We propose a tomography scheme capable of reconstructing the quantum state of an unknown mode of light. The complex mode structure of the investigated field is expressed by a single number—the mismatch between the probe and signal. This parameter is estimated as a part of the quantum tomography protocol. This opens up ways for reconstructions utilizing interference between independent sources.

We report the realization of quantum degenerate mixed gases of ytterbium (Yb) isotopes using all-optical methods. We have succeeded in cooling attractively interacting ${}^{176}\mathrm{Yb}$ atoms via sympathetic cooling down to below the Bose-Einstein transition temperature, coexisting with a stable condensate of ${}^{174}\mathrm{Yb}$ atoms with a repulsive interaction. We have observed a rapid atom loss in ${}^{176}\mathrm{Yb}$ atoms after cooling down below the transition temperature, which indicates the collapse of a ${}^{176}\mathrm{Yb}$ condensate. The sympathetic cooling technique has been applied to cool a ${}^{173}\mathrm{Yb}\text{−}{}^{174}\mathrm{Yb}$ Fermi-Bose mixture to the quantum degenerate regime.

We investigate the buildup of quasi-long-range order in the $XX$ chain with a transverse magnetic field at finite size. As the field is varied, the ground state of the system displays multiple level crossings producing a sequence of entanglement jumps. Using the partial fidelity and susceptibility, we study the transition to the thermodynamic limit and argue that the topological order can be described in terms of kink-antikink pairs and marked by edge spin entanglement.

Disentanglement dynamics of multipartite Greenberger-Horne-Zeilinger-type states $\mid {\Phi }_N⟩=\alpha {\mid 0⟩}^{\otimes N}+\beta {\mid 1⟩}^{\otimes N}$ due to local environments is studied. It was shown [L. Aolita et al. , Phys. Rev. Lett. 100, 080501 (2008)] that for $\mid \alpha ∕\beta \mid ⩾1$ it takes an infinite time for states $\mid {\Phi }_N⟩$ to become completely separable if their qubits are only exposed either to a phase-damping dynamics or to an amplitude-damping one. We show, however, that if both phase damping and amplitude damping are simultaneously active then the transition to complete separability takes just a finite time even for $\mid \alpha ∕\beta \mid ⩾1$. We further show that application of appropriate local operators can circumvent such a finite-time disentanglement.

High-accuracy nonrelativistic variational calculations employing explicitly correlated Gaussian basis functions have been performed to determine the energies and the expectation values of some operators for the lowest four ${}^{1}P_1$ states of the beryllium atom. The states correspond to the electron configurations $1s^{2}2s^{1}n{p}^1$, where $n=2$, 3, 4, and 5. The calculations were performed for both finite and infinite mass of the Be nucleus. The basis set for each state was grown to the level of $5000$ Gaussians. With that many functions we achieved a tight energy convergence. The reported values, to the best of our knowledge, are the most accurate ever obtained for the four states.

The $\mathrm{He}{\mathrm{H}}^{+}$ cation undergoes dissociative recombination with a free electron to produce neutral He and H fragments. We present calculations using ab initio quantum defects and Fano’s rovibrational frame-transformation technique, employing cation rovibrational wave functions satisfying outgoing wave boundary conditions, to obtain the recombination rate in both the low-energy $(1–300\mathrm{meV})$ and high-energy (ca. $0.6\text{hartree}$) regions. We obtain very good agreement with experimental results, demonstrating that this relatively simple method is able to reproduce observed rates for both indirect dissociative recombination, driven by rovibrationally autoionizing states in the low-energy region, and direct dissociative recombination, driven by electronically autoionizing Rydberg states attached to higher-energy excited cation channels.

A nonrelativistic system of three identical particles will display a rich set of universal features known as Efimov physics if the scattering length $a$ is much larger than the range $l$ of the underlying two-body interaction. An appropriate effective theory facilitates the derivation of both results in the $\mid a\mid \to \infty$ limit and finite-$l∕a$ corrections to observables of interest. Here we use such an effective-theory treatment to consider the impact of corrections linear in the two-body effective range, $r_s$, on the three-boson bound-state spectrum and recombination rate for $\mid a\mid ⪢\mid r_s\mid$. We do this by first deriving results appropriate to the strict limit $\mid a\mid \to \infty$ in coordinate space. We then extend these results to finite $a$ using once-subtracted momentum-space integral equations. We take the cutoff on these equations to be large compared to $1∕\mid r_s\mid$, and find that the first-order effects of $\mid r_s\mid$ are independent of the cutoff in this regime. We also discuss the implications of our results for experiments that probe three-body recombination in Bose-Einstein condensates near a Feshbach resonance.

