Collective Tunnelling of Strongly Interacting Cold Atoms in a Double-Well Potential

It is known that under resonance conditions, a group of strongly interacting bosonic atoms, trapped in a double-well potential, mimics a single particle, performing Rabi oscillations between the wells. By implication, all atoms need to tunnel at roughly the same time, even though the Bose–Hubbard Hamiltonian accounts only for one-atom-at-a-time transfers. The mechanism of this collective behavior is analyzed, the Rabi frequencies in the process are evaluated, and the limitation of this simple picture is discussed. In particular, it is shown that the small rapid oscillations superimposed on the slow Rabi cycle result from splitting the transferred cluster at the sudden onset of tunnelling, and disappear if tunnelling is turned on gradually.     

Infra-red free-carrier absorption due to impurity scattering in semiconducting quantum well structures

The theory of free-carrier absorption (FCA) is developed, in the extreme quantum limit when the carriers are assumed to populate only the lowest quantized energy level, for quasi-two and one-dimensional semiconducting quantum well structures where the carriers are scattered by ionized impurities. The radiation field is assumed to be polarized in the plane of the layer in the quasi-two-dimensional case and along the length of the wire in the quasi-one-dimensional case. Expressions for FCA are obtained for the cases where the impurities are either in the well (background impurities) or outside the well (remote impurities). Variation of FCA is numerically studied with photon frequency and well width.     

Stationary entanglement between macroscopic mechanical oscillators

We show that the optomechanical coupling between an optical cavity mode and two movable cavity mirrors is able to entangle two different macroscopic oscillation modes of the mirrors. This continuous variable entanglement is maintained by the light bouncing between the mirrors and is robust against thermal noise. In fact, it could be experimentally demonstrated using present technology. Received 2 September 2002 / Received in final form 10 October 2002 Published online 7 January 2003     

Luminescence and lifetime characteristics of microphases in KCl:KI:Pb mixed crystals

Absorption and luminiscence measurements were performed on lead-doped KCl:KI mixed single crystals. Strong differences were found between as-grown and quenched samples. New bands were observed in the absorption spectra of unquenched samples in the spectral region between the limit positions of the A bands, corresponding to chloride or iodide lattices. The strong band at 449 nm dominates the luminescence of these samples at low temperatures. Its kinetics have a complicated form and the decay time is in the interval from ns to ms. Quenched samples have a well-known luminescence spectrum caused by octahedral lead impurity centres in KCl single crystals. The kinetics, however, also indicate mixed chlorine and iodine coordination of lead in the investigated crystals.     

Single-electron charging spectra: from natural to artificial atoms

We present a theoretical study of the charging spectra in natural and artificial atoms. We apply a model electrostatic potential created by a homogenously charged sphere. This model potential allows for a continuous passage from the Coulomb potential of the nucleus to parabolic confinement potential of quantum dots. We consider electron systems with N=1,…,10 electrons with the use of the Hartree–Fock method. We discuss the qualitative similarities and differences between the chemical potential spectrum of electron systems bound to nucleus and confined in quantum dots.     

Influence of isovalent substitutions on absorption spectra of orthoferrities

The role of impurity ions in formation of the optical properties of rare-earth orthoferrites is investigated. Optical spectra of the substituted against unsubstituted orthoferrites are presented. The influence of different isovalent substitutions on the optical absorption of orthoferrites that are promising for magnetooptics is studied. Institute of Solid-State and Semiconductor Physics of the Academy of Sciences of Belarus, 17, P. Brovka St., Minsk, 220072, Belarus. Translated from zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 642–645, September–October, 1997.     

About Rotational Transitions and Muon Transfer in Muonic Hydrogen–Helium Systems

Hyperfine Interactions - Rotational J=1→J=0 transitions in muonic molecule, (3Heμd) J ++, in [(3Heμd)++,2e]–D and [(3Heμd)++,e]+–D collisions are considered. The...     

Renormalization of the two-photon vacuum polarization and the self energy vacuum polarization for a tightly bound electron

The renormalization method of Bogoljubov-Parasiuk-Hepp-Zimmermann (BPHZ) is used in order to derive the renormalized energy shift due to the gauge invariant K?llén-Sabry diagram of the two-photon vacuum polarization (VPVP) as well as the self energy vacuum polarization S(VP)E beyond the Uehling approximation. It is outlined, that no outer renormalization is required for the two-photon vacuum polarization and that only the inner renormalization has to be accomplished. It is shown that the so-called nongauge invariant spurious term is absent for a wide class of vacuum polarization (VP) diagrams if one applies the widely used spherical expansion of bound and free-electron propagator. This simplifies significantly calculations in bound state quantum electrodynamics. As one result of our paper the use of the BPHZ-approach in bound state QED is established. Received 28 September 2001