We study the algebraic structure of the one-dimensional Dirac oscillator by extending the concept of spin symmetry to a noncommutative case. An $SO(4)$ algebra is found connecting the eigenstates of the Dirac oscillator, in which the two elements of Cartan subalgebra are conserved quantities. Similar results are obtained in the Jaynes–Cummings model.

We propose a scenario to increase the probability of probabilistic quantum deletion and to enhance the fidelity of approximate quantum deletion for two non-orthogonal states via weak measurement. More interestingly, by pretreating the given non-orthogonal states, the probability of probabilistic quantum deletion and fidelity of approximate quantum deletion can reach 1. Since outcomes of the weak measurement that we required are probabilistic, we perform the subsequent deleting process only when the outcome of weak measurement is "yes". Remarkably, we find that our scenario has better performance in quantum information process; for example, it costs less quantum resources and time.

We propose a class of $n$-variable Boolean functions which can be used to implement quantum secure multiparty computation. We also give an implementation of a special quantum secure multiparty computation protocol. An advantage of our protocol is that only 1 qubit is needed to compute the $n$-tuple pairwise AND function, which is more efficient comparing with previous protocols. We demonstrate our protocol on the IBM quantum cloud platform, with a probability of correct output as high as 94.63%. Therefore, our protocol presents a promising generalization in realization of various secure multipartite quantum tasks.

We present an algorithm for the generalized search problem (searching $k$ marked items among $N$ items) based on a continuous Hamiltonian and exploiting resonance. This resonant algorithm has the same time complexity $O(\sqrt{N/k})$ as the Grover algorithm. A natural extension of the algorithm, incorporating auxiliary "monitor" qubits, can determine $k$ precisely, if it is unknown. The time complexity of our counting algorithm is $O(\sqrt{N})$, similar to the best quantum approximate counting algorithm, or better, given appropriate physical resources.

Chemically synthetic nanomotors can consume fuel in the environment and utilize the self-generated concentration gradient to self-propel themselves in the system. We study the collective dynamics of an ensemble of sphere dimers built from linked catalytic and noncatalytic monomers. Because of the confinement from the fuel field and the interactions among motors, the ensemble of dimer motors can self-organize into various nanostructures, such as a radial pattern in the spherical fuel field and a staggered radial pattern in a cylindrical fuel field. The influence of the dimer volume fraction on the self-assembly is also investigated and the formed nanostructures are analyzed in detail. The results presented here may give insight into the application of the self-assembly of active materials.

Dark solitons are common topological excitations in a wide array of nonlinear waves. The dark soliton excitation energy is crucial for exploring dark soliton dynamics and is necessarily calculated in a renormalized form due to its existence on a finite background. Despite its tremendous importance and success, the renormalized energy form was at first only suggested with no detailed derivation, and was then "derived" in the grand canonical ensemble. We revisit this fundamental problem and provide an alternative and intuitive derivation of the energy form from the fundamental field energy by utilizing a limiting procedure that conserves number of particles. Our derivation yields the same result, thus putting the dark soliton energy form on a solid basis.

Temperature is a fundamental thermodynamic variable for matter. Physical observables are often found to either increase or decrease with it, or show a non-monotonic dependence with peaks signaling underlying phase transitions or anomalies. Statistical field theory has established connection between temperature and time: a quantum ensemble with inverse temperature $\beta$ is formally equivalent to a dynamic system evolving along an imaginary time from 0 to $i\beta$ in the space one dimension higher. Here we report that a gas of hard-core bosons interacting with a thermal bath manifests an unexpected temperature-periodic oscillation of its macroscopic observables, arising from the microscopic origin of space-time locked translational symmetry breaking and crystalline ordering. Such a temperature crystal, supported by quantum Monte Carlo simulation, generalizes the concept of purely spatial density-wave order to the imaginary time axis for Euclidean action.

Employing recently developed magneto-optical trap recoil ion momentum spectroscopy (MOTRIMS) combined with cold atoms, strong laser pulse, and ultrafast technologies, we study momentum distributions of the multiply ionized cold rubidium (Rb) induced by the elliptically polarized laser pulses (35 fs, $1.3\times 10^{15}$ W/cm$^{2}$). The complete vector momenta of Rb$^{n+}$ ions up to charge state $n = 4$ are recorded with extremely high resolution (0.12 a.u. for Rb$^{+}$). Variations of characteristic multi-bands are displayed in momentum distributions because the ellipticity varies from the linear to circular polarization, are interpreted qualitatively with the classical over-barrier ionization model. Present momentum spectroscopy of cold heavy alkali atoms presents novel strong-field phenomena beyond the noble gases.

