Publications L.G. Suttorp since 1991 <br>
(Publications before 1991 are found <a href="publlgs2.html" > here </a>)<br>
<br>
</ul>

<li>Continued-fraction representation of the Kraus map for non-Markovian reservoir damping,
<br> A.J. van Wonderen and LGS, Journal of Physics A 51(2018)175304:1-24 <br>
Abstract: Quantum dissipation is studied for a discrete system that linearly interacts
with a reservoir of harmonic oscillators at thermal equilibrium.  Initial correlations
between system and reservoir are assumed to be absent. The dissipative dynamics as
determined by the unitary evolution of system and reservoir is described by a Kraus map
consisting of an infinite number of matrices. For all Laplace-transformed Kraus matrices
exact solutions are constructed in terms of continued fractions that depend on the pair
correlation functions of the reservoir. By performing factorizations in the Kraus map a
perturbation theory is set up that conserves in arbitrary perturbative order both
positivity and probability of the density matrix. The latter is determined by an integral
equation for a bitemporal matrix and a finite hierarchy for Kraus matrices.  In the lowest
perturbative order this hierarchy reduces to one equation for one Kraus matrix. Its
solution is given by a continued fraction of a much simpler structure as compared to the
non-perturbative case. In the lowest perturbative order our non-Markovian evolution equations
are applied to the damped Jaynes-Cummings model. From the solution for the atomic density
matrix it is found that the atom may remain in the state of maximum entropy for a
significant time span that depends on the initial energy of the radiation field.
<br>
Full text: <a href="./articles/jphysa2018.pdf" > pdf </a> </li><br>



<li>Hierarchies of sum rules for squares of spherical Bessel functions,
<br> LGS and A.J. van Wonderen, Integral Transforms and Special Functions 28 (2017)
156-165 <br>
Abstract: A four-term recurrence relation for squared spherical Bessel functions is
shown to yield closed-form expressions for several types of finite
weighted sums of these functions.  The resulting sum rules, which may
contain an arbitrarily large number of terms, are found to constitute
three independent hierarchies. Their use leads to an efficient numerical
evaluation of these sums.
<br>
Full text: <a href="./articles/sumrules.pdf" > pdf </a> </li><br> 

<li>Modified atomic decay rate near absorptive scatterers at finite temperature,
<br> LGS and A.J. van Wonderen, Physical Review A 92 (2015) 013843:1-16 <br>
Abstract: The change in the decay rate of an excited atom that is brought
about by extinction and thermal-radiation effects in a nearby dielectric
medium is determined from a quantummechanical model. The medium is a
collection of randomly distributed thermally-excited spherical scatterers
with absorptive properties. The modification of the decay rate is described
by a set of correction functions for which analytical expressions are
obtained as sums over contributions from the multipole moments of the
scatterers. The results for the modified decay rate as a function of the
distance between the excited atom and the dielectric medium show the
influence of absorption, scattering and thermal-radiation processes. Some
of these processes are found to be mutually counteractive. The changes in
the decay rate are compared to those following from an effective-medium
theory in which the discrete scatterers are replaced by a continuum.
<br>
Full text: <a href="./articles/pra15.pdf" > pdf </a> </li><br> 


<li>Kraus map for non-Markovian quantum dynamics driven by a thermal reservoir,
<br> A.J. van Wonderen and LGS, Europhysics Letters 102 (2013)
  60001:1-6 <br>
Abstract: Starting from unitary dynamics we study the evolution in time of a non-relativistic 
quantum system that exchanges energy with a thermal reservoir of harmonic oscillators. System 
and reservoir are assumed to be initially decorrelated. Reservoir correlation functions are 
factorized by means of a Kraus compliant version of Wick's theorem. As a result, the 
non-Markovian Kraus map for the system density operator can be completely expressed in terms of 
system potentials and reservoir pair correlation functions. An infinite hierarchy for the 
evolution operators of the Kraus map is derived. The system density operator is obtained as a 
time-ordered exponential containing a non-Markovian counterpart of the standard Markovian 
generator for dissipative dynamics. We specify a condition on this non-Markovian generator for 
return to thermal equilibrium. We set up a non-Markovian perturbation theory that preserves both 
trace and positivity of the system density operator.
<br>
Full text: <a href="./articles/europhyslett2013.pdf" > pdf </a> </li><br>

