Laser propulsion has been proposed for relativistic interstellar flights, but it faces the significant challenge of requiring extremely powerful laser radiation due to the inherently low momentum transfer between the beam and the sail. The photon-recycling technique increases thrust by transferring momentum through multiple reflections within a cavity setup, formed by the lightsail and a ground-based mirror in a laser system array. In this work, a delay differential model is developed to describe the evolution of the beam and thrust, incorporating both the Doppler effect and the round-trip time delay experienced by each beam component. With optimized multilayer reflectors, the thrust performance gain is shown to be significant for interstellar flight, although limited by diffraction and the necessity of removing harmful redshifted radiation that could overheat the lightsail. By balancing thrust performance with thermal stability, we derive a simple condition for determining the spectral requirements of the mirrors. Given a selected laser wavelength, this condition fully specifies the necessary properties of the cavity mirrors, enabling the same system to effectively support a range of launch protocols.

The design of metallic contact grids on the front side of thermophotovoltaic cells is critical because it can cause significant optical and electrical resistive losses, particularly in the near field. However, from the theoretical point of view, this effect has been either discarded or studied by means of extremely simplified models such as the shadowing methods, that consist of simply ignoring the fraction of the semiconductor surface covered by metal. Our study, based on a rigorous three-body theoretical framework and implemented using the scattering matrix approach with the Fourier modal method augmented with adaptive spatial resolution, provides deeper insight into the influence of the front metal contact grid. This approach allows direct access to the radiative power absorbed by the semiconductor, enabling the proposal of an alternative definition for the thermophotovoltaic cell efficiency. By modeling this grid as a metallic grating, we demonstrate its significant effect on the net radiative power absorbed by the cell and, consequently, on the generated electrical power. Our analysis reveals behaviors differing substantially from those predicted by previous simplistic approaches.

The Brewster effect, a reflectionless phenomenon stemming from directional dipole radiation, is a basic principle in polarization optics. Typically, its manifestation is confined to a specific incident angle and polarization. Here, we break this constraint using cascaded non-Hermitian metasurfaces on a dielectric substrate, which collectively tailor dipole radiation, thereby enabling a generalized Brewster effect for arbitrarily selected angles and polarizations. Intriguingly, we find that this generalized Brewster effect is associated with exceptional points. Moreover, it can be achieved via diverse metasurface configurations, including dielectric, metallic, lossy, and gain metasurfaces. Microwave experiments using cascaded lossy-metallic metasurfaces confirm our theory. Our findings connect Brewster physics with non-Hermitian optics and enable advanced reflectionless wave manipulation.

There have been impressive breakthroughs in semiconductor quantum dots in recent years, with single- and two-qubit gate fidelities matching other leading platforms and scalability still remaining a relative strength; however, due to qubit wiring considerations, mobile electron architectures have been proposed to facilitate upward scaling, and this opens the possibility of enlarging the motional amplitude for electric-dipole spin resonance (EDSR)-based qubit manipulation. In this work, we examine and demonstrate the possibility of significantly outperforming static-EDSR-type single-qubit pulsing by taking advantage of greater spatial mobility to achieve higher Rabi frequencies and reduce the effect of charge noise. Our theoretical results indicate that fidelities are ultimately bottlenecked by spin-valley physics, which can be suppressed through the use of quantum optimal control. We demonstrate that, across different potential regimes and competing physical models, shuttling-based single-qubit gates retain significant advantages over existing alternatives.

In this study, we employed first-principles calculations combined with the Boltzmann transport equation to investigate the thermal transport and thermoelectric properties of $\mathrm{Cs}\mathrm{Ca}X$ ($X=\mathrm{Bi},\mathrm{P}$). Both $\mathrm{Cs}\mathrm{Ca}\mathrm{Bi}$ and $\mathrm{Cs}\mathrm{Ca}\mathrm{P}$ exhibited low lattice thermal conductivity, with ${\kappa }_L$ values of $0.79$ and $0.81{\mathrm{Wm}}^{-1}{\mathrm{K}}^{-1}$, respectively, at room temperature. The strong anharmonicity in both materials was attributed to the rattlers behavior of $\mathrm{Cs}$ atoms. Furthermore, our analysis revealed an anomalous contribution of approximately 72.1% to ${\kappa }_L$ along the $a$ axis from the optical acoustic branches in $\mathrm{Cs}\mathrm{Ca}\mathrm{P}$. Through the investigation of vibrational modes, we found that this was primarily caused by the out-of-phase vibrations of $\mathrm{Ca}$ and $\mathrm{P}$ atoms. The flat bands near the valence-band maximum resulted in a high Seebeck coefficient, leading to a high power factor. Consequently, the ZT values for $p$-type $\mathrm{Cs}\mathrm{Ca}\mathrm{Bi}$ and $\mathrm{Cs}\mathrm{Ca}\mathrm{P}$ at 700 K under optimal doping conditions reached 2.99 and 2.97, respectively.

