ABSTRACT The fundamental limits of the power efficiency of an antenna are explored. The antenna i... more ABSTRACT The fundamental limits of the power efficiency of an antenna are explored. The antenna is confined in a sphere and all of the currents are assumed to run in a material with a conductivity that is a function of the radial coordinate. The analysis is based on the expansion of the electromagnetic fields in terms of vector spherical harmonics. Explicit expressions for the limits of efficiency are derived for different types of antennas.
We have experimentally demonstrated a decoy-state quantum key distribution scheme (QKD) with a he... more We have experimentally demonstrated a decoy-state quantum key distribution scheme (QKD) with a heralded single-photon source based on parametric down-conversion. What we used is a one-way BB84 protocol with a four-state and one-detector phase-coding scheme.
Journal of Physics a Mathematical and General, Nov 1, 2002
We propose an extension of quantum key distribution based on encoding the key into quNits, i.e. q... more We propose an extension of quantum key distribution based on encoding the key into quNits, i.e. quantum states in an N-dimensional Hilbert space. We estimate both the mutual information between the legitimate parties and the eavesdropper, and the error rate, as a function of the dimension of the Hilbert space. We derive the information gained by an eavesdropper using optimal incoherent attacks and an upper bound on the legitimate party error rate that ensures unconditional security when the eavesdropper uses finite coherent eavesdropping attacks. We also consider realistic systems where we assume that the detector dark count probability is not negligible.
Darwin is a cornerstone mission of the Horizons 2000+ program of the European Space Agency. It ha... more Darwin is a cornerstone mission of the Horizons 2000+ program of the European Space Agency. It has the express purpose of carrying out the first direct search for terrestrial exoplanets. Further, Darwin will also achieve hitherto unprecedented spatial resolution in the infrared wavelength region. The detection and study of terrestrial exoplanets promises to usher in a new era in science and will affect a broad spectrum of disciplines. The time line for the implementation of Darwin is now likely to be in the order of 10 years. This leads us to the possibility of addressing one of mankind's most fundamental questions already in the second decade of the 21st century.
Journal of the Optical Society of America a Optics Image Science and Vision, Jul 1, 2009
Soot particles can be formed in hydrocarbon flames as a result of an inefficient combustion proce... more Soot particles can be formed in hydrocarbon flames as a result of an inefficient combustion process. The particles are near-spherical, and at later stages in the soot growth process, they form chainlike sparse aggregates. When applying optical diagnostic methods, this aggregation influences the evaluation of soot properties based on assumptions of isolated particles. In this paper an efficient and accurate method for calculating scattering of light from these structures is presented. The method can handle aggregates with several hundred subparticles with no restrictions on shape, internal structure, or coagulation of the subparticles. The basic idea is that the induced dipole moments of the subparticles are determined from the solution of a quasi-static problem that can be solved with high accuracy by, e.g., the finite element method.
ABSTRACT Thurston obtained a classification of individual surface homeomorphisms via the dynamics... more ABSTRACT Thurston obtained a classification of individual surface homeomorphisms via the dynamics of the corresponding mapping class elements on Teichm\"uller space. In this paper we present certain extended versions of this, first, to random products of homeomorphisms and second, to holomorphic self-maps of Teichm\"uller spaces.
ABSTRACT The book under review contains proceedings of contributions presented at two co-organize... more ABSTRACT The book under review contains proceedings of contributions presented at two co-organized conferences on mathematical aspects of modeling wave phenomena, and on radio science and communications. Each contribution is written as a standard scientific paper of about ten pages which allows the authors to treat the problems in full detail. The subjects covered a variety of areas related to classical and quantum waves, linear and non-linear waves, including wave propagation modeling, inverse scattering modeling and wave imaging, and signal processing and analysis. In this sense, the authors study wave phenomena in contexts of different fields of application such as acoustics, electromagnetic waves, and quantum fluctuations and correlations in wave-guides.
