1,677 research outputs found
Scalability of Shor's algorithm with a limited set of rotation gates
Typical circuit implementations of Shor's algorithm involve controlled
rotation gates of magnitude where is the binary length of the
integer N to be factored. Such gates cannot be implemented exactly using
existing fault-tolerant techniques. Approximating a given controlled
rotation gate to within currently requires both
a number of qubits and number of fault-tolerant gates that grows polynomially
with . In this paper we show that this additional growth in space and time
complexity would severely limit the applicability of Shor's algorithm to large
integers. Consequently, we study in detail the effect of using only controlled
rotation gates with less than or equal to some . It is found
that integers up to length can be factored
without significant performance penalty implying that the cumbersome techniques
of fault-tolerant computation only need to be used to create controlled
rotation gates of magnitude if integers thousands of bits long are
desired factored. Explicit fault-tolerant constructions of such gates are also
discussed.Comment: Substantially revised version, twice as long as original. Two tables
converted into one 8-part figure, new section added on the construction of
arbitrary single-qubit rotations using only the fault-tolerant gate set.
Substantial additional discussion and explanatory figures added throughout.
(8 pages, 6 figures
The Trilinear Hamiltonian: A Zero Dimensional Model of Hawking Radiation from a Quantized Source
We investigate a quantum parametric amplifier with dynamical pump mode,
viewed as a zero-dimensional model of Hawking radiation from an evaporating
black hole. The conditions are derived under which the spectrum of particles
generated from vacuum fluctuations deviates from the thermal spectrum predicted
for the conventional parametric amplifier. We find that significant deviations
arise when the pump mode (black hole) has emitted nearly half of its initial
energy into the signal (Hawking radiation) and idler (in-falling particle)
modes. As a model of black hole dynamics, this finding lends support to the
view that late-time Hawking radiation contains information about the quantum
state of the black hole and is entangled with the black hole's quantum
gravitational degrees of freedom.Comment: 18 pages, 6 figures, Submitted to New Journal of Physics focus issue:
"Classical and Quantum Analogues for Gravitational Phenomena and Related
Effects
High-fidelity simulations of CdTe vapor deposition from a new bond-order potential-based molecular dynamics method
CdTe has been a special semiconductor for constructing the lowest-cost solar
cells and the CdTe-based Cd1-xZnxTe alloy has been the leading semiconductor
for radiation detection applications. The performance currently achieved for
the materials, however, is still far below the theoretical expectations. This
is because the property-limiting nanoscale defects that are easily formed
during the growth of CdTe crystals are difficult to explore in experiments.
Here we demonstrate the capability of a bond order potential-based molecular
dynamics method for predicting the crystalline growth of CdTe films during
vapor deposition simulations. Such a method may begin to enable defects
generated during vapor deposition of CdTe crystals to be accurately explored
The male of the species: a profile of men in nursing
Aim: To establish a profile of men in nursing in Western Australia and explore the perception of men in nursing from the perspective of male and female nurses.
Background: A project team, including some of the current authors, produced a YouTube video and DVD about men in nursing which led to further inquiry on this topic.
Design: The study employed a non-experimental, comparative, descriptive research design focused on a quantitative methodology, using an online survey in early 2014.
Method: A convenience sample incorporated registered and enrolled nurses and midwives in Western Australia.
Findings: The range of data included demographic information and the respondents’ perceptions of men in nursing were collected. Findings indicated that the main reasons for choosing a career in nursing or midwifery were similar for both genders. Common mis-perceptions of men in nursing included: most male nurses are gay; men are not suited to nursing and men are less caring and compassionate than women. Suggestions to promote nursing to men included: nurses are highly skilled professionals; there is the potential to make a difference for patients; nursing offers stable employment, professional diversity and opportunities for team work. There is a diminished awareness of opportunities for men in nursing and negative stereotypes related to men in nursing persist.
Conclusion: The study produced recommendations which included: using the right message to target the recruitment for men and promoting a more realistic understanding of the profile and perception of men in nursing
Entanglement dynamics of two qubits under the influence of external kicks and Gaussian pulses
We have investigated the dynamics of entanglement between two spin-1/2 qubits
that are subject to independent kick and Gaussian pulse type external magnetic
fields analytically as well as numerically. Dyson time ordering effect on the
dynamics is found to be important for the sequence of kicks. We show that
"almost-steady" high entanglement can be created between two initially
unentangled qubits by using carefully designed kick or pulse sequences
Single-qubit gates and measurements in the surface acoustic wave quantum computer
In the surface acoustic wave quantum computer, the spin state of an electron
trapped in a moving quantum dot comprises the physical qubit of the scheme. Via
detailed analytic and numerical modeling of the qubit dynamics, we discuss the
effect of excitations into higher-energy orbital states of the quantum dot that
occur when the qubits pass through magnetic fields. We describe how
single-qubit quantum operations, such as single-qubit rotations and
single-qubit measurements, can be performed using only localized static
magnetic fields. The models provide useful parameter regimes to be explored
experimentally when the requirements on semiconductor gate fabrication and the
nanomagnetics technology are met in the future.Comment: 13 pages, 10 figures, submitted to Phys. Rev.
