We study information transmission over a fully correlated amplitude damping channel acting on two qubits. We derive the single-shot classical channel capacity and show that entanglement is needed to achieve the channel best performance. We discuss the degradability properties of the channel and evaluate the quantum capacity for any value of the noise parameter. We finally compute the entanglement-assisted classical channel capacity.

Radiative deexcitation (RD) of the metastable $2S$ state of muonic hydrogen and deuterium atoms has been observed. In muonic hydrogen, we improve the precision on lifetime and population (formation probability) values for the short-lived $\mu p\left(2S\right)$ component, and give an upper limit for RD of long-lived $\mu p\left(2S\right)$ atoms. In muonic deuterium at 1 hPa, $3.1\pm 0.3$% of all stopped muons form $\mu d$($2S$) atoms. The short-lived $2S$ component has a population of $1.35{}_{-0.33}^{+0.57}$% and a lifetime of ${\tau }_{2S}^{\mathrm{short}}\left(\mu d\right)=138{}_{-34}^{+32}$ ns. We see evidence for RD of long-lived $\mu d\left(2S\right)$ with a lifetime of ${\tau }_{2S}^{\mathrm{long}}\left(\mu d\right)=1.15{}_{-0.53}^{+0.75}\mu \mathrm{s}$. This is interpreted as formation and decay of excited muonic molecules.

We investigate the differential cross sections for antiproton-impact ionization of H atoms within the framework of time-dependent close-coupling theory. A Fourier transform method is employed in order to extract the fully differential cross sections for a specific value of projectile momentum transfer. The method allows us to incorporate the information about the interaction between the incoming projectile and the target nucleus, the so-called nucleus-nucleus interaction, and to assess its effect on the fully differential cross sections and double differential cross sections in projectile variables.

We present results for total and partial cross sections for positron scattering from H${}_2$. The total scattering and positronium formation cross sections are reported between 0.5 and 200 eV. Total quasielastic and inelastic scattering cross sections are reported for energies between the positronium formation threshold and 50 eV, with quasielastic differential scattering cross sections reported at 1, 3, 5, 7, and 10 eV. Our results are compared with previous work, both experimental and theoretical, with particular attention paid to the region below the positronium formation threshold, where there are apparent discrepancies in previous work. A discussion of possible reasons for discrepancies between this and previous work is presented, including a focus on known systematic effects in the experimental results.

The dynamics of excitons in a one-dimensional ensemble with partial spatial order are studied. During optical excitation, cold Rydberg atoms spontaneously organize into regular spatial arrangements due to their mutual interactions. This emergent lattice is used as the starting point to study resonant energy transfer triggered by driving a $nS$ to $n^{\prime }P$ transition using a microwave field. The dynamics are probed by detecting the survival probability of atoms in the $nS$ Rydberg state. Experimental data qualitatively agree with our theoretical predictions including the mapping onto the $XXZ$ spin model in the strong-driving limit. Our results suggest that emergent Rydberg lattices provide an ideal platform to study coherent energy transfer in structured media without the need for externally imposed potentials.

We establish a theoretical model based on perturbation theory to show that the resonance-enhanced multiphoton-ionization photoelectron spectroscopy (REMPI-PS) in cesium (Cs) atom can be effectively enhanced and narrowed by appropriately shaping the femtosecond laser pulse, and the corresponding physical control processes can be well illustrated by considering the inter- and intragroup interferences involving on- and near-resonant three-photon excitation pathways. Consequently, a high-resolution REMPI-PS and fine energy-level diagram of the excited states can be obtained in spite of the broad femtosecond laser spectrum.

We present a theoretical study of the compressibility $\kappa$ in a Fermi gas with attractive contact interactions, providing predictions for the strongly attractive regime and the superfluid phase. Our work emphasizes the compressibility sum rule and gauge invariance as constraints on $\kappa$, and we show how within a Gor'kov-based $t$-matrix approach, these can be satisfied in the normal phase when no approximations are made. For tractability, approximations must be introduced, and it is believed that thermodynamical approaches to $\kappa$ are more reliable than correlation-function-based schemes. Contrasting with other studies in the literature, we present thermodynamic calculations of $\kappa$. As expected of an approximate approach, ours do not satisfy the compressibility sum rule. However, without adjusting parameters, they yield semiquantitative agreement with experiment and provide physical insight into similar results obtained via quantum Monte Carlo simulations.

The phases of a Bose-Einstein condensate (BEC) with light-induced spin-orbit coupling (SOC) are studied within the mean-field approximation. The mixed BEC phase, in which the system condenses in a superposition of two plane-wave states, is found to be stable for sufficiently small light-atom coupling, becoming unstable in a continuous fashion with increasing light-atom coupling. The structure of the phase diagram at fixed chemical potential for bosons with SOC is shown to imply an unusual density dependence for a trapped mixed BEC phase, the density of one dressed spin state increasing with increasing radius, providing a unique experimental signature of this state. The collective Bogoliubov sound mode is shown to also provide a signature of the mixed BEC state, vanishing as the boundary to the regime of phase separation is approached.