Applying quantum annealing or current quantum- and physics-inspired algorithms for multiple-input multiple-output (MIMO) detection always abandon the direct Gray-coded bit-to-symbol mapping in order to obtain Ising form, leading to inconsistency errors. This often results in slow convergence rates and error floor, particularly with high-order-modulations. We propose HOPbit, an alternative MIMO detector designed to address this issue by transforming the MIMO detection problem into a higher-order Ising problem while maintaining Gray-coded bit-to-symbol mapping. The method then employs the simulated probabilistic bits (p-bits) algorithm to directly solve higher-order Ising problem without degradation. This innovative strategy enables HOPbit to achieve rapid convergence and attain near-optimal maximum-likelihood performance in most scenarios, even those involving high-order-modulations. The experiments show that HOPbit surpasses ParaMax by several orders of magnitude in terms of bit error rate (BER) in the context of 12-user massive and large MIMO systems even with less computing resources. In addition, HOPbit achieves lower BER rates compared to other traditional detectors.

Multiphoton processes deteriorate the quantum nondemolition (QND) character of the dispersive readout in circuit QED, causing the readout to lag behind single- and two-qubit gates in both speed and fidelity. Alternative methods such as longitudinal readout have been proposed; however, it is unknown to what extent multiphoton processes hinder this approach. Here, we investigate the QND character of the longitudinal readout of the transmon qubit. We show that the deleterious effects that arise due to multiphoton transitions can be heavily suppressed with detuning because the longitudinal interaction strength is independent of the transmon-resonator detuning. We consider the effect of circuit disorder, the selection rules that act on the transmon, and the description of longitudinal readout in the classical limit of the transmon to qualitatively demonstrate that longitudinal readout is robust. We show that fast, high-fidelity QND readout of transmon qubits is possible with longitudinal coupling.

Quantum computation holds great potential in revolutionizing information processing, with high-fidelity quantum gates serving as the cornerstone for realizing fault-tolerant quantum architectures. Here, we present a robust protocol for implementing high-fidelity entangling gates in Rydberg atomic systems via unconventional geometric quantum control strategies. By removing the stringent zero-dynamical-phase constraint inherent to conventional nonadiabatic geometric quantum computation, our scheme achieves high flexibility in designing driving fields while simultaneously enhancing gate fidelity and resilience against various errors. Notably, our protocol enables direct extension to multiqubit controlled-phase gate construction, with the gate duration remaining independent of the number of qubits involved. The results establish a practical and scalable framework for error-resilient quantum operations in Rydberg platforms, with broad implications for both fault-tolerant quantum computing and the quantum simulation of complex many-body systems.

