High-dimensional quantum systems, known as qudits with dimension $d>2$, possess the capability to encode and process more information than traditional two-dimensional qubits. Entangled states serve as crucial resources for both quantum computation and quantum communication. On the basis of circuit quantum electrodynamics (QED) systems, we introduce an efficient scheme to deterministically generate high-dimensional multipartite entangled states of hybrid qutrits ($d=3$). Assuming a simple initial state has already been prepared with the use of local operations, our method requires only a single step to produce hybrid Greenberger-Horne-Zeilinger (GHZ) entangled states among circuit QED systems consisting of superconducting qutrits and a superconducting cavity. Remarkably, the number of steps and the operational time remain constant as the number of qutrits increases, highlighting the efficiency and scalability of our approach. Using numerical simulations for a three-dimensional hybrid GHZ state of seven qutrits, we demonstrate the feasibility of our scheme and study the effects of various parameters on the fidelity. The importance of this research is in directing the experimental creation of multipartite, high-dimensional, and hybrid GHZ states, which can then be used to enhance quantum communication protocols and computational processes.

Graphene nanomechanical resonators are well suited for the study of parametric oscillations. Their large frequency tunability and their pronounced nonlinearities enable an efficient modulation of their resonant frequencies. Here, we present measurements of the response of few-layer-graphene nanomechanical resonators, each driven by a large parametric pump at frequency $2\omega$ and a weak external drive at $\omega$, where $\omega$ is set near the mechanical resonant frequency ${\omega }_0$. The pump actuates the resonator beyond the threshold for large-amplitude parametric oscillations, while the drive breaks the symmetry between the parametric phase states. By increasing and decreasing a gate voltage to detune ${\omega }_0$ in the presence of the pump and the drive, we observe a double hysteresis in the response. The double hysteresis reveals the existence of two possible large-amplitude vibrational states whose phase difference is nearly $\pi$ radians. We deterministically prepare the resonator in either one of these states by cycling the gate voltage. We measure the stationary occupation probabilities of the two states in the presence of a white Gaussian force noise, and find that they strongly depend on the amplitude and on the phase of the external drive. The phase states of parametric oscillations with broken amplitude symmetry can be mapped to biased bimodal degrees of freedom, such as Ising spins in an external magnetic field. Therefore, they hold promise as units of binary information.

This work develops the thermal spectrum field theory in the dynamic steady state for photothermal fields under arbitrary optical excitation, utilizing a combined Fourier-Laplace formalism subject to generalized conductive and radiative boundary (surface) conditions. The theory represents a generalization of the thermal field spectral theory of opaque solids to photothermal spectroscopy of optically nonopaque media. The developed formalism introduces infrared thermophotonic emission as the spectrally resolved response of condensed media while eliminating signal background variations caused by incoherent (“decoherent”) leaky degrees of freedom inherent to diffusion physics. The theory is applied to ink-water mixtures with varying optical absorption coefficients. The Fourier-Laplace approach to photothermal spectroscopy demonstrates the absence of decoherent thermal energy superposition in the photothermal field, validates the dynamic steady-state nature of the recorded transient thermal waves, and enables accurate measurements of optical absorption, thermophotonic emission, and surface heat transfer coefficients.

The Rayleigh’s criterion imposes a minimum separation between two incoherent sources for them to be distinguishable via classical methods. In this work, we demonstrate the emergence of two-photon beats from the interference of a single reference photon and a photon coming from one of two transversally displaced incoherent sources. We also show that, apart from a factor of 2, the ultimate quantum precision in the estimation of any value of the distance between two weak thermal sources is achievable independently of the spatial structure of wave packet by performing a relatively low number of sampling measurements of the transverse momenta of the interfering photons without the need for any additional optics. The feasibility of this technique makes it an optimal candidate for important applications in microscopy, astronomy, and remote sensing.

