We propose a quantum interface which applies multiple passes of a pulse of light through an atomic sample with phase/polarization rotations in between the passes. Our proposal does not require nonclassical light input or measurements on the system, and it predicts rapidly growing entanglement of light and atoms from just coherent inputs. The proposed interface makes it possible to achieve a number of tasks within quantum-information processing, including teleportation between light and atoms, quantum memory for light, and squeezing of atomic and light variables.

The paper gives a thorough analysis of the spin-flipping action induced by the Faraday mirror on any qubit realized by a polarization-encoded single photon. The results of the theory show that the device acts as a nonuniversal NOT gate, in full agreement with quantum mechanical expectations. Furthermore, the universal optical compensation method devised by Martinelli, of common use in long distance quantum-cryptography, has been analyzed. All theoretical results are substantiated experimentally by the modern methods of quantum state tomography and entanglement-assisted quantum process tomography.

We present a method for creating fields that couple to neutral atoms in the same way that electromagnetic fields couple to charged particles. We show that this technique opens the door for a range of neutral atom experiments, including probing the interplay between periodic potentials and quantum Hall effects. Furthermore, we propose, and analyze, seemingly paradoxical geometries which can be engineered through these techniques. For example, we show how to create a ring of sites where an atom continuously reduces its potential energy by moving in a clockwise direction.

We have experimentally observed a “backward” (clockwise rotating) hysteresis cycle in the system of an optical ring cavity containing three-level ($\Lambda$-type configuration) rubidium atoms. The shape and direction of the observed hysteresis cycles can be easily controlled with experimental parameters. Such an interesting phenomenon is caused by the greatly modified absorption, dispersion, and nonlinear optical properties of the three-level atomic medium, due to the induced atomic coherence.

To find whether a set of reduced density matrices comes from a common multiparty state is a hard and important problem. In this paper, we do the following. (i) We introduce a method to find out some polytopes in one-party eigenvalue space which are sufficient conditions of this problem. (ii) We point out that there are some relations between the compatible conditions and the entanglement of pure states. And we show this idea more clearly in the three-qubit case. (iii) We investigate the relations between the compatibility problem and the invariants of a matrix set under some groups. Furthermore, we show that it is one of the reasons why the compatibility problems which involve the multiparty density matrices are much more difficult than the one-party case.

Analytic expressions for the direct, resonant, and interference contributions to the differential cross section of a resonant Auger process, produced by the inner-shell photoionization of a linear molecule either “fixed in space” or belonging to a gas of randomly oriented molecules, have been derived following Dill’s procedures [Dill et al., Phys. Rev. Lett. 45, 1393 (1980)], but going beyond the two-step approximation. Angle-resolved Auger spectra of the ${\mathrm{C}}_2{\mathrm{H}}_2$ molecule measured on top of the $\mathrm{C}1s\to {\pi }^{*}$ resonance [Kivimäki et al., J. Phys. B 30, 4279 (1997)] have been calculated together with asymmetry parameters, analyzing also the different contributions to the electron angular distributions.

Atom-atom scattering of bosonic one-dimensional (1D) atoms has been modeled successfully using a zero-range $\delta$-function potential, while that of bosonic 3D atoms has been modeled successfully using Fermi-Huang’s regularized $s$-wave pseudopotential. Here, we derive the eigenenergies of two spin-polarized 1D fermions under external harmonic confinement interacting through a zero-range potential, which only acts on odd-parity wave functions, analytically. We also present a divergent-free zero-range potential treatment of two spin-polarized 3D fermions under harmonic confinement. Our pseudopotential treatments are verified through numerical calculations for short-range model potentials.

We report the implementation of a two-dimensional Raman cooling scheme using sequential excitations along the orthogonal axes. Using square pulses, we have cooled a cloud of ultracold cesium atoms down to an rms velocity spread of 0.39(5) recoil velocities, corresponding to an effective transverse temperature of $30\mathrm{nK}$ $\left(0.15T_{\mathrm{rec}}\right)$. This technique can be useful to improve cold-atom atomic clocks and is particularly relevant for clocks in microgravity.

An effective-medium approach is used to derive a set of coupled-mode equations describing quadratic parametric interactions in a one-dimensional inhomogeneous medium of finite length. The solutions for both copropagating and counterpropagating interactions are used to study the quantum-mechanical process of spontaneous parametric down-conversion (SPDC). An example is studied in which the inhomogeneous medium is a photonic crystal. The effect that device geometry has on both the efficiency and bandwidth of SPDC is explored. With appropriate design, we find that it is possible not only to enhance the efficiency of SPDC, but also to generate broadband copropagating and narrowband counterpropagating down-converted light. A setup is proposed with the potential to act as a source of entangled photon pairs.

