We prove a scale-free, quantitative unique continuation
principle for functions in the range of the spectral projector
of a Schrödinger
operator
on a
cube of side
,
with bounded potential. Previously, such estimates were known
only for individual eigenfunctions and for spectral projectors
with
small
.
Such estimates are also called, depending on the context, uncertainty principles,
observability estimates, or spectral inequalities. Our main application of such an
estimate is to find lower bounds for the lifting of eigenvalues under semidefinite
positive perturbations, which in turn can be applied to derive a Wegner estimate for
random Schrödinger operators with nonlinear parameter-dependence. Another
application is an estimate of the control cost for the heat equation in a multiscale
domain in terms of geometric model parameters. Let us emphasize that previous
uncertainty principles for individual eigenfunctions or spectral projectors onto small
intervals were not sufficient to study such applications.
Keywords
uncertainty relation, spectral inequality, Wegner estimate,
control of heat equation, random Schroedinger operator