We investigate the pulse partitioning of a 6.3-mJ, 450-fs pulse at 1030 nm to produce plasma channels. At such moderate energies, splitting the energy into several subpulses reduces the ionization efficiency and thus does not extend the plasma lifetime. We numerically show that when sufficient energy to produce multifilamentation is available, splitting the pulse temporally in a pulse train increases the gas temperature compared to a filament bundle of the same energy. This could improve the mean free path of the free electrons, therefore enhancing the efficiency of discharge triggering.

Effective transition between the population-inverted optical eigenmodes of two coupled microcavities carrying mechanical oscillation realizes a phonon analog of optical two-level lasers. By providing an approach that linearizes the dynamical equations of weak nonlinear systems without relying on their steady states, we study such phonon laser action as a realistic dynamical process, which exhibits time-dependent stimulated phonon field amplification especially when one of the cavities is added with optical gain medium. The approach we present explicitly gives the conditions for the optimum phonon lasing, and thermal noise is found to be capable of facilitating the phonon laser action significantly.

We provide an alternative approach to relativistic dynamics based on the Feshbach projection technique. Instead of directly studying the Dirac equation, we derive a two-component equation for the upper spinor. This approach allows one to investigate the underlying physics in a different perspective. For particles with small mass such as the neutrino, the leading-order equation has a Hermitian effective Hamiltonian, implying there is no leakage between the upper and lower spinors. In the weak relativistic regime, the leading order corresponds to a non-Hermitian correction to the Pauli equation, which takes into account the nonzero possibility of finding the lower-spinor state and offers a more precise description.

$R$-matrix-with-time-dependence theory is applied to electron-impact ionization processes for He in the $S$-wave model. Cross sections for electron-impact excitation, ionization, and ionization with excitation processes for impact energies between 25 and 225 eV are in excellent agreement with benchmark cross sections. Ultrafast dynamics induced by a scattering event is observed through time-dependent signatures associated with autoionization from doubly excited states. Further insight into dynamics can be obtained through examination of the spin components of the time-dependent wave function.

The selection rules of high harmonic generation (HHG) are investigated using three-dimensional time-dependent density functional theory (TDDFT). From the harmonic spectra obtained with various real molecules and different forms of laser fields, several factors that contribute to selection rules are revealed. Extending the targets to stereoscopic molecules, it is shown that the allowed harmonics are dependent on the symmetries of the projections of molecules. For laser fields, the symmetries contributing to the selection rules are discussed according to Lissajous figures and their dynamical directivities. All the phenomena are explained by the symmetry of the full time-dependent Hamiltonian under a combined transformation. We present a systematic study on the selection rules and propose an intuitive method for the judgment of allowed harmonic orders, which can be extended to more complex molecules and various forms of laser pulses.

Molecular wave-packet dynamics in oxygen are studied in the time domain, using a single-color VUV-pump–VUV-probe scheme. 17-fs VUV pulses, centered at 161 nm are generated via high-order harmonic generation driven by an intense 800-nm pulse leading to VUV pulse energies that reach 1.$1\mu \text{J}$ per pulse. An all-reflective interferometric pump-probe scheme is used for studying the delay dependence of the molecular oxygen ion signal with simultaneous nonresonant photoionization of krypton as a precise timing-reference. Access to the excited dissociative state lifetime is provided by the resulting delay-dependent ${{\mathrm{O}}_2}^{+}$ signal, ultimately limited by the molecular ionization window. The ability to use a two-photon VUV probe provides the delay-dependent detection of ${\mathrm{O}}^{+}$ as an additional observable, extending the dissociation observation window.

We study the critical dynamics of matter waves at the three-dimensional Anderson mobility edge in cold-atom disorder quench experiments. General scaling arguments are supported by precision numerics for the spectral function, diffusion coefficient, and localization length in isotropic blue-detuned speckle potentials. We discuss signatures of critical slowdown in the time-dependent central column density of a spreading wave packet, and evaluate the prospects of observing anomalous diffusion right at criticality.

Thermal decoherence is a major obstacle to the realization of quantum coherence for massive mechanical oscillators. Although optical trapping has been used to reduce the thermal decoherence rate for such oscillators, it also increases the rate by subjecting the oscillator to stochastic forces resulting from the frequency fluctuations of the optical field, thereby setting a fundamental limit on the reduction. This is analogous to the noise penalty in an active feedback system. Here, we directly measure the rethermalization process for an initially cooled and optically trapped suspended mirror, and identify the current limiting decoherence rate as due to the optical trap. Our experimental study of the trap-induced decoherence rate will enable future advances in the probing of fundamental quantum mechanics in the bad-cavity regime, such as testing of deformed commutators.