<li>Quantized media with absorptive scatterers and modified atomic emission
  rates, <br> LGS and A.J. van Wonderen, Optics Communications 284 (2011)
  2943-2948 <br>
Abstract: Modifications in the spontaneous emission rate of an excited atom
  that are caused by extinction effects in a nearby dielectric medium are
  analyzed in a quantummechanical model, in which the medium consists of
  spherical scatterers with absorptive properties. Use of the dyadic Green
  function of the electromagnetic field near a dielectric sphere leads to
  an expression for the change in the emission rate as a series of
  multipole contributions for which analytical formules are obtained. The
  results for the modified emission rate as a function of the distance
  between the excited atom and the dielectric medium show the influence of
  both absorption and scattering processes. 
<br>
Full text: <a href="./articles/scatterers2.pdf" > pdf </a> </li><br>

<li>Atomic decay near a quantized medium of absorbing scatterers, <br> LGS
and A.J. van Wonderen, Journal of Physics B 43 (2010) 105501:1-12 <br>
Abstract: The decay of an excited atom in the presence of a medium that
both scatters and absorbs radiation is studied with the help of a
quantum-electrodynamical model. The medium is represented by a half-space
filled with a randomly distributed set of non-overlapping spheres, which
consist of a linear absorptive dielectric material. The absorption effects
are described by means of a quantized damped-polariton theory. It is found
that the effective susceptibility of the bulk does not fully account for
the medium-induced change in the atomic decay rate. In fact, surface
effects contribute to the modification of the decay properties as well. The
interplay of scattering and absorption in the total decay rate is discussed.
<br>
Full text: <a href="./articles/scatterers.pdf" > pdf </a> </li><br>

<li>Sum rules for correlation functions of ionic mixtures in arbitrary
dimension $d \geq 2$, <br> LGS, Journal of Physics A 41 (2008)
  495001:1-18 <br> 
Abstract: The correlations in classical multi-component ionic mixtures with
spatial dimension $d\geq 2$ are studied by using a restricted
grand-canonical ensemble and the associated hierarchy equations for the
correlation functions. Sum rules for the first few moments of the
two-particle correlation function are derived and their dependence on $d$
is established. By varying $d$ continuously near $d=2$ it is shown how the
sum rules for the two-dimensional mixture are related to those for mixtures
at higher $d$. <br>
Full text: <a href="./articles/mim.pdf" > pdf </a> </li><br>

<li>Field quantization in inhomogeneous anisotropic dielectrics
  with spatio-temporal dispersion,<br> LGS, Journal of Physics A 40 (2007)
  3697-3719 <br>
Abstract: A quantum damped-polariton model is constructed for an inhomogeneous
anisotropic linear dielectric with arbitrary dispersion in space and
time. The model Hamiltonian is completely diagonalized by determining the
creation and annihilation operators for the fundamental polariton modes as
specific linear combinations of the basic dynamical variables. Explicit
expressions are derived for the time-dependent operators describing the
electromagnetic field, the dielectric polarization and the noise term in
the latter. It is shown how to identify bath variables that generate the
dissipative dynamics of the medium. <br>
Full text: <a href="./articles/hbnonloc.pdf" > pdf </a> </li><br>

<li>Damping and dispersion of oscillating modes of a
multicomponent ionic mixture in a magnetic field,<br> G.A.Q. Salvati and LGS,
Physica A 371 (2006) 387-408 <br>
Abstract: The collective-mode spectrum of a multicomponent magnetized ionic mixture
for small wave number $k$ is studied with the use of magnetohydrodynamics
and formal kinetic theory. Apart from the usual thermal and diffusive
modes, the spectrum contains a set of four oscillating modes. By evaluating
the $k^2$ contributions to the eigenfrequencies, the damping and the dispersion
of these oscillating modes are determined. The long-range nature of the
Coulomb interactions is shown to imply that Burnett terms with higher-order
gradients in the linear phenomenological laws have to be taken into account
in order to obtain a full description of all damping and dispersion
effects.<br>
Full text: <a href="./articles/salv2.pdf" > pdf </a> </li><br>