We derive a generalized higher-order heat transport equation from first principles with the closure based on Onsager’s symmetry principle consistent second-order single-particle distribution function. The equation contains linear, nonlinear, local, nonlocal, and relaxation terms, and it unifies existing models, such as the Cattaneo-Vernotte model, the dual-phase-lag model, and phonon hydrodynamics, as special cases. The equation is analytically solved for (i) a thin-film semiconductor with diffusive boundaries to obtain effective thermal conductivity ($\kappa$) and heat flux ($\mathbf{q}$) as a function of film thickness, where the equation reduces to a similar form as phonon hydrodynamics, and (ii) for flux-limited behavior, where only nonlinear terms survive. The former analytical solution is compared with the in-house Monte Carlo solution of the Boltzmann transport equation using the phonon-dispersion relation and mean free path ($\lambda$) in the entire Brillouin zone for varying Knudsen number (Kn), previous experimental data, and other mesoscopic models. For the analytical solution of flux-limited behavior, by comparing the solution of the general equation with previous reports, we highlight the role of nonlinear terms, which have hitherto relied on phenomenological combinations rather than first-principles derivations. We further systematically investigate the Stokes approximation, i.e., $\mathbf{q}\ll {\lambda }^2{\mathrm{\nabla }}^2\mathbf{q}$, on the calculated $\kappa$ and $\mathbf{q}$ values and the use of first- and second-order boundary conditions. In particular, by explicit calculation of $\mathbf{q}$ and its higher-order derivatives across the entire simulation domain, we find that the assumption $\mathbf{q}\ll {\lambda }^2{\mathrm{\nabla }}^2\mathbf{q}$, which is often employed for $\mathrm{Kn}\gg 1$, is not applicable near boundaries. The study is significant because of the transport equation proposed here, which can be applied to a range of micro- and nanoscale heat transfer problems.

Recently, we have demonstrated that dye-doped soap and smectic bubbles can be used as lasers. Here we investigated smectic bubble lasers for their potential to measure pressure changes in both air and water and as microphones. Smectic bubbles consist of a very thin smectic liquid crystal film. In contrast to ordinary soap bubbles, smectic bubbles are highly stable. When illuminated with a pump laser, they exhibit whispering gallery mode lasing with sharp, regularly spaced peaks in the emission spectrum. The bubbles enable extremely precise measurement of pressure changes based on wavelength shifts of the lasing peaks. We have demonstrated that smectic bubbles can be inflated under water and used as water pressure sensors. Additionally, we have used smectic bubble lasers in air as highly sensitive microphones to detect sound waves across different frequencies with advantages over conventional microphones. Their extremely thin walls result in negligible acoustic impedance. Furthermore, bubble size changes due to pressure variations depend only on bubble volume, eliminating the need for calibration and making performance independent of manufacturing precision or defects. This also leads to a linear amplitude response, and a flat frequency response over a wide range of frequencies. Unlike most microphones, bubble lasers can measure arbitrarily small frequencies down to static pressure, making them promising candidates for acoustic wave detection in various applications.

We present a technique for detecting ultrahigh-frequency (UHF) radio fields using a three-photon Rydberg excitation scheme in a continuously laser-cooled sample of ${}^{87}\mathrm{Rb}$ atoms. By measuring Autler-Townes splitting, we demonstrate resonant detection of UHF fields with frequency range around 500–900 MHz through probing $n\mathrm{F}\to n\mathrm{G}$ transitions, achieving a lowest minimum detectable field of 2.5(6) mV/cm at 899 MHz. We also demonstrate continuous-time detection of a modulated rf signal, with a 3-dB bandwidth of 5.7(4) kHz at a carrier frequency of 899 MHz. Our approach employs atom loss spectroscopy rather than electromagnetically induced transparency , which enables detection while the atomic sample is simultaneously laser-cooled. We investigate this operating regime to determine the feasibility of combining the benefits of reduced thermal dephasing (and subsequent increased sensitivity) of cold atoms with the continuous operation associated with thermal atoms. Our continuous-time detection scheme provides an advantage over existing pulsed cold atom systems as we avoid the slow experimental duty cycles typically associated with replenishing the cold atom ensemble. We characterize the excitation scheme by varying laser detunings and analyze the impact and limitations due to various broadening mechanisms on the detection sensitivity.

