72 research outputs found
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
Single photon quantum non-demolition in the presence of inhomogeneous broadening
Electromagnetically induced transparency (EIT) has been often proposed for
generating nonlinear optical effects at the single photon level; in particular,
as a means to effect a quantum non-demolition measurement of a single photon
field. Previous treatments have usually considered homogeneously broadened
samples, but realisations in any medium will have to contend with inhomogeneous
broadening. Here we reappraise an earlier scheme [Munro \textit{et al.} Phys.
Rev. A \textbf{71}, 033819 (2005)] with respect to inhomogeneities and show an
alternative mode of operation that is preferred in an inhomogeneous
environment. We further show the implications of these results on a potential
implementation in diamond containing nitrogen-vacancy colour centres. Our
modelling shows that single mode waveguide structures of length in single-crystal diamond containing a dilute ensemble of NV
of only 200 centres are sufficient for quantum non-demolition measurements
using EIT-based weak nonlinear interactions.Comment: 21 pages, 9 figures (some in colour) at low resolution for arXiv
purpose
Spatial adiabatic passage in a realistic triple well structure
We investigate the evolution of an electron undergoing coherent tunneling via
adiabatic passage (CTAP) using the solution of the one-dimensional Schroedinger
equation in both space and time for a triple well potential. We find the
eigenspectrum and complete time evolution for a range of different pulsing
schemes. This also provides an example of a system that can be described with
the tools from both quantum optics and condensed matter. We find that while the
quantum optics description of the process captures most of the key physics,
there are important effects that can only be correctly described by a more
complete representation. This is an important point for applications such as
quantum information processing or quantum control where it is common practice
to use a reduced state space formulation of the quantum system in question.Comment: 10 pages, 12 figures (color online) - Published Versio
High speed quantum gates with cavity quantum electrodynamics
Cavity quantum electrodynamic schemes for quantum gates are amongst the
earliest quantum computing proposals. Despite continued progress, and the
dramatic recent demonstration of photon blockade, there are still issues with
optimal coupling and gate operation involving high-quality cavities. Here we
show dynamic control techniques that allow scalable cavity-QED based quantum
gates, that use the full bandwidth of the cavities. When applied to quantum
gates, these techniques allow an order of magnitude increase in operating
speed, and two orders of magnitude reduction in cavity Q, over passive
cavity-QED architectures. Our methods exploit Stark shift based Q-switching,
and are ideally suited to solid-state integrated optical approaches to quantum
computing.Comment: 4 pages, 3 figures, minor revision
An electrostatically defined serial triple quantum dot charged with few electrons
A serial triple quantum dot (TQD) electrostatically defined in a GaAs/AlGaAs
heterostructure is characterized by using a nearby quantum point contact as
charge detector. Ground state stability diagrams demonstrate control in the
regime of few electrons charging the TQD. An electrostatic model is developed
to determine the ground state charge configurations of the TQD. Numerical
calculations are compared with experimental results. In addition, the tunneling
conductance through all three quantum dots in series is studied. Quantum
cellular automata processes are identified, which are where charge
reconfiguration between two dots occurs in response to the addition of an
electron in the third dot.Comment: 12 pages, 9 figure
Evaluation of Skylab (EREP) data for forest and rangeland surveys
The author has identified the following significant results. Four widely separated sites (near Augusta, Georgia; Lead, South Dakota; Manitou, Colorado; and Redding, California) were selected as typical sites for forest inventory, forest stress, rangeland inventory, and atmospheric and solar measurements, respectively. Results indicated that Skylab S190B color photography is good for classification of Level 1 forest and nonforest land (90 to 95 percent correct) and could be used as a data base for sampling by small and medium scale photography using regression techniques. The accuracy of Level 2 forest and nonforest classes, however, varied from fair to poor. Results of plant community classification tests indicate that both visual and microdensitometric techniques can separate deciduous, conifirous, and grassland classes to the region level in the Ecoclass hierarchical classification system. There was no consistency in classifying tree categories at the series level by visual photointerpretation. The relationship between ground measurements and large scale photo measurements of foliar cover had a correlation coefficient of greater than 0.75. Some of the relationships, however, were site dependent
Non-Abelian geometrical control of a qubit in an NV center in diamond
We propose an approach for an optical qubit rotation in the negatively
charged nitrogen-vacancy (NV) center in diamond. The qubit is encoded in the
ground degenerate states at the relatively low temperature limit. The basic
idea of the rotation procedure is the non-Abelian geometric phase in an
adiabatic passage, which is produced by the nonadiabatic transition between the
two degenerate dark states. The feasibility is based on the success of modeling
the NV center as an excited-doublet four-level atom.Comment: 5 page
Identifying a Two-State Hamiltonian in the Presence of Decoherence
Mapping the system evolution of a two-state system allows the determination
of the effective system Hamiltonian directly. We show how this can be achieved
even if the system is decohering appreciably over the observation time. A
method to include various decoherence models is given and the limits of this
technique are explored. This technique is applicable both to the problem of
calibrating a control Hamiltonian for quantum computing applications and for
precision experiments in two-state quantum systems. For simple models of
decoherence, this method can be applied even when the decoherence time is
comparable to the oscillation period of the system.Comment: 8 pages, 6 figures. Minor corrections, published versio
Modeling Single Electron Transfer in Si:P Double Quantum Dots
Solid-state systems such as P donors in Si have considerable potential for
realization of scalable quantum computation. Recent experimental work in this
area has focused on implanted Si:P double quantum dots (DQDs) that represent a
preliminary step towards the realization of single donor charge-based qubits.
This paper focuses on the techniques involved in analyzing the charge transfer
within such DQD devices and understanding the impact of fabrication parameters
on this process. We show that misalignment between the buried dots and surface
gates affects the charge transfer behavior and identify some of the challenges
posed by reducing the size of the metallic dot to the few donor regime.Comment: 11 pages, 7 figures, submitted to Nanotechnolog
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