The positron-helium bound state

A variational calculation with a trial wave function including up to 17 parameters has been used to investigate the existence of a positron-helium bound state. The resulting binding energy was found to be greater than the helium binding energy, and thus it is believed that the positron does not get bound to a helium atom. The calculations provide also values of ground state helium energy and the corresponding wave functions.     

Two-phonon bound states in imperfect crystals

The question of the occurrence of two-phonon bound states in imperfect crystals is investigated. It is shown that the anharmonicity mediated two-phonon bound state which is present in perfect crystals gets modified due to the presence of impurities. Moreover, the possibility of the occurrence of a purely impurity mediated two-phonon bound state is demonstrated. The bound state frequencies are calculated using the simple Einstein oscillator model for the host phonons. The two-phonon density of states for the imperfect crystal thus obtained has peaks at the combination and difference frequencies of two host phonons besides the peaks at the bound state frequencies. For a perfect crystal the theory predicts a single peak at the two-phonon bound state frequency in conformity with experimental observations and other theoretical calculations. Experimental data on the two-phonon infrared absorption and Raman scattering from mixed crystals of GA_1−c Al _c P and Ge_1−c Si _c are analysed to provide evidence in support of impurity-mediated two-phonon bound states. The relevance of the zero frequency (difference spectrum) peak to the central peak observed in structural phase transitions, is conjectured; This work is a part of the thesis to be submitted by one of the authors (SS) in partial fulfilment of the degree of Doctor of Philosophy to Utkal University, Bhubaneswar, India.     

The three-boson bound state in massive QED2

We derive the (matrix-valued) Feynman rules of mass perturbation theory of the massive Schwinger model for non-zero vacuum angleϑ. Further, we discuss the properties of the three-boson bound state and compute — by a partial resummation of the mass perturbation series — its mass and its partial decay widths. This work was supported by a research stipendium of the Vienna University.     

Acoustically bound microfluidic bubble crystals

Bubbles confined in microchannels self-organize without directly contacting one another when excited by an external acoustic field. The bubbles tend to form periodic "crystal"-like lattices with a finite interbubble distance. This equilibrium distance can be adjusted by simply tuning the acoustic frequency. This new type of crystal is purely mediated by acoustic surface waves emitted by the pulsating bubbles. Because these waves are reflected at the channel boundaries, the bubbles interact with their own images across the boundary.     

Normal state of highly polarized Fermi gases: The bound state

We consider a highly polarized Fermi gas with a single ↓ atom within a Fermi sea of ↑ atoms. We extend a preceding many-body analysis to the case where a bound state is formed between the ↓ atom and an ↑ atom.     

The optical properties of virtual bound state alloys

Optical data on dilute CuNi, AuNi and AgPd alloys are examined in terms of the Anderson model. The results for AuNi and AgPd appear to be consistent with the model while those for CuNi are not. A consistent interpretation of the data is obtained when the effects of the s-d hybridization of the copper conduction states on the Anderson mixing matrix element, V_kd, are considered. The results suggest a rapid increase in V_kd as the energy ?_k approaches the copper d bands.     

Floquet-bloch waves in bound one-dimensional photonic crystals

Floquet-Bloch waves in a bound one-dimensional photonic crystal are considered. It is shown that a single Floquet-Bloch wave can be excited in a one-dimensional photonic crystal located between two homogeneous media. An exact solution of the wave equation corresponding to this case is represented in the form of a set of heterogeneous waves. For the case of incidence of the plane wave from a homogeneous medium on a bounded one-dimensional photonic crystal, the functions for the reflection and transmission coefficients are obtained based on the exact solution of the wave equation. It is shown that the transmission function for the one-dimensional photonic crystal has a form similar to that for the traditional Fabri-Perot interferometer and is determined by the interference of the Floquet-Bloch waves excited in the crystal. The evolution of the amplitude profile of the decaying Floquet-Bloch waves and the reflection spectrum of the bounded one-dimensional photonic crystal are considered in the first-order forbidden band.     

The boson-boson bound state in the massive Schwinger model

We use (fermion) mass perturbation theory for the massive Schwinger model to compute the boson-boson bound state mass in lowest order. For small fermion mass the lowest possible Fock state turns out to give the main contribution and leads to a second order result for the bound state mass.     

Non-adiabatic electron-phonon coupling in the two-sites two-electrons system

The electronic and ibrational properies of a system of two electrons or excitons at two sites are investgated in a simple model combining the ideas of the Hubbard and Holstein Hamiltonans. We analyse the competition of the interactions which enter this model as parameers for the transfer energyT, the (on-site) Coulomb energyU, the short-range electron-phonon coupling, represented by the stabilization energyS and the vibrational energy (). For the whole range of these parameters the spectrum of the 50 lowest eigenstates has been numerically determined. As in the adiabatic approximation (=0) the ground state suffers a structural change due to a charge transfer instability, ifS is sufficiently large. In the case of finite this transition to a distorted state is no longer sharply defined by a criticalS. With regard to the lowest excited states the electronic system can be described by the adiabatic ground state for smallS as well as for largeS. Correspondingly the eigenfunctions of undisplaced or displaced harmonic oscillators, respectively, yield the lattice dynamics. In the range of intermediateS the situation is more complicated. Here the relation between the eigenfunctions and the adiabatic potentials as well as the appearance of metastable states and their connection to the charge transfer is discussed at some length.     

