共查询到20条相似文献,搜索用时 15 毫秒
1.
M. Combescot O. Betbeder-Matibet 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(1):63-76
The purpose of this paper is to show how the diagrammatic expansion
in fermion exchanges of scalar products of N-composite-boson
(“coboson”) states can be obtained in a practical way. The hard
algebra on which this expansion is based, will be given in an independent publication.
Due to the composite nature of the particles, the scalar products
of N-coboson states do not reduce to a set of Kronecker symbols, as
for elementary bosons, but contain subtle exchange terms between two or
more cobosons. These terms originate from Pauli exclusion between the
fermionic components of the particles. While our many-body
theory for composite bosons leads to write these scalar products as
complicated sums of products of “Pauli scatterings” between
two cobosons, they in fact correspond to fermion exchanges
between any number P of quantum particles, with
2 ≤P≤N. These P-body exchanges are nicely represented by the
so-called “Shiva diagrams”, which are topologically different from
Feynman diagrams, due to the intrinsic many-body nature of the Pauli
exclusion from which they originate. These Shiva diagrams in fact
constitute the novel part of our composite-exciton many-body theory
which was up to now missing to get its full
diagrammatic representation. Using them, we can now “see” through
diagrams the physics of any quantity in which enters N interacting
excitons — or more generally N composite bosons —, with fermion
exchanges included in an
exact — and transparent — way. 相似文献
2.
M. Combescot O. Betbeder-Matibet F. Dubin 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(2):181-189
We have recently constructed a many-body theory for composite excitons, in
which the possible carrier exchanges between N excitons can be treated
exactly through a set of dimensionless “Pauli scatterings” between two
excitons. Many-body effects with free excitons turn out to be rather
simple because these excitons are the exact one-pair
eigenstates of the semiconductor Hamiltonian, in the absence of localized
traps. They consequently form a complete orthogonal basis for one-pair
states. As essentially all quantum particles known as bosons are
composite bosons, it is highly desirable to
extend this free exciton many-body theory to other kinds of
“cobosons” — a contraction for composite bosons — the physically
relevant ones being possibly not the exact one-pair eigenstates of
the system Hamiltonian. The purpose of this paper is
to derive the “Pauli scatterings” and the “interaction scatterings” of
these cobosons in terms of their wave functions and the interactions
which exist between the fermions from which they are
constructed. It is also explained how to calculate many-body effects in
such a very general composite boson system. 相似文献
3.
W. Pogosov M. Combescot 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(2):183-192
By using the composite many-body theory for Frenkel excitons we have recently developed, we here derive the ground state energy
of N Frenkel excitons in the Born approximation through the Hamiltonian mean value in a state made of N identical Q = 0 excitons. While this quantity reads as a density expansion in the case of Wannier excitons, due to many-body effects induced
by fermion exchanges between N composite particles, we show that the Hamiltonian mean value for N Frenkel excitons only contains
a first order term in density, just as for elementary bosons. Such a simple result comes from a subtle balance, difficult
to guess a priori, between fermion exchanges for two or more Frenkel excitons appearing in Coulomb term and the ones appearing
in the N exciton normalization factor – the cancellation being exact within terms in 1/Ns where Ns is the number of atomic sites in the sample. This result could make us naively believe that, due to the tight binding approximation
on which Frenkel excitons are based, these excitons are just bare elementary bosons while their composite nature definitely
appears at various stages in the precise calculation of the Hamiltonian mean value. 相似文献
4.
M. Combescot O. Betbeder-Matibet 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(1):33-46
This paper contains a detailed calculation of the photoinduced current density at third order in the coupling between a semiconductor
and a multifrequency photon field, starting from its standard textbook expression which reads in terms of a triple commutator.
Due to a major intrinsic problem linked to this triple commutator, such a derivation has been made possible quite recently
only, thanks to the tools developed in the composite-boson many-body theory we have recently constructed. The photoinduced
current density is shown to ultimately read in a compact form, in terms of the “Pauli scatterings” and “Coulomb scatterings”
for exciton-exciton interactions introduced in this theory. Representation of this third order response in Shiva diagrams,
which visualize interactions between excitons, is also given to better grasp the physics of the various contributions. 相似文献
5.
T. Enss W. Zwerger 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(3):383-389
We study the transition to fermion pair superfluidity in a mixture of interacting bosonic and fermionic atoms. The fermion
interaction induced by the bosons and the dynamical screening of the condensate phonons due to fermions are included using
the nonperturbative Hamiltonian flow equations. We determine the bosonic spectrum near the transition towards phase separation
and find that the superfluid transition temperature may be increased substantially due to phonon damping. 相似文献
6.
