We introduce a fast and highly efficient physically realizable bit swap. Employing readily available and scalable Josephson junction microtechnology, the design implements the recently introduced paradigm of momentum computing. Its nanosecond speeds and sub-Landauer thermodynamic efficiency arise from dynamically storing memory in momentum degrees of freedom. As such, during the swap, the microstate distribution is never near equilibrium and the memory-state dynamics fall far outside of stochastic thermodynamics that assumes detailed-balanced Markovian dynamics. The device implements a bit-swap operation—a fundamental operation necessary to build reversible universal computing. Extensive, physically calibrated simulations demonstrate that device performance is robust and that momentum computing can support thermodynamically efficient, high-speed, large-scale general-purpose computing that circumvents Landauer’s bound.

To achieve secure quantum key distribution, all imperfections in the source unit must be incorporated in a security proof and measured in the lab. Here we perform a proof-of-principle demonstration of the experimental techniques for characterizing the source phase and intensity fluctuation in commercial quantum key distribution systems. When we apply the measured phase-fluctuation intervals to the security proof that takes into account fluctuations in the state preparation, it predicts a key distribution distance of over $100\mathrm{km}$ of fiber. The measured intensity fluctuation intervals are, however, so large that the proof predicts zero key, indicating a source improvement may be needed. Our characterization methods pave the way for a future certification standard.

The problem of inverse design is rooted to the classical problem of inverse scattering. In general, these highly nonlinear and often ill-posed problems are solved via extensive optimization techniques. In this paper, we suggest an optimization-free method for the inverse design of a one-dimensional medium with spatially inhomogeneous dielectric constant $ϵ(z)$. In addition, we derive the governing equation of an analog problem—a time-dependent homogeneous medium—and use the same technique for inverse design of the temporal profile $ϵ(t)$ of a spatially homogeneous medium that is required to achieve a desired frequency response in $k$-space. Lastly, we use this optimization-free inversion approach to demonstrate the design of the reflection response such that the reflected wave undergoes a desired filtering, such as of Tchebychev type, differentiator, and a matched filter for chirp signal detection over additive Gaussian noise, which is of high potential significance in chirp radar and sonar applications.

Acoustic separation of suspension cells can be achieved by altering the properties of the cell medium. Cells of different types can then migrate in opposing directions in the sound field due to differences in their relative density and compressibility with respect to the surrounding fluid. For near-zero acoustic contrast the acoustic radiation force on cells becomes negligible, and it is the primary objective of this paper to study the interplay of acoustic radiation, acoustic streaming, and buoyancy in this regime and how it may affect the separation outcome. We study the three-dimensional acoustophoretic motion of suspension cells in homogeneous suspending media and link this to the underlying acoustofluidic mechanisms. Cell trajectories are measured by a defocused-image tracking approach, and we assess the technique's applicability for tracking cells by determining the associated error when measuring the out-of-image-plane component of the tracks. For cells at near-zero acoustic contrast, we observe strong effects of buoyancy and acoustic streaming and that small distributions of cell properties within a population leads to large differences in the cell motion patterns. A neural network was developed to classify experimental cell trajectories according to their acoustic contrast in different suspending media. Further, we compare the experimentally measured trajectories to a numerical model by generating simulated trajectories of cells.

Orbital-angular-momentum- (OAM) based photonic nonlinear interfaces, such as the nonlinear manipulation of a single-photon OAM state between the communication wavelength for entanglement distribution and the near-visible wavelength for quantum memories. Here, we experimentally demonstrate this kind of quantum state transformation for simultaneously adjusting the weight of the spatial OAM modes and operating the wavelength of single photons by effectively cascading the frequency conversion and electro-optical (EO) polarization coupling in a periodically poled lithium niobate crystal. The fidelity of the OAM state is measured to be higher than 95% before and after the frequency conversion. The results show that the OAM state of single photons can be modulated on demand by applying a transverse electric field across the nonlinear crystal. Our work demonstrates the integration and high performance of our proposed transformation interface, and paves a route toward connecting different remote nodes based on quantum memories in a large-scale OAM-encoded quantum network.