We present a scheme to realize electromagnetically induced grating in an ensemble of strongly interacting Rydberg atoms, which act as superatoms due to the dipole blockade mechanism. The ensemble of three-level cold Rydberg-dressed $\left({}^{87}\mathrm{Rb}\right)$ atoms follows a cascade configuration where a strong standing-wave control field and a weak probe pulse are employed. The diffraction intensity is influenced by the strength of the probe intensity, the control field strength, and the van der Waals (vdW) interaction. It is noticed that relatively large first-order diffraction can be obtained for low-input intensity with a small vdW shift and a strong control field. The scheme can be considered as an amicable solution to realize the atomic grating at the microscopic level, which can provide background- and dark-current-free diffraction.

A logical qubit based on electron-spin singlet-triplet states in a semiconductor double dot has emerged as one of the promising candidates for quantum information processing. Here we propose a systematic method to implement rapid quantum gates in the nanosecond time scale for both a single qubit and multiqubits, by applying adiabatic driving pulses with tunable velocity. This yields considerable high-fidelity gate operations reaching $99.9\%$ which are crucial to scalable quantum computation in a semiconductor-based architecture, even considering the demanding experimental constraints and realistic spin and charge noises.

Particle number fluctuations, no matter how small, are present in experimental setups. One should rigorously take these fluctuations into account, especially for entanglement detection. In this context, we generalize the spin-squeezing inequalities introduced by G. Tóth et al. [Phys. Rev. Lett. 99, 250405 (2007).]. These new inequalities are fulfilled by all separable states even when the number of particles is not constant and may present quantum fluctuations. These inequalities are useful for detecting entanglement in many-body systems when the superselection rule does not apply or when only a subspace of the total system Hilbert space is considered. We also define general dichotomic observables for which we obtain a coordinate-independent form of the generalized spin-squeezing inequalities. We give an example where our generalized coordinate-independent spin-squeezing inequalities present a clear advantage over the original ones.

Photoinduced reformation of chemical bonds is investigated in the ${\mathrm{CH}}_3\mathrm{Cl}$ molecule experimentally and computationally. The observation of stable ${\mathrm{HCl}}^{+}$ fragment formation after resonant Cl $2p$ photoexcitation is confirmed by an electron-ion coincidence experiment, and its possible creation mechanism is reported. We attribute the formation of ${\mathrm{HCl}}^{+}$ to specific final states populated by the resonant Auger decay. Quantum chemical computations support this attribution and suggest that in at least one of those states the system is placed on a potential energy surface which favors creation of ${\mathrm{HCl}}^{+}$ by moving one hydrogen atom to a closer proximity of the chlorine atom. This work demonstrates the effect of targeted core-shell excitation on the chemical bond breaking and reformation process, often called photoinduced chemistry.

In recent experiments, the relaxation dynamics of highly oblate, turbulent Bose-Einstein condensates (BECs) was investigated by measuring the vortex decay rates in various sample conditions [Phys. Rev. A 90, 063627 (2014)] and, separately, the thermal friction coefficient $\alpha$ for vortex motion was measured from the long-time evolution of a corotating vortex pair in a BEC [Phys. Rev. A 92, 051601(R) (2015)]. We present a comparative analysis of the experimental results, and find that the vortex decay rate $\mathrm{\Gamma }$ is almost linearly proportional to $\alpha$. We perform numerical simulations of the time evolution of a turbulent BEC using a point-vortex model equipped with longitudinal friction and vortex-antivortex pair annihilation, and observe that the linear dependence of $\mathrm{\Gamma }$ on $\alpha$ is quantitatively accounted for in the dissipative point-vortex model. The numerical simulations reveal that thermal friction in the experiment was too strong to allow for the emergence of a vortex-clustered state out of decaying turbulence.

We present an observation of zero-to-$\pi$ phase flips induced by Rabi oscillation in an unbalanced Ramsey atom interferometer. The phase shift and visibility are experimentally investigated by modulating either the polarization or duration of Raman lasers, and they are well explained by a theoretical model. In an atom interferometer, the $\pi$ phase flips are caused not only by the sign of Rabi frequency but also by the Rabi oscillation. Considering the $\pi$ phase flips, we propose the composite-light-pulse sequences for realizing the large-momentum-transfer beam splitter and mirror, which have the high immunity to the external phase noise in building the cold atom interferometer.

We show that the wave function in one spatial sector $x_1<x_2<\cdots <x_N$ (with $x_i$ being the coordinate of the $i\mathrm{th}$ particle) of a one-dimensional spinor gas with contact $s$-wave interaction, either bosonic or fermionic, can be mapped to the direct product of the wave function of a spinless Fermi gas with short-range $p$-wave interaction and that of a spin system governed by spin-parity projection operators. Applying this mapping to strongly interacting spinor gases, we obtain a generalized spin-chain model that captures both the static and dynamics properties of the system. Using this spin-chain model, we investigate the breathing-mode frequency and the quench dynamics of strongly interacting, harmonically trapped spinor gases.

