6 research outputs found
Competition between finite-size effects and dipole-dipole interactions in few-atom systems
In this paper, we study the competition between finite-size effects (i.e.
discernibility of particles) and dipole-dipole interactions in few-atom systems
coupled to the electromagnetic field in vacuum. We consider two hallmarks of
cooperative effects, superradiance and subradiance, and compute for each the
rate of energy radiated by the atoms and the coherence of the atomic state
during the time evolution. We adopt a statistical approach in order to extract
the typical behavior of the atomic dynamics and average over random atomic
distributions in spherical containers with prescribed with the
radiation wavenumber and the average interatomic distance. Our approach
allows us to highlight the tradeoff between finite-size effects and
dipole-dipole interactions in superradiance/subradiance. In particular, we show
the existence of an optimal value of for which the superradiant
intensity and coherence pulses are the less affected by dephasing effects
induced by dipole-dipole interactions and finite-size effects.Comment: 11 pages, 11 figure
Cooperative spontaneous emission from indistinguishable atoms in arbitrary motional quantum states
We investigate superradiance and subradiance of indistinguishable atoms with
quantized motional states, starting with an initial total state that factorizes
over the internal and external degrees of freedom of the atoms. Due to the
permutational symmetry of the motional state, the cooperative spontaneous
emission, governed by a recently derived master equation [F. Damanet et al.,
Phys. Rev. A 93, 022124 (2016)], depends only on two decay rates and
and a single parameter describing the
dipole-dipole shifts. We solve the dynamics exactly for atoms,
numerically for up to 30 atoms, and obtain the large--limit by amean-field
approach. We find that there is a critical difference that
depends on beyond which superradiance is lost. We show that exact
non-trivial dark states (i.e. states other than the ground state with vanishing
spontaneous emission) only exist for , and that those states
(dark when ) are subradiant when .Comment: 14 pages, 8 figure
Anticoherence of spin states with point group symmetries
We investigate multiqubit permutation-symmetric states with maximal entropy
of entanglement. Such states can be viewed as particular spin states, namely
anticoherent spin states. Using the Majorana representation of spin states in
terms of points on the unit sphere, we analyze the consequences of a
point-group symmetry in their arrangement on the quantum properties of the
corresponding state. We focus on the identification of anticoherent states (for
which all reduced density matrices in the symmetric subspace are maximally
mixed) associated with point-group symmetric sets of points. We provide three
different characterizations of anticoherence, and establish a link between
point symmetries, anticoherence and classes of states equivalent through
stochastic local operations with classical communication (SLOCC). We then
investigate in detail the case of small numbers of qubits, and construct
infinite families of anticoherent states with point-group symmetry of their
Majorana points, showing that anticoherent states do exist to arbitrary order.Comment: 15 pages, 5 figure