We studied the dynamic properties of ion guiding through nanocapillaries in insulating polyethylene terephthalate. The angular distribution of the transmitted ions was measured as a function of the charge deposited on the sample surface, which is a measure of time. The time evolution of the angular transmission profiles was acquired for the capillary diameters of 200 and $400\mathrm{nm}$. The tilt angle was varied from 0° to 6.5°. The transmission profiles appear as a superposition of essentially three localized peaks which exhibit significant changes in intensity as time varies. This observation provides evidence for the formation of temporary charge patches produced in the interior of the capillary besides the primary charge patch created in the entrance region.

Three alternative forms of harmonic spectra, based on the dipole moment, dipole velocity, and dipole acceleration, are compared by a numerical solution of the Schrödinger equation for a hydrogen atom interacting with a linearly polarized laser pulse, whose electric field is given by $E\left(t\right)=E_{0}f\left(t\right)\cos ({\omega }_{0}t+\eta )$ with Gaussian carrier envelope $f\left(t\right)=\exp (-t^2∕{\delta }^2)$. The carrier frequency ${\omega }_0$ is fixed to correspond to a wavelength of $800\mathrm{nm}$. Spectra for a selection of pulses, for which the intensity $I_0=c{\epsilon }_0{E}_0^2$, duration $T\propto \delta$, and carrier-envelope phase $\eta$ are systematically varied, show that, depending on $\eta$, all three forms are in good agreement for “weak” pulses with $I_0<I_b$, the over-barrier ionization threshold, but that marked differences among the three appear as the pulse becomes shorter and stronger $(I_0>I_b)$. Except for scalings by powers of the harmonic frequency, the three forms differ from one another only by “limit contributions” proportional to the expectation values of the dipole moment $⟨z\left(t_f\right)⟩$ or dipole velocity $⟨\dot{z}\left(t_f\right)⟩$ at the end $\left(t_f\right)$ of the pulse. For long, weak pulses the limit contributions are negligible, whereas for short, strong ones they are not. In the short, strong limit, where $⟨\dot{z}\left(t_f\right)⟩\ne 0$ and therefore $⟨z\left(t\right)⟩$ may increase without bound (i.e., the atom may ionize), depending on $\eta$, an “infinite-time” spectrum based on the acceleration form provides a convenient computational pathway to the corresponding infinite-time dipole-velocity spectrum, which is related directly to the experimentally measured “harmonic photon number spectrum” (HPNS). For short, intense pulses the HPNS is quite sensitive to $\eta$ and exhibits not only the usual odd harmonics but also even ones. The analysis also reveals that most of the harmonic photons are emitted during the passage of the pulse. Because of the divergence of $⟨z\left(t\right)⟩$ the dipole-moment form does not provide a numerically reliable route to the harmonic spectrum for very short (few-cycle), very intense laser pulses.

It is demonstrated that the well-known Smale-horseshoe chaos exists in the time evolution of the one-dimensional Bose-Einstein condensate (BEC) driven by the time-periodic harmonic or inverted-harmonic potential. A formally exact solution of the time-dependent Gross-Pitaevskii equation is constructed, which describes the matter shock waves with chaotic or periodic amplitudes and phases. When the periodic driving is switched off and the number of condensed atoms is conserved, we obtained the exact stationary states and nonstationary states. The former contains the stable “nonpropagated” shock wave, and in the latter the shock wave alternately collapses and grows for the harmonic trapping or propagates with exponentially increased shock-front speed for the antitrapping. It is revealed that the existence of chaos plays a role for suppressing the blast of matter wave. The results suggest a method for preparing the exponentially accelerated BEC shock waves or the stable stationary states.

We propose a scheme to produce continuous variable entanglement between phase-quadrature amplitudes of two light modes in an optomechanical system. For proper driving power and detuning, the entanglement is insensitive with bath temperature and $Q$ of the mechanical oscillator. Under realistic experimental conditions, we find that the entanglement could be very large even at room temperature.

We show that double-charge discrete optical vortices may be completely stable in hexagonal photonic lattices where single-charge vortices always exhibit dynamical instabilities. Even when unstable the double-charge vortices typically have a much weaker instability than the single-charge vortices, and thus their breakup occurs at longer propagation distances.

Effective transport of quantum information is an essential element of quantum computation. We consider the problem of transporting a quantum state by using a moving potential well while maintaining the encoded quantum information. In particular, we look at a set of cases where the input control defining the position of the potential well is subject to different types of distortion, each of which is motivated by experimental considerations. We show that even under these conditions, we are able to perfectly transfer the quantum information nonadiabatically over any given distance.

