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In the transportation sector, ammonia used as a power source plays a significant role in the scenario of carbon neutralization. However, the engine-out emissions correlations of ammonia-diesel dual-fuel (DF) engines are still unclear, especially the nitro-compounds of great concern and GHG. In this study, the engine-out emissions are evaluated by using a four-cylinder ammonia/diesel DF engine. Various operating conditions consisting of ammonia energy ratio (AER), engine load, and speed were carried out. Unburned NH3 increases with raising ammonia content but decreases with increasing engine load and speed. The NO+NO2 tendency shows a non-linearity trend with increasing ammonia content, while a trade-off correlation is linked to N2O. The N2O emission of ammonia engine significantly weakens the beneficial effect of GHG reduction, the 30% and 50% decarbonization targets need at least 40% and 60% ammonia energy without regard to N2O effect, while at least 65% and 80% ammonia energy respectively with considering N2O. N2O presents a parabolic-like tendency with AERs. Advanced pilot-diesel injection timing helps to reduce both NH3 and N2O, but this effect becomes insignificant as the AER is less than 0.4. A combustion strategy of the rapid heat release and ammonia-governed heat release respectively are revealed.

Quantum interference effects in the unmodulated quantum systems with light-matter interaction have been widely studied, such as electromagnetically induced transparency (EIT) and Autler-Townes splitting (ATS). However, the similar quantum interference effects in the Floquet systems (i.e., periodically modulated systems), which might cover rich new physics, were rarely studied. In this article, we investigate the quantum interference effects in the Floquet two- and three-level systems analytically and numerically. We show a coherent destruction tunneling effect in a lotuslike multipeak spectrum with a Floquet two-level system, where the intensity of the probe field is periodically modulated with a square-wave sequence. We demonstrate that the multipeak split into multiple transparency windows with tunable quantum interference if the Floquet system is asynchronously controlled via a third level. Based on phenomenological analysis with Akaike information criterion, we show that the symmetric central transparency window has a similar mechanism to the traditional ATS or EIT depending on the choice of parameters, additional with an extra degree of freedom to control the quantum interference provided by the modulation period. The other transparent windows are shown to be asymmetric, different from the traditional ATS and EIT windows. These nontrivial quantum interference effects open up a scope to explore the applications of the Floquet systems.

Exceptional points (EPs) are exotic degeneracies of non-Hermitian systems, where the eigenvalues and the corresponding eigenvectors simultaneously coalesce in parameter space, and these degeneracies are sensitive to tiny perturbations on the system. Here we report an experimental observation of the EP in a hybrid quantum system consisting of dense nitrogen (P1) centers in diamond coupled to a coplanar-waveguide resonator. These P1 centers can be divided into three subensembles of spins, and cross relaxation occurs among them. As a new method to demonstrate this EP, we pump a given spin subensemble with a drive field to tune the magnon-photon coupling in a wide range. We observe the EP in the middle spin subensemble coupled to the resonator mode, irrespective of which spin subensemble is actually driven. This robustness of the EP against pumping reveals the key role of the cross relaxation in P1 centers. It offers a novel way to convincingly prove the existence of the cross-relaxation effect via the EP., Comment: 16 pages, 10 figures

The ultra-wide bandgap of diamond distinguishes it from other semiconductors, in that all known defects have deep energy levels that are inactive at room temperature. Here, we present the effect of deep defects on the mechanical energy dissipation of single-crystal diamond experimentally and theoretically up to 973 K. Energy dissipation is found to increase with temperature and exhibits local maxima due to the interaction between phonons and deep defects activated at specific temperatures. A two-level model with deep energies is proposed to well explain the energy dissipation at elevated temperatures. It is evident that the removal of boron impurities can substantially increase the quality factor of room-temperature diamond mechanical resonators. The deep-energy nature of nitrogen bestows single-crystal diamond with outstanding low-intrinsic energy dissipation in mechanical resonators at room temperature or above., Comment: 6 pages, 4 figures

