The metastable hadronic helium atoms in microseconds lifetime are available in laboratory, and two-photon spectroscopy was reported recently. This exotic helium atom has an electron in the ground state and a negative hadron rotating around the helium nucleus. We theoretically study the excitation on hadronic helium by femtosecond pulse and elucidate the influence of moleculelike structure and rotation behavior on the photoelectron spectra and high-order harmonic generation. Because of the moleculelike structure, the electronic ground state consists of several angular orbitals. These angular orbitals can enhance photoelectron spectra at high energies, and also influence the harmonic generation spectra considerably. In particular, the harmonic spectra can occur at even harmonic orders because of the transition between these angular orbitals and continuum states. On the other side, the rotation behavior of hadron can induce a frequency shift in the harmonic spectra. The magnitude of the frequency shift depends on the orbiting speed of the hadron, which is considerable because the rotation period is in a few femtoseconds, a time scale that is comparable to that of infrared laser and is feasible in current laser experiments.

We have numerically calculated the single-band Wannier functions for interacting Bose gases in optical lattices with a self-consistent approach. We find that the Wannier functions are broadened by repulsive interaction. The tunneling parameter $J$ and the on-site interaction $U$ computed with the broadened Wannier functions are found to change significantly with the number of atoms per site. Our theory can explain the nonuniform atomic clock shift observed in Campbell et al., Science 313, 649 (2006).

We investigate the superfluid properties of a one-component Fermi gas with a uniaxially anisotropic $p$-wave pairing interaction, $U_x>U_y=U_z$ [where $U_i(i=x,y,z)$ is a $p_i$-wave pairing interaction]. This type of interaction is considered to be realized in a ${}^{40}\mathrm{K}$ Fermi gas. Including pairing fluctuations within a strong-coupling $T$-matrix theory, we determine the $p_x$-wave superfluid phase transition temperature $T_{\mathrm{c}}^{p_x}$, as well as the other phase transition temperature $T_{\mathrm{c}}^{p_x+i{p}_y}(<T_{\mathrm{c}}^{p_x})$, below which the superfluid order parameter has the $p_x+i{p}_y$-wave symmetry. In the normal state near $T_{\mathrm{c}}^{p_x}, p_x$-wave pairing fluctuations are shown to induce an anisotropic pseudogap phenomenon, where a dip structure in the angle-resolved density of states around $\omega =0$ is the most remarkable in the $p_x$ direction. In the $p_x$-wave superfluid phase $(T_{\mathrm{c}}^{p_x+i{p}_y}<T\le T_{\mathrm{c}}^{p_x})$, while the pseudogap in the $p_x$ direction continuously changes to the superfluid gap, the pseudogap in the perpendicular direction to the $p_x$ axis is found to continue developing because of enhanced $p_y$-wave and $p_z$-wave pairing fluctuations around the node of the $p_x$-wave superfluid order parameter. Since pairing fluctuations are always suppressed in the isotropic $s$-wave superfluid state, this phenomenon is peculiar to an unconventional Fermi superfluid with a nodal superfluid order parameter. Since the $p$-wave Fermi superfluid is the most promising non-$s$-wave pairing state in an ultracold Fermi gas, our results would contribute to understanding how the anisotropic pairing fluctuations, as well as the existence of plural superfluid phases, affect many-body properties of this unconventional Fermi superfluid.

One of the missing elements for realising an integrated optical circuit is a rectifying device playing the role of an optical diode. A proposal based on a pair of two-level atoms strongly coupled to a one-dimensional waveguide showed a promising behavior based on a semiclassical study [Fratini et al., Phys. Rev. Lett. 113, 243601 (2014)]. Our study in the full quantum regime shows that, in such a device, rectification is a purely multiphoton effect. For an input field in a coherent state, rectification reaches up to $70\%$ for the range of power in which one of the two atoms is excited, but not both.

The presence of losses in nonlinear photonic structures necessitates the introduction of active parts for wave power compensation resulting in unbalanced gain and loss landscapes where localized beam propagation is, in general, dynamically unstable. Here we provide generic sufficient conditions for the relation between the gain-loss and the refractive index profiles in order to ensure efficient wave trapping and stable propagation for a wide range of beam launching conditions such as initial power, angle of incidence, and position. The stability is a consequence of an underlying dynamic power balance mechanism related to a conserved quantity of wave dynamics.