The aim of this paper is to clarify the conceptual difference which
exists between the interactions of composite bosons and the interactions
of elementary bosons. A special focus is made on the physical processes
which are missed when composite bosons are replaced by elementary bosons.
Although what is here said directly applies to excitons, it is also valid
for composite bosons in other fields than semiconductor physics. We, in
particular, explain how the two elementary scatterings – Coulomb and
Pauli – of our many-body theory for composite excitons, can be extended
to a pair of fermions which is not an Hamiltonian eigenstate – as for
example a pair of trapped electrons, of current interest in quantum
information. 相似文献
7.
G. P. Miroshnichenko 《Journal of Experimental and Theoretical Physics》2009,109(2):193-206
A theory of the discrete photodetection of quantum jumps on the V configuration of atomic levels has been developed. A three-level
source atom is placed in a cavity excited by a resonance fluorescence field. The cavity is tuned to exact resonance with an
atomic transition. The cavity mode state is tested by a flux of unexcited (at the entrance) probe atoms passing through the
cavity. The energy states of the outgoing probe atoms are detected by ionization chambers, which are assumed ideal. This a
posteriori statistical information is indirectly related to the numerical characteristics of a measured quantum system consisting
of the source atom and cavity mode. The “tuning” conditions for a discrete photodetector, i.e., the rules for choosing the
parameters and durations of the interactions of the cavity mode with the probe and source atoms, intensities of the pump and
probe fields that are necessary for observing quantum jumps from the “bright” state to the “dark” one and vice versa, have
been determined. A two-state model that describes the dynamics of a quantum jump has been analyzed. The formulas have been
obtained for the observable characteristics of quantum jumps: the mean residence time of the quantum system in quasistationary
states (durations of the bright and dark periods), probabilities of quantum jumps, mean excitation levels of the quantized
cavity mode, etc. 相似文献
8.
B. C. Curley G. Rossi R. Ferrando R. L. Johnston 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):53-56
Ag–Au bimetallic “nanoalloy” clusters with 38 atoms have been
studied using a Gupta many-body potential combined with a genetic
algorithm search technique. Clear changes in structure are observed as
a function of Ag/Au composition and there is a clear tendency for
surface segregation of the Ag atoms. Cluster stability is found to
increase with increasing number of Au-Au and Ag-Au bonds and the
segregation has been rationalised in terms of bonds strengths and
elemental surface energies. 相似文献
9.
We discuss the one-dimensional Hubbard model, on finite sites spin chain, in context of the action of the direct product of two unitary groups SU(2)×SU(2). The symmetry revealed by this group is applicable in the procedure of exact diagonalization of the Hubbard Hamiltonian. This result combined with the translational symmetry, given as the basis of wavelets of the appropriate Fourier transforms, provides, besides the energy, additional conserved quantities, which are presented in the case of a half-filled, four sites spin chain. Since we are dealing with four elementary excitations, two quasiparticles called “spinons”, which carry spin, and two other called “holon” and “antyholon”, which carry charge, the usual spin-SU(2) algebra for spinons and the so called pseudospin-SU(2) algebra for holons and antiholons, provide four additional quantum numbers. 相似文献
10.
Different laser devices working as “atom diodes” for ultra-cold atoms
have been proposed recently. They transmit ground state level atoms coming
from
one side, say from the left, but reflect them when they come from the other
side.
We present and compare some of these models.
In all of them spontaneous decay is included
as an irreversible element which avoids backwards motion after the atom has
crossed the diode.
We also review the proposal of a cooling method based on an
“atom diode”. 相似文献
11.
C. Di Paola E. Bodo F. A. Gianturco 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(3):377-385
Calculations of the quantum structures describing the initial
solvation shells of bosonic helium atoms around a polar, ionic
system like LiH+ are reported, together with the corresponding
quantum energies. The calculations were carried out using the
Diffusion Monte Carlo (DMC) approach and parametric trial functions.
Its final radial and angular distributions for clusters of varying
size are analysed and discussed. The solvation of this ionic dopant
is shown to occur in a way which is strongly affected by the
orientational induction forces between the latter molecule and the
solvent atoms, indicating the onset of “snowball" structures
at the location of the dopant and the clear distinction
between “heliophilic" and “heliophobic" regions of microsolvation. 相似文献
12.
Igor Tikhonenkov 《Optics Communications》2006,264(2):321-325
We study the collective association dynamics of a cold Fermi gas of 2N atoms in M atomic modes into a single molecular bosonic mode. When the atomic translational motion is slow compared to the atom-molecule conversion rate, the many-body fermionic problem for 2M amplitudes is effectively reduced to a dynamical system of min{N, M} + 1 amplitudes, making the solution no more complex than the solution of a two-mode Bose-Einstein condensate and allowing realistic calculations with up to 104 particles. The many-body dynamics is shown to be formally similar to the dynamics of the bosonic system under the mapping of boson particles to fermion holes, producing collective enhancement effects due to many-particle constructive interference. 相似文献
13.