Quantum trajectories given by the quantum state diffusion theory are used to study the dynamics of a pair of qubits interacting with the quantized Duffing oscillator. The latter is a nonlinear dissipative and driven quantum system that in the semiclassical limit displays typical bifurcations and chaotic behavior of the classical model. It is shown that the oscillator part of the qubits-oscillator system in the semiclassical limit is well described by the classical model despite the oscillator-qubit interaction. On the other hand, exact quantum dynamics of the qubits pair is completely different from the classical model as long as there is non-negligible qubit-oscillator interaction. Dynamics of the interqubits entanglement and the qubits pair von Neumann entropy is studied in the deeply quantum and various degrees of semiclassical regimes and for different values of the oscillator’s bifurcation parameter. It is concluded that the decoherence of the qubits pair by the dissipative nonlinear oscillator is more effective when the oscillator is in the more classical regime, and if the semiclassical oscillator dynamics is chaotic rather than regular.

In this paper, with the weak cross-Kerr nonlinearity, we first present a special experimental scheme called controlled-path gate with which the realization of all possible bipartite positive-operator-value measurements of two-photon polarization states may be nearly deterministic. Following the same technique, the realization of quantum control gates, including the controlled-NOT gate, Fredkin gate, Toffoli gate, arbitrary controlled-U gate, and even arbitrary multicontrolled-U gate, are proposed. The corresponding probabilities are $1∕2$, $1∕8$, $2∕23$, etc., respectively. Only the coherent states are required but not any ancilla photons, and no coincidence measurement are required, which results in these gates being scalable. The structures of these gates are very simple, therefore we think they are feasible with the current experimental technology in optics.

We report on the high resolution photoassociation spectroscopy of a ${}^{87}\mathrm{Rb}$ spin-1 Bose-Einstein condensate to the $1_g\left(P_{3∕2}\right)$ $v=152$ excited molecular states. We demonstrate the use of spin dependent photoassociation to experimentally identify the molecular states and their corresponding initial scattering channel. These identifications are in excellent agreement with the eigenvalues of a hyperfine-rotational Hamiltonian. Using the observed spectra we estimate the change in scattering length and identify photoassociation laser light frequency ranges that maximize the change in the spin-dependent mean-field interaction energy.

The evolution of a molecular wave packet created by an ultrashort laser pulse in a system of two coupled bound states is investigated by quantum dynamics calculations and semiclassical theory. Under suitable dynamical quantum interference conditions, the wave packet may be split into two separable fractions that move in different but partially overlapping regions of the energetically available phase space. Each wave-packet part can be individually addressed in the divided parts of the molecular phase space, and they are shown to go through separate long-term collapse-revival cycles analogous to those of wave packets moving in single anharmonic potentials. In a pump-probe scheme, the dynamics of the system would look very different depending on what internuclear distances are probed. The regular dynamics observable in the separated parts of the phase space takes on a quite irregular appearance in the regions that are shared by the wave-packet components. The wave-packet regularity is shown to depend sensitively on the pump pulse wavelength, which is a reflection of the energy range over which the quantum interference conditions are maintained. These conditions, as well as the wave-packet fraction revival times, are well reproduced by semiclassical theory.

We present some general considerations on the properties of a two-component ultracold Fermi gas along the BEC-BCS crossover. It is shown that the interaction energy and the free energy can be written in terms of a single dimensionless function $h(\xi ,\tau )$, where $\xi =-{\left(k_F{a}_s\right)}^{-1}$ and $\tau =T∕T_F$. The function $h(\xi ,\tau )$ incorporates all the many-body physics and naturally occurs in other physical quantities as well. In particular, we show that the average rf-spectroscopy shift $\overline{\delta \omega }(\xi ,\tau )$ and the molecular fraction $f_c(\xi ,\tau )$ in the closed channel can be expressed in terms of $h(\xi ,\tau )$ and thus have identical temperature dependence. The conclusions should have testable consequences in future experiments.

We develop a formalism based on the projected Gross-Pitaevskii equation to simulate the finite-temperature collective mode experiments of Jin et al. [Phys. Rev. Lett. 78, 764 (1997)]. We examine the $m=0$ and $m=2$ quadrupolar modes on the temperature range $0.51T_c–0.83T_c$ and calculate the frequencies of, and phase between, the condensate and noncondensate modes, and the condensate mode damping rate. This study is the first quantitative comparison of the projected Gross-Pitaevskii equation to experimental results in a dynamical regime.

We investigate how entangled coherent states and superpositions of low intensity coherent states of non-Gaussian nature can be generated via nonresonant interaction between either two linearly or circularly polarized field modes and an ensemble of X-like four-level atoms placed in an optical cavity. We compare our results to recent experimental observations and argue that the non-Gaussian structure of the field states may be present in those systems.