Random lasing (RL) is based on the occurrence of a set of light-scattering events in an active medium that provides the optical feedback mechanism necessary to achieve laser emission. The inherent disorder present in biological tissues makes them good candidates for RL generation, with the optical detection of cancerous tissues as one of its most notable applications reported in recent years. Recently, we have also identified RL differences between brain samples of mice affected and nonaffected by Huntington’s disease (HD). HD is a neurodegenerative disorder caused by the mutation of the huntingtin gene, leading to the misfolding and aggregation of the huntingtin protein (HTT). Mutated HTT is mostly expressed in the brain, but it is also present in peripheral organs. From a medical perspective, it would be interesting to know whether RL maintains its discriminative potential for HD pathology in biological samples obtained through noninvasive procedures. In this paper, we report on the RL emission from blood samples of mice for the optical detection of HD in an observational case study. The RL signals from blood samples of five R6/1 mice, a mouse model of HD, are analyzed and compared with those from five control littermates. A multivariate statistical classification study is conducted, showing that RL holds a success rate over 80% in discriminating blood samples of R6/1 mice from their wild-type littermates.

Engineering high-order nonlinearities while suppressing lower-order terms is crucial for quantum error correction and state control in bosonic systems, yet it remains an outstanding challenge. Here, we introduce a general framework of a nonlinearity-engineered multiloop SQUID (NEMS) device, enabling the realization of arbitrary nonlinearities by tuning fluxes in multiple loops within superconducting circuits. We demonstrate specific examples of NEMS devices that selectively engineer cubic-, quartic-, and quintic-dominant interactions with suppressed parasitic couplings, showing great promise for realizing Kerr-cat bias-preserving cnot gates and stabilizing four-leg cat qubits. By opening avenues for tailoring nonlinear Hamiltonians of superconducting devices, this work enables sophisticated and precise manipulation of bosonic modes, with potential applications in quantum computation, simulation, and sensing.

Using an in-house Schrödinger-Poisson solver, we investigate the creation of a single hole-spin qubit inside a triple-gate triangular silicon fin field-effect transistor ($\mathrm{Si}$ FinFET) quantum device similar to experimental structures. The gate-induced formation of the required quantum dot is monitored based on the Luttinger-Kohn $6\times 6k\cdot p$ method, accounting for magnetic fields and strain to determine the qubit ground state. Strain arises from the inhomogeneous contraction of the different components of the FinFET when they are cooled to cryogenic temperatures. This leads to a renormalization of the qubit’s energy levels, thus impacting both the heavy-hole and light-hole populations, as well as their mixing. The dot length, band mixing, $g$-factor, and Larmor and Rabi frequencies of the considered device are extracted. In particular, we show that these metrics exhibit strong strain-dependent variations of their magnitude, thus underlining the importance of including realistic thermal-contraction scenarios when modeling hole-spin qubits.

Dopant-dopant and dopant-vacancy complexes in diamond can be exploited for the development of quantum computers, single-photon emitters, high-precision magnetic field sensing, and nanophotonic devices. While some dopant-vacancy complexes such as nitrogen- and silicon-vacancy centers are well studied, studies of other dopant and/or vacancy clusters are focused mainly on defect detection, with minimal investigation into their electronic features or how to tune their electronic and optical properties for specific applications. To this aim, we perform a thorough analysis of the coupled structural and electronic features of different dopant-dopant and dopant-vacancy cluster defects in diamond by means of first-principles calculations. We find that doping with $p$-type ($n$-type) dopant does not always lead to the creation of $p$-type ($n$-type) diamond structures, depending on the kind of cluster defect. We also identify the quantum mechanical descriptors that are most suitable to tune the electronic band gap about the Fermi level for each defect type. Finally, we propose how to choose suitable dopant atomic types, concentrations, and geometric environments to fabricate diamond-based materials for several technological applications such as electrodes, transparent conductive materials, intermediate-band photovoltaics, and multicolor emitters, among others.