<li>Multiple-scattering approach to interatomic interactions and
superradiance in inhomogeneous dielectrics,<br> M. Wubs, LGS and A. Lagendijk,
Physical Review A 70 (2004) 053823/1-17 <br>
Abstract: The dynamics of a collection of resonant atoms embedded inside an
inhomogeneous nondispersive and lossless dielectric is described with a
dipole Hamiltonian that is based on a canonical quantization theory. The
dielectric is described macroscopically by a position-dependent dielectric
function and the atoms as microscopic harmonic oscillators. We identify and
discuss the role of several types of Green tensors that describe the
spatio-temporal propagation of field operators. After integrating out the
atomic degrees of freedom, a multiple-scattering formalism emerges in which
an exact Lippmann-Schwinger equation for the electric field operator plays
a central role. The equation describes atoms as point sources and point
scatterers for light.  First, single-atom properties are calculated such as
position-dependent spontaneous-emission rates as well as differential cross
sections for elastic scattering and for resonance fluorescence. Secondly,
multi-atom processes are studied. It is shown that the medium modifies both
the resonant and the static parts of the dipole-dipole interactions.  These
interatomic interactions may cause the atoms to scatter and emit light
cooperatively. Unlike in free space, differences in position-dependent
emission rates and radiative line shifts influence cooperative decay in the
dielectric. As a generic example, it is shown that near a partially
reflecting plane there is a sharp transition from two-atom superradiance to
single-atom emission as the atomic positions are varied.<br>
Full text: <a href="./articles/wubs4.pdf" > pdf </a> </li><br>


<li>The oscillator model for dissipative QED in an inhomogeneous
dielectric,<br> A.J. van Wonderen and LGS, Journal of Physics A 37 (2004)
11101-11122 <br>
Abstract: The Ullersma model for the damped harmonic oscillator is coupled to 
the quantised electromagnetic field. All material parameters and 
interaction strengths are allowed to depend on position. The 
ensuing Hamiltonian is expressed in terms of canonical fields, and 
diagonalised by performing a normal-mode expansion. The commutation 
relations of the diagonalising operators are in agreement with the 
canonical commutation relations. For the proof we replace all sums 
of normal modes by complex integrals with the help of the residue 
theorem. The same technique helps us to explicitly calculate the 
quantum evolution of all canonical and electromagnetic fields. We 
identify the dielectric constant and the Green function of the wave 
equation for the electric field. Both functions are meromorphic in 
the complex frequency plane. The solution of the extended 
Ullersma model is in keeping with well-known phenomenological rules 
for setting up quantum electrodynamics in an absorptive and 
spatially inhomogeneous dielectric. To establish this fundamental 
justification, we subject the reservoir of independent harmonic 
oscillators to a continuum limit. The resonant frequencies of the 
reservoir are smeared out over the real axis. Consequently, the 
poles of both the dielectric constant and the Green function unite 
to form a branch cut. Performing an analytic continuation beyond 
this branch cut, we find that the long-time behaviour of the 
quantised electric field is completely determined by the sources of 
the reservoir. Through a Riemann-Lebesgue argument we demonstrate 
that the field itself tends to zero, whereas its quantum 
fluctuations stay alive. We argue that the last feature may have 
important consequences for application of entanglement and related 
processes in quantum devices. <br>
Full text: <a href="./articles/wonderen7.pdf" > pdf </a> </li><br>


<li>Fano diagonalization of a polariton model for an inhomogeneous
absorptive dielectric,<br> LGS and
A.J. van Wonderen, Europhysics Letters 67 (2004) 766-772 <br>
Abstract: The Hamiltonian of a polariton model for an inhomogeneous linear absorptive
dielectric is diagonalized by means of Fano's diagonalization method. The
creation and annihilation operators for the independent normal modes are
explicitly found as linear combinations of the canonical operators. The
coefficients in these combinations depend on the tensorial Green function
that governs the propagation of electromagnetic waves through the
dielectric. The time-dependent electromagnetic fields in the Heisenberg
picture are given in terms of the diagonalizing operators. These results
justify the phenomenological quantization of the electromagnetic field in
an absorptive dielectric. <br>
Full text: <a href="./articles/euro.pdf" > pdf </a> </li><br>

