Evaporative cooling is a process that is essential in creating Bose-Einstein condensates in dilute atomic gasses. This process has often been simulated based on a model using a truncated Boltzmann distribution. This model assumes that the energy distribution up to the threshold energy can still be described by a Boltzmann distribution: it assumes detailed balance up to the threshold energy. However, the evolution of the distribution function in time is not taken into account. Here we solve the kinetic Boltzmann equation for a gas undergoing evaporative cooling in a harmonic and linear trap in order to determine the evolution of the energy distribution. The magnitude of the discrepancy with the truncated Boltzmannmodel is calculated by including a polynomial expansion of the distribution function. We find that up to 35% fewer particles are found in the high-energy tail of the distribution with respect to the truncated Boltzmann distribution and up to 15% more collisions are needed to reach quantum degeneracy. Supported by a detailed investigation of the particle loss rate at different energies, we conclude that the limited occupation of high-energy states during the evaporation process causes the lowering of the evaporation speed and efficiency.

We study a quantum Bose-Fermi mixture near a broad Feshbach resonance at zero temperature. Within a quantum field theoretical model, a two-step Gaussian approximation allows us to capture the main features of the quantum phase diagram. We show that a repulsive boson-boson interaction is necessary for thermodynamic stability. The quantum phase diagram is mapped in chemical-potential and density space, and both first- and second-order quantum phase transitions are found. We discuss typical characteristics of the first-order transition, such as hysteresis or a droplet formation of the condensate, which may be searched for experimentally.

We determine the low-energy properties of a trapped Bose gas split in two by a potential barrier over the whole range of barrier heights and asymmetry between the wells. For either weak or strong coupling between the wells, our two-mode theory yields a two-site Bose-Hubbard Hamiltonian with the tunneling, interaction, and bias parameters calculated simply using an explicit form of two mode functions. When the potential barrier is relatively low, most of the particles occupy the condensate mode and our theory reduces to a two-mode version of the Bogoliubov theory, which gives a satisfactory estimate of the spatial shape and energy of the lowest collective excitation. When the barrier is high, our theory generalizes the standard two-site Bose-Hubbard model into the case of asymmetric modes, and correctly predicts a full separation of the modes in the limit of strong separation of the wells. We provide explicit analytic forms for the number squeezing and coherence as a function of particle number and temperature. We compare our theory to other two-mode theories for bosons in a double well and discuss their validity in different parameter regimes.

We analyze the various phases exhibited by a system of ultracold bosons in a periodic optical superlattice using the mean-field decoupling approximation. We investigate for a wide range of commensurate and incommensurate densities. We find the gapless superfluid phase, the gapped Mott insulator phase, and gapped insulator phases with distinct density wave orders.

The effects of dynamics of continuous-variable entanglement under the various kinds of environments on quantum teleportation are quantitatively investigated. Only under assumption of the weak system-reservoir interaction, the evolution of teleportation fidelity is analytically derived and is numerically plotted in terms of environment parameters including reservoir temperature and its spectral density, without Markovian and rotating wave approximations. We find that the fidelity of teleportation is a monotonically decreasing function for Markovian interaction in Ohmic-like environments, while it oscillates for non-Markovian ones. According to the dynamical laws of teleportation, teleportation with better performances can be implemented by selecting the appropriate time.

We apply the frozen-correlation approximation (FCA) to analyze double ionization of helium by energetic highly charged ions. In this model the double ionization amplitude is represented in terms of single ionization amplitudes, which we evaluate within the continuum distorted wave-eikonal initial state (CDW-EIS) approach. Correlation effects are incorporated in the initial and final states, but are neglected during the time the collision process takes place. We implement the FCA using the Monte Carlo event generator technique, which allows us to generate theoretical event files and to compare theory and experiment using the same analysis tools. The comparison with previous theoretical results and with experimental data demonstrates, on the one hand, the validity of our earlier simple models to account for higher-order mechanisms, and, on the other hand, the robustness of the FCA.

