We present experimental and theoretical results showing the improved beam quality and reduced divergence of an atom laser produced by an optical Raman transition, compared to one produced by an rf transition. We show that Raman outcoupling can eliminate the diverging lens effect that the condensate has on the outcoupled atoms. This substantially improves the beam quality of the atom laser, and the improvement may be greater than a factor of 10 for experiments with tight trapping potentials. We show that Raman outcoupling can produce atom lasers whose quality is only limited by the wave function shape of the condensate that produces them, typically a factor of 1.3 above the Heisenberg limit.

For a series of incoherent and ultracold atoms with an orbital angular momentum (or vortices) released from an optical lattice, we consider the density-density correlation of this freely expanding ultracold gases. Because of the unique phase structure originating from the quantized angular momentum, it is shown that the phase structure plays an important role in the distribution of the density-density correlation through the appearance of crescent-shaped peaks accompanying the ordinary round-shaped peaks. In particular, it is found that the orientation of the crescent-shaped peaks corresponds with the rotation direction of the atoms prepared in the optical lattices.

We provide several formulas that determine the optimal number of entangled bits (ebits) that a general entanglement-assisted quantum code requires. Our first theorem gives a formula that applies to an arbitrary entanglement-assisted block code. Corollaries of this theorem give formulas that apply to a code imported from two classical binary block codes, to a code imported from a classical quaternary block code, and to a continuous-variable entanglement-assisted quantum block code. Finally, we conjecture two formulas that apply to entanglement-assisted quantum convolutional codes.

Cross sections of charge transfer for ${\text{Si}}^{3+}$ ions with atomic hydrogen at collision energies of $\approx 40–2500\text{eV}/\text{u}$ were carried out using a merged-beam technique at the Multicharged Ion Research Facility at Oak Ridge National Laboratory. The data span an energy range in which both molecular orbital close coupling (MOCC) and classical trajectory Monte Carlo (CTMC) calculations are available. The influence of quantum mechanical effects of the ionic core as predicted by MOCC is clearly seen in our results. However, discrepancies between our experiment and MOCC results toward higher collision energies are observed. At energies above 1000 eV/u good agreement is found with CTMC results.

This Brief Report presents an improved theoretical description of dissociative recombination of ${\text{HCO}}^{+}$ and ${\text{DCO}}^{+}$ ions with a low-energy electron. In a previous theoretical study [Mikhailov et al., Phys. Rev. A 74, 032707 (2006)] on ${\text{HCO}}^{+}$, the vibrational motion along the CO coordinate was neglected. Here, all vibrational degrees of freedom, including the CO stretch coordinate, are taken into account. The theoretical dissociative recombination cross section obtained is similar to the previous theoretical result at low collision energies $\left(<0.1\text{eV}\right)$ but somewhat larger at higher $\left(>0.1\text{eV}\right)$ energies. Therefore, the present study suggests that motion along the CO coordinate does not play a significant role in the process at low collision energies. The theoretical cross section is still approximately 2–3 times lower than the data from a recent merged-beam experiment.

We report the observation of significant enhancement in the transfer of laser-cooled ${}^{87}\text{R}\text{b}$ atoms between two vertically separated magneto-optical traps (MOTs) when an appropriately tuned and aligned hollow laser beam was used. In the experimental setup, the lower MOT was loaded from a continuous flux of atoms ejected from the upper MOT by a resonant push beam. The observed enhancement appears to be mainly due to a slowing down of atoms by the hollow beam after being ejected from the upper MOT.

We study theoretically the detachment of ${\text{H}}^{-}$ by a linearly polarized few-cycle laser pulse. We show that the angularly resolved distribution of the electrons is very sensitive to the carrier envelope phase (CEP) and the duration of the short laser pulse. This in turn provides an additional means to measure the CEP of a laser pulse at lower laser intensities.

