2,529 research outputs found
Efficient multiqubit entanglement via a spin-bus
We propose an experimentally feasible architecture with controllable
long-range couplings built up from local exchange interactions. The scheme
consists of a spin-bus, with strong, always-on interactions, coupled
dynamically to external qubits of the Loss and DiVincenzo type. Long-range
correlations are enabled by a spectral gap occurring in a finite-size chain.
The bus can also form a hub for multiqubit entangling operations. We show how
multiqubit gates may be used to efficiently generate -states (an important
entanglement resource). The spin-bus therefore provides a route for scalable
solid-state quantum computation, using currently available experimental
resources.Comment: Published versio
Caracterização de raças de Pyrenophora tritici-repentis, agente etiológico da mancha amarela do trigo, no sul do Brasil.
bitstream/CNPT-2010/40333/1/p-bp60.pd
Can we always get the entanglement entropy from the Kadanoff-Baym equations? The case of the T-matrix approximation
We study the time-dependent transmission of entanglement entropy through an
out-of-equilibrium model interacting device in a quantum transport set-up. The
dynamics is performed via the Kadanoff-Baym equations within many-body
perturbation theory. The double occupancy , needed to determine the entanglement entropy, is obtained from
the equations of motion of the single-particle Green's function. A remarkable
result of our calculations is that can become negative, thus not permitting to evaluate the
entanglement entropy. This is a shortcoming of approximate, and yet conserving,
many-body self-energies. Among the tested perturbation schemes, the -matrix
approximation stands out for two reasons: it compares well to exact results in
the low density regime and it always provides a non-negative . For the second part of this statement, we
give an analytical proof. Finally, the transmission of entanglement across the
device is diminished by interactions but can be amplified by a current flowing
through the system.Comment: 6 pages, 6 figure
Global control and fast solid-state donor electron spin quantum computing
We propose a scheme for quantum information processing based on donor
electron spins in semiconductors, with an architecture complementary to the
original Kane proposal. We show that a naive implementation of electron spin
qubits provides only modest improvement over the Kane scheme, however through
the introduction of global gate control we are able to take full advantage of
the fast electron evolution timescales. We estimate that the latent clock speed
is 100-1000 times that of the nuclear spin quantum computer with the ratio
approaching the level.Comment: 9 pages, 9 figure
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