Partial differential equations (PDEs) are crucial for modeling various physical phenomena such as heat transfer, fluid flow, and electromagnetic waves. In computer-aided engineering (CAE), the ability to handle fine resolutions and large computational models is essential for improving product performance and reducing development costs. However, solving large-scale PDEs, particularly for systems with spatially varying material properties, poses significant computational challenges. In this paper, we propose a quantum algorithm for solving second-order linear PDEs of nonconservative systems with spatially varying parameters, using the linear combination of the Hamiltonian simulation (LCHS) method. Our approach transforms those PDEs into ordinary differential equations represented by qubit operators, through spatial discretization using the finite-difference method. Then, we provide an algorithm that efficiently constructs the operator corresponding to the spatially varying parameters of PDEs via a logic minimization technique, which reduces the number of terms and subsequently the circuit depth. We also develop a scalable method for realizing a quantum circuit for LCHS, using a tensor-network-based technique, specifically a matrix product state (MPS). We validate our method with applications to the acoustic equation with spatially varying parameters and the dissipative heat equation. Our approach includes a detailed recipe for constructing quantum circuits for PDEs, leveraging efficient encoding of spatially varying parameters of PDEs and scalable implementation of LCHS, which we believe marks a significant step towards advancing quantum computing’s role in solving practical engineering problems.

The two-qubit entangler is one of the most important components of quantum computers. The cross-cross resonance (CCR) gate has recently been proposed and shown to operate faster than the cross-resonance (CR) gate as an iSWAP gate. However, unlike the CR gate, the CCR gate requires frequency modifications of the input microwave pulses induced by a Stark shift. We present a theoretical study on the CCR gate in the two-transmon system. Using the Schrieffer-Wolff transformation and the rotating-wave approximation, we obtain both the effective Hamiltonian and the input microwave pulse frequencies of the CCR gate. It is well known that the static $ZZ$ term degrades the performance of the CR gate in the transmon system. For the CCR gate, an additional dynamic $ZZ$ term arises from the combined coupling to the qubits by the input microwave pulses, whose strength increases as the product of the two pulse amplitudes ${\mathrm{\Omega }}_0{\mathrm{\Omega }}_1$. We perform numerical simulations using the set of parameters for the IBM Hanoi quantum processor. We show that the CCR gate has a phase tunability and that varying the relative phase of the input microwave pulses can significantly improve the gate performance. This demonstrates that the static $ZZ$ term in the CCR gate can be effectively reduced by optimizing the relative phase of the input microwave pulses.

Quantum infrared spectroscopy (QIRS), which harnesses the quantum interference between entangled visible and infrared photon-pair-generation processes in a nonlinear quantum interferometer, has attracted considerable attention for realizing infrared spectroscopy with high-performance visible detectors and light sources. However, a shortcoming of QIRS is its vulnerability to wave-front distortion caused by the sample structure, which can degrade the quantum interference. To address this problem, we propose employing the attenuated total-reflection (ATR) method, which utilizes close contact between the sample and a prism. The ATR method is one of the most utilized methods in infrared spectroscopy since it can be used to measure various types of materials, such as liquid, film, and powder samples, and is therefore useful for real-world applications. Here, we report wavelength-tunable ATR-QIRS measurements. We constructed a Michelson-type nonlinear quantum interferometer with a ${\mathrm{Ca}\mathrm{F}}_2$ prism, and measured the absorption of water OH-stretching (approximately $3\text{μ}\mathrm{m}$). The transmission spectrum obtained by our ATR-QIRS system shows good agreement with a numerically calculated transmission spectrum using the Fresnel equation.

We report on studies of the plasmonic Fabry-Pérot resonator, which features a metallic grid lithographically fabricated on both sides of a silicon substrate. It is found that the resonator effectively accumulates and enhances the electric field of the incident electromagnetic wave. We have managed to directly measure the field enhancement by placing a diode detector inside the resonator. A remarkable $\times 45$ amplification in the detector responsivity is achieved in the terahertz frequency range. The observed effect contrasts with that occurring in a high-$Q$ Fabry-Pérot resonator with/without resistive sidewalls, where there is no enhancement of the external electromagnetic field.