We pose the fundamental question of communication properties of primitives irrespectively of their implementation. To illustrate the idea we introduce the concept of entanglement-swapping boxes, i.e., we consider any quantum operations which perform entanglement swapping, not necessarily via simple quantum teleportation. We ask a question about the properties of such boxes, i.e., what local operations and how much classical communication are needed to perform them. We also ask if any box which performs entanglement swapping can be used to establish classical communication. We show that each box needs at least two bits of classical communication to perform it. It is also shown that each box can be used for classical communication and, most importantly, that there exist boxes which allow one to communicate at most one bit. Surprisingly we find basic irreversibility in the process of entanglement swapping with respect to its classical communication properties.

We present a measurement of the branching ratios from the $6P_{3∕2}$ state of $\mathrm{Ba}\mathrm{II}$ into all dipole-allowed decay channels ($6S_{1∕2}$, $5D_{3∕2}$, and $5D_{5∕2}$). Measurements were performed on single ${}^{138}{\mathrm{Ba}}^{+}$ ions in a linear Paul trap with a frequency-doubled mode-locked Ti:sapphire laser resonant with the $6S_{1∕2}\to 6P_{3∕2}$ transition at $455\mathrm{nm}$ by detection of electron shelving into the dark $5D_{5∕2}$ state. By driving a $\pi$ Rabi rotation with a single femtosecond pulse, an absolute measurement of the branching ratio to $5D_{5∕2}$ state was performed. Combined with a measurement of the relative decay rates into $5D_{3∕2}$ and $5D_{5∕2}$ states performed with long trains of highly attenuated $455\mathrm{nm}$ pulses, it allowed the extraction of the absolute ratios of the other two decays. Relative strengths normalized to unity are found to be $0.756\pm 0.046$, $0.0290\pm 0.0015$, and $0.215\pm 0.0064$ for $6S_{1∕2}$, $5D_{3∕2}$, and $5D_{5∕2}$, respectively. This approximately constitutes a threefold improvement over the best previous measurements and is a sufficient level of precision to compare to calculated values for dipole matrix elements.

We consider macroscopic, mesoscopic, and “$S$-scopic” quantum superpositions of eigenstates of an observable and develop some signatures for their existence. We define the extent, or size $S$ of a superposition, with respect to an observable $\widehat{x}$, as being the range of outcomes of $\widehat{x}$ predicted by that superposition. Such superpositions are referred to as generalized $S$-scopic superpositions to distinguish them from the extreme superpositions that superpose only the two states that have a difference $S$ in their prediction for the observable. We also consider generalized $S$-scopic superpositions of coherent states. We explore the constraints that are placed on the statistics if we suppose a system to be described by mixtures of superpositions that are restricted in size. In this way we arrive at experimental criteria that are sufficient to deduce the existence of a generalized $S$-scopic superposition. The signatures developed are useful where one is able to demonstrate a degree of squeezing. We also discuss how the signatures enable a new type of Einstein-Podolsky-Rosen gedanken experiment.

We consider the set $\mathcal{Q}$ of quantum correlation vectors for two observers, each with two possible binary measurements. Quadric (hyperbolic) inequalities which are satisfied by every $q∊\mathcal{Q}$ are proved, and equality holds on a two-dimensional manifold consisting of the local boxes and all quantum correlation vectors that maximally violate the Clauser-Horne-Shimony-Holt (CHSH) inequality. The quadric inequalities are tightly related to the CHSH inequality; they are their iterated versions. Consequently, it is proved that $\mathcal{Q}$ is contained in a hyperbolic cube whose axes lie along the nonlocal (Popescu-Rohrlich) boxes. As an application, a tight constraint on the rate of local boxes that must be present in every quantum correlation is derived. The inequalities allow one to test the validity of quantum mechanics on the basis of data available from experiments which test the violation of the CHSH inequality. It is noted how these results can be generalized to the case of $n$ sites, each with two possible binary measurements.

We consider the method of entanglement witness operator to verify genuine multipartite entanglement for single-particle $W$ states involving $N$ parties. In particular, linear optical schemes using photodetectors and beam splitters are proposed to implement two different types of witness operator in experiment. The first scheme that requires only a single measurement setting is shown to detect genuine multipartite entanglement for the overall efficiency beyond $1-1/N$. On the other hand, the second scheme with $N+1$ measurement settings achieves success at a significantly lowered efficiency than $1-1/N$.

