The symmetrization postulate in quantum mechanics is formally reflected in the appearance of an exchange phase governing the symmetry of identical-particle global states under particle swapping. Many indirect measurements of this fundamental phase have been reported thus far, but a direct observation has been achieved only recently for photons. Here, we propose a general scheme capable of directly measuring the exchange phase of any type of particle (bosons, fermions, or anyons), exploiting the operational framework of spatially localized operations and classical communication. We experimentally implement it on an all-optical platform, providing a proof of principle for different simulated exchange phases. As a by-product, we supply a direct measurement of the real bosonic exchange phase of photons. Additionally, we analyze the performance of the proposed scheme when mixtures of particles of different nature are injected. Our results confirm the symmetrization tenet and provide a tool to explore it in various scenarios. Finally, we show that the proposed setup is suited to generating indistinguishability-driven $\mathrm{NOON}$ states useful for quantum-enhanced phase estimation.

The nitrogen-vacancy center (NVC) in a diamond is a promising platform for Floquet engineering. Using the synchronized readout, we investigate the NVC’s Floquet state driven by the Carr-Purcell sequence in a large-amplitude ac magnetic field. We observe the dynamics represented as Bessel functions up to 211th order in a systematic and quantitative agreement with the theoretical model. Furthermore, numerical calculations show that the effect of finite pulse duration and error limits the modulation amplitude available for Floquet engineering. This work provides an approach to precisely investigate Floquet engineering, showing the extendable range of modulation amplitude for two-level systems.

Networks of semiconducting single-walled carbon nanotubes (SWCNTs) are interesting thermoelectric materials due to the interplay between CNT and network properties. Here, we present a unified model to explain charge and energy transport in SWCNT networks. We use the steady-state master equation for the random resistor network containing both intra- and intertube resistances, as defined through their one-dimensional density of states that are modulated by static Gaussian disorder. The tube-resistance dependence on the carrier density and disorder is described through the Landauer formalism. Electrical and thermoelectric properties of the network are obtained by solving Kirchhoff’s laws through a modified nodal analysis, where we use the Boltzmann-transport formalism to obtain the conductivity, Seebeck coefficient, and electronic contribution to the thermal conductivity. The model provides a consistent description of a wide range of previously published experimental data for temperature and charge-carrier-density-dependent conductivities and Seebeck coefficients, with energetic disorder being the main factor to explain the experimentally observed mobility upswing with carrier concentration. Moreover, we show that, for lower disorder energies, the Lorentz factor obtained from the simulation is in accordance with the Wiedemann-Franz law for degenerate-band semiconductors. At higher disorder, deviations from simple band behavior are found. Suppressed disorder energy and lattice thermal conductivity can be the key to higher thermoelectric figures of merit, zT, in SWCNT networks, possibly approaching or even exceeding zT = 1. The general understanding of transport phenomena will help the selection of chirality, composition, and charge-carrier density of SWCNT networks to improve their efficiency of thermoelectric energy conversion.

High-performance interrogation of an inductor-capacitor microsensor has been a long-standing challenge due to the limited size of the sensor. Parity-time ($PT$) symmetry, an intriguing concept originated from quantum physics, has been utilized to improve the spectral resolution and sensitivity of the conventional readout circuit, while the $PT$-symmetry condition has to be satisfied. In this work, a sandwich-type wireless capacitance readout mechanism based on perturbed $PT$-symmetric electronic trimer without manual tuning of the reader circuit is proposed. Theoretical eigenvalue analysis by solving the system equations shows that the system exhibits single real mode in weak coupling regime whose eigenfrequency changes in response to the capacitance of the neutral resonator. Furthermore, the proposed readout system exhibits wider readout capacitance range compared to the standard $PT$-symmetry-based system while retaining higher $Q$ factor compared to the conventional readout method, which has been validated with the experimental prototype based on printed circuit board. Our work not only enriches the underlying theory of non-Hermitian physics, but also shows potential applications in scenarios where longer interrogation distance is required, such as implanted medical devices, parameter detection in harsh environment, etc.

