14,336 research outputs found
Long-range and selective coupler for superconducting flux qubits
We propose a qubit-qubit coupling scheme for superconducting flux quantum
bits (qubits), where a quantized Josephson junction resonator and microwave
irradiation are utilized. The junction is used as a tunable inductance
controlled by changing the bias current flowing through the junction, and thus
the circuit works as a tunable resonator. This enables us to make any qubits
interact with the resonator. Entanglement between two of many qubits whose
level splittings satisfy some conditions, is formed by microwave irradiation
causing a two-photon Rabi oscillation. Since the size of the resonator can be
as large as sub-millimeters and qubits interact with it via mutual inductance,
our scheme makes it possible to construct a quantum gate involving remote
qubitsComment: 8 pages, 4 figure
Ising and Spin orders in Iron-based Superconductors
Motivated by recent neutron scattering experiments, we study the ordering of
spins in the iron-based superconductors La(O_{1-x}F_x)FeAs, assuming them in
proximity to a Mott insulator in the phase diagram. The ground state of the
parent system with x = 0 is a spin density wave with ordering wave vector Q =
(0, \pi) or (\pi, 0). Upon raising the temperature, we find the system to
restore SU(2) symmetry, while an Ising symmetry remains broken, explaining the
experimentally observed lattice distortion to a monoclinic crystal structure.
Upon further temperature increase, the spins finally disorder at a second
transition. The phase transition driven by doping with charge carriers
similarly splits into an O(3) transition, and an Ising transition with z = 3 at
larger doping.Comment: 4.5 pages, 2 figure
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