24,336 research outputs found
Quantum Multiobservable Control
We present deterministic algorithms for the simultaneous control of an
arbitrary number of quantum observables. Unlike optimal control approaches
based on cost function optimization, quantum multiobservable tracking control
(MOTC) is capable of tracking predetermined homotopic trajectories to target
expectation values in the space of multiobservables. The convergence of these
algorithms is facilitated by the favorable critical topology of quantum control
landscapes. Fundamental properties of quantum multiobservable control
landscapes that underlie the efficiency of MOTC, including the multiobservable
controllability Gramian, are introduced. The effects of multiple control
objectives on the structure and complexity of optimal fields are examined. With
minor modifications, the techniques described herein can be applied to general
quantum multiobjective control problems.Comment: To appear in Physical Review
Singularity-free quantum tracking control of molecular rotor orientation
Quantum tracking control aims to identify applied fields to steer the
expectation values of particular observables along desired paths in time. The
associated temporal fields can be identified by inverting the underlying
dynamical equations for the observables. However, fields found in this manner
are often plagued by undesirable singularities. In this paper we consider a
planar molecular rotor, and derive singularity-free tracking expressions for
the fields that steer the expectation of the orientation of the rotor along
desired trajectories in time. Simulations are presented that utilize two
orthogonal control electric fields to drive the orientation of the rotor along
a series of designated tracks
Quantum Brain: A Recurrent Quantum Neural Network Model to Describe Eye Tracking of Moving Targets
A theoretical quantum brain model is proposed using a nonlinear Schroedinger
wave equation. The model proposes that there exists a quantum process that
mediates the collective response of a neural lattice (classical brain). The
model is used to explain eye movements when tracking moving targets. Using a
Recurrent Quantum Neural Network(RQNN) while simulating the quantum brain
model, two very interesting phenomena are observed. First, as eye sensor data
is processed in a classical brain, a wave packet is triggered in the quantum
brain. This wave packet moves like a particle. Second, when the eye tracks a
fixed target, this wave packet moves not in a continuous but rather in a
discrete mode. This result reminds one of the saccadic movements of the eye
consisting of 'jumps' and 'rests'. However, such a saccadic movement is
intertwined with smooth pursuit movements when the eye has to track a dynamic
trajectory. In a sense, this is the first theoretical model explaining the
experimental observation reported concerning eye movements in a static scene
situation. The resulting prediction is found to be very precise and efficient
in comparison to classical objective modeling schemes such as the Kalman
filter.Comment: 7 pages, 7 figures submitted to Physical Review Letter
Feedback control of spin systems
The feedback stabilization problem for ensembles of coupled spin 1/2 systems
is discussed from a control theoretic perspective. The noninvasive nature of
the bulk measurement allows for a fully unitary and deterministic closed loop.
The Lyapunov-based feedback design presented does not require spins that are
selectively addressable. With this method, it is possible to obtain control
inputs also for difficult tasks, like suppressing undesired couplings in
identical spin systems.Comment: 16 pages, 15 figure
Quantum Control Landscapes
Numerous lines of experimental, numerical and analytical evidence indicate
that it is surprisingly easy to locate optimal controls steering quantum
dynamical systems to desired objectives. This has enabled the control of
complex quantum systems despite the expense of solving the Schrodinger equation
in simulations and the complicating effects of environmental decoherence in the
laboratory. Recent work indicates that this simplicity originates in universal
properties of the solution sets to quantum control problems that are
fundamentally different from their classical counterparts. Here, we review
studies that aim to systematically characterize these properties, enabling the
classification of quantum control mechanisms and the design of globally
efficient quantum control algorithms.Comment: 45 pages, 15 figures; International Reviews in Physical Chemistry,
Vol. 26, Iss. 4, pp. 671-735 (2007
Classically entangled optical beams for high-speed kinematic sensing
Tracking the kinematics of fast-moving objects is an important diagnostic
tool for science and engineering. Existing optical methods include high-speed
CCD/CMOS imaging, streak cameras, lidar, serial time-encoded imaging and
sequentially timed all-optical mapping. Here, we demonstrate an entirely new
approach to positional and directional sensing based on the concept of
classical entanglement in vector beams of light. The measurement principle
relies on the intrinsic correlations existing in such beams between transverse
spatial modes and polarization. The latter can be determined from intensity
measurements with only a few fast photodiodes, greatly outperforming the
bandwidth of current CCD/CMOS devices. In this way, our setup enables
two-dimensional real-time sensing with temporal resolution in the GHz range. We
expect the concept to open up new directions in photonics-based metrology and
sensing.Comment: v2 includes the real-time measurement from the published version.
Reference [29] added. Minor experimental details added on page
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