<li>Field quantization in inhomogeneous absorptive dielectrics,<br> LGS and
M. Wubs, Physical Review A 70 (2004) 013816/1-18 <br>
Abstract: The quantization of the electromagnetic field in a
three-dimensional inhomogeneous dielectric medium with losses is carried
out in the framework of a damped-polariton model with an arbitrary spatial
dependence of its parameters. The equations of motion for the canonical
variables are solved explicitly by means of Laplace transformations for
both positive and negative time. The dielectric susceptibility and the
quantum noise-current density are identified in terms of the dynamical
variables and parameters of the model. The operators that diagonalize the
Hamiltonian are found as linear combinations of the canonical variables,
with coefficients depending on the electric susceptibility and the
dielectric Green function. The complete time dependence of the
electromagnetic field and of the dielectric polarization is determined. Our
results provide a microscopic justification of the phenomenological
quantization scheme for the electromagnetic field in inhomogeneous
dielectrics.<br>
Full text: <a href="./articles/wubs5.pdf" > pdf </a> </li><br>

<li>Spontaneous-emission rates in finite photonic
crystals of plane scatterers,<br> M. Wubs, LGS and A. Lagendijk, Physical Review
E 69 (2004) 016616/1-17 <br>
Abstract: The concept of a plane scatterer that was developed earlier for scalar
waves is generalized so that polarization of light is included. Starting
from a Lippmann-Schwinger formalism for vector waves, we show that the
Green function has to be regularized before T matrices can be defined in a
consistent way. After the regularization, optical modes and Green
functions are determined exactly for finite structures built up of an
arbitrary number of parallel planes, at arbitrary positions, and where each
plane can have different optical properties. The model is applied to the
special case of finite crystals consisting of regularly spaced identical
planes, where analytical methods can be taken further and only light
numerical tasks remain. The formalism is used to calculate position- and
orientation-dependent spontaneous-emission rates inside and near the
finite photonic crystals. The results show that emission rates and
reflection properties can differ strongly for scalar and for vector
waves. The finite size of the crystal influences the emission rates. For
parallel dipoles close to a plane, emission into guided modes gives rise
to a peak in the frequency-dependent emission rate.<br>
Full text: <a href="./articles/wubs3.pdf" > pdf </a> </li><br>

<li>Multipole interaction between atoms and their photonic
environment,<br> M. Wubs, LGS and A. Lagendijk, Physical Review A 68 (2003)
013822/1-16 <br>
Abstract: Macroscopic field quantization is presented for a nondispersive
photonic dielectric environment, both in the absence and presence of guest
atoms.  Starting with a minimal-coupling Lagrangian, a careful look at
functional derivatives shows how to obtain Maxwell's equations before and
after choosing a suitable gauge. A Hamiltonian is derived with a
multipolar interaction between the guest atoms and the electromagnetic
field. Canonical variables and fields are determined and in particular, the
field canonically conjugate to the vector potential is identified by
functional differentiation as minus the full displacement field. An
important result is that inside the dielectric a dipole couples to a field
that is neither the (transverse) electric nor the macroscopic displacement
field. The dielectric function is different from the bulk dielectric
function at the position of the dipole, so that local-field effects must
be taken into account.<br>
Full text: <a href="./articles/wubs2.pdf" > pd f</a> </li><br>

<li>Time correlations in a confined magnetized free-electron gas,<br> LGS,
Journal of Physics A 36 (2003) 8223-8247 <br>
Abstract: The time-dependent pair correlation functions for a degenerate
ideal quantum gas of charged particles in a uniform magnetic field are
studied on the basis of equilibrium statistics. In particular, the
influence of a flat hard wall on the correlations is investigated, both for
a perpendicular and a parallel orientation of the wall with respect to the
field. The coherent and incoherent parts of the time-dependent structure
function in position space are determined from an expansion in terms of the
eigenfunctions of the one-particle Hamiltonian. For the bulk of the system,
the intermediate scattering function and the dynamical structure factor
are derived by taking successive Fourier transforms. In the vicinity of the
wall the time-dependent coherent structure function is found to decay
faster than in the bulk. For coinciding positions near the wall the form
of the structure function turns out to be independent of the orientation
of the wall. Numerical results are shown to corroborate these
findings.<br>
Full text: <a href="articles/timen.pdf" > pdf </a>  </li><br>