The trapped ions confined in a surface-electrode trap (SET) could be free from rf heating if they stay at the rf potential null of the potential well. We report our effort to compensate three-dimensionally for the micromotion of a single $^{40}$Ca$^{+}$ ion near the rf potential null, which largely suppresses the ion's heating and thus helps to achieve the cooling of the ion down to $3.4$ mK, which is very close to the Doppler limit. This is the prerequisite of the sideband cooling in our SET.

We study the superfluid behavior of a population imbalanced ultracold atomic Fermi gases with a short range attractive interaction in a one-dimensional (1D) optical lattice, using a pairing fluctuation theory. We show that, besides widespread pseudogap phenomena and intermediate temperature superfluidity, the superfluid phase is readily destroyed except in a limited region of the parameter space. We find a new mechanism for pair hopping, assisted by the excessive majority fermions, in the presence of continuum-lattice mixing, which leads to an unusual constant Bose-Einstein condensate (BEC) asymptote for $T_{\rm c}$ that is independent of pairing strength. In result, on the BEC side of unitarity, superfluidity, when it exists, may be strongly enhanced by population imbalance.

FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

A monolithic 0–$f$ scheme-based femtosecond optical frequency comb directly driven by a high-power Ti:sapphire laser oscillator is demonstrated. The spectrum covering from 650 nm to 950 nm is generated from the Ti:sapphire oscillator with a repetition rate of 170 MHz. The average output power up to 630 mW is delivered under the pump power of 4.5 W. A 44-dB signal-to-noise ratio (SNR) of the carrier-envelope phase offset (CEO) beat note is achieved under the resolution of 100 kHz and is long-term stabilized to a reference source at 20 MHz. The integrated phase noise (IPN) in the range from 1 Hz to 1 MHz is calculated to be 138 mrad, corresponding to the timing jitter of 63 as at the central wavelength of 790 nm.

A dark pulse mode-locked laser is experimentally demonstrated using the indium tin oxide (ITO) coated D-shape fiber as a saturable absorber (SA). Using the polishing wheel technique, a D-shape single mode fiber was fabricated. A 60-nm-thick layer of ITO was deposited over the D-shape fiber using the electron beam deposition method. The SA has a saturation intensity of 40.32 MW/cm$^{2}$ and a modulation depth of 3.5%. A stable dark pulse mode-locked laser was observed at a central wavelength of 1559.4 nm with repetition rate 0.98 MHz, pulse width 370 ns and signal-to-noise ratio 61 dB.

Spectral beam combining is an effective way to achieve high-brightness direct diode laser output. We present an experimental study on spectral beam combining with external cavity based on transmission grating. Using a series of cylindrical transform lenses with different focal lengths, spectral beaming combining efficiency is greatly improved, and the results of wavelength intervals are consistent with the theoretical calculations. With the injection current of 90 A, a 75.1 W cw 930 nm output power with wavelength span of 18.6 nm and spectral beam combining efficiency of 92.7% is achieved, the beam parameter product is 5.77 mm$\cdot$mrad.

Square microdisks with round corners are fabricated using a standard GaN-based blue LED on Si substrates. Whispering gallery-like modes in the square microdisks are investigated by finite-difference time-domain simulation. The simulation results reveal that the round corners in square microdisks can substantially suppress the number of light propagation paths and further reduce the number of optical modes. A confocal micro-photoluminescence is performed to analyze the optical properties of the square microdisks at room temperature. The single-mode dominant resonant emission is obtained in the square microdisk with corner radius of 1.5 μm.

We propose a design of tunable double-band perfect absorbers based on the resonance absorption in acoustic metasurfaces with nesting helical tracks and deep-subwavelength thicknesses ($ < \lambda /30$ with $\lambda$ being the operation wavelength). By rotating the cover cap with an open aperture on the nesting helical tracks, we can tailor the effective lengths of resonant tubular cavities in the absorber at will, while the absorption peak frequency is flexibly shifted in spectrum and the acoustic impedance is roughly matched with air. The simulated particle velocity fields at different configurations reveal that sound absorption mainly occurs at the open aperture. Our experiment measurements agree well with the theoretical analysis and simulation, demonstrating the wide-spectrum and tunable absorption performance of the designed flat acoustic device.

