We apply the truncated Wigner method to the process of three-body recombination in ultracold Bose gases. We find that within the validity regime of the Wigner truncation for two-body scattering, three-body recombination can be treated using a set of coupled stochastic differential equations that include diffusion terms, and can be simulated using known numerical methods. As an example we investigate the behavior of a simple homogeneous Bose gas, finding a very slight increase of the loss rate compared to that obtained by using the standard method.

We use a time-dependent dynamical mean-field-hydrodynamic model to study mixing-demixing in a degenerate fermion-fermion mixture (DFFM). It is demonstrated that with the increase of interspecies repulsion and/or trapping frequencies, a mixed state of a DFFM could turn into a fully demixed state in both three-dimensional spherically symmetric as well as quasi-one-dimensional configurations. Such a demixed state of a DFFM could be experimentally realized by varying an external magnetic field near a fermion-fermion Feshbach resonance, which will result in an increase of interspecies fermion-fermion repulsion, and/or by increasing the external trap frequencies.

We report a narrow angular distribution of 0.8°, close to that expected from the aspect ratio, for guiding of highly charged ions through a well-ordered, parallel $\mathrm{Si}{\mathrm{O}}_2$ nanocapillaries target. These capillaries were obtained by thermally oxidizing a $25\text{−}\mu \mathrm{m}$-thick membrane of silicon nanocapillaries fabricated by photoassisted electrochemical etching. The diameter of the uniformly distributed capillaries was $100\mathrm{nm}$. We observed ${\mathrm{Ne}}^{7+}$ ions being transmitted through these nanocapillaries with a decreasing transmitted intensity up to a factor 100, when increasing the capillary tilt angles up to 4°. The narrower angular distribution in comparison to polyethylene terephthalate capillaries is discussed and it is shown that the $\mathrm{Si}{\mathrm{O}}_2$ results support the model of self-organized charge patches formed at the capillary entrance.

We compute the energy absorbed by a one-dimensional system of cold bosonic atoms in an optical lattice subjected to lattice amplitude modulation periodic with time. We perform the calculation for the superfluid and the Mott insulator created by a weak lattice, and the Mott insulator in a strong lattice potential. For the latter case we show results for three-dimensional systems as well. Our calculations, based on bosonization techniques and strong-coupling methods, go beyond standard Bogoliubov theory. We show that the energy absorption rate exhibits distinctive features of low-dimensional systems and Luttinger liquid physics. We compare our results with experiments and find good agreement.

We calculate the dispersive properties of a single-sided cavity coupled to a single dipole. We show that when a field is resonant with the dipole and the Purcell factor exceeds the bare cavity reflection coefficient, the field experiences a $\pi$ phase shift relative to reflection from a bare cavity. We then show that optically Stark shifting the dipole resonance with a second field creates large Kerr nonlinearities. An approximate expression for the total number of photons needed to create a $\pi$ phase shift is derived.

We report on a theoretical study of the ionization process of ${\mathrm{Xe}}^{*}$ Rydberg atoms colliding with a metal surface, in the presence of an external electric field. The evolution of the ${\mathrm{Xe}}^{*}$ outer electron is studied by a wave packet propagation approach, allowing to include all dynamical aspects of the collision, in particular nonadiabatic inter-Rydberg transitions. We investigate how the different ${\mathrm{Xe}}^{*}$ Stark states formed in the external field couple together and ionize on the surface and how the different polarizations of the electronic cloud in the ${\mathrm{Xe}}^{*}$ states are reflected in their ionization properties. We show that the presence of the external electric field can significantly perturb the dynamics of the ionization process. Our results account for recent results from Dunning et al. [Nucl. Inst. Meth. B 203, 69 (2003)]. In particular, it is explained how the external electric field present in the experimental procedure of Dunning et al. leads to the apparent absence of a polarization effect in the ionization process.

The time-dependent Schrödinger equation is solved numerically to investigate laser-assisted charge transfer in ${\mathrm{He}}^{2+}+\mathrm{H}+nh\nu$ collisions at $1\mathrm{keV}$ in the semiclassical impact parameter approach. Laser polarizations parallel and perpendicular to the projectile trajectory are studied. For both polarizations even a moderately intense laser $(I_0=3.5\times {10}^{12}\mathrm{W}∕{\mathrm{cm}}^2)$ significantly increases the reaction probability. In addition, we find that the relative collision-laser phase has little influence on the charge transfer. We focus on parameters more favorable to experiment.

