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Quantum defects have shown to play an essential role for the non-radiative recombination in metal halide perovskites (MHPs). Nonetheless, the processes of charge transfer-assisted by defects are still ambiguous. Herein, we theoretically study the non-radiative multiphonon processes among different types of quantum defects in MHPs using Markvart model for the induced mechanisms of electron-electron and electron-phonon interactions, respectively. We find that charge carrier can transfer between the neighboring levels of the same type shallow defects by multiphonon processes, but it will be distinctly suppressed with the increasing of the defect depth. For the non-radiation multiphonon transitions between donor- and acceptor-like defects, the processes are very fast and independence of the defect depth, which provide a possible explanation for the blinking phenomena of photoluminescence spectra in recent experiment. We also discuss the temperature dependence of these multiphonon processes and find that their variational trends depend on the comparison of Huang-Rhys factor with the emitted phonon number. These theoretical results fill some gaps of defect-assisted non-radiative processes in the perovskites materials.

Thermal convection of fluid is a more efficient way than diffusion to carry heat from hot sources to cold places. Here, we experimentally study the Rayleigh-B\'enard convection of aqueous glycerol solution in a cubic cell with suspensions of rod-like particles made of polydimethylsiloxane (PDMS). The particles are inertial due to their large thermal expansion coefficient and finite sizes. The thermal expansion coefficient of the particles is three times larger than that of the background fluid. This contrast makes the suspended particles lighter than the local fluid in hot regions and heavier in cold regions. The heat transport is enhanced at relatively large Rayleigh number ($Ra$) but reduced at small $Ra$. We demonstrate that the increase of Nusselt number arises from the particle-boundary layer interactions: the particles act as ``active'' mixers of the flow and temperature fields across the boundary layers.

It is commonly believed that a massive real scalar field $\phi$ only mediates short-range interactions on the scale of its Compton wavelength via the Yukawa potential. However, in the nonperturbative regime of nonlinear self coupling, $\phi$ can also mediate larger scale interactions. Moreover, the classical potential, namely, the static configuration of $\phi$ in the presence of an external source, is not always unique for given boundary conditions. In this paper, a complete set of finite-energy potentials (FEPs) induced by a Gaussian source is identified in one, two, and three spatial dimensions when the nonlinearity is of the Mexican-hat type, which is often prescribed to induce spontaneous symmetry breaking. In the size-strength parameter space of the source, phase boundaries are mapped out, across which the number of FEPs differ. Additionally, softer phase transitions are delineated according to whether the potential exhibits a light horizon at which $\phi$ vanishes. The light horizon is of physical significance when $\phi$ couples with other particles. For example, when $\phi$ is the Higgs field, all elementary particles become massless at the light horizon. It is remarkable that white dwarfs and neutron stars are potentially in a phase where light horizons exist, whose outer radii are a few times the star sizes. Moreover, suppose elementary fermions of mass greater than $\sim10^3$ GeV exist, then they may also be surrounded by light horizons with radii comparable to the Higgs Compton wavelength. Finally, nonperturbative states may also be realized in condensed matter systems, wherein phase transitions are controllable using localized sources., Comment: 16 pages, 6 figures, 1 table

Deep learning has rapidly become a widespread tool in both scientific and commercial endeavors. Milestones of deep learning exceeding human performance have been achieved for a growing number of tasks over the past several years, across areas as diverse as game-playing, natural-language translation, and medical-image analysis. However, continued progress is increasingly hampered by the high energy costs associated with training and running deep neural networks on electronic processors. Optical neural networks have attracted attention as an alternative physical platform for deep learning, as it has been theoretically predicted that they can fundamentally achieve higher energy efficiency than neural networks deployed on conventional digital computers. Here, we experimentally demonstrate an optical neural network achieving 99% accuracy on handwritten-digit classification using ~3.2 detected photons per weight multiplication and ~90% accuracy using ~0.64 photons (~$2.4 \times 10^{-19}$ J of optical energy) per weight multiplication. This performance was achieved using a custom free-space optical processor that executes matrix-vector multiplications in a massively parallel fashion, with up to ~0.5 million scalar (weight) multiplications performed at the same time. Using commercially available optical components and standard neural-network training methods, we demonstrated that optical neural networks can operate near the standard quantum limit with extremely low optical powers and still achieve high accuracy. Our results provide a proof-of-principle for low-optical-power operation, and with careful system design including the surrounding electronics used for data storage and control, open up a path to realizing optical processors that require only $10^{-16}$ J total energy per scalar multiplication -- which is orders of magnitude more efficient than current digital processors., Comment: 42 pages, 21 figures

We study the decay of the SM Higgs boson to a massive charm quark pair at the next-to-next-to-leading order QCD and next-to-leading order electroweak. At the second order of QCD coupling, we consider the exact calculation of flavour-singlet contributions where the Higgs boson couples to the internal top and bottom quark. Helpful information on the running mass effects related to Yukawa coupling may be obtained by analyzing this process. High precision production for $h\to c\bar{c}$ within the SM makes it possible to search for new physics that may induce relatively large interactions related to the charm quark. As an example, we evaluate the axion-like particle associate production with a charm quark pair in the Higgs decay and obtain some constraints for the corresponding parameters under some assumptions., Comment: 18 pages, 7 figures

