Table of contents

With the first issue of 2006 Journal of Physics B: Atomic, Molecular and Optical Physics (J. Phys. B) has successfully incorporated the former journal J. Opt. B. Under the well known and recognized name Journal of Physics B: Atomic, Molecular and Optical Physics the new merged journal will have a much wider scope, serving both the atomic, molecular and optical community and the quantum optics community.

We have already taken a visible measure towards this direction in 2005 with the publication of a special issue on the occasion of Einstein's annus mirabilis 100 years before. This issue, edited by 2005 Nobel laureate Ted Hänsch, Horst Schmidt-Böcking and Herbert Walther, provides a wide and deep survey of leading research in the fields J. Phys. B will promote in the years to come. You will also find the broadening in scope reflected in the scientific interests of the members of the new Editorial Board of J. Phys. B.

J. Phys. B continues its dedication to innovative collision physics. At the same time it is ready to prominently disseminate with its wider scope the new and exciting research developments in connection with ultracold gases and new light sources which will deliver intense pulses of much shorter wave- and pulse length than available in the past, creating new research possibilities for atomic and molecular physics.

As Editor-in-Chief I would also like to take the opportunity to thank the staff at the Institute of Physics, and especially of J. Phys. B, for all the work they have put into the journal over the last year with preparing the incorporation of J. Opt. B into J. Phys. B while continuing their much appreciated high quality service to readers and authors. In this spirit I wish all of you a good and scientifically exciting year 2006.

We study the formation of matter-wave soliton trains in Bose–Einstein condensates confined in a box-like potential. We find that the generation of 'real' solitons understood as multipeak structures undergoing elastic collisions is possible if the condensate is released from the box into the harmonic trap only within well-defined time intervals. When the box-like potential is switched off outside the existing time windows, the number of peaks in a train changes resembling missing solitons observed in recent experiment (Strecker et al 2002 Nature417 150). Our findings indicate that a new way of generating soliton trains in condensates through the temporal, matter-wave Talbot effect is possible.

Partial photoionization cross sections (PCSs), σ_n, leading to final states of singly ionized helium, He⁺(n), were measured in the region of doubly excited helium below the ionization thresholds I₈ and I₉. The experiments were performed at BESSY II at high photon resolution, ΔE ≅ 6 meV, using a time-of-flight electron spectrometer. A comparison with recent eigenchannel R-matrix calculations reveals good agreement. The results of these measurements underline previous studies on quantum chaos in helium, which were mainly based on theoretical results. They also allow a critical assessment of the theoretical methods that produce the data used for a statistical analysis of double-excitation states with respect to quantum chaos, which is expected to occur very close to the double-ionization threshold. PCSs provide additional information to that derivable from total cross sections (TCSs). In the present PCS spectra, the resonance 8, 4₁₀ of the secondary series, which could not be resolved in the TCS, is clearly observed.

Experiments on the sub-femtosecond time scale performed in recent years and their theoretical background are reviewed in this article. We present the essentials of the generation of attosecond pulses, phase-stabilized few-cycle laser pulses, and applications to sub-femtosecond control of electronic motion and time-resolved spectroscopy of atoms and molecules. An outlook on emerging pulse-generation techniques and time-resolved imaging of electronic and molecular structure is included.

Controlled-NOT operation is an important unit of quantum computation. We propose an experimentally feasible scheme of remote controlled-NOT operation using entanglement between two atomic ensembles. The scheme involves laser manipulation of atomic ensembles, adjustable quarter- and half-wave plates, beam splitters, polarizing beam splitters and single-photon detectors, and well fits the status of the current experimental technology.

We present an experimental scheme of preparing the Greenberger–Horne–Zeilinger (GHZ) state and the W state with distant atoms trapped in spatially separate cavities by detecting cavity decay through single-photon detectors, based on the original ideas of photon-interference-induced entanglement between bipartite (Feng X L, Zhang Z M, Li X D, Li S D, Gong S Q and Xu Z Z 2003 Phys. Rev. Lett.90 217902). The scheme can be generalized to prepare the general n-qubit GHZ state and W state.

