777 research outputs found
Netherlandic Treasures
"Netherlandic Treasures" is a selection of some of the most notable Dutch and Flemish printed books, manuscripts, and maps held by the University of Michigan Library: the earliest, most beautiful, rarest, or the most unusual. A special point has been made to tell how and why these materials have been acquired over the years.http://deepblue.lib.umich.edu/bitstream/2027.42/120264/1/Netherlandic_treasures_14.pd
Geometric quantum gates robust against stochastic control errors
We analyze a scheme for quantum computation where quantum gates can be
continuously changed from standard dynamic gates to purely geometric ones.
These gates are enacted by controlling a set of parameters that are subject to
unwanted stochastic fluctuations. This kind of noise results in a departure
from the ideal case that can be quantified by a gate fidelity. We find that the
maximum of this fidelity corresponds to quantum gates with a vanishing
dynamical phase.Comment: 4 pager
Quantum state reconstruction with imperfect rotations on an inhomogeneously broadened ensemble of qubits
We present a method for performing quantum state reconstruction on qubits and
qubit registers in the presence of decoherence and inhomogeneous broadening.
The method assumes only rudimentary single qubit rotations as well as knowledge
of decoherence and loss mechanisms. We show that full state reconstruction is
possible even in the case where single qubit rotations may only be performed
imperfectly. Furthermore we show that for ensemble quantum computing proposals,
quantum state reconstruction is possible even if the ensemble experiences
inhomogeneous broadening and if only imperfect qubit manipulations are
available during state preparation and reconstruction.Comment: 6 pages, 5 figure
Protected Rabi oscillation induced by natural interactions among physical qubits
For a system composed of nine qubits, we show that natural interactions among
the qubits induce the time evolution that can be regarded, at discrete times,
as the Rabi oscillation of a logical qubit. Neither fine tuning of the
parameters nor switching of the interactions is necessary. Although
straightforward application of quantum error correction fails, we propose a
protocol by which the logical Rabi oscillation is protected against all
single-qubit errors. The present method thus opens a simple and realistic way
of protecting the unitary time evolution against noise.Comment: In this revised manuscript, new sections V, VI, VII and new
appendices A, B, C have been added to give detailed discussions. 13 pages, 4
figure
Experimental implementation of high-fidelity unconventional geometric quantum gates using NMR interferometer
Following a key idea of unconventional geometric quantum computation
developed earlier [Phys. Rev. Lett. 91, 197902 (2003)], here we propose a more
general scheme in such an intriguing way: , where and are respectively the dynamic and
geometric phases accumulated in the quantum gate operation, with as a
constant and being dependent only on the geometric feature of the
operation. More arrestingly, we demonstrate the first experiment to implement a
universal set of such kind of generalized unconventional geometric quantum
gates with high fidelity in an NMR system.Comment: 4 pages, 3 figure
High fidelity measurement of singlet-triplet states in a quantum dot
We demonstrate experimentally a read-out method that distinguishes between
two-electron spin states in a quantum dot. This scheme combines the advantages
of the two existing mechanisms for spin-to-charge conversion with single-shot
charge detection: a large difference in energy between the two states and a
large difference in tunnel rate between the states and a reservoir. As a
result, a spin measurement fidelity of 97% was achieved, which is much higher
than previously reported fidelities.Comment: 4 pages, 1 figur
Nanoscale Electrostatic Control of Oxide Interfaces
We develop a robust and versatile platform to define nanostructures at oxide
interfaces via patterned top gates. Using LaAlO/SrTiO as a model
system, we demonstrate controllable electrostatic confinement of electrons to
nanoscale regions in the conducting interface. The excellent gate response,
ultra-low leakage currents, and long term stability of these gates allow us to
perform a variety of studies in different device geometries from room
temperature down to 50 mK. Using a split-gate device we demonstrate the
formation of a narrow conducting channel whose width can be controllably
reduced via the application of appropriate gate voltages. We also show that a
single narrow gate can be used to induce locally a superconducting to
insulating transition. Furthermore, in the superconducting regime we see
indications of a gate-voltage controlled Josephson effect.Comment: Version after peer review; includes additional data on
superconductivit
Cooperative effects in Josephson junctions in a cavity in the strong coupling regime
We analyze the behavior of systems of two and three qubits made by Josephson
junctions, treated in the two level approximation, driven by a radiation mode
in a cavity. The regime we consider is a strong coupling one recently
experimentally reached for a single junction. Rabi oscillations are obtained
with the frequency proportional to integer order Bessel functions in the limit
of a large photon number, similarly to the case of the single qubit. A
selection rule is derived for the appearance of Rabi oscillations. A quantum
amplifier built with a large number of Josephson junctions in a cavity in the
strong coupling regime is also described.Comment: 9 pages, no figures. Version accepted for publication in Physical
Review
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