<li>Correlations in a confined magnetized free-electron gas,<br>
M.M. Kettenis and LGS, Journal of Physics A 34 (2001) 7991-8013.<br>
Abstract: Equilibrium quantum statistical methods are used to study the pair
correlation function for a magnetized free-electron gas in the presence of
a hard wall that is parallel to the field. With the help of a
path-integral technique and a Green function representation, the
modifications in the correlation function caused by the wall are
determined both for a non-degenerate and for a completely degenerate
gas. In the latter case the asymptotic behaviour of the correlation
function for large position differences in the direction parallel to the
wall and perpendicular to the field, is found to change from Gaussian in
the bulk to algebraic near the wall.<br>
Full text: <a href="articles/ket3n.pdf" > pdf </a> </li><br>

<li>Magnetohydrodynamics for a multicomponent ionic mixture,<br>
G.A.Q. Salvati and LGS, Physica A 299 (2001) 378-404.<br>
Abstract: The magnetohydrodynamical equations for a multi-component magnetized
ionic mixture are used to derive the spectrum of collective modes for small
wave numbers. The results are compared with those from formal kinetic
theory , which is based on the microscopic balance equations and a
projection-operator formalism. The comparison leads to a set of
Green-Kubo-type expressions for the phenomenological coefficients
occurring in the magnetohydrodynamical treatment.<br>
Full text: <a href="articles/salv1n.pdf" > pdf </a> </li><br>

<li>Transient QED effects in absorbing dielectrics,<br> M. Wubs and LGS,
Physical Review A 63 (2001) 043809/1-14. <br>
Abstract: The spontaneous-emission rate of a radiating atom reaches its
time-independent equilibrium value after an initial transient regime. In
this paper, we consider the associated relaxation effects of the
spontaneous-decay rate of atoms in dispersive and absorbing dielectric
media for atomic-transition frequencies near material resonances. A quantum
mechanical description of such media is furnished by a damped-polariton
model in which absorption is taken into account through coupling to a
bath. We show how all field and matter operators in this theory can be
expressed in terms of the bath operators at an initial time. The
consistency of these solutions for the field and matter operators are found
to depend on the validity of certain velocity sum rules. The transient
effects in the spontaneous-decay rate are studied with the help of several
specific models for the dielectric constant, which are shown to follow from
the general theory by adopting particular forms of the bath coupling
constant.<br>
Full text: <a href="articles/wubs1n.pdf" > pdf </a> </li><br>

<li>Path-decomposition and edge effects in a magnetized electron gas,<br>
LGS, J. de Physique IV Proc. 10 (2000) 461-464.<br>
Abstract: The influence of boundaries on the properties of a magnetized
free-electron gas is discussed with the help of a path-integral
representation for the temperature Green function. By using a suitable
decomposition of the paths the profiles of the excess particle density and
the current density are analysed. The asymptotic behaviour of these
profiles towards the bulk is found to depend sensitively on the degree of
degeneracy.<br>
Full text: <a href="articles/stmalo.pdf" > pdf </a> </li><br>

<li>Path-decomposition expansion and edge effects in a confined magnetized
free-electron gas,<br> M.M. Kettenis and LGS, Journal of Physics A 32
(1999) 8209-8223.<br>
Abstract: Path-integral methods can be used to derive a `path-decomposition
expansion' for the temperature Green function of a magnetized free-electron
gas confined by a hard wall. With the help of this expansion the asymptotic
behaviour of the profiles for the excess particle density and the electric
current density far from the edge is determined for arbitrary values of the
magnetic field strength. The asymptotics are found to depend sensitively on
the degree of degeneracy. For a non-degenerate electron gas the asymptotic
profiles are essentially Gaussian (albeit modulated by a Bessel function),
on a length scale that is a function of the magnetic field strength and the
temperature. For a completely degenerate electron gas the asymptotic
behaviour is again proportional to a Gaussian, with a scale that is the
magnetic length in this case. The prefactors are polynomial and logarithmic
functions of the distance from the wall, which depend on the number of
filled Landau levels n. As a consequence, the Gaussian asymptotic decay
sets in at distances that are large compared with the magnetic length
multiplied by square root n.<br>
Full text: <a href="articles/ket2n.pdf" > pdf </a> </li><br>

<li>Statistics of quantum-electrodynamical plasmas in external magnetic
fields,<br> LGS, in: Strongly Coupled Coulomb Systems , eds.  G.J. Kalman
e.a., (Plenum Press, 1998) 705-708. <br>
Full text: <a href="articles/boston.pdf" > pdf </a> </li><br>