We show that the five possible ordered states in a two-dimensional quantum spin-1/2 system with long-range exchange interactions (Néel, ladder, Peierls, longitudinal-domain, and transversal-domain states) can be realized in a binary Rydberg-dressed BEC system in the supersolid phase. In such a system, blockade phenomenon is shown to also occur for pairs of different excited-state atoms, which results in similar intraspecies and interspecies long-range interactions between ground-state atoms. It suggests that a pseudospin system can be possibly formed in the ground state of ultracold rubidium.

We extend a recent method to shortcut the adiabatic following to internal bosonic Josephson junctions in which the control parameter is the linear coupling between the modes. The approach is based on the mapping between the two-site Bose-Hubbard Hamiltonian and a one-dimensional effective Schrödinger-like equation, valid in the large-$N$ (number of particles) limit. Our method can be readily implemented in current internal bosonic Josephson junctions and it substantially improves the production of spin squeezing with respect to the usually employed linear rampings.

We propose to create an effective magnetic field for photons in photonic crystal resonator lattices using the magneto-optical effect. The inter-resonator coupling is mediated by magneto-optical waveguides or magneto-optical resonators, and thus the coupling between the nearest-neighbor photonic crystal resonators acquire a direction-dependent phase. The effective magnetic field can be realized with a proper choice of the spatial distribution of such a direction-dependent phase.

It is well known that high-order harmonic generation (HHG) from extended targets differs substantially from that of isolated atoms. Phase matching during propagation plays a major role in defining the extent of the spatial regions in the target that contribute constructively to the final yield. Typically, the understanding of this process is simplified by considering phase-matching effects along the field propagation axis, defining a longitudinal coherence length. In this paper we explore the role of phase matching in the transverse direction. The definition of a transversal coherence length appears fundamental to understanding propagation of harmonics generated by focalized laser beams. We present experimental results—-supported by theory—in which transversal phase matching plays the leading role in the macroscopic HHG.

We present large enhancement of the nonlinear wave mixing process (third-harmonic generation) in photonic-band-gap materials made of negative and positive index media, at the band edge of the zero-$\overline{n}$ band gap. Incorporating metamaterial-based, electromagnetically induced transparency (EIT)–like resonance in the nonlinear layer leads to unprecedented line narrowing of the generated third harmonic. This scheme permits the mapping of the narrow EIT resonance at the fundamental frequency to the generated third-harmonic frequency with even narrower line shape.

Using the weak measurement (WM) and quantum measurement reversal (QMR) approach, robust state transfer and entanglement distribution can be realized in the spin-$\frac{1}{2}$ Heisenberg chain. We find that the ultrahigh fidelity and long distance of quantum state transfer with certain success probability can be obtained using proper WM and QMR, i.e., the average fidelity of a general pure state from $80\%$ to almost $100\%$, which is almost size independent. We also find that the distance and quality of entanglement distribution for the Bell state and the general Werner mixed state can be obviously improved by the WM and QMR approach.

The partial adiabatic search algorithm was introduced in Tulsi's paper [Phys. Rev. A 80, 052328 (2009)] as a modification of the usual adiabatic algorithm for a quantum search with the idea that most of the interesting computation only happens over a very short range of the adiabatic path. By focusing on that restricted range, one can potentially gain an advantage by reducing the control requirements on the system, enabling a uniform rate of evolution. In this Comment, we point out an oversight in Tulsi's paper [Phys. Rev. A 80, 052328 (2009)] that invalidates its proof. However, the argument can be corrected, and the calculations in Tulsi's paper [Phys. Rev. A 80, 052328 (2009)] are then sufficient to show that the scheme still works. Nevertheless, subsequent works [Phys. Rev. A 82, 034304 (2010), Chin. Phys. B 20, 040309 (2011), Chin. Phys. B 21, 010306 (2012), AASRI Procedia 1, 5862 (2012), and Quantum Inf. Process. 12, 2689 (2013)] cannot all be recovered in the same way.

We report the observation of forward-propagating UV stimulated emission in atmospheric nitrogen pumped, at a standoff distance of 2.6 m, by an energetic laser pulse at a wavelength of 1053 nm and with the duration in the picosecond range. The generated optical gain at 337 nm is seeded by third harmonic of the pump beam. This demonstration is an important step towards the development of techniques for standoff optical sensing in the atmosphere.

We present a method to detect properties of quantum channels, assuming that some a priori information about the form of the channel is available. The method is based on a correspondence with entanglement detection methods for multipartite density matrices based on witness operators. We first illustrate the method in the case of entanglement-breaking channels and nonseparable random unitary channels and show how it can be implemented experimentally by means of local measurements. We then study the detection of nonseparable maps and show that for pairs of systems of dimension higher than two the detection operators are not the same as in the random unitary case, highlighting a richer separability structure of quantum channels with respect to quantum states. Finally we consider the set of PPT maps, developing a technique to reveal NPT maps.

We schedule the Steane [[7,1,3]] error correction on a model ion-trap architecture with ballistic transport. We compare the level-1 error rates for syndrome extraction using the Shor method of ancilla prepared in verified cat states to the DiVincenzo-Aliferis method without verification. The study examines how the quantum error correction circuit latency and error vary with the number of available ancilla and the choice of protocol for ancilla preparation and measurement. We find that, with few exceptions, the DiVincenzo-Aliferis method without cat-state verification outperforms the standard Shor method. We also find that an additional ancilla always reduces the latency but does not significantly change the error due to the high memory fidelity.