Weyl semimetals, such as ${\mathrm{Ta}\mathrm{Ir}\mathrm{Te}}_4$, characterized by their unique band structures and exotic transport phenomena, have become a central focus in modern electronics. Despite extensive research, a systematic understanding of the impact of heterogeneous integration on the electronic and optical properties of ${\mathrm{Ta}\mathrm{Ir}\mathrm{Te}}_4$ device remains elusive. We have carried out density-functional theory combined with nonequilibrium Green’s function formalism calculations for ${\mathrm{Ta}\mathrm{Ir}\mathrm{Te}}_4/{\mathrm{W}\mathrm{Te}}_2$, ${\mathrm{Ta}\mathrm{Ir}\mathrm{Te}}_4/{\mathrm{Mo}\mathrm{Te}}_2$, and ${\mathrm{Ta}\mathrm{Ir}\mathrm{Te}}_4/$h-BN heterostructures, aiming to understand the manipulation of photoresponse through various band alignment strategies. The underlying impacts of interlayer interactions, charge transfer and build-in electric field on the electronic properties are carefully investigated. We design a dual-probe photodetector device to understand the overall photoresponse enhancement of the heterogeneous integration by decomposing into the specific strain, interlayer transition, band overlap, and symmetry lowering mechanics. These van der Waals integrations provide an ideal platform for studying band alignment physics in self-powered optoelectronic devices.

Compact localized states (CLSs) associated with flat bands (FBs) exhibit significant potential for wave localization and enhanced wave-matter interactions. The Lieb lattice, characterized by its unique bipartite and chiral symmetries, features a dispersionless FB cutting through the Dirac points, distinguishing it from other lattices and providing substantial flexibility for controlling CLS configurations. Herein, we investigate theoretically the generation and manipulation of CLSs in a two-dimensional dielectric photonic crystal (PC) with a Lieb lattice. Particularly, to address the inevitable non-nearest-neighboring interactions of the lattice sites, we propose an optimized strategy by embedding perfect electric conductors between dielectric sites, enabling the first observation of an ideal FB in Lieb PCs; this closely matches the tight-binding model that considers only the nearest-neighbor coupling. Furthermore, by leveraging the robust CLS in Lieb PCs, we demonstrate the on-demand design of diverse localized mode patterns through CLS engineering and showcase their selective optical excitation. These advancements offer promising applications in on-chip optical routing and switching, as well as in the design of high-performance cavity-based photonic devices.

Electrons trapped on the surface of superfluid helium have been thought of as a useful resource for quantum computing. Such electrons show long coherence of their surface-bound (Rydberg) states combined with their easy electrostatic manipulation. Recent proposals have explored the possibility of coupling the spin state of an electron and the state of its quantized motion, with the promise of a highly scalable two-dimensional architecture for a quantum computer. However, despite recent progress in the detection of quantized lateral motion of electrons using a circuit-QED setup, manipulation of a small number of electrons and their quantum state detection remains a challenging problem. Here, we report on the detection of the Rydberg transition of electrons on superfluid helium in an on-chip microchannel device in which electrons are moved and trapped by a set of electrostatic gates. A highly sensitive image-charge detection system allows us to not only resolve the transition spectra of such electrons, but also perform the device characterization. The demonstrated sensitivity shows the feasibility of detecting the Rydberg transition of a single electron, which can open an alternate pathway for a nondestructive spin-state readout.

Quantum error-correcting codes typically do not account for quantum state transitions—leakage—out of the computational subspace. Since these errors can last for multiple detection rounds, they can significantly contribute to logical errors. It is therefore important to understand how to numerically model them efficiently. Fully quantum simulations of leakage require more levels per leaked qubit, which substantially limits the system sizes that may be simulated. To address this, we introduce a subspace twirling approximation (STA) on quantum channels that preserves the incoherence between the computational and leakage subspaces. The assumption of incoherence enables the quantum simulation of leakage at little computational overhead. We motivate the approximation’s validity by showing that incoherence is achieved naturally during repeated stabilizer measurements. Additionally, we provide various simulation results which show that the STA yields accurate error-correction statistics in the repetition and surface codes with physical error parameters.

