369,021 research outputs found
Mirror Inversion of Quantum States in Linear Registers
Transfer of data in linear quantum registers can be significantly simplified
with pre-engineered but not dynamically controlled inter-qubit couplings. We
show how to implement a mirror inversion of the state of the register in each
excitation subspace with respect to the centre of the register. Our
construction is especially appealing as it requires no dynamical control over
individual inter-qubit interactions. If, however, individual control of the
interactions is available then the mirror inversion operation can be performed
on any substring of qubits in the register. In this case a sequence of mirror
inversions can generate any permutation of a quantum state of the involved
qubits.Comment: 4 page
Direct inversion of rigid-body rotational dynamics
The global linearization (inversion) of rigid-body rotational dynamics is reviewed and representations in terms of quaternions and direction cosines are compared. Certain properties common to quaternions and direction cosines that make their use preferable to Euler angles and that simplify the inversion procedure are described. Applications of the inversion procedure for state estimation and attitude control are discussed. To avoid complexities caused by aerodynamics, an example of direct inversion for linear feedback control of spacecraft attitude is given
Recursive inversion of externally defined linear systems
The approximate inversion of an internally unknown linear system, given by its impulse response sequence, by an inverse system having a finite impulse response, is considered. The recursive least squares procedure is shown to have an exact initialization, based on the triangular Toeplitz structure of the matrix involved. The proposed approach also suggests solutions to the problems of system identification and compensation
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