222 research outputs found
Delocalized Entanglement of Atoms in optical Lattices
We show how to detect and quantify entanglement of atoms in optical lattices
in terms of correlations functions of the momentum distribution. These
distributions can be measured directly in the experiments. We introduce two
kinds of entanglement measures related to the position and the spin of the
atoms
Quantum simulators, continuous-time automata, and translationally invariant systems
The general problem of finding the ground state energy of lattice
Hamiltonians is known to be very hard, even for a quantum computer. We show
here that this is the case even for translationally invariant systems. We also
show that a quantum computer can be built in a 1D chain with a fixed,
translationally invariant Hamitonian consisting of nearest--neighbor
interactions only. The result of the computation is obtained after a prescribed
time with high probability.Comment: partily rewritten and important references include
Counterexample to an additivity conjecture for output purity of quantum channels
A conjecture arising naturally in the investigation of additivity of
classical information capacity of quantum channels states that the maximal
purity of outputs from a quantum channel, as measured by the p-norm, should be
multiplicative with respect to the tensor product of channels. We disprove this
conjecture for p>4.79. The same example (with p=infinity) also disproves a
conjecture for the multiplicativity of the injective norm of Hilbert space
tensor products.Comment: 3 pages, 3 figures, revte
Quantum state engineering, purification, and number resolved photon detection with high finesse optical cavities
We propose and analyze a multi-functional setup consisting of high finesse
optical cavities, beam splitters, and phase shifters. The basic scheme projects
arbitrary photonic two-mode input states onto the subspace spanned by the
product of Fock states |n>|n> with n=0,1,2,.... This protocol does not only
provide the possibility to conditionally generate highly entangled photon
number states as resource for quantum information protocols but also allows one
to test and hence purify this type of quantum states in a communication
scenario, which is of great practical importance. The scheme is especially
attractive as a generalization to many modes allows for distribution and
purification of entanglement in networks. In an alternative working mode, the
setup allows of quantum non demolition number resolved photodetection in the
optical domain.Comment: 14 pages, 10 figure
Ensemble Quantum Computation with atoms in periodic potentials
We show how to perform universal quantum computation with atoms confined in
optical lattices which works both in the presence of defects and without
individual addressing. The method is based on using the defects in the lattice,
wherever they are, both to ``mark'' different copies on which ensemble quantum
computation is carried out and to define pointer atoms which perform the
quantum gates. We also show how to overcome the problem of scalability on this
system
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