical, and mechanical properties. However, developing enhancement-mode transistors compatible with current semiconductor technologies remains challenging. Here, we introduce a class of two-dimensional semiconductors—all-armchair-edged Xenes—the band gaps of which can be continuously tuned by adjusting the nanoribbon width or applying uniaxial strain. We demonstrate that a single circularly polarized light field induces different band gap variations for spin-up and spin-down electrons, enabling efficient spin filtering. Tensile strain enhances edge-state interactions, significantly increasing the band gap, especially in wider nanoribbons. Based on these findings, we propose an enhancement-mode field-effect transistor controlled solely by either left- or right-circularly polarized light and connected to topological insulator leads. The transistor’s threshold parameters, breakdown voltage, and output characteristics can be tailored by adjusting its channel width. Moreover, by adjusting the intensity and chirality of the light, we can selectively generate spin-up or spin-down currents. Using computer vision techniques, we propose a method to accurately reconstruct an all-armchair-edged lattice structure from scanning tunneling microscopy images.

Silicon ($\mathrm{Si}$)-graphite (Gr) composite anodes are crucial for high-energy-density lithium-ion batteries; however, the unclear correlations between component spatial distribution and performance hinder their practical application. Herein, based on a coupled electrochemical-mechanical model integrated with experimental validation, we systematically evaluate layered and homogeneous electrode configurations. Simulation results show that the migration of $\mathrm{Si}$ from the current collector to the separator side maximizes the transport of ${\mathrm{Li}}^{+}$ and electrons, thereby reducing the ${\mathrm{Li}}^{+}$ concentration gradient and lowering the electrode polarization. Positioning $\mathrm{Si}$ near the separator (top-layered $\mathrm{Si}$) promotes synchronized lithiation between $\mathrm{Si}$ and Gr, effectively suppressing interfacial ${\mathrm{Li}}^{+}$ crosstalk. In contrast, homogeneous models reveal that $\mathrm{Si}$ lithiation significantly reduces the lithiation degree of adjacent Gr regions. This leads to complex interactions among ${\mathrm{Li}}^{+}$ fluxes, electrolyte concentration gradients, and stress-strain fields, resulting in inferior lithiation kinetics compared to top-layered $\mathrm{Si}$ configurations. Experimental verification confirms superior cycling stability in top-layered $\mathrm{Si}$ architectures. These findings highlight the limitations of $\mathrm{Si}$ near the bottom current-collector side and homogeneous designs, providing guidance for optimizing electrode structures to mitigate polarization and capacity fading.

Understanding heat transport at the graphene-polymer ($\mathrm{Gr}$-polymer) interface is the key to improve the thermal conductivity of $\mathrm{Gr}$-based nanocomposites. Here, we fabricate poly (methyl methacrylate)/graphene (PMMA/$\mathrm{Gr}$) nanolaminates and find an ultrahigh increase of the in-plane thermal conductivity (8.9 ± 0.9 W${\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$) compared to net PMMA and the thermal conductivity anisotropy (approximately equal to 53) at low $\mathrm{Gr}$ loading (1 vol. %). The strong anisotropic thermal conduction can be attributed to the predominantly in-plane oriented $\mathrm{Gr}$ nanoflake and, intriguingly, the graphene-induced planar alignment of PMMA in the proximity of $\mathrm{Gr}$, as revealed by polarized infrared spectroscopic (p-IR) imaging, nano-FTIR and IR s-SNOM. We demonstrated the contribution of interface-induced confinement to the observed thermal property, providing deeper insights into heat transport at the $\mathrm{Gr}$-polymer interface.

Recent progress has demonstrated that chiral-anomaly bulk states can achieve similar properties to those of topological valley-Hall edge states by using a reverse strategy of boundary-induced chiral transport phenomena in some bulk modes. However, the experimental attainment of chiral-anomaly bulk states in an electromagnetic system is rarely reported. In this paper, we experimentally confirm a magnetic resonance designer surface-plasmon crystal (SPC) composed of metallic patterns deposited on a dielectric substrate, which can demonstrate boundary-induced chiral-anomaly bulk states by exploiting appropriate perfect electrical conductor boundary conditions in a finite-size two-dimensional Dirac semimetal waveguide. The proposed magnetic resonance SPC is radically distinct from photonic crystals based on Bragg scattering. The dispersion and frequency responses of the chiral transport bulk states can be tuned by adjusting the magnetic resonance frequency. Moreover, the proposed SPC can utilize almost all available guiding space, which greatly improves the utilization of materials. It is expected that the present results can be scaled to other frequencies by changing the proportional size of the magnetic resonance unit cell, which could open the possibility of designing more compact, space-efficient, and robust electromagnetic wave and microfunctional devices.