Searcharxiv⌕ Search

arXiv subjects

Uffe V. Poulsen

Publications and source records attributed to Uffe V. Poulsen.

10 recordsLinked to original sources
arXiv2012

Directional emission of single photons from small atomic samples

We provide a formalism to describe deterministic emission of single photons with tailored spatial and temporal profiles from a regular array of multi-level atoms. We assume that a single collective excitation is initially shared by all the atoms in a metastable atomic state, and that this state is coupled by a classical laser field to an optically excited state which rapidly decays to the ground atomic state. Our model accounts for the different field polarization components via re-absorption and emission of light by the Zeeman manifold of optically excited states.

quant-ph↗
arXiv2009

Correlations in local measurements on a quantum state, and complementarity as an explanation of nonclassicality

We consider the classical correlations that two observers can extract by measurements on a bipartite quantum state, and we discuss how they are related to the quantum mutual information of the state. We show with several examples how complementarity gives rise to a gap between the quantum and the classical correlations, and we relate our quantitative finding to the so-called classical correlation locked in a quantum state. We derive upper bounds for the sum of classical correlation obtained by measurements in different mutually unbiased bases and we show that the complementarity gap is also present in the deterministic quantum computation with one quantum bit.

quant-ph↗
arXiv2008

Atomic quantum superposition state generation via optical probing

We analyze the performance of a protocol to prepare an atomic ensemble in a superposition of two macroscopically distinguishable states. The protocol relies on conditional measurements performed on a light field, which interacts with the atoms inside an optical cavity prior to detection, and we investigate cavity enhanced probing with continuous beams of both coherent and squeezed light. The stochastic master equations used in the analysis are expressed in terms of the Hamiltonian of the probed system and the interaction between the probed system and the probe field and are thus quite generally applicable.

quant-ph↗
arXiv2007

Pair correlated atoms with a twist

We present an analysis of the quantum state resulting from the dissociation of diatomic molecules prepared in a condensate vortex state. The many-body state preserves the rotational symmetry of the system in quantum correlated states by having two equally populated components with angular momentum adding to unity. A simple two-mode analysis and a full quantum field analysis is presented for the case of non-interacting atoms and weak depletion of the molecular condensate.

cond-mat.other↗
arXiv2005

Unitarity as preservation of entropy and entanglement in quantum systems

The logical structure of Quantum Mechanics (QM) and its relation to other fundamental principles of Nature has been for decades a subject of intensive research. In particular, the question whether the dynamical axiom of QM can be derived from other principles has been often considered. In this contribution, we show that unitary evolutions arise as a consequences of demanding preservation of entropy in the evolution of a single pure quantum system, and preservation of entanglement in the evolution of composite quantum systems.

quant-ph↗
arXiv2002

Scattering of atoms on a Bose-Einstein condensate

We study the scattering properties of a Bose-Einstein condensate held in a finite depth well when the incoming particles are identical to the ones in the condensate. We calculate phase shifts and corresponding transmission and reflection coefficients, and we show that the transmission times can be negative, i.e., the atomic wavepacket seemingly leaves the condensate before it arrives.

cond-mat↗
arXiv2001

A quantum beam splitter for atoms

An interferometric method is proposed to controllably split an atomic condensate in two spatial components with strongly reduced population fluctuations. All steps in our proposal are in current use in cold atom laboratories, and we show with a theoretical calculation that our proposal is very robust against imperfections of the interferometer.

cond-mat↗
arXiv2001

Positive P simulations of spin squeezing in a two-component Bose condensate

The collisional interaction in a Bose condensate represents a non-linearity which in analogy with non-linear optics gives rise to unique quantum features. In this paper we apply a Monte Carlo method based on the positive P pseudo-probability distribution from quantum optics to analyze the efficiency of spin squeezing by collisions in a two-component condensate. The squeezing can be controlled by choosing appropiate collision parameters or by manipulating the motional states of the two components.

quant-ph↗
arXiv2000

Squeezed Condensates

We analyse the atomic state obtained by photo-dissociation of a molecular Bose-Einstein-condensate. This process is equivalent to down-conversion in quantum optics where it is responsible for squeezing of the field amplitudes. Monte Carlo simulations derived from the Positive P description of the system, and approximate equations for second moments of the atomic field operators are introduced to describe the early stages of the process -- not amenable to the usual mean-field description.

cond-mat↗