We study the interaction of dielectric rods and disks with the laser field of a high-finesse cavity. The quantum master equation for the coupled particle-cavity dynamics, including Rayleigh scattering, is derived for particle sizes comparable to the laser wavelength. We demonstrate that such anisotropic nanoparticles can be captured from free flight at velocities higher than those required to capture dielectric spheres of the same volume and that efficient rotranslational cavity cooling into the deep quantum regime is achievable.

Recently it was shown that the quantum behavior of an intense cavity field can be revealed by measuring the steady atomic correlations between two ideal atoms which interact with the same leaking cavity mode. Considering a weak atom-field coupling regime and large average number of photons in the cavity mode ($\overline{n}$), one expects that a semiclassical theory could explain the whole dynamics of the system. However, this system presents the generation of correlations between the atoms, which is a signature of the quantumness of the cavity field, even in the limit of $\overline{n}\gg 1$ [D. Z. Rossatto et al., Phys. Rev. Lett. 107, 153601 (2011)]. Here, we extend this result by investigating the relaxation time for such a system. We have shown that the relaxation time of the system varies proportionally to $\overline{n}$ for a coherent driving, but it is inversely proportional to $\overline{n}$ for an incoherent pumping. Thus, the time required to observe the manifestation of the quantum aspects of a cavity field on the atomic correlations diverges as $\overline{n}$ tends to macroscopic values due to a coherent driving, while it goes to zero for incoherent pumping. For a coherent driving, we can also see that this system presents metastability, i.e., first the atomic system reaches a quasistationary state which lasts for a long time interval, but eventually it reaches the real steady state. We have also discussed the effects of small atomic decay. In this case, the steady correlations between the atoms disappear for long times, but the intense cavity field is still able to generate atomic correlations at intermediate times. Then, considering a real scenario, we would be able to monitor the quantumness of a cavity field in a certain time interval.

We consider light-induced binding and motion of dielectric microparticles in an optical waveguide that gives rise to a backaction effect such as light transmission oscillating with time. Modeling the particles by dielectric slabs allows us to solve the problem analytically and obtain a rich variety of dynamical regimes both for Newtonian and damped motion. This variety is clearly reflected in temporal oscillations of the light transmission. The characteristic frequencies of the oscillations are within the ultrasound range of the order of ${10}^5$ kHz for micron-size particles and injected power of the order of 100 mW. In addition, we consider dynamics of a dielectric particle, driven by light propagating inside a Fabry-Perot resonator. These phenomena pave a way for optical driving and monitoring of the motion of particles in waveguides and resonators.

Experiments during the past 2 years have shown strong resonant photon-magnon coupling in microwave cavities, while coupling in the optical regime was demonstrated very recently for the first time. Unlike with microwaves, the coupling in optical cavities is parametric, akin to optomechanical systems. This line of research promises to evolve into a new field of optomagnonics, aimed at the coherent manipulation of elementary magnetic excitations in solid-state systems by optical means. In this work we derive the microscopic optomagnonic Hamiltonian. In the linear regime the system reduces to the well-known optomechanical case, with remarkably large coupling. Going beyond that, we study the optically induced nonlinear classical dynamics of a macrospin. In the fast-cavity regime we obtain an effective equation of motion for the spin and show that the light field induces a dissipative term reminiscent of Gilbert damping. The induced dissipation coefficient, however, can change sign on the Bloch sphere, giving rise to self-sustained oscillations. When the full dynamics of the system is considered, the system can enter a chaotic regime by successive period doubling of the oscillations.

We investigate the efficiency of quantum adiabatic optimization when overcoming potential barriers to get from a local to a global minimum. Specifically we look at $n$ qubit systems with symmetric cost functions $f:{\{0,1\}}^n\to \mathbb{R}$, where the ground state must tunnel through a potential barrier of width $n^{\alpha }$ and height $n^{\beta }$. By the quantum adiabatic theorem the time delay sufficient to ensure tunneling grows quadratically with the inverse spectral gap during this tunneling process. We analyze barrier sizes with $1/2\le \alpha +\beta$ and $\alpha <1/2$ and show that the minimum gap scales polynomially as $n^{1/2-\alpha -\beta }$ when $2\alpha +\beta \le 1$ and exponentially as $n^{-\beta /2}exp(-C{n}^{(2\alpha +\beta -1)/2})$ when $1<2\alpha +\beta$. Our proof uses elementary techniques and confirms and extends an unpublished folklore result by Goldstone from 2002, which used large spin and instanton methods. Parts of our result also refine recent results by Kong and Crosson [arXiv:1511.06991] and Jiang et al. [arXiv:1603.01293] about the exponential gap scaling.