Convection offers a dynamic and flexible approach to achieving a variety of alternative physical phenomena beyond pure conduction. Here, we demonstrate that thermal metamaterials with convection modulation enable the realization of non-Hermitian topological edge modes and bulk-mode criticality. We illustrate that a periodic modulation can induce localized edge modes within the band gap. The temperature field of the topological state is localized at the edge rings, decaying exponentially at a fixed rate. Additionally, we introduce an extended-localized criticality through the quasiperiodic convection modulation in thermotics. The convections have an advantage of fantastic tunability in the application. Our work proposes a scheme for implementing topological modes and bulk-mode criticality through modulating convection in diffusion systems, paving the way for the design of reconfigurable thermal devices.

We present the investigation of optical transitions in an $\mathrm{Ga}\mathrm{Sb}/\mathrm{Ga}\mathrm{In}\mathrm{As}\mathrm{Sb}$-based heterostructure through different experimental and numerical methods. The transitions had high-temperature stability, with them being observed in the 10–300 K temperature range. Four pronounced optical transitions are observed at low temperature with three of them being nonpolarized and one showing a degree of linear polarization higher than 60%. Time-resolved measurements of the transitions showed a complex carrier dynamics with several distinct processes related to the investigated interface. Using several numerical methods, we identified that the highly polarized transition originates from the first electron state in the $\mathrm{Ga}\mathrm{In}\mathrm{As}\mathrm{Sb}$ layer and a two-dimensional hole gas created within a triangular quantum well at the interface with the p-type doped $\mathrm{Ga}\mathrm{Sb}$ layer. The optical polarization of the signal originates in directional elongation of the atomic bonds enhanced by possible local composition fluctuations and the inheritance of these properties by the signal from the triangular quantum well. Such physical phenomena have the potential to be used as an internal polarizing filter in structures designed for midinfrared optoelectronics.

Quantum teleportation is not merely a fascinating corollary of quantum entanglement, it also finds utility in quantum processing and circuit compilation. In this paper, we measure and track the entanglement and fidelity of two-qubit states prepared on a 127-qubit IBM Quantum computer, as one of the qubits is teleported across 19 qubits. We design, evaluate, and compare two distinct approaches to teleportation: postselected measurement categorization and dynamic circuit corrections based on midcircuit measurements, and compare with direct-state transportation using swap gates. By optimally choosing the teleportation path, which exhibits the highest total negativity entanglement measure across nearest-neighbor pairs, we show the entanglement of a two-qubit graph state is sustained after at least 19 hops in teleportation using the postselection approach and 17 hops using the dynamic circuit approach. We observe a higher level of teleported entanglement in paths determined from two-qubit negativities compared to those obtained from gate errors, demonstrating an advantage in using the negativity map over the gate error map for compiling quantum circuits.

Continuous-variable measurement-device-independent quantum key distribution (CV-MDI QKD) can address vulnerabilities on the detection side of a QKD system. The core of this protocol involves continuous-variable Bell measurements performed by an untrusted third party. However, in high-speed systems, spectrum broadening causes Bell measurements to deviate from the ideal single-mode scenario, resulting in mode mismatches, reduced performance, and compromised security. Here, we introduce temporal modes (TMs) to analyze the performance of CV-MDI QKD under continuous-mode scenarios. The mismatch between Bob’s transmitting mode and Bell-measurement mode has a more significant effect on system performance compared to that on Alice’s side. When the Bell receiver is close to Bob and the mismatch is set to just 5%, the transmission distance drastically decreases from 87.96 km to 18.50 km. In comparison, the same mismatch for Alice reduces the distance to 86.83 km. This greater degradation on Bob’s side can be attributed to the asymmetry in the data modification step. Furthermore, the mismatch in TM characteristics leads to a significant reduction in the secret key rate by 83% when the transmission distance is set to 15 km, which severely limits the practical usability of the protocol over specific distances. These results indicate that, in scenarios involving continuous-mode interference, such as large-scale MDI network setups, careful consideration of each user’s TM characteristics is crucial. Rigorous precalibration of these modes is essential to ensure the system’s reliability and efficiency.