Relativistic two-body bound state in motion

For an approximately relativistic Hamiltonian properties of a two-body bound state are investigated as a function of the total momentum. These are the relativistic energy-momentum relation for the bound-state energy eigenvalue, integral and local deformation properties of the bound-state wave function, and the weakly singular short-range behaviour.     

Second bound state of PsH

The existence of a second bound state of PsH that is electronically stable and also stable against positron annihilation by the normal 2gamma and 3gamma processes is demonstrated by explicit calculation. The state can be found in the ;{2,4}S;{o} symmetries with the two electrons in a spin-triplet state. The binding energy against dissociation into the H(2p)+Ps(2p) channel was 7.03 x 10;(-4) hartree. The dominant decay mode of the states will be radiative decay into a configuration that autoionizes or undergoes positron annihilation. The NaPs system of the same symmetry is also electronically stable with a binding energy of 1.514 x 10;(-3) hartree with respect to the Na(3p)+Ps(2p) channel.     

Electron-positron scaling in bound state models

We investigate scaling assuming a generalized vector meson dominance picture. The vector mesons are described as relativistic quark-antiquark bound states by a Bethe-Salpeter equation which yields the mass spectrum and the coupling to e⁺e^? pairs. We discuss the spin structure and find that scaling can occur only for a γ_μ type amplitude. We solve the BS equation using a generalized WKB approximation and find scaling, independent of the detailed shape of the interaction. This means that scaling in e⁺e^? annihilation does not select a particular “confinement potential”. The scaling constant depends on the current renormalization constant and on the details of the relativistic spin structure.     

Luminescence of bound excitons in NaI and RbI crystals

X-ray induced luminescence spectra were for the first time investigated at 4.2–100 K in the vicinity of fundamental absorption of NaI crystals cleaved in liquid helium. Besides the luminescence of the free exciton and its LO replicas an additional band due to radiative annihilation of bound excitons appears in NaI crystals, as was earlier observed in RbI crystals. The obtained value of the binding energy of excitons is 50 and 60 meV for NaI and RbI, respectively. The nature of the shallow trap in the crystals of wide-gap insulators is discussed.     

Superconducting virtual bound state alloys

Static and dynamic properties of superconducting alloys containing resonant impurity scattering centers are considered. The formation of bound states within the energy gap is described and connected with locald-level correlations induced by superconductivity. The effect of the bound states on the exactly solubled-spin dynamics is investigated by evaluating the impurity atom's magnetic excitation spectrum. Finite impurity concentrations are treated within a self-consistent approximation scheme. For increasing impurity content the bound states merge to impurity bands which tend to suppress superconductivity. The relevance of the simple extra orbital model is discussed in connection with the interpretation of pressure-induced variations on the properties of superconductors alloyed with ambivalent rare earth ions.     

The invisible Majorana bound state at the helical edge

The presence of a Majorana bound state in condensed matter systems is often associated to a zero bias peak in conductance measurements. Here, we analyze a system were this paradigm is violated. A Majorana bound state is always present at the interface between a quantum spin Hall system that is magnetically gapped and a quantum spin Hall system gapped by proximity induced s-wave superconductivity. However, the linear conductance could be either zero or non-zero and quantized depending on the energy and length scales of the barriers. The transition between the two values is reminiscent of the topological phase transition in proximitized spin–orbit coupled quantum wires in the presence of an applied magnetic field. We interpret the behavior of the conductance in terms of scattering states at both zero and non-zero energy.     

Off-shell effects in the three-nucleon bound state

Phase-shift-equivalent separable potentials are used to study the sensitivity of the triton binding energy E_T to the off-shell behavior of the two-nucleon T matrix. It is found that the deuteron wave function significantly constrains the theoretical uncertainty in E_T and that the properties of the off-shell T matrix at intermediate energies are only weakly reflected in E_T.     

Experimental bound entanglement in a four-photon state

Bound entanglement is central to many exciting theoretical results in quantum information processing, but has thus far not been experimentally realized. In this work, we consider a one-parameter family of four-qubit Smolin states. We experimentally produce these states in the polarization of four optical photons produced from parametric down-conversion. Within a range of the parameter, we show that our states are entangled and undistillable, and thus bound entangled. Using these bound-entangled states we demonstrate entanglement unlocking.     

The representation of bound state wavefunctions by spherical Hankel functions

The representation of a nucleon bound state by a single Hankel function is generalised such that the bound state is expanded as a linear combination of Hankel functions of the samel-value. The singularity at the origin due to the use of Hankel functions is removed. The arguments and coefficients of the expansion are determined by a variational method.