$(\mathrm{In},\mathrm{Ga})\mathrm{N}$-based light-emitting diodes (LEDs) are known to suffer from low electron-hole wave-function overlap due to a high piezoelectric field. Staggered $(\mathrm{In},\mathrm{Ga})\mathrm{N}$ quantum wells (QWs) are proposed to increase the wave-function overlap and improve the efficiency of LEDs, especially for long-wavelength emitters. In this work, we show evidence that the growth of staggered QWs by plasma-assisted molecular beam epitaxy has another beneficial effect, as it allows a reduction in the formation of defects, responsible for nonradiative Shockley-Read-Hall recombination, at the bottom interface of the QW. Staggered QWs comprised an $(\mathrm{In},\mathrm{Ga})\mathrm{N}$ layer of an intermediate $\mathrm{In}$ content between the barrier and the QW. We show that insertion of such a layer results in a significant increase of the luminescence intensity, even if the calculated wave-function overlap drops. We study the dependence of the thickness of such an intermediate-$\mathrm{In}$-content layer on photoluminescence intensity behavior. Staggered QWs exhibit increased cathodoluminescence homogeneity that is a fingerprint of a lower density of defects, in contrast to standard QWs for which a high density of dark spots is observed in QW-emission mapping. Transmission electron microscopy of standard QWs reveals the formation of basal-plane stacking faults and voids that can result from vacancy aggregation. A stepwise increase of the $\mathrm{In}$ content in staggered QWs prevents the formation of point defects and results in an increased luminescence efficiency. The $\mathrm{In}$-composition difference between the barrier and the well is, therefore, a key parameter to control the formation of point defects in the high-$\mathrm{In}$-content QWs, influencing the luminescence efficiency. Characteristics of the cyan laser diode (LD) utilizing staggered QWs are presented.

Optomechanical crystal cavities (OMCCs) are fundamental nanostructures for a wide range of phenomena and applications. Usually, optomechanical interaction in such OMCCs is limited to a single optical mode and a unique mechanical mode. In this sense, eliminating the single-mode constraint—for instance, by adding more mechanical modes—should enable more complex physical phenomena, giving rise to a context of multimode optomechanical interaction. However, a general method to produce in a controlled way multiple mechanical modes with large coupling rates in OMCCs is still missing. In this work, we present a route to confine multiple GHz mechanical modes coupled to the same optical field with similar optomechanical coupling rates—up to 400 kHz—by OMCC engineering. In essence, we increase the number of unit cells (consisting of a silicon nanobrick perforated by circular holes with corrugations at both its sides) in the adiabatic transition between the cavity center and the mirror region. Remarkably, the mechanical modes in our cavities are located within a full phononic band gap, which is a key requirement to achieve ultrahigh mechanical $Q$ factors at cryogenic temperatures. The multimode behavior in a full phononic band gap and the easiness of realization using standard silicon nanotechnology make our OMCCs highly appealing for applications in the classical and quantum realms.

The evaluation of the specific power absorption of magnetic nanoparticles (MNPs) for magnetic hyperthermia (MH) applications has been performed through either local temperature probing or magnetic measurements so far. Each of these methods has advantages and drawbacks, and the concurrent use of both techniques offers the most reliable results. In this work, we propose an alternative strategy based on thermographic images to obtain two-dimensional temperature maps that allow the determination of the power absorption and other relevant thermodynamic parameters in MH experiments in a noninvasive way. This procedure and analysis are convenient to determine the heating performance of MNPs under the viscous conditions of in vitro and in vivo assays and to follow the time evolution of the temperature spatial distribution in the sample simultaneously. For this purpose, iron-oxide MNPs with 25-nm average diameter are coated with glucose and dispersed into different 8% polyacrylamide gels, which serve as phantoms that emulate intracellular viscosity. Power absorption experiments are performed under ac magnetic fields ($H=$ 32 kA/m; $f=$ 350 kHz) and the temperature evolution of the sample is monitored through a commercial thermographic camera (resolution, $240\times 180$ pixels; temperature accuracy, 2 K). To complement this simple setup, we design a program consisting of a detailed procedure for extracting graphical information from the video frames and obtaining spatiotemporal temperature profiles. The analysis of these profiles allows us to gather information on temperature, energy, power, and heat flux during the MH experiments. This method and analysis allows us to identify spatial inhomogeneities in samples, such as different local MNP density, which is extremely useful for the development of the therapy in vitro and the application in vivo where MNP aggregation is often present.

Nondiffracting light beams receive substantial attention in various areas due to their properties of diffractionless propagation and achievable subwavelength beam size. Extending the propagation distance and compressing the beam size of nondiffracting beams are crucial to their practical applications. However, it remains challenging to achieve nondiffracting light beams with a subwavelength subdiffracting transverse size and a long propagation distance with controllable intensity profiles in both transverse and longitudinal directions. Here, we propose an optimization method to generate an ultralong-superoscillation nondiffracting light beam with full control of the beam intensity profile. A 45λ-long-superoscillation nondiffracting light beam, the transverse sizes of which are within the range of 0.37λ–0.4λ along the propagation axis, is experimentally demonstrated by a metalens based on continuous phase modulation using geometrical phase metasurfaces. Our method provides an attractive way to controllably generate ultralong-superoscillation nondiffracting beams on a subwavelength scale and might find fascinating applications in optical manipulation, materials processing, data storage, microscopy, and spectroscopy.