Hybrid structures incorporating both III-nitride and transition-metal dichalcogenide (TMD) semiconductors have strong application potential for light harvesting and optoelectronics. Here, we have investigated the properties of hybrid structures based on a ${\mathrm{Mo}\mathrm{Se}}_2$ monolayer coupled to an $\mathrm{In}\mathrm{Ga}\mathrm{N}$ quantum well (QW). The coupling efficiency is controlled by a thin $\mathrm{Ga}\mathrm{N}$ barrier of variable thickness located between them. Time-integrated and time-resolved microphotoluminescence experiments show a quenching of the $\mathrm{In}\mathrm{Ga}\mathrm{N}$ QW exciton emission, which increases with the decrease of the $\mathrm{Ga}\mathrm{N}$ barrier thickness d: the PL intensity is reduced by a factor of three for d = 1 nm as a consequence of carrier transfer to the ${\mathrm{Mo}\mathrm{Se}}_2$ monolayer. This interplay between the two semiconductors is confirmed by time-resolved photoluminescence spectroscopy, highlighting a clear reduction of the QW exciton lifetime in the presence of the monolayer. Interestingly, the coupling between the QW and the TMD monolayer is also demonstrated by measuring optically the excitonic transport properties in the quantum well: the exciton diffusion length decreases in the presence of the ${\mathrm{Mo}\mathrm{Se}}_2$ monolayer. Measuring dependences as a function of temperature highlights the role played by localization effects in the QW. All these results can be effectively interpreted by a type-II band alignment between the $\mathrm{In}\mathrm{Ga}\mathrm{N}$ QW and the ${\mathrm{Mo}\mathrm{Se}}_2$ monolayer and a tunneling process between the two semiconductors.

We suggest a dynamical mechanism for angular sorting of subwavelength particles according to their resonances and sizes, realized using the forces imposed by acoustic (ultrasound) waves with different wavelengths. We analyze how the acoustic force acting on a small particle depends on its size relative to the ultrasound wavelength, and how the detuning between the two different beams influences the size range and angular distribution for unambiguous sorting outcomes for a given size range. We predict a range of scenarios that depend on the particular materials, and we provide several feasible examples and discuss their practical realization.

We compare methods for signal classification applied to voltage traces from transition edge sensors (TES) which are photon-number resolving detectors fundamental for accessing quantum advantages in information processing, communication, and metrology. We quantify the effect of numerical analysis on the distinction of such signals. Furthermore, we explore dimensionality reduction techniques to create interpretable and precise photon-number embeddings. We demonstrate that the preservation of local data structures of some nonlinear methods is an accurate way to achieve unsupervised classification of TES traces. We do so by considering a confidence metric that quantifies the overlap of the photon-number clusters inside a latent space. Furthermore, we demonstrate that for our dataset previous methods such as the signal’s area and principal component analysis can resolve up to 16 photons with confidence above 90% whereas nonlinear techniques can resolve up to 21 photons with the same confidence threshold. In addition, we showcase implementations of neural networks to leverage information within local structures, aiming to increase confidence in assigning photon numbers. Finally, we demonstrate the advantage of some nonlinear methods to detect and remove outlier signals.

In recent years, rare-earth oxyhalides and transition-metal nitride halides have been reported as gate dielectrics in field-effect transistor (FET) applications. However, chalcogenide halides have been rarely explored as gate dielectrics. In this work, we systematically evaluated the potential of $\mathrm{Sc}XY$ ($X$ = $\mathrm{S},\mathrm{Se},\mathrm{Te}$; $Y$ = $\mathrm{Cl},\mathrm{Br},\mathrm{I}$) monolayers as replacements for hBN, focusing on their stability, electronic properties, dielectric properties, and leakage current through first-principles calculations. Based on analyses of stability and band gap, we identified five monolayers, namely $\mathrm{Sc}\mathrm{S}Y$ ($Y$ = $\mathrm{Cl},\mathrm{Br},\mathrm{I}$), $\mathrm{Sc}\mathrm{Se}\mathrm{Br}$, and $\mathrm{Sc}\mathrm{Se}\mathrm{I}$, which are easily exfoliable and exhibit both thermodynamic and dynamic stability, with large band gaps (>2.0 eV). These materials also exhibit favorable band offsets, high dielectric constants (${\epsilon }_{\parallel }^0\sim 14.36-18.54$ and ${\epsilon }_{\mathrm{\perp }}^0\sim 3.25-4.35$), high breakdown strength (0.99 – 1.54 MV/cm), and low leakage currents (<${10}^{-6}$ A ${\mathrm{cm}}^{-2}$), indicating their potential as gate dielectric materials. Notably, the $\mathrm{Sc}\mathrm{SBr}$ monolayer stands out as the most promising candidate among the five ScXY monolayers, owing to its highest breakdown strength (1.54 MV/cm), largest conduction band minimum (CBM) offset, and the lowest leakage current (<${10}^{-10}$ A ${\mathrm{cm}}^{-2}$). Our study offers valuable insights into the development of chalcogenide halide gate dielectrics for next-generation electronic devices.