Strong "quantum" chaos in the global ballooning mode spectrum of three-dimensional plasmas
The spectrum of ideal magnetohydrodynamic (MHD) pressure-driven (ballooning)
modes in strongly nonaxisymmetric toroidal systems is difficult to analyze
numerically owing to the singular nature of ideal MHD caused by lack of an
inherent scale length. In this paper, ideal MHD is regularized by using a
-space cutoff, making the ray tracing for the WKB ballooning formalism a
chaotic Hamiltonian billiard problem. The minimum width of the toroidal Fourier
spectrum needed for resolving toroidally localized ballooning modes with a
global eigenvalue code is estimated from the Weyl formula. This
phase-space-volume estimation method is applied to two stellarator cases.Comment: 4 pages typeset, including 2 figures. Paper accepted for publication
in Phys. Rev. Letter
Entanglement Evolution in the Presence of Decoherence
The entanglement of two qubits, each defined as an effective two-level, spin
1/2 system, is investigated for the case that the qubits interact via a
Heisenberg XY interaction and are subject to decoherence due to population
relaxation and thermal effects. For zero temperature, the time dependent
concurrence is studied analytically and numerically for some typical initial
states, including a separable (unentangled) initial state. An analytical
formula for non-zero steady state concurrence is found for any initial state,
and optimal parameter values for maximizing steady state concurrence are given.
The steady state concurrence is found analytically to remain non-zero for low,
finite temperatures. We also identify the contributions of global and local
coherence to the steady state entanglement.Comment: 12 pages, 4 figures. The second version of this paper has been
significantly expanded in response to referee comments. The revised
manuscript has been accepted for publication in Journal of Physics
Entanglement, measurement, and conditional evolution of the Kondo singlet interacting with a mesoscopic detector
We investigate various aspects of the Kondo singlet in a quantum dot (QD)
electrostatically coupled to a mesoscopic detector. The two subsystems are
represented by an entangled state between the Kondo singlet and the
charge-dependent detector state. We show that the phase-coherence of the Kondo
singlet is destroyed in a way that is sensitive to the charge-state information
restored both in the magnitude and in the phase of the scattering coefficients
of the detector. We also introduce the notion of the `conditional evolution' of
the Kondo singlet under projective measurement on the detector. Our study
reveals that the state of the composite system is disentangled upon this
measurement. The Kondo singlet evolves into a particular state with a fixed
number of electrons in the quantum dot. Its relaxation time is shown to be
sensitive only to the QD-charge dependence of the transmission probability in
the detector, which implies that the phase information is erased in this
conditional evolution process. We discuss implications of our observations in
view of the possible experimental realization.Comment: Focus issue on "Interference in Mesoscopic Systems" of New J. Phy
Multiobjective genetic programming can improve the explanatory capabilities of mechanism-based models of social systems
The generative approach to social science, in which agent-based simulations (or other complex systems models) are executed to reproduce a known social phenomenon, is an important tool for realist explanation. However, a generative model, when suitably calibrated and validated using empirical data, represents just one viable candidate set of entities and mechanisms. The model only partially addresses the needs of an abductive reasoning process - specifically it does not provide insight into other viable sets of entities or mechanisms, nor suggest which of these are fundamentally constitutive for the phenomenon to exist. In this
paper, we propose a new model discovery framework that more fully captures the needs of realist explanation. The framework exploits the implicit ontology of an existing human-built
generative model to propose and test a plurality of new candidate model structures. Genetic programming is used to automate this search process. A multi-objective approach is used, which enables multiple perspectives on the value of any particular generative model - such as goodness-of-fit, parsimony, and interpretability - to be represented simultaneously. We demonstrate this new framework using a complex systems modeling case study of change and stasis in societal alcohol use patterns in the US over the period 1980-2010. The framework is successful in identifying three competing explanations of these alcohol use patterns, using novel integrations of social role theory not previously considered by the human modeler. Practitioners in complex systems modeling should use model discovery to improve the explanatory utility of the generative approach to realist social science
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