Brillouin-based optomechanical systems with high-frequency acoustic modes provide a promising platform for implementing quantum-information processing and wavelength conversion applications, and for probing macroscopic quantum effects. Achieving strong coupling through electrostrictive Brillouin interaction is essential for coupling the massive mechanical mode to an optical field, thereby controlling and characterizing the mechanical state. However, achieving strong coupling at room temperature has proven challenging due to fast mechanical decay rates. While Brillouin strong coupling has been demonstrated, a comprehensive characterization of the system in this regime is still lacking. Here, we report an optomechanical system with independent control over pumping power and frequency detuning to achieve and characterize the strong-coupling regime of a bulk acoustic-wave resonator. Through spectral analysis of the cavity reflectivity, we identify clear signatures of strong coupling, namely, normal-mode splitting and an avoided crossing in the detuned spectra, while estimating the mechanical linewidth ${\mathrm{\Gamma }}_m/2\pi =7.13\mathrm{M}\mathrm{Hz}$ and the single-photon coupling rate $g_0/2\pi =7.76\mathrm{Hz}$ of our system. Our results provide valuable insights into the performance of room-temperature macroscopic mechanical systems and their applications in hybrid quantum devices.

In this paper, we propose a coherent perfect absorber for the underwater ultrasound regime (MHz frequencies), inspired by the mechanism of Salisbury, which relies on reflective conductive sheets. By leveraging a silicon-based acoustoelastic metasurface with thin periodic slits acting as Fabry-Pérot resonators, and by focusing on realizing an efficient ultrasound underwater steel bandgap mirror, we observe coherent perfect absorption (CPA) both numerically and experimentally at frequencies around 0.6 and 1.2 MHz, with the latter exhibiting strong absorption of coherent acoustic wave energy by the water due to the intense spatial confinement of pressure within the slits. The robustness of this CPA device is also demonstrated, in particular with respect to oblique incidence. Due to the simplicity of our design, we expect it to open avenues in underwater ultrasonics, with many applications for ultrasound imaging and stealth, to name a few.

Single-photon sources (SPSs) hold the potential to enhance the performance of quantum key distribution (QKD). QKD systems using SPS often require cryogenic cooling, while recent QKD attempts using SPS operating at room temperature have failed to achieve long-distance transmission due to the SPS not operating at telecommunication wavelength. In this work, we have successfully demonstrated QKD using a room-temperature SPS at telecommunication wavelength. The SPS used in this work is based on point defects hosted by gallium nitride ($\mathrm{Ga}\mathrm{N}$) thin films grown on sapphire substrates. We employed a time-bin and phase-encoding scheme to perform the BB84 and reference-frame-independent QKD protocols over a 33-km fiber spool, achieving a secure key rate of $7.58\times {10}^{-7}$ per pulse. Moreover, we also implemented a metropolitan QKD experiment over a 30-km deployed fiber, achieving a secure key rate of $6.06\times {10}^{-8}$ per pulse. These results broaden the prospects for future use of SPS in commercial QKD applications.