We propose a possible experiment aimed at a joint measurement of two noncommuting spin-1/2 components and analyze its physical meaning. We demonstrate that switching of a strong spin-orbit interaction, e.g., in a solid-state or a cold-atom system, for a short time interval simulates a simultaneous von Neumann measurement of the operators ${\sigma }_x$ and ${\sigma }_y$. With the spin dynamics mapped onto the quantum coordinate-space motion, such an experiment determines averages of ${\sigma }_x$ and ${\sigma }_y$ over the duration of the measurement, however short the latter may be. These time averages, unlike the instantaneous values of ${\sigma }_x$ and ${\sigma }_y$, may be evaluated simultaneously to an arbitrary accuracy.

We propose indium (In) as a possible candidate for observing the permanent electric dipole moment (EDM) arising from violations of parity ($P$) and time-reversal ($T$) symmetries. This atom has been laser cooled and therefore the measurement of its EDM has the potential of improving on the current best EDM limit for a paramagnetic atom, which comes from thallium. We report the results of our calculations of the EDM enhancement factor due to the electron EDM and the ratio of the atomic EDM to the electron-nucleus scalar-pseudoscalar (S-PS) interaction coupling constant in In within the framework of the relativistic coupled cluster theory. It might be possible to get new limits for the electron EDM and the S-PS $CP$-violating coupling constant by combining the results of our calculations with the measured value of the EDM of In when it is available. These limits could have important implications for the standard model (SM) of particle physics.

Exact calculation of the condensate fraction in multidimensional inhomogeneous interacting Bose systems in a confining potential of arbitrary shape is a difficult computational problem. We have developed an iterative procedure which allows us to calculate the condensate fraction as well as the corresponding eigenfunction of the one-body density matrix. We successfully validate this procedure in diffusion Monte Carlo simulations of a Bose gas in an optical lattice at zero temperature. We also discuss the relation between different criteria used for testing coherence in cold Bose systems, such as the fraction of particles that are superfluid, condensed, or in the zero-momentum state.

Coherent control of a quantum system is limited both by the decoherence due to environment and the quantum nature of the control agent. The high fidelity of control demanded by fault-tolerant quantum computation and the intrinsic interest in nonclassical effects from the interplay between control and dissipation are motivations for a detailed study of the interaction dynamics between the quantum system and the macroscopic environment and control agent. We present a detailed time-evolution study of a two-level system interacting with a laser pulse and the electromagnetic vacuum in the multimode Jaynes-Cummings model. A diagrammatic formalism allows easy identification of coherent dynamics and relaxation of the two-level system. We demonstrate a computational method of dynamics with precise error bounds for fast operations versus slow decoherence, spanning the Markovian and non-Markovian regimes. Comparison against an exact model solution of our results with existing approximations of the master equation shows the lack of accuracy in the latter.

With the quantum diffusion approach, the probability of passing through the parabolic barrier and the quasistationary thermal decay rate from a metastable state are examined in the limit of linear coupling both in momentum and in coordinate between a collective subsystem and the environment. An increase of passing probability with friction coefficient is demonstrated to occur at subbarrier energies.

We discuss the coupling of two identical atoms, separated by a metal or metamaterial slab, through surface modes. We show that the coupling through the surface modes can induce entanglement. We discuss how to control the coupling for the metal or metamaterial slab by adjusting the symmetrical and antisymmetrical property of the surface modes. We analyze the dispersion relation of the surface modes and study the parameter ranges that support the surface modes with the same properties. Our results have potential applications in quantum communication and quantum computation.

The effect of an external electric field on the magnetically induced ${}^6$Li-${}^{40}$K Feshbach resonance is investigated theoretically by using the asymptotic bound state model (ABM). An electric field can modify the position and width of the Feshbach resonance to varying extent. However, it hardly changes the background scattering length in the case without open-channel resonance. The width of the $s$-wave resonance resulting from the $p$-wave bound state becomes narrow under the action of a strong electric field. The effects of electric field on orbital angular momentum and electronic state of the Feshbach molecule are also discussed.

