243 research outputs found
Transmission of ultracold atoms through a micromaser: detuning effects
The transmission probability of ultracold atoms through a micromaser is
studied in the general case where a detuning between the cavity mode and the
atomic transition frequencies is present. We generalize previous results
established in the resonant case (zero detuning) for the mesa mode function. In
particular, it is shown that the velocity selection of cold atoms passing
through the micromaser can be very easily tuned and enhanced using a
non-resonant field inside the cavity. Also, the transmission probability
exhibits with respect to the detuning very sharp resonances that could define
single cavity devices for high accuracy metrology purposes (atomic clocks).Comment: 5 pages, 7 figure
Reply to 'Comment on "Detuning effects in the one-photon mazer" '
We refute in this Reply the criticisms made by M. Abdel-Aty [Phys. Rev. A 70,
047801 (2004)]. We show that none of them are founded and we demonstrate very
explicitly what is wrong in the arguments developed by this author.Comment: 5 pages, 2 figure
Multiqubit symmetric states with maximally mixed one-qubit reductions
We present a comprehensive study of maximally entangled symmetric states of
arbitrary numbers of qubits in the sense of the maximal mixedness of the
one-qubit reduced density operator. A general criterion is provided to easily
identify whether given symmetric states are maximally entangled in that respect
or not. We show that these maximally entangled symmetric (MES) states are the
only symmetric states for which the expectation value of the associated
collective spin of the system vanishes, as well as in corollary the dipole
moment of the Husimi function. We establish the link between this kind of
maximal entanglement, the anticoherence properties of spin states, and the
degree of polarization of light fields. We analyze the relationship between the
MES states and the classes of states equivalent through stochastic local
operations with classical communication (SLOCC). We provide a nonexistence
criterion of MES states within SLOCC classes of qubit states and show in
particular that the symmetric Dicke state SLOCC classes never contain such MES
states, with the only exception of the balanced Dicke state class for even
numbers of qubits. The 4-qubit system is analyzed exhaustively and all MES
states of this system are identified and characterized. Finally the
entanglement content of MES states is analyzed with respect to the geometric
and barycentric measures of entanglement, as well as to the generalized
N-tangle. We show that the geometric entanglement of MES states is ensured to
be larger than or equal to 1/2, but also that MES states are not in general the
symmetric states that maximize the investigated entanglement measures.Comment: 12 pages, 4 figure
Entanglement robustness against particle loss in multiqubit systems
When some of the parties of a multipartite entangled pure state are lost, the
question arises whether the residual mixed state is also entangled, in which
case the initial entangled pure state is said to be robust against particle
loss. In this paper, we investigate this entanglement robustness for -qubit
pure states. We identify exhaustively all entangled states that are fragile,
i.e., not robust, with respect to the loss of any single qubit of the system.
We also study the entanglement robustness properties of symmetric states and
put these properties in the perspective of the classification of states with
respect to stochastic local operations assisted with classic communication
(SLOCC classification).Comment: Published version, 7 page
Scattering theory of walking droplets in the presence of obstacles
We aim to describe a droplet bouncing on a vibrating bath using a simple and
highly versatile model inspired from quantum mechanics. Close to the Faraday
instability, a long-lived surface wave is created at each bounce, which serves
as a pilot wave for the droplet. This leads to so called walking droplets or
walkers. Since the seminal experiment by {\it Couder et al} [Phys. Rev. Lett.
{\bf 97}, 154101 (2006)] there have been many attempts to accurately reproduce
the experimental results. We propose to describe the trajectories of a walker
using a Green function approach. The Green function is related to the Helmholtz
equation with Neumann boundary conditions on the obstacle(s) and outgoing
boundary conditions at infinity. For a single-slit geometry our model is
exactly solvable and reproduces some general features observed experimentally.
It stands for a promising candidate to account for the presence of arbitrary
boundaries in the walker's dynamics.Comment: 17 pages, 5 figure
1s2s2p23d 6L - 1s2p33d 6D, L=F, D, P Transitions in O IV, F V and Ne VI
We present observations of VUV transitions between doubly excited sextet
states in O IV, F V and Ne VI. Spectra were produced by collisions of an O+
beam with a solid carbon target. We also studied spectra obtained previously of
F V and Ne VI. Some observed lines were assigned to the 1s2s2p23d 6L - 1s2p33d
6D, L=F, D, P electric-dipole transitions, and compared with results of MCHF
(with QED and higher-order corrections) and MCDF calculations. 42 new lines
have been identified. Highly excited sextet states in five-electron ions
provide a new form of energy storage and are possible candidates for VUV and
x-ray lasers.Comment: 11 pages, 12 figure
Permutationally invariant processes in arbitrary multiqudit systems
We establish the theoretical framework for an exact description of the open system dynamics of permutationally invariant (PI) states in arbitrary N-qudit systems when this dynamics preserves the PI symmetry over time. Thanks to Schur-Weyl duality powerful formalism, we identify an orthonormal operator basis in the PI operator subspace of the Liouville space onto which the master equation can be projected and we provide the exact expansion coefficients in the most general case. Our approach does not require to compute the Schur transform as it operates directly within the restricted operator subspace, whose dimension only scales polynomially with the number of qudits. We introduce the concept of -symbol matrix that proves to be very useful in this context
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