Realizing practical quantum computing requires overcoming a number of computation errors and the limitation of device size, which have intensively been tackled by quantum error mitigation. As a unified approach of noise-agnostic quantum error mitigation, generalized quantum subspace expansion (GSE) has lately been proposed to be remarkably robust regarding stochastic and coherent errors, integrating quantum subspace expansion and virtual state purification. However, the requirement in GSE to perform entangled measurements between copies of the quantum states remains a significant drawback under the current situation of quantum devices with a restricted number of qubits and their connectivity. In this work, we propose “Dual-GSE,” a resource-efficient implementation of GSE to circumvent this overhead by constructing an ansatz of error-mitigated quantum states via dual-state purification without state copies. Remarkably, the proposed method can further simulate larger quantum systems beyond the size of available quantum hardware, achieved by a suitable ansatz construction inspired by the divide-and-conquer strategy that classically reintroduces the effect of entanglement. While classically forging the entanglement comes with additional cost, the total sampling overhead can be notably reduced by reuse of the same Pauli expectation values among divided-and-conquered subsystems. We comprehensively analyze the advantages and overhead of Dual-GSE and perform numerical simulations of the eight-qubit transverse-field Ising model under various setups. Our results demonstrate that Dual-GSE estimates the ground state energy with high accuracy under gate noise with low mitigation overhead and practical sampling cost.

Unidirectional guided resonances (UGRs), which are eigenstates that radiate exclusively in a single channel, are promising for advancing diverse photonic devices. However, existing approaches face an inherent trade-off between achieving high-Q factors and maximizing the radiation-asymmetry ratios. To address this challenge, we propose a scheme that exploits both out-of-plane and in-plane couplings to generate bound states in the continuum with precise radial and rotational control in momentum space. This approach effectively decouples the Q factors of UGRs from their radiation-asymmetry ratios. As a result, we achieve UGRs with Q factors exceeding ${10}^4$, which is 1–2 orders of magnitude higher than traditional UGRs. Furthermore, we demonstrate the ability to reverse the emission direction of these UGRs, leading to a broad range of radiation-asymmetry ratios from −53 to 55 dB. We further validate the practical realization of high-Q UGRs using a silicon-on-silica system. Our findings provide a versatile method for generating high-Q UGRs, offering alternative pathways for innovations in nonlinear optics, light-matter interactions, and advanced optoelectronic applications.

The negatively charged nitrogen vacancy center in diamond is widely used for quantum sensing due to the sensitivity of the spin triplet in the electronic ground state to external perturbations such as strain and electromagnetic fields, which makes it an excellent probe for changes in these perturbations. The spin state can be measured through optically detected magnetic resonance, which is most commonly achieved by detecting the photoluminescence after exciting the spin-triplet transition. Recently, methods have been proposed and demonstrated that use the absorption of the infrared singlet transition at 1042 nm instead. These methods, however, require cryogenic temperatures or external cavities to enhance the absorption signal. Here, we report on our efforts to optimize the magnetometer sensitivity at room temperature and without cavities. We reach a sensitivity of $18\mathrm{pT}/\sqrt{\mathrm{Hz}}$, surpassing previously reported values, and a calculated shot-noise limit of $5\mathrm{pT}/\sqrt{\mathrm{Hz}}$ . We also report on a defect that is native to diamond grown by chemical vapor deposition and thus absent in high-pressure high-temperature diamond, the excitation of which impacts the measured singlet absorption signal.

This study focuses on the application of microscopic ghost imaging (MGI) in live cell imaging and classification. High-resolution imaging is performed on human red blood cells, 293T cells, and three types of cancer cell line (Caov3, Molm13, and Ishikawa) with the use of MGI. Subsequently, cell classification is conducted with the random forest classifier based on image features and bucket detection data, respectively. The imaging results reveal the characteristic biconcave disk structure of red blood cells. Moreover, significant morphological and aggregation differences are observed between the similarly sized 293T cells and the three cancer cell lines. In terms of classification, the maximum accuracy achieved on the basis of image features is 73%. Remarkably, classification using bucket data achieves an accuracy of 88% even at an extremely low sampling rate (0.03%), with accuracy stabilizing at around 94% as the sampling rate increases to 0.12%. Principal component analysis of the bucket data further demonstrates significant feature differences among the cell lines. This study not only demonstrates the advantages of MGI in live cell imaging but also uncovers the potential of bucket data for efficient cell classification. These findings provide valuable insights and methods for applications in biomedical imaging, drug screening, and clinical diagnostics.