The bowing of the energy of the three lowest band-to-band transitions in $\beta \text{−}({\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}{)}_2{\mathrm{O}}_3$ alloys is resolved using a combined density-functional theory (DFT) and generalized spectroscopic ellipsometry approach. The DFT calculations of the electronic band structure of both $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ and $\theta \text{−}{\mathrm{Al}}_2{\mathrm{O}}_3$ allow the linear portion of the energy shift in the alloys to be extracted, and provide a method for quantifying the role of coherent strain present in the $\beta \text{−}({\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}{)}_2{\mathrm{O}}_3$ thin films on (010) $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ substrates. The energies of band-to-band transitions are obtained using the spectroscopic ellipsometry eigenpolarization model approach [A. Mock et al., Phys. Rev. B 95, 165202 (2017)]. After subtracting the effects of strain, which also induces additional bowing and after subtraction of the linear portion of the energy shift due to alloying, the bowing parameters associated with the three lowest band-to-band transitions in monoclinic $\beta \text{−}({\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}{)}_2{\mathrm{O}}_3$ are found.

Collective decision making is vital for recent information and communications technologies. In our previous research, we mathematically derived conflict-free joint decision making that optimally satisfies players’ probabilistic preference profiles. However, two problems exist regarding the optimal joint decision-making method. First, as the number of choices increases, the computational cost of calculating the optimal joint selection probability matrix explodes. Second, to derive the optimal joint selection probability matrix, all players must disclose their probabilistic preferences. Now, it is noteworthy that explicit calculation of the joint probability distribution is not necessarily needed; what is necessary for collective decisions is sampling. This study examines several sampling methods that converge to heuristic joint selection probability matrices that satisfy players’ preferences. We show that they can significantly reduce the above problems of computational cost and confidentiality. We analyze the probability distribution each of the sampling methods converges to, as well as the computational cost required and the confidentiality secured. In particular, we introduce two conflict-free joint sampling methods through the quantum interference of photons. The first system allows the players to hide their choices while satisfying the players’ preferences almost perfectly when they have the same preferences. The second system, where the physical nature of light replaces the expensive computational cost, also conceals their choices under the assumption that they have a trusted third party.

The grain-size effect of permittivity has been widely studied and its phenomenological theory is well established. In this work, we use such grain-size-effect theory to examine the grain-size effect of flexoelectricity, which has been overlooked so far. Two typical flexoelectric materials are employed, namely, ferroelectric ${\mathrm{Ba}\mathrm{Ti}\mathrm{O}}_3$ ceramics and paraelectric ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_3$ ceramics. The results suggest that the variation of the intrinsic flexoelectric coefficient is completely synchronized with the variation of the grain-size-dependent permittivity for ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_3$ ceramics. However, this synchronization is overturned in ${\mathrm{Ba}\mathrm{Ti}\mathrm{O}}_3$ ceramics, the flexoelectric coefficient of which increases with the grain size rather than dielectric permittivity. Under a flexoelectric field, it is proven that the polarization deflection of the 180° domains (more likely to exist for large grain sizes) dominates the flexoelectricity of ferroelectric ${\mathrm{Ba}\mathrm{Ti}\mathrm{O}}_3$ ceramics. The observed flexoelectric grain-size effect is beneficial for the design of bulk materials with a high flexoelectric coefficient and provides a simple and effective way to improve the performance of actuators and sensors based on bulk flexoelectricity.

Superconducting microwave circuits with Josephson junctions, the major platform for quantum computing, can only reach the full capability when connected. This requires an efficient protocol to distribute microwave entanglement. While quantum computers typically use discrete-variable (DV) methods for information encoding, the entire continuous-variable (CV) degree of freedom in electromagnetic fields must be utilized to achieve the highest entanglement distribution rate. Here, we propose a hybrid protocol to resolve the incompatibility between DV microwave quantum computers and CV quantum communications. CV microwave entanglement is distributed using optical swapping of optical-microwave entanglement pairs. To interface with DV microwave quantum computers, we further design a hybrid circuit to simultaneously convert and distill high-quality DV entanglement from noisy CV entanglement. The hybrid circuit is trained with machine-learning algorithms, ensuring high entanglement fidelity and generation rate. Our work not only provides a practical method to realize efficient quantum links for superconducting microwave quantum computers, but also opens avenues to bridge the gap between DV and CV quantum systems.

Strain and composition play a fundamental role in semiconductor physics, since they are means to tune the electronic and optical properties of a material and hence develop alternative devices. Today it is still a challenge to measure strain in epitaxial systems in a nondestructive manner, which becomes especially important in strain-engineered devices that often are subjected to intense stress. In this work, we demonstrate a microscopic mapping of the full tensors of strain and lattice orientation by means of scanning x-ray diffraction microscopy. We develop a formalism to extract all components of strain and orientation from a set of scanning diffraction measurements and apply the technique to a patterned ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ double layer to study strain relaxation and indium incorporation phenomena. The contributions due to varying indium content and threading dislocations are separated and analyzed.