<li>Generalized master equation for systems in nonideal cavities with
squeezed baths,<br> R.W.F. van der Plank and LGS, European Physical Journal
D 3 (1998) 183-193.<br>
Abstract: The master equation for the density operator of a system in a lossy
cavity, which is coupled to a squeezed bath, is generalized so as to
include the effects of an enhanced loss through a mirror of finite
transmittivity. As compared to the standard master equation, which is valid
for a nearly-perfect cavity, the generalized master equation is found to
contain additional terms that account for an effective squeezed-light
mixing at the nonideal mirror and for the interplay of the photon loss and
the interaction within the cavity. As an example, the new master equation
is used to study the influence of the enhanced losses on the photon
statistics of a localized degenerate parametric oscillator. It is found
that considerable changes in the photon distribution can occur as soon as
the quality of the mirror becomes less than perfect.<br>
Full text: <a href="articles/plank4.pdf" > pdf </a> </li><br>

<li>Charge and current density profiles of a degenerate magnetized
free-electron gas near a hard wall,<br> M.M. Kettenis and LGS, Journal of
Physics A 31 (1998) 6547-6560.<br>
Abstract: The charge and current densities of a completely degenerate
free-electron gas in a uniform magnetic field are found to have a damped
oscillatory spatial dependence near a wall that is parallel to the magnetic
field. For large distances from the wall the behaviour of the associated
profile functions are analysed by means of systematic asymptotic
expansions. Both densities are shown to decay to their bulk values through
a Gaussian tail, with prefactors that depend algebraically and
logarithmically on the distance from the wall.<br>
Full text: <a href="articles/ket1n.pdf" > pdf </a> </li><br>

<li>Spontaneous emission from an atom in a nonideal cavity: application of
a generalized master equation,<br> R.W.F. van der Plank and LGS, Physical
Review A 54 (1996) 2464-2473.<br>
Abstract: The decay of an excited two-level atom in a cavity with mirrors of
finite transmittivity is studied with the help of a generalized multimode
master equation that has been established recently. The time evolution of
the decaying atom is obtained by accounting for the interaction with
infinitely many quasimodes. The analytical and numerical results are
compared with those of the standard multimode master equation and of a
universe-mode approach.<br>
Full text: <a href="articles/plank3.pdf" > pdf </a> </li><br>

<li>Edge effects in magnetoplasmas,<br> LGS, in: Strongly Coupled Plasma
Physics, World Scientific (1996) 381-386.<br>
Abstract: Edge effects in magnetized charged-particle systems are 
discussed with the help of a multiple-reflection expansion for the Green 
function. The profiles of the density and the electric current are determined 
both for the non-degenerate and the highly degenerate case. The asymptotic 
form of the profiles near the bulk is found to be exponentially decaying in 
both cases.<br>
Full text: <a href="articles/binz.pdf" > pdf </a> </li><br>

<li>Generalization of damping theory for cavities with mirrors of finite
transmittivity,<br> R.W.F. van der Plank and LGS, Physical Review A 53
(1996) 1791-1800.<br>
Abstract: Standard damping theory is generalized to incorporate the effects of
finite mirror transmittivity. The correction to the standard Langevin
equation for the quasimode annihilation operator is determined in first
order in the transmittivity of the mirrors. From the Langevin equation an
effective master equation is derived. As an example, we study the decay of
a single two-level atom at a fixed position in a nonideal cavity. For this
case we find a modification of the damped Rabi oscillations, which depends
on the atomic position.<br>
Full text: <a href="articles/plank2.pdf" > pdf </a> </li><br>

<li>Boundary effects in a magnetized free-electron gas: Green function
approach,<br> P. John and LGS, Journal of Physics A 28 (1995)
6087-6097.<br>
Abstract: A Green function approach to the boundary effects of a free-electron
gas in a magnetic field is presented. It is shown that truncation of the
multiple-reflection expansion for the Green function of a confined system
is not justified if a magnetic field is present, even for a system with
flat boundaries. Using the full expansion we calculate the profiles for the
particle density, the current density and the components of the pressure
tensor near the boundary.<br>
Full text: <a href="articles/john5n.pdf" > pdf </a> </li><br>

<li>Output photon statistics for a beam splitter with input squeezed
light,<br> R.W.F. van der Plank and LGS, Optics Communications 112 (1994)
145-150.<br>
Abstract: The mixing of (quadrature-) squeezed states by a lossless beam splitter
is studied. Two generating functions describing the outgoing-photon
distribution are calculated. With the use of these generating functions the
distribution is determined explicitly for some special cases.<br>
Full text: <a href="articles/plank1n.pdf" > pdf </a> </li><br>