The propagation of acoustic waves is a fundamental topic in shallow ocean acoustics. We numerically demonstrate a three-dimensional zone of silence consisting of a circular tube with gradient index metamaterials attached to its rigid wall. The cloaking effect is verified by fine agreement with analytical calculations.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

The Rayleigh–Taylor instability at the weakly nonlinear (WN) stage in spherical geometry is studied by numerical simulation. The mode coupling processes are revealed. The results are consistent with the WN model based on parameter expansion, while higher order effects are found to be non-negligible. For Legendre mode perturbation $P_n(\cos\theta)$, the nonlinear saturation amplitude (NSA) of the fundamental mode decreases with the mode number $n$. When $n$ is large, the spherical NSA is lower than the corresponding planar one. However, for large $n$, the planar NSA can be recovered by applying Fourier transformation to the bubble/spike near the equator and calculating the NSA of the converted trigonometric harmonic.

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

Apatite ceramics Ca$_{10}$(PO$_{4})_{6}$$X_{2}$ ($X=$F, OH) were prepared by the standard solid state sintering method and irradiated with He ions under a fluence of $5\times 10^{16}$ ions/cm$^{2}$ at 450 $^{\circ}\!$C. Irradiation induced formation and growth of the He bubbles were observed by a transmission electron microscope. Hydroxyapatite Ca$_{10}$(PO$_{4})_{6}$(OH)$_{2}$ and fluoroapatite Ca$_{10}$(PO$_{4})_{6}$F$_{2}$ with different He bubble morphologies indicate the influence of OH$^{-}$/F$^{-}$ substitution on the He-ion annealing efficiency, as well as the structure itself, which affects the process of He bubble evolution and formation. The grain boundaries also act as sinks to accumulate He bubbles. No obvious irradiation damage but slight intensity reduction and left shift of diffraction peaks were observed according to the grazing incidence x-ray diffraction and Raman spectra characterizations, indicating that defects of interstitials and vacancies were generated.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Employing Monte Carlo simulations based on the cluster expansion, the special quasi-random structures and first-principles calculations, we systematically investigate the structure transition of BeZnO$_2$ alloys from the ordered to the disordered phase driven by the increased synthesis temperature, together with the solid-state phase diagram. It is found that by controlling the ordering parameter at the mixed sublattice, the band structure can vary continuously from a wide direct band gap of 4.61 eV for the fully ordered structure to a relatively narrow direct band gap of 3.60 eV for the fully disordered structure. Therefore, a better optical performance could be achieved simply by controlling the synthesis temperature, which determines the ordering parameters and thus the band gaps.

Three-dimensional (3D) topological insulators (TIs) are candidate materials for various electronic and spintronic devices due to their strong spin-orbit coupling and unique surface electronic structure. Rapid, low-cost preparation of large-area TI thin films compatible with conventional semiconductor technology is the key to the practical applications of TIs. Here we show that wafer-sized Bi$_{2}$Te$_{3}$ family TI and magnetic TI films with decent quality and well-controlled composition and properties can be prepared on amorphous SiO$_{2}$/Si substrates by magnetron cosputtering. The SiO$_{2}$/Si substrates enable us to electrically tune (Bi$_{1-x}$Sb$_{x})_{2}$Te$_{3}$ and Cr-doped (Bi$_{1-x}$Sb$_{x})_{2}$Te$_{3}$ TI films between p-type and n-type behavior and thus study the phenomena associated with topological surface states, such as the quantum anomalous Hall effect (QAHE). This work significantly facilitates the fabrication of TI-based devices for electronic and spintronic applications.

Single crystal rare-earth magnets, such as hexagonal-close-packed gadolinium, usually have a large second order anisotropy $K_2$ and a negative first order anisotropy $K_1$ at low temperatures, which are difficult to explain using microscopic theories. An atomic scale effective spin Hamiltonian ${\mathcal F}[\{{\boldsymbol S}_i\}]$ is proposed, which, apart from the usual isotropic nearest neighbor coupling $J$, consists of two new terms that are different for in-plane and out-of-plane neighbors and which are characterized by two new couplings $C_1$ and $C_2$, respectively. The hybrid Monte–Carlo method is utilized to sample this system to the desired Boltzmann-like distribution $\exp(-{\mathcal F}/k_{_{\rm B}}T)$. It is found that $K_2$ and $K_1$ are compatible with the experimental values and arise naturally from the exchange anisotropy $C_1$ and $C_2$, which are less than 0.01$\%$ in magnitude of the isotropic exchange energy $J$. This new model spin Hamiltonian can also be applied to study other magnetic properties.

We report a quantum Monte Carlo study of the phase transition between antiferromagnetic and valence-bond solid ground states in the square-lattice $S=1/2$ $J$–$Q$ model. The critical correlation function of the $Q$ terms gives a scaling dimension corresponding to the value $\nu = 0.455 \pm 0.002$ of the correlation-length exponent. This value agrees with previous (less precise) results from conventional methods, e.g., finite-size scaling of the near-critical order parameters. We also study the $Q$-derivatives of the Binder cumulants of the order parameters for $L^2$ lattices with $L$ up to $448$. The slope grows as $L^{1/\nu}$ with a value of $\nu$ consistent with the scaling dimension of the $Q$ term. There are no indications of runaway flow to a first-order phase transition. The mutually consistent estimates of $\nu$ provide compelling support for a continuous deconfined quantum-critical point.

