143 research outputs found
The mean king's problem: Spin 1
We show how one can ascertain the values of four mutually complementary
observables of a spin-1 degree of freedom.Comment: to appear in Zeitschrift fur Naturforschung,3 page
Remarks on 2-q-bit states
We distinguish six classes of families of locally equivalent states in a
straightforward scheme for classifying all 2-q-bit states; four of the classes
consist of two subclasses each. The simple criteria that we stated recently for
checking a given state's positivity and separability are justified, and we
discuss some important properties of Lewenstein-Sanpera decompositions. An
upper bound is conjectured for the sum of the degree of separability of a
2-q-bit state and its concurrence.Comment: 17 page
Density Functional of a Two-Dimensional Gas of Dipolar Atoms: Thomas-Fermi-Dirac Treatment
We derive the density functional for the ground-state energy of a
two-dimensional, spin-polarized gas of neutral fermionic atoms with
magnetic-dipole interaction, in the Thomas-Fermi-Dirac approximation. For many
atoms in a harmonic trap, we give analytical solutions for the single-particle
spatial density and the ground-state energy, in dependence on the interaction
strength, and we discuss the weak-interaction limit that is relevant for
experiments. We then lift the restriction of full spin polarization and account
for a time-independent inhomogeneous external magnetic field. The field
strength necessary to ensure full spin polarization is derived.Comment: 12 pages, 4 figures, 1 tabl
Experimental proposal for symmetric minimal two-qubit state tomography
We propose an experiment that realizes a symmetric informationally complete
(SIC) probability-operator measurement (POM) in the four-dimensional Hilbert
space of a qubit pair. The qubit pair is carried by a single photon as a
polarization qubit and a path qubit. The implementation of the SIC POM is
accomplished with the means of linear optics. The experimental scheme exploits
a new approach to SIC POMs that uses a two-step process: a measurement with
full-rank outcomes, followed by a projective measurement on a basis that is
chosen in accordance with the result of the first measurement. The basis of the
first measurement and the four bases of the second measurements are pairwise
unbiased --- a hint at a possibly profound link between SIC POMs and mutually
unbiased bases.Comment: 4 pages, 2 figure
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