We show that bosonic fields may present anyonic behavior when interacting with a fermion in a Jaynes-Cummings-like model. The proposal is accomplished via the interaction of a two-level system with two quantized modes of a harmonic oscillator; under suitable conditions, the system acquires a fractional geometric phase. A crucial role is played by the entanglement of the system eigenstates, which provides a two-dimensional confinement in the effective evolution of the system, leading to the anyonic behavior. For a particular choice of parameters, we show that it is possible to transmute the statistics of the system continually from fermions to bosons. We also present an experimental proposal, in an ion-trap setup, in which fractional statistical features can be generated, controlled, and measured.

In quantum mechanics and quantum information, to establish the orthogonal bases is a useful means. The existence of unextendible product bases impels us to study the ‘entanglement bases’ problems. In this paper, the concepts of entanglement bases and exact-entanglement bases are defined, and a theorem about exact-entanglement bases is given. We discuss the general structures of the orthogonal complete bases. Two examples of applications are given. At last, we discuss the problem of transformation of the general structure forms.

We propose a method for realizing two-qubit quantum phase gate with 4-level systems in cavity QED. In this proposal, the two logical states of a qubit are represented by the two lowest levels of each system, and two intermediate levels of each system are utilized to facilitate coherent control and manipulation of quantum states of the qubits. The present method does not involve cavity-photon population during the operation. In addition, we show that the gate can be achieved using only two-step operations.

Recent experiments have demonstrated superradiant Raman scattering from a Bose-Einstein condensate driven by a single off-resonant laser beam. We present a quantum theory describing this phenomenon, showing Raman amplification of matter wave due to collective atomic recoil from 3-level atoms in a $\Lambda$-configuration. When atoms are initially in a single lower internal state, a closed two-level system is realized between atoms with different internal states, and entangled atom-photon pairs can be generated. When atoms are initially prepared in both the lower internal states, a fraction of atoms recoiling in the backward direction can be generated.

Polar photodissociation of ${\mathrm{CF}}_n{\mathrm{Cl}}_{4-n}(n=0–2)$ has been studied using synchrotron radiation within the energy range 195–217 eV. The first observations of negative photoion fragments from these molecules after core excitation are reported. In addition to observing a number of previously known resonances two additional resonant states, just above the $\mathrm{Cl}2p$ ionization limit, are observed and play an important role in the polar photodissociation process. The difficulties in identifying these above threshold spin-split features using negative photoion spectroscopy are discussed.

Using experiment and modeling, we show that the data set generated when a learning algorithm is used to optimize a quantum system can help to uncover the physics behind the process being optimized. In particular, by optimizing the process of high-harmonic generation using shaped light pulses, we generate a large data set and analyze its statistical behavior. This behavior is then compared with theoretical predictions, verifying our understanding of the attosecond dynamics of high-harmonic generation and uncovering an anomalous region of parameter space.

We address the dynamics induced by collective atomic recoil in a Bose-Einstein condensate in the presence of radiation losses and atomic decoherence. In particular, we focus on the linear regime of the lasing mechanism, and analyze the effects of losses and decoherence on the generation of entanglement. The dynamics is that of three bosons, two atomic modes interacting with a single-mode radiation field, coupled with a bath of oscillators. The resulting three-mode dissipative Master equation is solved analytically in terms of the Wigner function. We examine in details the two complementary limits of high-$Q$ cavity and bad cavity, the latter corresponding to the so-called superradiant regime, both in the quasiclassical and quantum regimes. We found that three-mode entanglement as well as two-mode atom-atom and atom-radiation entanglement is generally robust against losses and decoherence, thus making the present system a good candidate for the experimental observation of entanglement in condensate systems. In particular, steady-state entanglement may be obtained both between atoms with opposite momenta and between atoms and photons.

Clusters of metal atoms at a fixed size can assume different structural arrangements, known as isomers, which may have nearly the same energy. Therefore, at given experimental conditions distribution of these isomers can be present. While the size selection is a relatively common technique, the isomer selection is not; it is therefore more difficult to obtain information about a single isomer. We report here on isomer-specific spectroscopy of ${\mathrm{Ag}}_9$ clusters together with ab initio calculations allowing to identify the isomer responsible for the measured excitation pattern and fluorescence.

By definition, the Kraus representation of a harmonic oscillator suffering from the environment effect, modeled as the amplitude damping or the phase damping, is directly given by a simple operator algebra solution. As examples and applications, we first give a Kraus representation of a single qubit whose computational basis states are defined as bosonic vacuum and single particle number states. We further discuss the environment effect on qubits whose computational basis states are defined as the bosonic odd and even coherent states. The environment effects on entangled qubits defined by two different kinds of computational basis are compared with the use of fidelity.

We have improved our previous mixed configuration-interaction and perturbation-theory $(\mathrm{CI}+\mathrm{MBPT})$ methods by including all second-order Coulomb and lowest-order Breit terms. The method is applied in calculations of $E1$ matrix elements for the two $2s^2\to 2s2p$ transitions of light Be-like ions. The results are in good agreement with experiments and other precise calculations. The length and velocity transition amplitudes are also more consistent.