We study theoretically terahertz generation in two-color laser-gas interactions based on a transient photocurrent model. We show that terahertz generation depends on the laser pulse duration and intensity of the two-color laser field. Furthermore, the terahertz amplitude increases with an increase of the laser pulse duration at low laser intensity, but decreases with an increase of the laser pulse duration at high laser intensity. Our analysis shows that the ionization events play an important role in terahertz generation and the terahertz amplitude is determined by the superposition of contributions from individual ionization events.

We present a theory that explains the experimentally observed crystallization of a dilute dysprosium condensate into a lattice of droplets. The key ingredient of our theory is a conservative three-body interaction which stabilizes the droplets against collapse to high-density spikes. Our theory reproduces the experimental observations, and provides insight into the many-body properties of the droplet phase. Notably, we show that it is unlikely that a supersolid was obtained in experiments, however, our results suggest a strategy to realize this phase.

We study the performance of a partially correlated amplitude damping channel acting on two qubits. We derive lower bounds for the single-shot classical capacity by studying two kinds of quantum ensembles, one which allows us to maximize the Holevo quantity for the memoryless channel and the other allowing the same task but for the full-memory channel. In these two cases we also show the amount of entanglement which is involved in achieving the maximum of the Holevo quantity. For the single-shot quantum capacity we discuss both a lower and an upper bound, achieving a good estimate for high values of the channel transmissivity. We finally compute the entanglement-assisted classical channel capacity.

Using potential models, we analyze range corrections to the universal law dictated by the Efimov theory of three bosons. In the case of finite-range interactions, we have observed that at first order, it is necessary to supplement the theory with one finite-range parameter ${\mathrm{\Gamma }}_n^3$ for each specific $n$ level [A. Kievsky and M. Gattobigio, Phys. Rev. A 87, 052719 (2013)]. The value of ${\mathrm{\Gamma }}_n^3$ depends on the way the potentials are changed to tune the scattering length toward the unitary limit. In this work, we analyze a particular path in which the length $r_B=a-a_B$, measuring the difference between the two-body scattering length $a$ and the energy-scattering length $a_B$, is almost constant. Analyzing systems with very different scales, such as atomic or nuclear systems, we observe that the finite-range parameter remains almost constant along the path with a numerical value of ${\mathrm{\Gamma }}_0^3\approx 0.87$ for the ground-state level. This observation suggests the possibility of constructing a single universal function that incorporates finite-range effects for this class of paths. The result is used to estimate the three-body parameter ${\kappa }_{*}$ in the case of real atomic systems brought to the unitary limit through broad Feshbach resonances. Furthermore, we show that the finite-range parameter can be put in relation to the two-body contact $C_2$ at the unitary limit.

We describe a quasiperiodic optical lattice, created by a physical realization of the abstract cut-and-project construction underlying all quasicrystals. The resulting potential is a generalization of the Fibonacci tiling. Calculation of the energies and wave functions of ultracold atoms loaded into such a lattice demonstrate a multifractal energy spectrum, a singular continuous momentum-space structure, and the existence of controllable edge states. These results open the door to cold atom quantum simulation experiments in tunable or dynamic quasicrystalline potentials, including topological pumping of edge states and phasonic spectroscopy.

We present calculations on the ratio between double and single ionization of helium by a strong laser pulse at a wavelength of 780 nm using the quantitative rescattering (QRS) model. According to this model, the yield for the doubly charged ion $\mathrm{He}^{2+}$ can be obtained by multiplying the returning electron wave packet (RWP) with the total cross sections (TCSs) for electron impact ionization and electron impact excitation of $\mathrm{He}^{+}$ in the singlet spin channel. The singlet constraint was imposed since the interaction of the helium atom with the laser and the recollision processes both preserve the total spin of the system. An $R$-matrix (close-coupling) code is used to obtain accurate TCSs, while the RWPs, according to the QRS, are calculated by the strong-field approximation for high-energy photoelectrons. The laser field, which lowers the required energy for the electron to escape from the nucleus at the time of recollision, is also taken into account. The simulated results are in good agreement with the measured $\mathrm{He}^{2+}\text{/}\mathrm{He}^{+}$ ratio over a broad range of laser intensities. The result demonstrates that the QRS approach based on the rescattering model is fully capable of quantitatively interpreting nonsequential double ionization processes.

