1,324 research outputs found
Measurable quantum geometric phase from a rotating single spin
We demonstrate that the internal magnetic states of a single nitrogen-vacancy
defect, within a rotating diamond crystal, acquire geometric phases. The
geometric phase shift is manifest as a relative phase between components of a
superposition of magnetic substates. We demonstrate that under reasonable
experimental conditions a phase shift of up to four radians could be measured.
Such a measurement of the accumulation of a geometric phase, due to macroscopic
rotation, would be the first for a single atom-scale quantum system.Comment: 5 pages, 2 figures: Accepted for publication in Physical Review
Letter
Single atom-scale diamond defect allows large Aharonov-Casher phase
We propose an experiment that would produce and measure a large
Aharonov-Casher (A-C) phase in a solid-state system under macroscopic motion. A
diamond crystal is mounted on a spinning disk in the presence of a uniform
electric field. Internal magnetic states of a single NV defect, replacing
interferometer trajectories, are coherently controlled by microwave pulses. The
A-C phase shift is manifested as a relative phase, of up to 17 radians, between
components of a superposition of magnetic substates, which is two orders of
magnitude larger than that measured in any other atom-scale quantum system.Comment: 5 pages, 2 figure
Quantum Error Correction on Linear Nearest Neighbor Qubit Arrays
A minimal depth quantum circuit implementing 5-qubit quantum error correction
in a manner optimized for a linear nearest neighbor architecture is described.
The canonical decomposition is used to construct fast and simple gates that
incorporate the necessary swap operations. Simulations of the circuit's
performance when subjected to discrete and continuous errors are presented. The
relationship between the error rate of a physical qubit and that of a logical
qubit is investigated with emphasis on determining the concatenated error
correction threshold.Comment: 4 pages, 5 figure
Quantum information transport to multiple receivers
The importance of transporting quantum information and entanglement with high
fidelity cannot be overemphasized. We present a scheme based on adiabatic
passage that allows for transportation of a qubit, operator measurements and
entanglement, using a 1-D array of quantum sites with a single sender (Alice)
and multiple receivers (Bobs). Alice need not know which Bob is the receiver,
and if several Bobs try to receive the signal, they obtain a superposition
state which can be used to realize two-qubit operator measurements for the
generation of maximally entangled states.Comment: Modified in view of referee's comments, new author added, natural
scheme for operator measurements identified, hence W state preparation
replaced with GHZ state preparation via operator measurements. 4 pages, 3
figure
Matterwave Transport Without Transit
Classically it is impossible to have transport without transit, i.e., if the
points one, two and three lie sequentially along a path then an object moving
from one to three must, at some point in time, be located at two. However, for
a quantum particle in a three-well system it is possible to transport the
particle between wells one and three such that the probability of finding it at
any time in the classically accessible state in well two is negligible. We
consider theoretically the analogous scenario for a Bose-Einstein condensate
confined within a three well system. In particular, we predict the adiabatic
transportation of an interacting Bose-Einstein condensate of 2000 Li atoms from
well one to well three without transiting the allowed intermediate region. To
an observer of this macroscopic quantum effect it would appear that, over a
timescale of the order of one second, the condensate had transported, but not
transited, a macroscopic distance of 20 microns between wells one and three.Comment: 6 pages, 4 figure
Loss of Spin Entanglement For Accelerated Electrons in Electric and Magnetic Fields
Using an open quantum system we calculate the time dependence of the
concurrence between two maximally entangled electron spins with one accelerated
uniformly in the presence of a constant magnetic field and the other at rest
and isolated from fields. We find at high Rindler temperature the proper time
for the entanglement to be extinguished is proportional to the inverse of the
acceleration cubed.Comment: 10 pages, 4 figures, appendix and other discussion added, fixed some
typographical errors and some references were correcte
Nanoscale magnetometry through quantum control of nitrogen-vacancy centres in rotationally diffusing nanodiamonds
The confluence of quantum physics and biology is driving a new generation of
quantum-based sensing and imaging technology capable of harnessing the power of
quantum effects to provide tools to understand the fundamental processes of
life. One of the most promising systems in this area is the nitrogen-vacancy
centre in diamond - a natural spin qubit which remarkably has all the right
attributes for nanoscale sensing in ambient biological conditions. Typically
the nitrogen-vacancy qubits are fixed in tightly controlled/isolated
experimental conditions. In this work quantum control principles of
nitrogen-vacancy magnetometry are developed for a randomly diffusing diamond
nanocrystal. We find that the accumulation of geometric phases, due to the
rotation of the nanodiamond plays a crucial role in the application of a
diffusing nanodiamond as a bio-label and magnetometer. Specifically, we show
that a freely diffusing nanodiamond can offer real-time information about local
magnetic fields and its own rotational behaviour, beyond continuous optically
detected magnetic resonance monitoring, in parallel with operation as a
fluorescent biomarker.Comment: 9 pages, with 5 figure
Optically induced spin to charge transduction in donor spin read-out
The proposed read-out configuration D+D- for the Kane Si:P
architecture[Nature 393, 133 (1998)] depends on spin-dependent electron
tunneling between donors, induced adiabatically by surface gates. However,
previous work has shown that since the doubly occupied donor state is so
shallow the dwell-time of the read-out state is less than the required time for
measurement using a single electron transistor (SET). We propose and analyse
single-spin read-out using optically induced spin to charge transduction, and
show that the top gate biases, required for qubit selection, are significantly
less than those demanded by the Kane scheme, thereby increasing the D+D-
lifetime. Implications for singlet-triplet discrimination for electron spin
qubits are also discussed.Comment: 8 pages, 10 figures; added reference, corrected typ
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