The problem of covert communication over Multiple-Input Multiple-Output (MIMO) Additive White Gaussian Noise (AWGN) channels is investigated, in which a transmitter attempts to reliably communicate with a legitimate receiver while avoiding detection by a passive adversary. The covert capacity of the MIMO AWGN is characterized under a variational distance covertness constraint when the MIMO channel matrices are static and known. The characterization of the covert capacity is also extended to a class of channels in which the legitimate channel matrix is known but the adversary's channel matrix is only known up to a rank and a spectral norm constraint., Comment: 22 pages, 1 figure, accepted to Transactions on Information Forensics & Security

In strong electromagnetic fields, unique plasma phenomena and applications emerge, whose description requires recently developed theories and simulations [Y. Shi, Ph.D. thesis, Princeton University (2018)]. In the classical regime, to quantify effects of strong magnetic fields on three-wave interactions, a convenient formula is derived by solving the fluid model to the second order in general geometry. As an application, magnetic resonances are exploited to mediate laser pulse compression, using which higher intensity pulses can be produced in wider frequency ranges, as confirmed by particle-in-cell simulations. In even stronger fields, relativistic-quantum effects become important, and a plasma model based on scalar quantum electrodynamics (QED) is developed, which unveils observable corrections to Faraday rotation and cyclotron absorption in strongly magnetized plasmas. Beyond the perturbative regime, lattice QED is extended as a numerical tool for plasma physics, using which the transition from wakefield acceleration to electron-positron pair production is captured when laser intensity exceeds the Schwinger threshold., Comment: APS DPP 2020 Invited Talk TI01.00001

In cellular vortical flows, namely arrays of counter-rotating vortices, short but flexible filaments can show simple random walks through their stretch-coil interactions with flow stagnation points. Here, we study the dynamics of semi-rigid filaments long enough to broadly sample the vortical field. Using simulation, we find a surprising variety of long-time transport behavior -- random walks, ballistic transport, and trapping -- depending upon the filament's relative length and effective flexibility. Moreover, we find that filaments execute L\'evy walks whose diffusion exponents generally decrease with increasing filament length, until transitioning to Brownian walks. Lyapunov exponents likewise increase with length. Even completely rigid filaments, whose dynamics is finite-dimensional, show a surprising variety of transport states and chaos. Fast filament dispersal is related to an underlying geometry of ``conveyor belts''. Evidence for these various transport states are found in experiments using arrays of counter-rotating rollers, immersed in a fluid and transporting a flexible ribbon.

We calculate the masses of the $QQ\bar{q}\bar{q}$ ($Q=c,b$; $q=u,d,s$) tetraquark states with the aid of heavy diquark-antiquark symmetry (HDAS) and the chromomagnetic interaction (CMI) model. The masses of the highest-spin ($J=2$) tetraquarks that have only the $(QQ)_{\bar{3}_c}(\bar{q}\bar{q})_{3_c}$ color structure are related with those of conventional hadrons using HDAS. Thereafter, the masses of their partner states are determined with the mass splittings in the CMI model. Our numerical results reveal that: (i) the lightest $cc\bar{n}\bar{n}$ ($n=u,d$) is an $I(J^P)=0(1^+)$ state around 3929 MeV (53 MeV above the $DD^*$ threshold) and none of the double-charm tetraquarks are stable; (ii) the stable double-bottom tetraquarks are the lowest $0(1^+)$ $bb\bar{n}\bar{n}$ around 10488 MeV ($\approx116$ MeV below the $BB^*$ threshold) and the lowest $1/2(1^+)$ $bb\bar{n}\bar{s}$ around 10671 MeV ($\approx20$ MeV below the $BB_s^*/B_sB^*$ threshold); and (iii) the two lowest $bc\bar{n}\bar{n}$ tetraquarks, namely the lowest $0(0^+)$ around 7167 MeV and the lowest $0(1^+)$ around 7223 MeV, are near-threshold states. Moreover, we discuss the constraints on the masses of double-heavy hadrons. Specifically, for the lowest nonstrange tetraquarks, we obtain $T_{cc}<3965$ MeV, $T_{bb}<10627$ MeV, and $T_{bc}<7199$ MeV., Comment: 19 pages, 4 figures, and 11 tables

Upsilon (1S) decay to Xi_cc +anything is studied. It is shown that the branching ratio can be as significant as that of Upsilon (1S) decay to J/Psi +anything. The non-relativistic heavy quark effective theory framework is employed for the calculation on the decay width. Measurements on the production of Xi_cc and likely production characteristic of the partonic state with four charm quarks at BELLE2 are suggested., Comment: 13 pages, 6 figs, language updated in the 2nd version

As a milestone for general-purpose computing machines, we demonstrate that quantum processors can be programmed to efficiently simulate dynamics that are not native to the hardware. Moreover, on noisy devices without error correction, we show that simulation results are significantly improved when the quantum program is compiled using modular gates instead of a restricted set of standard gates. We demonstrate the general methodology by solving a cubic interaction problem, which appears in nonlinear optics, gauge theories, as well as plasma and fluid dynamics. To encode the nonnative Hamiltonian evolution, we decompose the Hilbert space into a direct sum of invariant subspaces in which the nonlinear problem is mapped to a finite-dimensional Hamiltonian simulation problem. In a three-states example, the resultant unitary evolution is realized by a product of ~20 standard gates, using which ~10 simulation steps can be carried out on state-of-the-art quantum hardware before results are corrupted by decoherence. In comparison, the simulation depth is improved by more than an order of magnitude when the unitary evolution is realized as a single cubic gate, which is compiled directly using optimal control. Alternatively, parametric gates may also be compiled by interpolating control pulses. Modular gates thus obtained provide high-fidelity building blocks for quantum Hamiltonian simulations., Comment: 4 figures. pages 1-6 are main text and bibliography, and pages 7-8 are supplemental material