Recently, we have witnessed great progress in the field of medical imaging classification by adopting deep neural networks. However, the recent advanced models still require accessing sufficiently large and representative datasets for training, which is often unfeasible in clinically realistic environments. When trained on limited datasets, the deep neural network is lack of generalization capability, as the trained deep neural network on data within a certain distribution (e.g. the data captured by a certain device vendor or patient population) may not be able to generalize to the data with another distribution. In this paper, we introduce a simple but effective approach to improve the generalization capability of deep neural networks in the field of medical imaging classification. Motivated by the observation that the domain variability of the medical images is to some extent compact, we propose to learn a representative feature space through variational encoding with a novel linear-dependency regularization term to capture the shareable information among medical data collected from different domains. As a result, the trained neural network is expected to equip with better generalization capability to the "unseen" medical data. Experimental results on two challenging medical imaging classification tasks indicate that our method can achieve better cross-domain generalization capability compared with state-of-the-art baselines., Comment: Accepted by NeurIPS, 2020

Floquet theory combined with the generalized Van Vleck nearly degenerate perturbation theory, has been widely employed for studying various two-level systems that are driven by external fields via the time-dependent longitudinal (i.e., diagonal) couplings. However, three-level systems strongly driven by the time-dependent transverse (i.e., off-diagonal) couplings have rarely been investigated, due to the breakdown of the traditional rotating wave approximation. Meanwhile, the conventional perturbation theory is not directly applicable, since a small parameter for the perturbed part is no longer apparent. Here we develop a double-unitary-transformation approach to deal with the periodically modulated and strongly driven systems, where the time-dependent Hamiltonian has large off-diagonal elements. The first unitary transformation converts the strong off-diagonal elements to the diagonal ones, and the second enables us to harness the generalized Van Vleck perturbation theory to deal with the transformed Floquet matrix and also allows us to reduce the infinite-dimensional Floquet Hamiltonian to a finite effective one. For a strongly modulated three-level system, with the combination of the Floquet theory and the transformed generalized Van Vleck perturbation theory, we obtain analytical results of the system, which agree well with exact numerical solutions. This method offers a useful tool to analytically study the multi-level systems with strong transverse couplings., Comment: 13 pages, 10 figures

One key issue in the probability density function (PDF) approach for disperse two-phase turbulent flows is to close the diffusion term in the phase space. This study aimed to derive a kinetic equation for particle dispersion in turbulent flows by ensemble averaging over all possible realisations of state transition paths in the phase space. The probability density function is expanded as a series in terms of the cumulants of particle paths in the phase space, by introducing a local path density operator to identify the distribution of particle paths. The expansion enables us to directly obtain a kinetic equation with the diffusion term in closed form. The kinetic equation derived in this study has following features that: (1) it has its coefficients expressed as functions of the cumulants of particle paths in the phase space; (2) it applies to particle dispersion by non-Gaussian random forcing with long correlation time scales; (3) it presents new mechanisms responsible for particle diffusion. An application of the kinetic equation is also presented in this paper.

We experimentally demonstrate strong coupling between the ferromagnetic magnons in a small yttrium-iron-garnet (YIG) sphere and the drive-field-induced dressed states of a superconducting qubit, which gives rise to the double dressing of the superconducting qubit. The YIG sphere and the superconducting qubit are embedded in a microwave cavity and the effective coupling between them is mediated by the virtual cavity photons. The theoretical results fit the experimental observations well in a wide region of the drive-field power resonantly applied to the superconducting qubit and reveal that the driven qubit-magnon hybrid quantum system can be harnessed to emulate a particle-hole-symmetric pair coupled to a bosonic mode. This hybrid quantum system offers a novel platform for quantum simulation of the composite quasi-particles consisting of fermions and bosons., Comment: 6 pages, 4 figures