We perform accurate investigation of stability of localized vortices in an effectively two-dimensional (“pancake-shaped”) trapped Bose-Einstein condensate with negative scattering length. The analysis combines computation of the stability eigenvalues and direct simulations. The states with vorticity $S=1$ are stable in a third of their existence region, $0<N<(1∕3)N_{\max }^{(S=1)}$, where $N$ is the number of atoms, and $N_{\max }^{(S=1)}$ is the corresponding collapse threshold. Stable vortices easily self-trap from arbitrary initial configurations with embedded vorticity. In an adjacent interval, $(1∕3)N_{\max }^{(S=1)}<N<0.43N_{\max }^{(S=1)}$, the unstable vortex periodically splits in twofragments and recombines. At $N>0.43N_{\max }^{(S=1)}$, the fragments do not recombine, as each one collapses by itself. The results are compared with those in the full three-dimensional (3D) Gross-Pitaevskii equation. In a moderately anisotropic 3D configuration, with the aspect ratio $\sqrt{10}$, the stability interval of the $S=1$ vortices occupies $\approx 40\%$ of their existence region, hence the two-dimensional (2D) limit provides for a reasonable approximation in this case. For the isotropic 3D configuration, the stability interval expands to 65% of the existence domain. Overall, the vorticity heightens the actual collapse threshold by a factor of up to $2$. All vortices with $S⩾2$ are unstable.

A system of cascaded qubits interacting via the one-way exchange of photons is studied. While for general operating conditions the system evolves to a superposition of Bell states (a dark state) in the long-time limit, under a particular resonance condition no steady state is reached within a finite time. We analyze the conditional quantum evolution (quantum trajectories) to characterize the asymptotic behavior under this resonance condition. A distinct bimodality is observed: for perfect qubit coupling, the system either evolves to a maximally entangled Bell state without emitting photons (the dark state) or executes a sustained entangled-state cycle—random switching between a pair of Bell states while emitting a continuous photon stream; for imperfect coupling, two entangled-state cycles coexist, between which a random selection is made from one quantum trajectory to another.

We demonstrate a scheme for producing polarization-entangled photons of different wavelengths. The scheme is a variation of the conventional single-crystal, frequency-degenerate type-II scheme and offers similar brightness, quality of entanglement, and ease of alignment.

Though all-or-nothing oblivious transfer and one-out-of-two oblivious transfer are equivalent in classical cryptography, we here show that a protocol built upon secure quantum all-or-nothing oblivious transfer cannot satisfy the rigorous definition of quantum one-out-of-two oblivious transfer due to the nature of quantum cryptography. Thus the securities of the two oblivious transfer protocols are not equivalent at the quantum level.

In quantum cryptography the optimal eavesdropping strategy requires that the eavesdropper uses ancillas and quantum memories in order to optimize her information. What happens if the eavesdropper has no quantum memory? It is shown that in this case the eavesdropper obtains a better information/disturbance trade-off by adopting the simple intercept/resend strategy.

The sensitivity analysis for the time-dependent variational principle (TDVP) with constraints for parametrized wave functions [K. Ohta, Phys. Rev. A 70, 022503 (2004)] is investigated to assess the geodesic deviation caused by external parameters. The constraints for the sensitivity functions, inherited from the TDVP, are dealt with their consistency conditions. As an example of the sensitivity analysis, the geodesic deviation in the neighborhood of stationary states is investigated for general wave functions.

We show that the single-site entanglement of a generic spin-1/2 fermionic lattice system can be used as a reliable marker of a finite-order quantum phase transition, given certain provisos. We discuss the information contained in the single-site entanglement measure, and provide illustrations from the Mott–Hubbard metal-insulator transitions of the one-dimensional (1D) Hubbard model, and the (1D) Hubbard model with long-range hopping.

Carbon and oxygen dimers with charge states $1+$ and $3+$ were implanted into $\mathrm{GaAs}$ along the [100] direction at an energy of $0.5\mathrm{MeV}∕\mathrm{atom}$. The defect depth profiles are extracted from Rutherford backscattering spectrometry and channeling. The depth profile of carbon is extracted from secondary ion mass spectrometry measurements. The defect density produced by dimer ions is larger than monomer ions. The depth profile of carbon in dimer implanted $\mathrm{GaAs}$ is deeper than that of monomer implanted $\mathrm{GaAs}$ showing negative molecular effect. The defect depth profile of oxygen dimer implanted $\mathrm{GaAs}$ is deeper for $3+$ than that for $1+$ charge state. This indicates that energy loss of ${\mathrm{O}}_2^{3+}$ is smaller than that of ${\mathrm{O}}_2^{+}$. It is attributed to charge asymmetry and a higher degree of alignment of ${\mathrm{O}}_2^{3+}$ along the [100] axis of $\mathrm{GaAs}$.