We investigate the response of two three-body Coulomb systems when driven by attosecond half-cycle pulses: The electron transfer between two hydrogen atomic centers and the double ionization of the helium atom. Using very short half-cycle pulses (HCPs) which effectively deliver “kicks” to the electrons, we first study how a carefully chosen sequence of HCPs can be used to control to which of one of the two fixed atomic centers the electron gets reattached (HCP assisted electron transfer). Moving from one electron in two atomic centers to two electrons in one atomic center we then study the double ionization from the ground state of He by a sequence of attosecond time-scale HCPs, with each electron receiving effectively a “kick” from each HCP. We investigate how the net electric field of the sequence of HCPs affects the total and differential ionization probabilities.

We demonstrate Faraday spectroscopy with a high duty cycle and sampling rate using atoms confined to a blue-detuned optical trap. Our trap consists of a crossed pair of high-charge-number hollow laser beams, which forms a dark, boxlike potential. We have used this to measure transient magnetic fields in a $500\text{−}\mu \text{m}$-diameter spot over a 400 ms time window with nearly unit duty cycle at a 500-Hz sampling rate. We use these measurements to quantify and compensate time-varying magnetic fields to $\approx 10$ nT per time sample.

We investigate the superfluid phase transition in a gas of Fermi atoms loaded on a three-dimensional optical lattice. When the lattice potential is strong, this system can be well described by an attractive Hubbard model. In this model, we calculate the superfluid phase transition temperature $T_{\mathrm{c}}$, including both superfluid and (spin and charge) density fluctuations within the self-consistent $t$-matrix theory and fluctuation exchange approximation, respectively. Since we treat these fluctuations in a consistent manner, our theory satisfies the required particle-hole symmetry over the entire BCS–Bose-Einstein-condensation (BEC) crossover region. We show that charge density fluctuations compete against superfluid fluctuations near the half-filling, leading to the suppression of $T_{\mathrm{c}}$. As a result, the maximum $T_{\mathrm{c}}$ is obtained away from the half-filling. Since the strong density fluctuations originate from the nesting property of the Fermi surface at the half-filling (which is absent in a uniform gas with no lattice potential), our results would be useful in considering lattice effects on strong-coupling superfluidity.

The core structure of multiply quantized vortices is theoretically investigated in a fermionic superfluid near Feshbach resonance. Under population imbalance in two hyperfine spin states, the vortex core is filled in by the “paramagnetic moment.” Here, we find the spatial oscillation of the magnetization inside the core sensitively due to the topological structure of the pairing field, in the range from the weak-coupling regime to the unitary limit. This magnetization inside the giant core reveals the winding number of the vortex and directly results from the low-lying quasiparticle states bound inside the core. It is therefore proposed that the density profile experiment using phase contrast imaging can provide the spectroscopy of novel core level structures in giant vortices. To help understand these outcomes, we also derive an analytic solution for the low-lying quasiparticle states inside the core of a multiply quantized vortex.

We show that the simultaneous application of a copropagating saturating pump and a counterpropagating coherent beam can be used to burn a narrow spectral hole within the absorption line of the optical transition in a Doppler-broadened medium. The large index of refraction of this hole slows down a light pulse by a factor of about ${10}^4$. In addition, we propose a method to create two-color slow light pulses with simultaneous gain by employing a bichromatic field to saturate the medium.

We report on a spectral asymmetry in cw-pumped type-II spontaneous parametric down-conversion. We observe that when the pump beam is focused, the spectra of ordinary and extraordinary down-converted photons broaden unequally. Theoretical analysis indicates that this asymmetry can be attributed to the difference in the angular dispersion (walk-off) of the two kinds of photons, coupled with the well-known correlation between wavelength and emission direction.

We have developed a time-dependent approach using the $\mathit{R}$-matrix basis sets to obtain ejected-electron momentum distributions, and apply it to Ne irradiated by a sequence of two ultrashort light pulses. The approach fully includes the competition between ejection of electrons with different magnetic quantum number $m$. The momentum distributions show interferences due to the time delay between the two ultrashort pulses. Interferences are also observed in the momentum distributions for emission of the inner 2$\mathit{s}$ electron.