Physical systems in the time domain may exhibit analogous phenomena in real space, such as time crystals, time-domain Fresnel lenses, and modulational interference in a qubit. Here we report the experimental realization of time-domain grating using a superconducting qutrit in periodically modulated probe and control fields via two schemes: Simultaneous modulation and complementary modulation. Both experimental and numerical results exhibit modulated Autler-Townes (AT) and modulation-induced diffraction (MID) effects. Theoretical results also confirm that the peak positions of the interference fringes of AT and MID effects are determined by the usual two-level relative phases, while the observed diffraction fringes, appearing only in the complementary modulation, are however related to the three-level relative phase. Further analysis indicates that such a single-atom time-domain diffraction originates from the correlation effect between the two time-domain gratings. Moreover, we find that the widths of the diffraction fringes are independent of the control-field power. Our results shed light on the experimental exploration of quantum coherence for modulated multi-level systems and may find promising applications in fast all-microwave switches and quantum-gate operations in the strong-driving regime.

A new optimized extreme learning machine- (ELM-) based method for power system transient stability prediction (TSP) using synchrophasors is presented in this paper. First, the input features symbolizing the transient stability of power systems are extracted from synchronized measurements. Then, an ELM classifier is employed to build the TSP model. And finally, the optimal parameters of the model are optimized by using the improved particle swarm optimization (IPSO) algorithm. The novelty of the proposal is in the fact that it improves the prediction performance of the ELM-based TSP model by using IPSO to optimize the parameters of the model with synchrophasors. And finally, based on the test results on both IEEE 39-bus system and a large-scale real power system, the correctness and validity of the presented approach are verified., Comment: Accepted by Mathematical Problems in Engineering

For a stochastic system, its evolution from one state to another can have a large number of possible paths. Non-uniformity in the field of system variables leads the local dynamics in state transition varies considerably from path to path and thus the distribution of the paths affects statistical characteristics of the system. Such a characteristic can be referred to as path-dependence of a system, and long-time correlation is an intrinsic feature of path-dependence systems. We employed a local path density operator to describe the distribution of state transition paths, and based on which we derived a new kinetic equation for path-dependent systems. The kinetic equation is similar in form to the Kramers-Moyal expansion, but with its expansion coefficients determined by the cumulants with respect to state transition paths, instead of transition moments. This characteristic makes it capable of accounting for the non-local feature of systems, which is essential in studies of large scale systems where the path-dependence is prominent. Short-time correlation approximation is also discussed. It shows that the cumulants of state transition paths are equivalent to jump moments when correlation time scales are infinitesimal, as makes the kinetic equation derived in this paper has the same physical consideration of the Fokker-Planck equation for Markov processes., Comment: re-written the formulation

Magnon-polaritons are hybrid light-matter quasiparticles originating from the strong coupling between magnons and photons. They have emerged as a potential candidate for implementing quantum transducers and memories. Owing to the dampings of both photons and magnons, the polaritons have limited lifetimes. However, stationary magnon-polariton states can be reached by a dynamical balance between pumping and losses, so the intrinsical nonequilibrium system may be described by a non-Hermitian Hamiltonian. Here we design a tunable cavity quantum electrodynamics system with a small ferromagnetic sphere in a microwave cavity and engineer the dissipations of photons and magnons to create cavity magnon-polaritons which have non-Hermitian spectral degeneracies. By tuning the magnon-photon coupling strength, we observe the polaritonic coherent perfect absorption and demonstrate the phase transition at the exceptional point. Our experiment offers a novel macroscopic quantum platform to explore the non-Hermitian physics of the cavity magnon-polaritons., Comment: Published version (including Supplementary Information), 7+5 pages, 3+2 figures

We report the first observation of the magnon-polariton bistability in a cavity magnonics system consisting of cavity photons strongly interacting with the magnons in a small yttrium iron garnet (YIG) sphere. The bistable behaviors are emerged as sharp frequency switchings of the cavity magnon-polaritons (CMPs) and related to the transition between states with large and small number of polaritons. In our experiment, we align, respectively, the [100] and [110] crystallographic axes of the YIG sphere parallel to the static magnetic field and find very different bistable behaviors (e.g., clockwise and counter-clockwise hysteresis loops) in these two cases. The experimental results are well fitted and explained as being due to the Kerr nonlinearity with either positive or negative coefficient. Moreover, when the magnetic field is tuned away from the anticrossing point of CMPs, we observe simultaneous bistability of both magnons and cavity photons by applying a drive field on the lower branch., Comment: 6 pages, 4 figures