Direct and inverse scattering from dispersive media are studied in the time domain. The media are... more Direct and inverse scattering from dispersive media are studied in the time domain. The media are one-dimensional and homogeneous but can be im- pedance mismatched to the surrounding media. A time domain method,is introduced where the reflection and transmission kernels are obtained from Volterra equations of the second kind. Numerical examples are given based upon both synthetic and measured
ABSTRACT The fundamental limits of the power efficiency of an antenna are explored. The antenna i... more ABSTRACT The fundamental limits of the power efficiency of an antenna are explored. The antenna is confined in a sphere and all of the currents are assumed to run in a material with a conductivity that is a function of the radial coordinate. The analysis is based on the expansion of the electromagnetic fields in terms of vector spherical harmonics. Explicit expressions for the limits of efficiency are derived for different types of antennas.
We have experimentally demonstrated a decoy-state quantum key distribution scheme (QKD) with a he... more We have experimentally demonstrated a decoy-state quantum key distribution scheme (QKD) with a heralded single-photon source based on parametric down-conversion. What we used is a one-way BB84 protocol with a four-state and one-detector phase-coding scheme.
Journal of Physics a Mathematical and General, Nov 1, 2002
We propose an extension of quantum key distribution based on encoding the key into quNits, i.e. q... more We propose an extension of quantum key distribution based on encoding the key into quNits, i.e. quantum states in an N-dimensional Hilbert space. We estimate both the mutual information between the legitimate parties and the eavesdropper, and the error rate, as a function of the dimension of the Hilbert space. We derive the information gained by an eavesdropper using optimal incoherent attacks and an upper bound on the legitimate party error rate that ensures unconditional security when the eavesdropper uses finite coherent eavesdropping attacks. We also consider realistic systems where we assume that the detector dark count probability is not negligible.
Darwin is a cornerstone mission of the Horizons 2000+ program of the European Space Agency. It ha... more Darwin is a cornerstone mission of the Horizons 2000+ program of the European Space Agency. It has the express purpose of carrying out the first direct search for terrestrial exoplanets. Further, Darwin will also achieve hitherto unprecedented spatial resolution in the infrared wavelength region. The detection and study of terrestrial exoplanets promises to usher in a new era in science and will affect a broad spectrum of disciplines. The time line for the implementation of Darwin is now likely to be in the order of 10 years. This leads us to the possibility of addressing one of mankind's most fundamental questions already in the second decade of the 21st century.
Journal of the Optical Society of America a Optics Image Science and Vision, Jul 1, 2009
Soot particles can be formed in hydrocarbon flames as a result of an inefficient combustion proce... more Soot particles can be formed in hydrocarbon flames as a result of an inefficient combustion process. The particles are near-spherical, and at later stages in the soot growth process, they form chainlike sparse aggregates. When applying optical diagnostic methods, this aggregation influences the evaluation of soot properties based on assumptions of isolated particles. In this paper an efficient and accurate method for calculating scattering of light from these structures is presented. The method can handle aggregates with several hundred subparticles with no restrictions on shape, internal structure, or coagulation of the subparticles. The basic idea is that the induced dipole moments of the subparticles are determined from the solution of a quasi-static problem that can be solved with high accuracy by, e.g., the finite element method.
ABSTRACT Thurston obtained a classification of individual surface homeomorphisms via the dynamics... more ABSTRACT Thurston obtained a classification of individual surface homeomorphisms via the dynamics of the corresponding mapping class elements on Teichm\"uller space. In this paper we present certain extended versions of this, first, to random products of homeomorphisms and second, to holomorphic self-maps of Teichm\"uller spaces.
ABSTRACT The book under review contains proceedings of contributions presented at two co-organize... more ABSTRACT The book under review contains proceedings of contributions presented at two co-organized conferences on mathematical aspects of modeling wave phenomena, and on radio science and communications. Each contribution is written as a standard scientific paper of about ten pages which allows the authors to treat the problems in full detail. The subjects covered a variety of areas related to classical and quantum waves, linear and non-linear waves, including wave propagation modeling, inverse scattering modeling and wave imaging, and signal processing and analysis. In this sense, the authors study wave phenomena in contexts of different fields of application such as acoustics, electromagnetic waves, and quantum fluctuations and correlations in wave-guides.
Direct and inverse scattering from dispersive media are studied in the time domain. The media are... more Direct and inverse scattering from dispersive media are studied in the time domain. The media are one-dimensional and homogeneous but can be im- pedance mismatched to the surrounding media. A time domain method,is introduced where the reflection and transmission kernels are obtained from Volterra equations of the second kind. Numerical examples are given based upon both synthetic and measured
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Papers by Anders Karlsson