Lecturer: Prof. Jonathan Dowling
Affiliation: Hearne Institute for Theoretical Physics,
Department of Physics & Astronomy,
Louisiana State University
Abstract:
Quantum number-path
entanglement is a resource
for super-sensitive quantum
metrology and in particular
provides for sub-shot noise
or even Heisenberg-limited
sensitivity. However, such
number-path entanglement
has thought to have been
resource intensive to create
in the first place --- typically
requiring either very strong
nonlinearities, or
nondeterministic preparation
schemes with feed-forward,
which are difficult to
implement. Very recently,
arising from the study of
quantum random walks with
multi-photon walkers, as well
as the study of the
computational complexity of
passive linear optical
interferometers fed with
single-photon inputs, it has
been shown that such
passive linear optical
devices generate a super-
exponentially large amount
of number-path
entanglement. A logical
question to ask is whether
this entanglement may be
exploited for quantum
metrology. We answer that
question here in the
affirmative by showing that a
simple, passive, linear-
optical interferometer --- fed
with only uncorrelated,
single-photon inputs,
coupled with simple, single-
mode, disjoint photo-
detection --- is capable of
significantly beating the
shot-noise limit. Our result
implies a pathway forward to
practical quantum metrology
with readily available
technology.