Achieving good acoustic particle or cell separation performance requires skilled operators, who must carefully fine-tune the input parameters (actuation voltages, flow rates, and flow split ratios). Often the fine-tuning is done by time-consuming parameter sweeps, which are tedious and expensive. Here, we present a straightforward model-based approach to determining input parameters that yield optimal separation performance. The optimal parameters are a function of the device performance, the material properties of the separation species (compressibility, density, size), and the properties of the buffer (compressibility and density). The device performance is assessed by a calibration step, while the material properties are combined into the mobility ratio and measured by the in-flow mobility-ratio method, which is introduced in this work. The optimal separation settings are validated by separating green fluorescent $7.8$-$\text{μ}\mathrm{m}$ particles from red fluorescent $4.9$-$\text{μ}\mathrm{m}$ particles.

We demonstrate theoretically and experimentally that linear coupling due to the backscattering between two counterpropagating modes in a Kerr microresonator leads to extreme sensitivity of the intensity asymmetry of nonlinear light states to the relative phase between the bidirectional pumps of equal power. In the absence of linear coupling, the relative pump phase does not affect counterpropagating intraresonator intensities, and two asymmetric states arise due to spontaneous symmetry breaking. Contrariwise, in the presence of weak linear intermode coupling, the asymmetry of the states is deterministically controlled via changes in phase (for all phases except 0 and $\pi$). Spontaneous symmetry breaking at zero phase is suppressed when the linear intermode coupling is increased, while for the $\pi$ phase it can be enhanced, so that the overall threshold for the spontaneous symmetry breaking can be significantly lower for nonzero linear coupling. These results are key for a fundamental understanding of the processes in Kerr resonators and other systems with Kerr-like nonlinearities and linear intermode coupling and have high prospects for the development of photonic devices, such as ultrasensitive sensors.

Concurrent natural time scales related to relaxation, recombination, trapping, and drifting processes rule the semiconductor heterostructures’ response to external drives when charge carrier fluxes are induced. This paper highlights the role of stoichiometry not only for the quantitative tuning of the electron-hole dynamics, but also for significant qualitative contrasts of time-resolved optical responses during the operation of resonant tunneling devices. Therefore, similar device architectures and different compositions have been compared to elucidate the correlation among structural parameters, radiative recombination processes, and electron-hole pair and minority-carrier relaxation mechanisms. When these ingredients intermix with the electronic structure in Sb-based tunneling devices, it is proven possible to assess various time scales according to the intensity of the current flux, contrary to what has been observed in As-based tunneling devices with similar design and transport characteristics. These time scales are strongly affected by the filling process in the $\mathrm{\Gamma }$ and $L$ states in Sb-based double-barrier quantum wells and by the small separation between these states, compared to similar heterostructures based on As.

Antimonide-based type-II superlattices represent a promising alternative to mercury cadmium telluride in infrared imaging applications. Among the original motivations for the development of type-II superlattices as a material system for infrared photodetectors is Auger engineering, the possibility of tailoring Auger processes to increase the “intrinsic” minority carrier lifetime at long wavelengths. We investigate Auger transitions in antimonide-based superlattices by means of a nonequilibrium Green’s function model based on a multiband description of the electronic structure and a GW treatment of carrier-carrier interactions. As carrier-phonon interactions mediated by acoustic deformation potential and polar optical scattering are included by means of appropriate self-energies, the resulting GW Auger rates may be considered as “phonon-dressed.” The spatial and spectral resolution afforded by the model provides a clear, graphical representation of the transitions contributing to the recombination process. A detailed study of Auger transitions in conventional and polytype superlattice absorbers demonstrates the effectiveness of the proposed approach for the design of Auger-suppressed infrared photodetectors. The calculated Auger coefficients are in good agreement with measurements extracted from pulsed threshold current densities of midwave infrared lasers with active regions realized with type-II quantum wells.