The energy of classical macroscopic fields in a linear medium is derived from a microscopic quantum electrodynamic model of the system, examining the effects of dispersion and the enhanced energy density. The result differs from the usual electromagnetic energy that is derived from the macroscopic Maxwell equations using Poynting's theorem.

We present a hybrid atom chip which combines a permanent magnetic film with a micromachined current-carrying structure used to realize a Bose–Einstein condensate (BEC). A novel TbGdFeCo material with large perpendicular magnetization has been tailored to allow small scale, stable magnetic potentials for ultracold atoms. We are able to produce ⁸⁷Rb BEC in a magnetic trap based on either the permanent magnetic film or the current-carrying structure. Using the condensate as a magnetic field probe we perform cold atom magnetometry to profile both the field magnitude and gradient as a function of distance from the magnetic film surface. Finally, we discuss future directions for our permanent magnetic film atom chip.

We report the observation of single photon emission from single SiV (silicon-vacancy) centres in diamond produced by ion implantation. The high photostability and the narrow emission bandwidth of about 5 nm at room temperature make SiV centres interesting as a single photon source in practical quantum cryptography. We discuss problems that arise from the nonradiaditve transitions which lower the brightness of the source.

We investigate numerically the response of an atomic Bose–Einstein condensate to a weakly-elliptical rotating trap over a large range of rotation frequencies. We analyse the quadrupolar shape oscillation excited by rotation, and discriminate between its stable and unstable regimes. In the latter case, where a vortex lattice forms, we compare with experimental observations and find good agreement. By examining the role of thermal atoms in the process, we infer that the process is temperature-independent, and show how terminating the rotation gives control over the number of vortices in the lattice. We also study the case of critical rotation at the trap frequency, and observe large centre-of-mass oscillations of the condensate.

Evolution of a Bose–Einstein condensate subject to a time-dependent external perturbation can be described by a time-dependent number-conserving Bogoliubov theory: a condensate initially in its ground state Bogoliubov vacuum evolves into a time-dependent excited state which can be formally written as a time-dependent Bogoliubov vacuum annihilated by time-dependent quasiparticle annihilation operators. We prove that any Bogoliubov vacuum can be brought to a diagonal form in a time-dependent orthonormal basis. This diagonal form is tailored for simulations of quantum measurements on an excited condensate. As an example we work out phase imprinting of a dark soliton followed by a density measurement.

A formalism is introduced to describe a number of physical processes that may break down the coherence of a matter wave over a characteristic length scale l. In a second-quantized description, an appropriate master equation for a set of bosonic 'modes' (such as atoms in a lattice, in a tight-binding approximation) is derived. Two kinds of 'localizing processes' are discussed in some detail and shown to lead to master equations of this general form: spontaneous emission, and modulation by external random potentials. Some of the dynamical consequences of these processes are considered: in particular, it is shown that they generically lead to a damping of the motion of the matter-wave currents, and may also cause a 'flattening' of the density distribution of a trapped condensate at rest.

We present complete collisional-radiative modelling results for the soft x-ray emission lines of Fe¹⁶⁺ in the 15 Å–17 Å range. These lines have been the subject of much controversy in the astrophysical and laboratory plasma community. Radiative transition rates are generated from fully relativistic atomic structure calculations. Electron-impact excitation cross sections are determined using a fully relativistic R-matrix method employing 139 coupled atomic levels through n = 5. We find that, in all cases, using a simple ratio of the collisional rate coefficient times a radiative branching factor is not sufficient to model the widely used diagnostic line ratios. One has to include the effects of collisional-radiative cascades in a population model to achieve accurate line ratios. Our line ratio results agree well with several previous calculations and reasonably well with tokamak experimental measurements, assuming a Maxwellian electron-energy distribution. Our modelling results for four EBIT line ratios, assuming a narrow Gaussian electron-energy distribution, are in generally poor agreement with all four NIST measurements but are in better agreement with the two LLNL measurements. These results suggest the need for an investigation of the theoretical polarization calculations that are required to interpret the EBIT line ratio measurements.