<li>Boundary effects in the pressure of a confined magnetized electron
gas,<br> P. John and LGS, Physica A 210 (1994) 237-256. <br>
Abstract: The role of boundary effects in the pressure of a magnetized quantum
plasma is determined by evaluating the spatial dependence of the mechanical
pressure tenser for several simplified model systems, namely for a
non-interacting magnetized electron gas in either a slab geometry or in a
harmonic confining potential. From the pressure profiles it is shown that
the bulk and surface values of the pressure are related in such a way that
an earlier result on the difference between the thermodynamic and the
mechanical pressure in a magnetized quantum plasma is confirmed.<br>
Full text: <a href="articles/john4n.pdf" > pdf </a> </li><br>

<li>Pressure and compressibility in a quantum one-component plasma,<br>
P. John and LGS, Journal of Physics A 27 (1994) 6053-6065. <br>
Abstract: With the help of scaling methods, a general relation is established
between the thermodynamic pressure and the mechanical pressure tensor of an
equilibrium one-component plasma in a magnetic field. The mechanical
pressure tenser is shown to be anisotropic. A general proof of the
compressibility sum rule for a magnetized quantum plasma is
presented. Finally, fourth-order wavenumber inequalities for the static
charge correlation function are derived.<br>
Full text: <a href="articles/john3n.pdf" > pdf </a> </li><br>

<li>Fluctuations properties and collective modes of quantum plasmas in a
magnetic field,<br> LGS, in: Strongly Coupled Plasma Physics, University of
Rochester Press (1993) 105-108.<br>
Abstract: A complete set of equilibrium fluctuation formulas for the charge 
density, the momentum density and the energy density of a magnetized 
one-component quantum plasma is presented. The derivation is based on the use 
of equations of motion for Fourier-transformed imaginary-time Green functions. 
The resulting formulas depend both on the strength and the orientation of the 
magnetic field. They are a basic ingredient for the derivation of the 
collective-mode spectrum in the long-wavelength limit. Projection-operator 
methods are used to establish explicit expressions for the mode frequencies of 
a magnetized quantum plasma up to second order in the wave number.<br>
Full text: <a href="articles/roch.pdf" > pdf </a> </li><br>

<li>Pressure and compressibility of a quantum plasma in a magnetic
field,<br> LGS, Contributions in Plasma Physics 33 (1993) 503-512.<br>
Abstract: The equilibrium pressure tensor that occurs in the momentum balance
equation for a quantum plasma in a magnetic field is shown to be
anisotropic. Its relation to the pressure that follows from thermodynamics
is elucidated. A general proof of the compressibility rule for a magnetized
quantum plasma is presented.<br>
Full text: <a href="articles/rostock.pdf" > pdf </a> </li><br>

<li>Collective modes of the quantum one-component plasma in a magnetic
field,<br> P. John and LGS, Physica A 197 (1993) 613-628.<br>
Abstract: The authors derive the collective modes of a quantum one-component
plasma in a magnetic field by using a projection operator technique. With
the help of these modes the long-time behaviour of the time correlation
functions for the charge density, the current density and the energy
density is determined in the limit of small wavenumbers.<br>
Full text: <a href="articles/john2n.pdf" > pdf </a> </li><br>

<li>Equilibrium fluctuations formulas for the quantum one-component plasma
in a magnetic field,<br> P. John and LGS, Physica A 192 (1993) 280-304.<br>
Abstract: The authors derive a complete set of equilibrium fluctuation formulae
for the charge density, the current density and the energy density of the
quantum one-component plasma in a magnetic field. The derivation is based
on the use of imaginary-time-dependent Green functions and their Kubo
transforms. It is shown how the fluctuation formulae involving
Kubo-transformed quantities can be established directly, even in the
absence of a detailed knowledge of the full imaginary-time dependence of
the Green functions. The resulting fluctuation formulae for the Kubo
transforms are found to have a considerably simpler structure than those
for the equal-imaginary-time observables.<br>
Full text: <a href="articles/john1.pdf" > pdf </a> </li><br>