Compared with the metal antenna metasurface, the dielectric metasurface has better optical characteristics and smaller ohmic loss in the optical band, which makes it superior. An elliptical cylindrical nanostructured antenna is designed using GaP with excellent transmission characteristics in the visible band. This structure has a transmission efficiency of up to 0.96 in the visible light band. Based on the Pancharatnam–Berry (PB) phase control principle, the metasurface structure composed of the antennas is studied, and its abnormal refraction metasurface and focusing meta-lens are analyzed. It is a highly efficient sub-wavelength structure, and promises great potential for the applications of circular polarization optics, nanolithography, dense storage and biophotonics.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Sintering of polycrystalline diamond with selenium was investigated under pressure of 6.5–10.5 GPa at a constant temperature of 1850 $^{\circ}\!$C. A new carbon-selenium compound with a most plausible chemical formula of SeC and a WC-type hexagonal structure (space group $P\bar{6}m2$) has been discovered in the recovered samples sintered at 10.5 GPa and 1850 $^{\circ}\!$C. Refined lattice parameters are as follows: $a = 2.9277(4)$ Å, $c = 2.8620(4)$ Å, $V = 21.245(4)$ Å$^{3}$. The diamond compacts hot-pressed at 10.5 GPa have excellent mechanical properties with a Vickers hardness of about 68 GPa at a loading force of 19.6 N. Diamond intergrowths observed in these samples may have benefited from the catalytic effects of Se/SeC on the nucleation and crystal growth of diamond.

One-dimensional (1D) transition metal phosphides (TMPs) with large specific surface areas, high charge transfer efficiency and excellent electrical conductivity have attracted significant attention in hydrogen evolution reaction (HER) as versatile and active catalysts. Herein, the sub-4 nm Mo-Co$_{2}$P ultrafine nanorods (NRs) anchored on reduced graphene oxide (rGO) were successfully synthesized by a colloidal mesostructured strategy. Electrochemical test results reveal that the Mo-Co$_{2}$P@rGO electrode exhibits superior activity with overpotentials of 204 mV and Tafel slope of 88 mV/dec for HER at 10 mA/cm$^{2}$, relative to the Co$_{2}$P@rGO electrode in 0.5 M H$_{2}$SO$_{4}$ solution. This improvement could be ascribed to the Mo doping, which results in more active sites, higher electrical conductivity and faster electron-transfer rates. This versatile strategy will provide a promising pathway for transition metal-doped compounds as an efficient catalyst.

Perpendicularly magnetized $L1_{0}$-MnAl thin films with Co$_{2}$MnSi buffer layers were prepared on GaAs (001) substrates by molecular-beam epitaxy (MBE). The samples with high crystalline quality show a maximum uniaxial perpendicular magnetic anisotropy constant of $1.4\times 10^{7}$ erg/cm$^{3}$. Ultrafast spin dynamics with a magnetization precession frequency up to 200 GHz was investigated by using time-resolved magneto-optical Kerr effect (TRMOKE) measurements, from which the Gilbert damping constant $\alpha$ of epitaxial $L1_{0}$-MnAl thin films is evaluated to be less than 0.0175. This work provides an important reference for analyzing the current-induced magnetization switching process in MnAl-based spintronic devices.

Coronavirus Disease 2019 (COVID-19), caused by the novel coronavirus, has spread rapidly across China. Consequently, there is an urgent need to sort and develop novel agents for the prevention and treatment of viral infections. A rapid structure-based virtual screening is used for the evaluation of current commercial drugs, with structures of human angiotensin converting enzyme II (ACE2), and viral main protease, spike, envelope, membrane and nucleocapsid proteins. Our results reveal that the reported drugs Arbidol, Chloroquine and Remdesivir may hinder the entry and release of virions through the bindings with ACE2, spike and envelope proteins. Due to the similar binding patterns, NHC ($\beta$-d-N4-hydroxycytidine) and Triazavirin are also in prospects for clinical use. Main protease (3CLpro) is likely to be a feasible target of drug design. The screening results to target 3CLpro reveal that Mitoguazone, Metformin, Biguanide Hydrochloride, Gallic acid, Caffeic acid, Sulfaguanidine and Acetylcysteine seem be possible inhibitors and have potential application in the clinical therapy of COVID-19.