Vladimir Kalitvianski 《Central European Journal of Physics》2009,7(1):1-11
We show that the electrostatic potential of an atomic nucleus “seen” by a fast charged projectile at short distances is quantum
mechanically smeared due to nucleus motion around the atomic center of inertia. For example, the size of the “positive charge
cloud” in the Hydrogen ground state is much larger than the proper proton size. For target atoms in excited initial states,
the effect is even larger. The elastic scattering at large angles is generally weaker than the Rutherford scattering since
the effective potential at short distances is softer than the Colombian one due to a natural “cutoff”. In addition, the large-angle
scattering leads to target atom excitations due to pushing the nucleus (⇒ inelastic processes). The Rutherford cross section
is in fact inclusive rather than elastic. These results are analogous to those from QED. Non-relativistic atomic calculations
are presented. The difference and the value of these calculations arise from nonperturbatively (exact) nucleus “dressing”
that immediately leads to correct physical results and to significant technical simplifications. In these respects a nucleus
bound in an atom is a simple but rather realistic model of a “dressed” charge in the QFT. This idea is briefly demonstrated
on a real electron model (electronium) which is free from infinities.
相似文献
14.
15.
Retrieval of the quasi-optimal signal activating the excitable systems using preceding noise samples
We propose a method for obtaining a signal leading to the activation of an excitable dynamic system for a signal energy close
to minimal. The efficiency of this technique, which is based on recording and processing of noise samples preceding the activation
was tested using the FitzHugh–Nagumo, Hodgkin–Huxley, and Luo–Rudy models as examples. It is shown that the proposed procedure
gives good results when the noise intensity is smaller than or close to the system activation energy. The criteria of “low”
and “high” intensities of fluctuations are proposed. The method of increasing the stability of the excitable system with respect
to “low-intensity” noise by filtering or another way of suppression of the spectral components that make the main contribution
to the energetically optimal activation signal is justified. The relation between eigenvalues of the linearized system of
the Hamiltonian equations, which describe the optimal trajectories and the activation signal, and eigenvalues of the excitable
system linearized near the initial equilibroum state is found. 相似文献
16.
We discuss a type of measurement in which a macroscopically large angular momentum (spin) is “created” nonlocally by the measurement
of just a few atoms from a double Fock state. This procedure apparently leads to a blatant nonconservation of a macroscopic
variable—the local angular momentum. We argue that while this gedankenexperiment provides a striking illustration of several counter-intuitive features of quantum mechanics, it does not imply a non-local
violation of the conservation of angular momentum. 相似文献
17.
G. Kónya G. Szirmai P. Domokos 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,65(1-2):33-42
We develop a mean-field model describing the Hamiltonian interaction of ultracold atoms and the optical field in a cavity. The Bose-Einstein condensate is properly defined by means of a grand-canonical approach. The model is efficient because only the relevant excitation modes are taken into account. However, the model goes beyond the two-mode subspace necessary to describe the self-organization quantum phase transition observed recently. We calculate all the second-order correlations of the coupled atom field and radiation field hybrid bosonic system, including the entanglement between the two types of fields. 相似文献
18.
The Gross-Neveu model provides a unique opportunity to apply relativistic many-body techniques (Dirac-Hartree approximation, RPA) in a context where all calculations can be done analytically and — in the largeN limit — yield the exact results. The physical fermion as well as multifermion (baryon) and fermion-antifermion (meson) bound states are discussed in this spirit, with special emphasis on the role of the Dirac sea.Supported by the Bundesministerium für Forschung und Technologie 相似文献
19.
In this paper it is shown that (i) there exists an alternative definition of the superoperator resolvent for calculation of
difference energy satisfying linked cluster theorem for a coupled-cluster choice of the ground-state function which may even
be approximate; (ii) the pole-structure of this propagator-like function in superoperator form is shown to contain information
similar to that contained in the conventional propagator. (iii) It is demonstrated that suitable “Killer conditions” and completeness
of the “operator manifold”—essential for understanding the pole-structure of the propagator—can be established both for an
exact and an approximate ground state function in a coupled-cluster form. (iv) It is also demonstrated that difference energies
calculated with these propagator-like functions are identical to those obtained from a linear response theory in a coupled-cluster
form put forward recently by Mukherjeeet al and Monkhorst. 相似文献