Using several variants of the laser photoelectron attachment method, we have measured the energy-dependent yield for I⁻ formation resulting from dissociative electron attachment (DEA) to CF₃I molecules over the energy range 0.5–500 meV. One approach involved a static target gas (T_G = 300 K) and pulsed electron production/anion extraction. In another approach, a collimated target was provided by a differentially pumped, seeded supersonic beam (10% CF₃I in helium carrier gas, stagnation pressure 1 bar, nozzle temperature 300 K and 600 K). At the onsets for excitation of one and two quanta for the C–I stretching mode ν₃, clear downward cusps are detected. With reference to the recommended thermal DEA rate coefficient k_A(T_e = T_G = 300 K) = 1.9 × 10⁻⁷ cm³ s⁻¹, a new highly resolved absolute cross section for I⁻ formation has been determined. Our experimental results are well reproduced by a cross section calculated in the framework of the resonance R-matrix theory. The input for the theory includes the known energetic and structural parameters of the neutral molecule and its anion and adopts a revised vertical attachment energy and a surface amplitude chosen to reproduce the thermal DEA rate coefficient. The theory is also applied to predict absolute cross sections for vibrational excitation of the C–I stretching mode ν₃. Using our experimental and theoretical DEA cross sections we derive rate coefficients for Rydberg electron transfer (RET) and the dependence of the rate coefficients for free electron attachment of a Maxwellian electron ensemble on the mean electron energy from 0.002 to 2 eV at the constant gas temperature T_G = 300 K; in both cases good agreement is observed with direct RET and swarm measurements.

In this work, we analyse and compare the continuous variable tripartite entanglement available from the use of two concurrent or cascaded χ⁽²⁾ nonlinearities. We examine both idealized travelling-wave models and more experimentally realistic intracavity models, showing that tripartite entangled outputs are readily producible. These may be a useful resource for applications such as quantum cryptography and teleportation.

A fundamental limit to the stability of a single-ion optical frequency standard is set by quantum noise in the measurement of the internal state of the ion. We discuss how the interrogation sequence and the processing of the atomic resonance signal can be optimized in order to obtain the highest possible stability under realistic experimental conditions. A servo algorithm is presented that stabilizes a laser frequency to the single-ion signal and that eliminates errors due to laser frequency drift. Numerical simulations of the servo characteristics are compared to experimental data from a frequency comparison of two single-ion standards based on a transition at 688 THz in ¹⁷¹Yb⁺. Experimentally, an instability σ_y(100 s) = 9 × 10⁻¹⁶ is obtained in the frequency difference between both standards.

A completely general formalism is developed to describe the energy E^disp = ∑_sC_s/R^s of dispersion interaction between two atoms in spherically symmetric states. Explicit expressions are given up to the tenth order of perturbation theory for the dispersion energy E^disp and dispersion coefficients C_s. The method could, in principle, be used to derive the expressions for any s while including all contributing orders of perturbation theory for asymptotic interaction between two atoms. The theory is applied to the calculation of the complete series up to s = 30 for two hydrogen atoms in their ground state. A pseudo-state series expansion of the two-atom Green function gives rapid convergence of the series for radial matrix elements. The numerical values of C_s are computed up to C₃₀ to a relative accuracy of 10⁻⁷ or better. The dispersion coefficients for the hydrogen–antihydrogen interaction are obtained from the H–H coefficients by simply taking the absolute magnitude of C_s.

We test a non-equilibrium approach to study the behaviour of a Bose–Fermi mixture of alkali atoms in the presence of a Feshbach resonance between bosons and fermions. To this end we derive the Hartree–Fock–Bogoliubov (HFB) equations of motion for the interacting system. This approach has proven very successful in the study of resonant systems composed of Bose particles and Fermi particles. However, when applied to a Bose–Fermi mixture, the HFB theory fails to identify even the correct binding energy of molecules in the appropriate limit. Through a more rigorous analysis we are able to ascribe this difference to the peculiar role that noncondensed bosons play in the Bose–Fermi pair correlation, which is the mechanism through which molecules are formed. We therefore conclude that molecular formation in Bose–Fermi mixtures is driven by three-point and higher-order correlations in the gas.