We experimentally demonstrate magnon Kerr effect in a cavity-magnon system, where magnons in a small yttrium iron garnet (YIG) sphere are strongly but dispersively coupled to the photons in a three-dimensional cavity. When the YIG sphere is pumped to generate considerable magnons, the Kerr effect yields a perceptible shift of the cavity's central frequency and more appreciable shifts of the magnon modes. We derive an analytical relation between the magnon frequency shift and the drive power for the uniformly magnetized YIG sphere and find that it agrees very well with the experimental results of the Kittel mode. Our study paves the way to explore nonlinear effects in the cavity-magnon system., Comment: 9 pages, 5 figures

Electromagnetically induced transparency (EIT) has been realized in atomic systems, but fulfilling the EIT conditions for artificial atoms made from superconducting circuits is a more difficult task. Here we report an experimental observation of the EIT in a tunable three-dimensional transmon by probing the cavity transmission. To fulfill the EIT conditions, we tune the transmon to adjust its damping rates by utilizing the effect of the cavity on the transmon states. From the experimental observations, we clearly identify the EIT and Autler-Townes splitting (ATS) regimes as well as the transition regime in between. Also, the experimental data demonstrate that the threshold $\Omega_{\rm AIC}$ determined by the Akaike information criterion can describe the EIT-ATS transition better than the threshold $\Omega_{\rm EIT}$ given by the EIT theory., Comment: 8 pages, 6 figures

We develop a theory for the quantum circuit consisting of a superconducting loop interrupted by four Josephson junctions and pierced by a magnetic flux (either static or time-dependent). In addition to the similarity with the typical three-junction flux qubit in the double-well regime, we demonstrate the difference of the four-junction circuit from its three-junction analogue, including its advantages over the latter. Moreover, the four-junction circuit in the single-well regime is also investigated. Our theory provides a tool to explore the physical properties of this four-junction superconducting circuit., Comment: 9 pages, 4 figures

Hybridizing collective spin excitations and a cavity with high cooperativity provides a new research subject in the field of cavity quantum electrodynamics and can also have potential applications to quantum information. Here we report an experimental study of cavity quantum electrodynamics with ferromagnetic magnons in a small yttrium-iron-garnet (YIG) sphere at both cryogenic and room temperatures. We observe for the first time a strong coupling of the same cavity mode to both a ferromagnetic-resonance (FMR) mode and a magnetostatic (MS) mode near FMR in the quantum limit. This is achieved at a temperature ~ 22 mK, where the average microwave photon number in the cavity is less than one. At room temperature, we also observe strong coupling of the cavity mode to the FMR mode in the same YIG sphere and find a slight increase of the damping rate of the FMR mode. These observations reveal the extraordinary robustness of the FMR mode against temperature. However, the MS mode becomes unobservable at room temperature in the measured transmission spectrum of the microwave cavity containing the YIG sphere. Our numerical simulations show that this is due to a drastic increase of the damping rate of the MS mode., Comment: 11 pages, 7 figures, 1 table

We theoretically investigate the tunneling-induced transparency (TIT) and the Autler-Townes (AT) doublet and triplet in a triple-quantum-dot system. For the resonant tunneling case, we show that the TIT induces a transparency dip in a weak-tunneling regime and no anticrossing occurs in the eigenenergies of the system Hamiltonian. However, in a strong-tunneling regime, we show that the TIT evolves to the AT splitting, which results in a well-resolved doublet and double anticrossings. For the off-resonance case, we demonstrate that, in the weak-tunneling regime, the double TIT is realized with a new detuning-dependent dip, where the anticrossing is also absent. In the strong-tunneling regime, the AT triplet is realized with triple anticrossings and a wide detuning-dependent transparency window by manipulating one of the energy-level detunings. Our results can be applied to quantum measurement and quantum-optics devices in solid systems., Comment: 8 pages, 5 figures