To design fast memory devices, we need material combinations that can facilitate fast read and write operations. We present a heterostructure comprising a two-dimensional (2D) magnet and a 2D topological insulator (TI) as a viable option for designing fast memory devices. We theoretically model the spin-charge dynamics between 2D magnets and 2D TIs. Using the adiabatic approximation, we combine the nonequilibrium Green’s function method for spin-dependent electron transport and a time-quantified Monte Carlo method for simulating magnetization dynamics. We show that it is possible to switch a magnetic domain of a ferromagnet using the spin torque from spin-polarized edge states of a 2D TI. We show further that the switching of 2D magnets by TIs is strongly dependent on the interface exchange ($J_{\mathrm{int}}$), and an optimal interface exchange, is required for efficient switching. Finally, we compare experimentally grown Cr compounds and show that Cr compounds with higher anisotropy (such as $\mathrm{Cr}{\mathrm{I}}_3$) result in a lower switching speed but a more stable magnetic order.

The two-dimensional homojunction is promising in electronic and optoelectronic applications. However, its performance is restricted by lattice mismatch and the depletion region. Here, we construct a monolayer $\mathrm{In}\mathrm{Se}$-based p-i-n homojunction photodetector. It presents high photoelectric conversion with a wide light response in the photon-energy range from 1.4 to 5 eV, which induces a photocurrent density of 13.13 nA ${\mathrm{m}}^{-1}$ and a photoresponsivity of 0.022 A ${\mathrm{W}}^{-1}$. Moreover, the gate voltage improves the photocurrent and photoresponsivity almost fourfold. Additionally, the increasing dielectric constant of the substrate decreases the photocurrent spectral width, and a low doping concentration is suitable for photodetectors due to high mobility. These results indicate that the two-dimensional p-i-n homojunction is promising for future photoelectric devices.

We report the characteristic magnetic properties of several members of the family of rare-earth garnets, ${\mathrm{Gd}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ (GGG), ${\mathrm{Dy}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$, ${\mathrm{Tb}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$, and ${\mathrm{Nd}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$, and compare their relative potential utility for magnetocaloric cooling, including their minimal adiabatic demagnetization refrigeration (ADR) temperatures and relative cooling parameters. A main objective of this work concerns the identification of potential improvements over the magnetocaloric properties of GGG for use in low-temperature ADR cryostats. Using ${\mathrm{Tb}}^{+3}$ and ${\mathrm{Dy}}^{+3}$ at the rare-earth site offers, in principle, a higher saturation magnetization and ${\mathrm{Nd}}^{+3}$ gives a lower de Gennes factor and therefore potentially reduced magnetic transition temperatures, limiting the useful temperature range. Our results show that ${\mathrm{Dy}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ yields an optimal relative cooling parameter at low applied fields and low limiting temperatures, which would allow for the design of more efficient ADR cryostats.

We present a flexible method to study the optical properties of an ${\mathrm{Er}}^{3+}$ ensemble in $\mathrm{Si}$ accessed via resonant excitation and in situ single-photon detection. The technique allows an efficient resonant photoluminescence detection of optically active centers with weak oscillator strength in transparent crystals without the need for nanofabrication on the sample. We observe 70 ${\mathrm{Er}}^{3+}$ resonances in $\mathrm{Si}$, of which 62 resonances have not been observed in the literature, with optical lifetimes ranging from 0.5 to 1.5 ms. We observe inhomogeneous broadening of less than 400 MHz and an upper bound on the homogeneous linewidth of 0.75 and 1.4 MHz for two separate resonances. These narrow, stable resonances confirm ${\mathrm{Er}}^{3+}$ in $\mathrm{Si}$ as a promising quantum information candidate. We discuss the use of this technique for rapid characterization of future samples, with the aim of enhancing the prevalence of sites which are favorable for quantum information applications.

Quantum secure direct communication (QSDC) can directly transmit secrete messages through a quantum channel. Device-independent (DI) QSDC can guarantee the communication security relying only on the observation of the Bell-inequality violation, but not on any detailed description or trust of the inner workings of users’ devices. In the paper, we propose a DI-QSDC protocol with practical highly efficient single-photon sources. The communication parties construct the entanglement channel from single photons by adopting the heralded architecture, which makes the message-leakage rate independent of the photon-transmission loss. The secure communication distance and the practical communication efficiency of the current DI-QSDC protocol are about 6 times and 600 times of those in the original DI-QSDC protocol. Combining with the entanglement purification, the parties can construct the nearly perfect entanglement channel and completely eliminate the message leakage. This DI-QSDC protocol may have useful applications in the future quantum communication field.

