17,768 research outputs found
Experimentally Attainable Optimal Pulse Shapes Obtained with the Aid of Genetic Algorithms
We propose a methodology to design optimal pulses for achieving quantum
optimal control on molecular systems. Our approach constrains pulse shapes to
linear combinations of a fixed number of experimentally relevant pulse
functions. Quantum optimal control is obtained by maximizing a multi-target
fitness function with genetic algorithms. As a first application of the
methodology we generated an optimal pulse that successfully maximized the yield
on a selected dissociation channel of a diatomic molecule. Our pulse is
obtained as a linear combination of linearly chirped pulse functions. Data
recorded along the evolution of the genetic algorithm contained important
information regarding the interplay between radiative and diabatic processes.
We performed a principal component analysis on these data to retrieve the most
relevant processes along the optimal path. Our proposed methodology could be
useful for performing quantum optimal control on more complex systems by
employing a wider variety of pulse shape functions.Comment: 7 pages, 6 figure
Optimal control theory for unitary transformations
The dynamics of a quantum system driven by an external field is well
described by a unitary transformation generated by a time dependent
Hamiltonian. The inverse problem of finding the field that generates a specific
unitary transformation is the subject of study. The unitary transformation
which can represent an algorithm in a quantum computation is imposed on a
subset of quantum states embedded in a larger Hilbert space. Optimal control
theory (OCT) is used to solve the inversion problem irrespective of the initial
input state. A unified formalism, based on the Krotov method is developed
leading to a new scheme. The schemes are compared for the inversion of a
two-qubit Fourier transform using as registers the vibrational levels of the
electronic state of Na. Raman-like transitions through the
electronic state induce the transitions. Light fields are found
that are able to implement the Fourier transform within a picosecond time
scale. Such fields can be obtained by pulse-shaping techniques of a femtosecond
pulse. Out of the schemes studied the square modulus scheme converges fastest.
A study of the implementation of the qubit Fourier transform in the Na
molecule was carried out for up to 5 qubits. The classical computation effort
required to obtain the algorithm with a given fidelity is estimated to scale
exponentially with the number of levels. The observed moderate scaling of the
pulse intensity with the number of qubits in the transformation is
rationalized.Comment: 32 pages, 6 figure
Theory of selective excitation in Stimulated Raman Scattering
A semiclassical model is used to investigate the possibility of selectively
exciting one of two closely spaced, uncoupled Raman transitions. The duration
of the intense pump pulse that creates the Raman coherence is shorter than the
vibrational period of a molecule (impulsive regime of interaction). Pulse
shapes are found that provide either enhancement or suppression of particular
vibrational excitations.Comment: RevTeX4,10 pages, 5 figures, submitted to Phys.Rev.
Introduction to Quantum Algorithms for Physics and Chemistry
In this introductory review, we focus on applications of quantum computation
to problems of interest in physics and chemistry. We describe quantum
simulation algorithms that have been developed for electronic-structure
problems, thermal-state preparation, simulation of time dynamics, adiabatic
quantum simulation, and density functional theory.Comment: 44 pages, 5 figures; comments or suggestions for improvement are
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Monitoring Ion Channel Function In Real Time Through Quantum Decoherence
In drug discovery research there is a clear and urgent need for non-invasive
detection of cell membrane ion channel operation with wide-field capability.
Existing techniques are generally invasive, require specialized nano
structures, or are only applicable to certain ion channel species. We show that
quantum nanotechnology has enormous potential to provide a novel solution to
this problem. The nitrogen-vacancy (NV) centre in nano-diamond is currently of
great interest as a novel single atom quantum probe for nanoscale processes.
However, until now, beyond the use of diamond nanocrystals as fluorescence
markers, nothing was known about the quantum behaviour of a NV probe in the
complex room temperature extra-cellular environment. For the first time we
explore in detail the quantum dynamics of a NV probe in proximity to the ion
channel, lipid bilayer and surrounding aqueous environment. Our theoretical
results indicate that real-time detection of ion channel operation at
millisecond resolution is possible by directly monitoring the quantum
decoherence of the NV probe. With the potential to scan and scale-up to an
array-based system this conclusion may have wide ranging implications for
nanoscale biology and drug discovery.Comment: 7 pages, 6 figure
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