Electron-impact excitation cross sections from the ground state to the individual magnetic sublevels of the excited state $1s2s^{2}2p_{1/2}J=1$ for highly charged berylliumlike ions have been calculated by using a fully relativistic distorted-wave (RDW) method. The degrees of linear polarization of the corresponding radiations are obtained. It is found that the Breit interaction makes the linear polarization of radiations decrease, and this character becomes more evident with increasing of incident electron energy. For a given energy in threshold units, the linear polarization without the Breit interaction included increases very slowly as the atomic number increases, however, the linear polarization with the Breit interaction included decreases rapidly. These characteristics are very different from the conclusions for the linear polarization of the same radiations but formed by the dielectronic recombination process [Phys. Rev. Lett. 103, 113001 (2009)], in which the Breit interaction makes the linear polarization increase, and the linear polarization with the Breit interaction included increases with increasing of the atomic number.

Absolute cross sections for electron-impact dissociation of N${}_2$D${}^{+}$ producing N${}_2^{+}$, ND${}^{+}$, and N${}^{+}$ ion fragments were measured in the 5- to 100-eV range using a crossed electron-ion beams technique. In the 5- to 20-eV region, in which dissociative excitation (DE) is the principal contributing mechanism, N${}_2^{+}$ production dominates. The N${}_2^{+}$ + D dissociation channel shows a large resonant-like structure in the DE cross section, as observed previously in electron impact dissociation of triatomic dihydride species [M. Fogle, E. M. Bahati, M. E. Bannister, S. H. M. Deng, C. R. Vane, R. D. Thomas, and V. Zhaunerchyk, Phys. Rev. A 82, 042720 (2010)]. In the dissociative ionization (DI) region, 20- to 100-eV, N${}_2^{+}$, ND${}^{+}$, and N${}^{+}$ ion fragment production are comparable. The observance of the ND${}^{+}$ and N${}^{+}$ ion fragments indicate breaking of the $\mathrm{N}-\mathrm{N}$ bond along certain dissociation channels.

In this work, the efficient electron loss process was observed for the transmission of 10- to 18-keV Cu${}^{-}$ and Cl${}^{-}$ ions through Al${}_2$O${}_3$ nanocapillaries. The fractions of the scattered particles were simultaneously measured using a position-sensitive microchannel plate detector. The neutrals were guided through the capillary via multiple grazing scattering. In particular, the scattered Cl${}^{-}$ ions were observed in the transmission, whereas no Cu${}^{-}$ ion was formed. In contrast to highly charged ions, these results support strongly the fact that the scattering events dominate the transport of negative ions through the nanocapillaries and that there is no direct evidence for the formation of negative charge patches inside the capillaries which are able to repulse and guide negative ions efficiently.

The coherent nonlinear tunneling dynamics of a boson-fermion mixture in a double-well potential is studied in this paper. Four types of phase are found for the mixture. The first one is two species localizing in different potential wells. The second one is two species coexisting in the same well. The third one is two species equally populated in two wells. The fourth one is one species equally populated in two wells while the other species is in one well. The phase transitions among these four states have been investigated. The interspecies and intraspecies interactions as well as bosonic and fermionic numbers can dramatically affect these phase transitions.

We study the simplest optomechanical system with a focus on the bistable regime. The covariance matrix formalism allows us to study both cooling and entanglement in a unified framework. We identify two key factors governing entanglement; namely, the bistability parameter (i.e., the distance from the end of a stable branch in the bistable regime) and the effective detuning, and we describe the optimum regime where entanglement is greatest. We also show that, in general, entanglement is a nonmonotonic function of optomechanical coupling. This is especially important in understanding the optomechanical entanglement of the second stable branch.

We have theoretically demonstrated femtosecond pulse manipulation at the nanoscale using the plasmonic snowflake antenna’s ability to localize light over a broad spectrum. To analyze the interaction of the incident femtosecond pulse with the plasmonic nanoantenna, we first decompose the diffraction limited incident femtosecond pulse into its spectral components. The interaction of each spectral component with the nanoantenna is analyzed using finite element technique. The time domain response of the plasmonic antenna is obtained using inverse Fourier transformation. It is shown that the rich spectral characteristics of the plasmonic snowflake nanoantenna allow manipulation of the femtosecond pulses over a wide spectrum. Light localization around the gap region of the nanoantenna is shown for femtosecond pulses. As the alignment of incident light polarization is varied, different antenna elements oscillate, which in turn creates a different spectrum and a distinct femtosecond response.