<li>Second-moment sum rules for correlation functions in a classical ionic
mixture,<br> LGS, in: Physics of Nonideal Plasmas, eds. W. Ebeling e.a.,
Teubner (1992) 73-80.<br>
Abstract: The complete set of second-moment sum rules for the correlation functions 
of arbitrarily high order describing a classical multi-component ionic 
mixture in equilibrium is derived from the grand-canonical ensemble. The 
connection of these sum rules with the large-scale behaviour of 
fluctuations in an ionic mixture is pointed out.<br>
Full text: <a href="articles/berlijn.pdf" > pdf </a> </li><br>

<li>Asymptotic behavior of correlation functions for electric potential and
field fluctuations in a classical one-component plasma,<br> LGS, Journal of
Statistical Physics 66 (1992) 1343-1357.<br>
Abstract: The correlations of the electric potential fluctuations in a classical
one-component plasma are studied for large distances between the
observation points. The two-point correlation function for these
fluctuations is known to decay slowly for large distances, even if
exponential clustering holds for the charge correlation functions. In this
paper the asymptotic behavior of the general k-point electric potential
correlation functions is analyzed. Each of these correlation functions can
be split into a reducible part, which is given by a sum of products of
lower-order correlation functions, and a remaining irreducible part. It is
shown, on the basis of an exponential clustering hypothesis for the charge
correlation functions, that for all k>or=3D3 the irreducible parts of the
electric potential correlation functions decay faster than any inverse
power of the distance, if one or more of the observation points move far
away from the others. Hence, the two-point electric potential correlation
function is the only one with a slow algebraic decay. The same statement
holds for the correlation functions of the electric field fluctuations.<br>
Full text: <a href="articles/asymptn.pdf" > pdf </a> </li><br>

<li>Dispersive optical bistability in a nonideal Fabry-Perot 
cavity II. Numerical results on side-mode instabilities,<br> A.J. van Wonderen 
and LGS, Zeitschrift fur Physik B 83 (1991)  143-151.<br>
Abstract: For pt.I see ibid., vol.83, p.135 (1991). Instabilities in the nearest
side-modes are predicted for dispersive optical bistability in a nonideal
Fabry-Perot cavity. The results are based on a linear stability analysis of
the Maxwell-Bloch equations. This analysis leads to a boundary value
problem for a four-dimensional set of linear differential equations, which
the authors have solved numerically. The findings show that the instability
spectrum strongly depends on the detuning parameters and on the
transmission coefficient of the cavity mirrors. If the atomic detuning
gradually increases, instability domains are found to merge. If moreover
the cavity detuning grows, instabilities spread along the upper branch of
the bistability curve, even for high values of the medium response
time. The authors have made a comparison between our results and recent
experimental data, the outcome of which is satisfactory from a qualitative
point of view. Finally, they show that the side-mode instabilities for
dispersive optical bistability in a Fabry-Perot cavity are incorrectly
predicted, if a so-called equivalent ring cavity is adopted as a model.<br>
Full text: <a href="articles/wonderen6.pdf" > pdf </a></li><br>

<li>Dispersive optical bistability in a nonideal Fabry-Perot cavity
I. Stability analysis of the Maxwell-Bloch equations,<br> A.J. van Wonderen
and LGS, Zeitschrift fur Physik B 83 (1991) 135-142.<br>
Abstract: A stability analysis is performed for optical bistability in a
Fabry-Perot cavity with mirrors of arbitrary transmission coefficient. The
mixed absorptive and dispersive regime is covered. In order to describe the
system we use the Maxwell-Bloch equations formulated in terms of slowly
varying envelopes. Standing-wave effects are completely taken into account
by refraining from a truncation of the harmonic expansions for the
polarization and the inversion density. The authors represent the solutions
of the linearized Bloch hierarchy in terms of Chebyshev polynomials
depending on the stationary electric field envelopes. In this way, they
reduce the stability problem to a four-dimensional set of linear
differential equations. Together with a couple of boundary conditions these
equations govern the spatial behaviour of the deviations of the forward and
the backward electric field envelopes. The final stability problem becomes
much simpler in the uniform-field limit and in the adiabatic limit. If one
chooses the stationary backward electric field equal to zero one recovers
results that were derived earlier for the case of a ring cavity.<br>
Full text: <a href="articles/wonderen5n.pdf" > pdf </a> </li><br>

</ul>
(Publications before 1991 are found <a href="publlgs2.html" > here. </a>)<br>