The stochastic artificial neural network is widely studied nowadays, since it may address the critical issue of uncertainty quantification demanded in many application scenarios. At the hardware level, it calls for devices that can emulate stochastic weight-modification behaviors of synapses with high efficiency. In this work, we propose a stochastic spintronic synapse based on spin-torque-induced stochastic magnetic domain-wall (DW) dynamics, including stochastic DW generation by spin-transfer torque and deterministic DW motion induced by spin-orbit torque. The former plays the role of updating the synaptic weights stochastically, while the latter gives rise to multistates, namely, the analog property of the synapse. The proposed DW-based stochastic synapse requires few devices to implement sufficient resistance states. The neural-network-level simulation demonstrates that a spiking neural network based on these stochastic synapses is capable of classifying breast cancer data with a high accuracy of 95.7%.

Pulsating flows are common in many industrial, scientific, and natural fluidic systems. However, because the oscillatory flow component disturbs, e.g., optical measurements, deposition, or industrial processes, it is rarely desired. Moreover, in physiological conditions, pulsation control is desired. We explore the effect of using a plant-inspired nonlinear resistor to smooth the output of a peristaltic pump. Incorporating a 3D printed millifluidic biomimetic device reduces the oscillation amplitudes by 3 orders of magnitude, from $100\mathrm{\%}$ to $0.1\mathrm{\%}$ of the output flow rate. This represents a tenfold improvement relative to a purely linear resistive-capacitive approach. The observed flow kinetics compare well to a predictive model of peristaltic transport, allowing the further development of optimized fluid-handling systems driven by pulsatile flow. Applications to particle tracking and jetting are considered.

In conventional spintronic devices, ferromagnetic materials are used, which have a magnetization dynamics timescale of around nanoseconds, setting a limit for the switching speed. Increasing the magnetization switching speed has been one of the major challenges for spintronic research. In this work we take advantage of the ultrafast magnetic dynamics in ferrimagnetic materials instead of ferromagnets, and we use femtosecond laser pulses and a plasmonic photoconductive switch to create THz electrical pulses for ferrimagnetic switching by spin-orbit torque. By anomalous Hall and magneto-optic Kerr effect (MOKE) measurement, we demonstrate the robust THz-electrical-pulse-driven magnetization switching of ferrimagnetic $\mathrm{Gd}\text{−}\mathrm{Fe}\text{−}\mathrm{Co}$. The time-resolved MOKE shows more than 50-GHz magnetic resonance frequency of $\mathrm{Gd}\text{−}\mathrm{Fe}\text{−}\mathrm{Co}$, indicating faster than 20-ps magnetic dynamics. X-ray magnetic circular dichroism demonstrates the antiferromagnetically coupled $\mathrm{Fe}$ and $\mathrm{Gd}$ sublattices. Our work provides a promising route to realize ultrafast operation speed for nonvolatile magnetic memory and logic applications.

The spectrally narrow, spin-dependent optical transitions of nitrogen-vacancy (N-$V$) center defects in diamond can be harnessed for quantum networking applications. Key to such networking schemes is the generation of indistinguishable photons. Two challenges limit scalability in such systems: defect-to-defect variations of the optical transition frequencies caused by local strain variation, and spectral diffusion of the optical frequencies on repeated measurement caused by photoexcitation of nearby charge traps. In this experimental study we undertake a group-theoretic approach to quantifying spectral diffusion and strain, decomposing each into components corresponding to Jahn-Teller symmetries of the N-$V$ center. We investigate correlations between the components of strain, spectral diffusion, and depth from the surface, finding that strain and spectral diffusion are each dominated by longitudinal perturbations. We also find a weak negative correlation between transverse static strain and total spectral diffusion, suggesting that transverse strain provides some degree of protection from spectral diffusion. Additionally, we find that spectral diffusion becomes more pronounced with increasing depth in the diamond bulk. Our symmetry-decomposed technique for quantifying spectral diffusion can be valuable for understanding how a given nanoscale charge trap environment influences spectral diffusion and for developing strategies of mitigation.