Realization of robust coherent quantum phase slips represents a significant experimental challenge. Here we propose a new design consisting of multiple nanowire junctions to realize a phase-slip flux qubit. It admits good tunability provided by gate voltages applied on superconducting islands separating nanowire junctions. In addition, the gates and junctions can be identical or distinct to each other leading to symmetric and asymmetric setups. We find that the asymmetry can improve the performance of the proposed device, compared with the symmetric case. In particular, it can enhance the effective rate of collective quantum phase slips. Furthermore, we demonstrate how to couple two such devices via a mutual inductance. This is potentially useful for quantum gate operations. Our investigation on how symmetry in multiple nanowire junctions affects the device performance should be useful for the application of phase-slip flux qubits in quantum information processing and quantum metrology., Comment: 12 pages, 6 figures

In quantum information processing, knowledge of the noise in the system is crucial for high-precision manipulation and tomography of coherent quantum operations. Existing strategies for identifying this noise require the use of additional quantum devices or control pulses. We present a noise-identification method directly based on the system's non-Markovian response of an ensemble measurement to the noise. The noise spectrum is identified by reversing the response relationship in the frequency domain. For illustration, the method is applied to superconducting charge qubits, but it is equally applicable to any type of qubits. We find that the identification strategy recovers the well-known Fermi's golden rule under the lowest-order perturbation approximation, which corresponds to the Markovian limit when the measurement time is much longer than the noise correlation time. Beyond such approximation, it is possible to further improve the precision at the so-called optimal point by incorporating the transient response data in the non-Markovian regime. This method is verified with experimental data from coherent oscillations in a superconducting charge qubit., Comment: 9 pages, 5 figures

We propose an experimentally realizable hybrid quantum circuit for achieving a strong coupling between a spin ensemble and a transmission-line resonator via a superconducting flux qubit used as a data bus. The resulting coupling can be used to transfer quantum information between the spin ensemble and the resonator. In particular, in contrast to the direct coupling without a data bus, our approach requires far less spins to achieve a strong coupling between the spin ensemble and the resonator (e.g., three to four orders of magnitude less). This proposed hybrid quantum circuit could enable a long-time quantum memory when storing information in the spin ensemble, and allows the possibility to explore nonlinear effects in the ultrastrong-coupling regime., Comment: 10 pages, 4 figures

In order to support the design and study of sophisticated large scale transition edge sensor (TES) circuits, we use basic SPICE elements to develop device models for TESs based on the superfluid-normal fluid theory. In contrast to previous studies, our device model is not limited to small signal simulation, and it relies only on device parameters that have clear physical meaning and can be easily measured. We integrate the device models in design kits based on powerful EDA tools such as CADENCE and OrCAD, and use them for versatile simulations of TES circuits. Comparing our simulation results with published experimental data, we find good agreement which suggests that device models based on the two-fluid theory can be used to predict the behavior of TES circuits reliably and hence they are valuable for assisting the design of sophisticated TES circuits., Comment: 10pages,11figures. Accepted to IEEE Trans. Appl. Supercond

We show that there is a correlation between the invariant mass of the produced \Lambda K^+, \Lambda K^+\pi^+\pi^- or \Lambda K^+ \pi^+\pi^-\pi^+\pi^- system in the exclusive reaction pp\to p\Lambda K^+\pi^+\pi^-\pi^+\pi^- and the longitudinal or transverse momentum of $\Lambda$. Together with the longitudinal and transverse momentum dependence of Lambda polarization observed in inclusive reactions, such a correlation implies a dependence of Lambda polarization on these invariant masses. The qualitative features of this dependence are consistent with the recent observation by E766 collaboration at BNL. A quantitative estimation has been made using an event generator for $pp$ collisions. A detailed comparison with the data is made., Comment: 10 pages with 3 figures, submitted to J. Phys. G