Using the fractional statistical properties of so-called anyonic particles, we present solutions of the Schrödinger equation for up to six strongly interacting particles in one-dimensional confinement that interpolate the usual bosonic and fermionic limits. These solutions are exact to linear order in the inverse coupling strength of the zero-range interaction of our model. Specifically, we consider two-component mixtures of anyons and use these to eludicate the mixing-demixing properties of both balanced and imbalanced systems. Importantly, we demonstrate that the degree of demixing depends sensitively on the external trap in which the particles are confined. We also show how one may in principle probe the statistical parameter of an anyonic system by injection a strongly interacting impurity and doing spectral or tunneling measurements.

Understanding the formation of Cooper pairs and the resulting thermodynamic properties of low-dimensional Fermi gases is an important area of research, which may help build our understanding of other low-dimensional systems, such as high-temperature superconductors. In lower dimensions, quantum fluctuations are expected to play an increasingly important role, and the reliability of strong-coupling theories becomes questionable. Here, we present a comparison of recent thermodynamic measurements and theoretical predictions from different many-body $T$-matrix theories for a two-dimensional strongly interacting Fermi gas in the normal state. We find that the fully self-consistent $T$-matrix theory provides the best description of the experimental data over a wide range of temperatures and interatomic interactions.

In this paper, we propose a method to calculate the fine structure of kinetic energy of laser-produced plasma, which bridges the two parts of researches of plasma channel usually studied independently of each other, i.e., the extension of the length of plasma filament and the prolongation of the lifetime of plasma channel generated by the laser pulse. The kinetic energy structure of the plasma channel is calculated by solving the motion equation of ionized electrons and utilizing the ionization rate as the weighting factor. With the study on the laser intensity, we analyze the formation mechanisms of the kinetic energy structure. This work holds great promise for optimizing the initial conditions of the evolutions of plasma channel after the laser pulse.

We demonstrate that yttrium iron garnet microspheres support optical whispering-gallery modes similar to those in nonmagnetic dielectric materials. The direction of the ferromagnetic moment tunes both the resonant frequency via the Voigt effect as well as the degree of polarization rotation via the Faraday effect. An understanding of the magneto-optical coupling in whispering-gallery modes, where the propagation direction rotates with respect to the magnetization, is fundamental to the emerging field of cavity optomagnonics.

We study the classically driven two-level system with its center-of-mass motion vibrating in a harmonic trap and coupled to the photons in a two-mode cavity. The first mode is resonant to the driving field and an electronic transition. The second mode is off-resonant, forming a vibrational-assisted Raman transition. Using an exact numerical method, we investigate the quantum dynamics of the light emitted by the atom and the cavity modes. We analyze and compare the corresponding atomic and intracavity photon spectra for a range of the driving laser field and the cavity coupling strengths. The results provide better understanding of the effects of the laser field and atom-cavity coupling strengths on quantum interference effects and photon blockade, particularly the Mollow's triplet and the Autler-Townes splitting in the good and bad cavity limits.

We describe a practical experimental protocol for robustly characterizing the error rates of non-Clifford gates associated with dihedral groups, including small single-qubit rotations. Our dihedral benchmarking protocol is a generalization of randomized benchmarking that relaxes the usual unitary 2-design condition. Combining this protocol with existing randomized benchmarking schemes enables practical universal gate sets for quantum information processing to be characterized in a way that is robust against state-preparation and measurement errors. In particular, our protocol enables direct benchmarking of the $\pi /8$ gate even under the gate-dependent error model that is expected in leading approaches to fault-tolerant quantum computation.

We find dynamical invariants for open quantum systems described by the non-Markovian quantum-state-diffusion (QSD) equation. In stark contrast to closed systems where the dynamical invariant can be identical to the system density operator, these dynamical invariants no longer share the equation of motion for the density operator. Moreover, the invariants obtained with a biorthonormal basis can be used to render an exact solution to the QSD equation and the corresponding non-Markovian dynamics without using master equations or numerical simulations. Significantly we show that we can apply these dynamical invariants to reverse engineering a Hamiltonian that is capable of driving the system to the target state, providing a different way to design control strategy for open quantum systems.