The advent of optical frequency standards with ultimate uncertainties in the low $1\times {10}^{-18}$ requires femtosecond frequency combs to support a similar level of resolution in the spectral transfer and the computation of optical frequency ratios. The related experimental challenges grow together with the number of optical frequencies to be measured simultaneously, as in many cases the comb’s optical power does not allow reliable beatnote counting or tracking in all the spectral regions of interest. Here we describe the use of a track-and-hold amplifier to implement the gated detection, a previously proposed technique for improving the signal-to-noise ratio of the beatnote between a low-power tooth of the frequency comb and a continuous-wave laser. We demonstrate a 12-dB improvement in the signal-to-noise ratio of beatnotes involving a broadband-spanning optical comb as compared to traditional detection schemes. Our approach enables reliable and cycle-slip-free spectral purity transfer and reduces the system sensitivity to power drops in the comb spectrum. Being based on a single chip, it is robust, versatile, and easily embedded in more complex experimental schemes.

We propose that photon blockade can be enabled by a two-photon absorption environment. The validity of this conclusion is confirmed by studying the blockade in a driven single-mode cavity. The feature of this environmentally induced photon blockade is that the nonlinear interaction in the system is not needed, which is entirely different from the conventional and the unconventional blockade mechanisms. We clearly give the physics behind this blockade mechanism. And the advantages of this environmentally induced photon blockade are discovered by comparing it with the conventional mechanism in a weakly driven region. In addition, we show that the proposal can be generalized straightforwardly to realize environmentally induced photon blockade in two coupled single-mode cavities.

Entanglement between distant massive mechanical oscillators is of particular interest in quantum-enabled devices due to its potential applications in distributed quantum information processing. Here we propose how to achieve nonreciprocal remote entanglement between two spatially separated mechanical oscillators within a cascaded optomechanical configuration, where the two optomechanical resonators are indirectly coupled through a telecommunication fiber. We show that by selectively spinning the optomechanical resonators, one can break the time-reversal symmetry of this compound system via the Sagnac effect, and more excitingly, enhance the indirect couplings between the mechanical oscillators via the individual optimizations of light-motion interaction in each optomechanical resonator. This ability allows us to generate and manipulate nonreciprocal entanglement between distant mechanical oscillators, that is, entanglement can be achieved only through driving the system from one specific input direction but not the other. Moreover, in the case of two frequency-mismatched mechanical oscillators, it is also found that the degree of the generated nonreciprocal entanglement is counterintuitively enhanced in comparison with its reciprocal counterparts, which are otherwise unattainable in static cascaded systems with a single-tone driving laser. Our work, which is well within the feasibility of current experimental capabilities, provides an enticing opportunity to explore the nonclassical correlations between distant massive objects and facilitates a variety of emerging quantum technologies ranging from quantum information processing to quantum sensing.

Deterministic generation of single photons is essential for many quantum information technologies. A bulk optical nonlinearity emitting a photon pair, where the measurement of one of the photons heralds the presence of the other, is commonly used with the caveat that the single-photon emission rate is constrained due to a trade-off between multiphoton events and pair emission rate. Using an efficient and low noise photon-number-resolving superconducting nanowire detector we herald, in real time, a single photon at telecommunication wavelength. We perform a second-order photon correlation $g^2(0)$ measurement of the signal mode conditioned on the measured photon number of the idler mode for various pump powers and demonstrate an improvement of a heralded single-photon source. We develop an analytical model using a phase-space formalism that encompasses all multiphoton effects and relevant imperfections, such as loss and multiple Schmidt modes. We perform a maximum-likelihood fit to test the agreement of the model to the data and extract the best-fit mean photon number $\mu$ of the pair source for each pump power. A maximum reduction of $0.118\pm 0.012$ in the photon $g^2(0)$ correlation function at $\mu =0.327\pm 0.007$ is obtained, indicating a strong suppression of multiphoton emissions. For a fixed $g^2(0)=7\times {10}^{-3}$, we increase the single pair generation probability by 25%. Our experiment, built using fiber-coupled and off-the-shelf components, delineates a path to engineering ideal sources of single photons.

We investigate the stimulated emission of superradiant atoms coupled to a waveguide induced by a coherent-state photon pulse. We provide an analytical result when a short $\pi$ pulse is incident, which shows that the atoms emit photons coherently into the output pulse, which remains a coherent state in the short pulse limit. An incident pulse is amplified in a phase-preserving manner, where noise is added almost entirely in the phase direction in phase space. This property improves the ratio of the intensity signal to noise after the amplification for sufficiently short pulses. This is a unique feature different from general phase-preserving linear amplifiers, where the signal-to-noise ratio deteriorates in the amplification process. We also discuss the dependence of the photon-emission probability on pulse parameters, such as the pulse area and the duration.