title: Linear optical quantum metrology with single photons: exploiting spontaneously generated entanglement to beat the shot-noise limit.
abstract: Quantum number-path entanglement is a resource for supersensitive quantum metrology and in particular provides for sub-shot-noise or even Heisenberg-limited sensitivity. However, such number-path entanglement has been thought to be resource intensive to create in the first place--typically requiring either very strong nonlinearities, or nondeterministic preparation schemes with feedforward, which are difficult to implement. Very recently, arising from the study of quantum random walks with multiphoton 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 superexponentially 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 photodetection--is capable of significantly beating the shot-noise limit. Our result implies a pathway forward to practical quantum metrology with readily available technology.
authors.affiliation: Department of Physics and Astronomy, Centre for Engineered Quantum Systems, Macquarie University, Sydney NSW 2113, Australia.
authors.forename: Keith R
authors.initials: KR
authors.lastname: Motes
authors.affiliation: Hearne Institute for Theoretical Physics and Department of Physics & Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Olson
authors.affiliation: Hearne Institute for Theoretical Physics and Department of Physics & Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
authors.forename: Evan J
authors.initials: EJ
authors.lastname: Rabeaux
authors.affiliation: Hearne Institute for Theoretical Physics and Department of Physics & Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Dowling
authors.affiliation: Boise State University, Boise, Idaho 83725, USA.
authors.forename: S Jay
authors.initials: SJ
authors.lastname: Olson
authors.affiliation: Department of Physics and Astronomy, Centre for Engineered Quantum Systems, Macquarie University, Sydney NSW 2113, Australia.|Centre for Quantum Computation and Intelligent Systems (QCIS), Faculty of Engineering & Information Technology, University of Technology, Sydney NSW 2007, Australia.
authors.forename: Peter P
authors.initials: PP
authors.lastname: Rohde