Precise control of individual particles is crucial for biomedical diagnostics, i.e., single-cell analysis and drug delivery. Acoustic tweezers have shown promise as a precise method for capturing microscale objects, but the spatial selectivity remains challenging to achieve with traditional electroacoustic transducers. An alternative to traditional ultrasound generation is to use photoacoustic conversion from laser pulses, allowing easy customization of acoustic field using optical light patterns, but this approach suffers from low efficiency of photoacoustic conversion. Here, we propose a field-hybridization technique to combine a hologram-generated photoacoustic field with a high-power featureless electroacoustic field. Theoretical and experimental validation show that while the force remains limited to the low pN range, the hybridization amplifies the photoacoustic radiation force by a factor of 80. By adjusting phase difference between electroacoustic and photoacoustic sources, the direction of particle motion can be reversed. The maximum trapping force is reached within 40 μm from the laser spot, which suggests that the method could enable highly precise and selective manipulation.

Coherent and dissipative couplings, respectively characterized by energy level repulsion and attraction, each have different applications for quantum information processing. Thus, a system in which both coherent and dissipative couplings are tunable on demand and in situ is tantalizing. A first step towards this goal is the two-tone driving of two bosonic modes, whose experimental signature was shown to exhibit controllable level repulsion and attraction by changing the phase and amplitude of one drive. However, whether the underlying physics is that of coherent and dissipative couplings has not been clarified, and cannot be concluded solely from the measured resonances (or antiresonances) of the system. Here, we show how the physics at play can be analyzed theoretically. Combining this theory with realistic finite-element simulations, we deduce that the observation of level attraction originates from interferences due to the measurement setup, and not dissipative coupling. Beyond the clarification of the origin of level attraction attributed to interference, our work demonstrates how effective Hamiltonians should be derived to appropriately describe the physics.

Interfacial Dzyaloshinskii-Moriya interaction (IFDMI) leads to noncollinear spin configurations within the magnetic layers of multilayer heterostructures, while its interlayer counterpart (ILDMI) minimizes chiral states between the layers. Here, we demonstrate that the symmetries of these interactions are very different, even though both arise from pairwise exchange interactions between magnetic sites mediated by nonmagnetic atoms. By deriving respective boundary conditions for the exchange operator and solving the associated boundary value problem, we show that, unlike IFDMI, which does not contribute to the FMR frequencies, ILDMI alters the frequencies of the fundamental FMR modes and can be separated from other contributions in an FMR experiment.

We propose a superconducting microwave relaxation oscillator based on a nanowire shunted by a resistor and an inductor controlled by quasiparticle injection from a tunnel junction positioned on it: the QUISTRON. This device exhibits relaxation oscillator behavior with dc voltage–controlled frequency tuning and dc bias. The device frequency is modulated via the tunnel junction, which induces localized heating by injecting quasiparticles. This heating mechanism modulates the nanowire switching current, enabling relaxation oscillations when it falls below the bias current. We simulate the device operating principles and its performance across various parameters, including different choices of shunt resistor, shunt inductance, and bath temperature ranging from 20 mK to 1 K. The device showed oscillation with a frequency range approximately between 1 and 10 GHz and total energy dissipation per cycle of approximately $100$ zJ. Our results suggest that this design offers a promising platform for compact, tunable superconducting oscillators in the microwave spectrum with potential applications in quantum information processing, microwave technology, and ultralow-power electronics. The straightforward frequency control mechanism and integration potential make this device an attractive candidate for superconducting microwave local oscillators.

Achieving high-quality solutions faster than classical solvers on computationally hard problems is a challenge for quantum optimization to deliver utility. Using a superconducting quantum computer, we experimentally investigate the performance of a hybrid quantum-classical algorithm inspired by semidefinite programming approaches for solving the maximum-cut problem on 3-regular graphs up to several thousand variables. We leverage the structure of the input problems to address sizes beyond what current quantum machines can naively handle. We attain an average approximation ratio of 99% over a random ensemble of thousands of problem instances. We benchmark the quantum solver against similarly high-performing classical heuristics, including the gurobi optimizer, simulated annealing, and the Burer-Monteiro algorithm. A run-time analysis shows that the quantum solver on large-scale problems is competitive against gurobi but short of others on a projected 100-qubit quantum computer. We explore multiple leads to close the gap and discuss prospects for a practical quantum speedup.