Nanosecond electron pulses are appealing for ultrafast imaging and electron-gating applications, where tunable currents and narrow energy spreads are desirable. Here, we demonstrate photoemission from a Schottky emitter triggered by nanosecond laser pulses. Using photon energies optimally tuned to the emission potential barrier, we generate pulses containing over ${10}^5$ electrons with energy spreads below 1 eV by means of a prompt single-photon photoemission process. These results are consistent with a theoretical model of laser-triggered electron emission and energetic broadening during propagation and can be widely implemented.

The thermoelectric energy-conversion efficiency is significantly enhanced by introducing magnetism. Doping $\mathrm{Cr}$ atoms in a ${\mathrm{Cu}}_2{\mathrm{Sn}\mathrm{S}}_3(\mathrm{CTS})$ matrix modifies the electron density of state (e-DOS) and causes a special electron-transport mechanism by localized impurity spin moments. The localized spin moments cause a spin-spin exchange interaction with the spin of itinerant electrons of the CTS matrix. This is clearly verified in M-T measurement, which deviated from Curie’s law. The figure of merit (zT) of the magnetic nanocomposite was 8 times higher than that of pristine CTS by the synergetic effect of modifying e-DOS near the Fermi level and electron transport by localized spin moments.

In the design optimization of ion-cavity interfaces for quantum networking applications, difficulties occur due to the many competing figures of merit and highly interdependent design constraints, many of which present “soft limits,” which are amenable to improvement at the cost of engineering time. In this work, we present a systematic approach to this problem that offers a means to identify efficient and robust operating regimes and to elucidate the trade-offs involved in the design process, allowing engineering efforts to be focused on the most sensitive and critical parameters. We show that in many relevant cases it is possible to approximately separate the geometric aspects of the cooperativity from those associated with the atomic system and the mirror surfaces themselves, greatly simplifying the optimization procedure. Although our approach to optimization can be applied to most operating regimes, here we consider cavities suitable for typical ion-trapping experiments and with substantial transverse misalignment of the mirrors. We find that cavities with mirror misalignments of many micrometers can still offer very high photon extraction efficiencies, offering an appealing route to the scalable production of ion-cavity interfaces for large-scale quantum networks.

Several current searches for physics beyond the standard model are based on measuring the electron-capture (EC) decay of radionuclides implanted into cryogenic high-resolution sensors. The sensitivity of these experiments has already reached the level where systematic effects related to atomic state energy changes from the host material are a limiting factor. One example is a neutrino mass study based on the nuclear EC decay of ${}^7\mathrm{Be}$ to ${}^7\mathrm{Li}$ inside cryogenic $\mathrm{Ta}$-based sensors. To understand the material effects at the required level, we use density-functional theory to model the electronic structure of lithium atoms in different atomic environments of the polycrystalline $\mathrm{Ta}$ absorber film. The calculations reveal that the $\mathrm{Li}$ 1s binding energies can vary by more than 2 eV due to insertion at different lattice sites, at grain boundaries, in disordered $\mathrm{Ta}$, and in the vicinity of various impurities. However, the total range of $\mathrm{Li}$ 1s shifts does not exceed 4 eV, even for extreme amorphous disorder. Furthermore, when investigating the effects on the $\mathrm{Li}$ 2s levels, we find broadening of more than 5 eV due to hybridization with the $\mathrm{Ta}$ band structure. Material effects are shown to contribute significantly to peak broadening in $\mathrm{Ta}$-based sensors that are used to search for physics beyond the standard model in the EC decay of ${}^7\mathrm{Be}$, but they do not explain the full extent of observed broadening. Understanding these in-medium effects will be required for current- and future-generation experiments that observe low-energy radiation from the EC decay of implanted isotopes to evaluate potential limitations on the measurement sensitivity.

Phononic frequency combs represent the mechanical analog of optical frequency combs. Several independent experimental studies have demonstrated the onset and evolution frequency comb response in a variety of micro- and nanoelectromechanical devices in recent years. A theoretical basis for exploring and understanding the conditions for comb generation and evolution with varying driving parameters is essential to enable future practical applications. Here, we present the comparison between modeling and experimental results on the generation and evolution mechanism of phononic frequency combs in a nonlinear micromechanical resonator from the perspective of coherent energy transfer between two mechanical modes. Phononic frequency combs emerge in a strong coupling regime involving nonlinear resonances when the amplitudes and phases of two coupled mechanical modes are modulated via coherent energy transfer. The spacing and number of comb teeth can be analytically estimated based on modeling the nature of the interaction of the coupled modes under the specified driving conditions. As the driving conditions are varied, the phononic frequency comb evolves into different forms and a phenomenological model for the system is established to accurately predict the evolution of phononic frequency combs. The alignment between experiment and model provides a basis for the engineering of this phenomenon in future device applications.