The multi-longitudinal-mode dynamics of a semiconductor laser is studied theoretically, based on traveling-wave equations for the slowly varying amplitudes of the counterpropagating optical fields in the laser cavity, coupled to an equation for the carrier population dynamics. The model considers key ingredients describing the semiconductor medium, such as the spatial variations of the carriers and optical fields in the longitudinal direction, a parabolic frequency-dependent gain and phase-amplitude coupling, and does not assume a priori a fixed number of active longitudinal modes. We find deterministic out-of-phase modal oscillations which leave the sum of total modal intensities nearly constant. These oscillations become faster as the injection current increases, in good agreement with recent experimental observations. In our model the origin of modal oscillations is spatial hole burning in the envelope of the carrier grating, which is due to the interaction of different longitudinal modes. We also observe switching and hopping of the lasing modes in accordance with the experiments.

Optimally extracting information from measurements performed on a physical system requires an accurate model of the measurement interaction. Continuously probing the collective spin of an alkali-metal atom cloud via its interaction with an off-resonant optical probe is an important example of such a measurement where realistic modeling at the quantum level is possible using standard techniques from atomic physics. Typically, however, tutorial descriptions of this technique have neglected the multilevel structure of realistic atoms for the sake of simplification. We account for the full multilevel structure of alkali-metal atoms and derive the irreducible form of the polarizability Hamiltonian describing a typical dispersive quantum measurement. For a specific set of parameters, we then show that semiclassical predictions of the theory are consistent with our experimental observations of polarization scattering by a polarized cloud of laser-cooled cesium atoms. We also derive the signal-to-noise ratio under a single-measurement trial and use this to predict the rate of spin squeezing with multilevel alkali-metal atoms for arbitrary detuning of the probe beam.

We discuss the appearance of Zeno or anti-Zeno effects in an exponentially decaying system. We consider the quantum dynamics of a continuously monitored two level system interacting with a squeezed bath. We find that the behavior of the system depends critically on the way in which the squeezed bath is prepared. For specific choices of the squeezing phase the system shows Zeno or anti-Zeno effects in conditions for which it would decay exponentially if no measurements were done. This result allows for a clear interpretation in terms of the equivalent spin system interacting with a fictitious magnetic field.

We discuss a system comprising two nonlinear (Kerr-like) oscillators coupled mutually by a nonlinear interaction. The system is excited by an external coherent field that is resonant to the frequency of one of the oscillators. We show that the coupler evolution can be closed within a finite set of $n$-photon states, analogously as in the nonlinear quantum scissors model. Moreover, for this type of evolution our system can be treated as a Bell-like state generator. Thanks to the nonlinear nature of both oscillators and their internal coupling, these states can be generated even if the system exhibits its energy dissipating nature, contrary to systems with linear couplings.

We consider the entanglement of two remote qubits induced by local interaction with the two-mode nonclassical state fields. We investigate the transfer of entanglement from different two-mode nonclassical state fields to a pair of separable and mixed qubits. We find that no matter what state the qubit subsystem is initially prepared in, at the specific time $gt\simeq 11.07$ the entanglement of the Bell state fields can be almost completely transferred to the qubit subsystem, i.e., the Bell state fields can drive an initially separable and very mixed state of qubits into an almost pure highly entangled state suitable for quantum information processing. For the entangled coherent state fields $\mid u⟩=N_1(\mid \alpha ,-\alpha ⟩+\mid -\alpha ,\alpha ⟩)$ and $\mid u^{\prime }⟩=N_2(\mid \alpha ,-\alpha ⟩-\mid -\alpha ,\alpha ⟩)$ we find that when $\mid \alpha \mid$ is small, the dynamic behaviors of the entanglement between two qubits are quite different. For $\mid u⟩$ there is almost no entanglement between two qubits while for $\mid u^{\prime }⟩$ the dynamic behavior of the entanglement between two qubits is very similar to that of the Bell state field. For large $\mid \alpha \mid$ we find that the dynamic behaviors of entanglement between two qubits are almost the same for these two fields, and when $gt\sim \mid \alpha \mid \pi$ the entanglement between two qubits reaches its maximum and is almost independent of initial mixedness of the qubit subsystem. For the two-mode squeezed vacuum state field we find that when $r\sim 0.86$ and $gt\simeq 11.07$ the entanglement transfer reaches its maximum which also almost does not depend on the initial mixedness of the qubit subsystem.