measures the phase shift between two pathways of
light using the open system dynamics of the elec-
tromagnetic field of an optical cavity inside a quan-
tum feedback loop (Clark et al., 2016b). This scheme
should be of immediate practical interest, since it re-
quires neither efficient optical non-linearities nor en-
tangled photons.
ACKNOWLEDGEMENTS
AS and AB acknowledge financial support from
the UK EPSRC-funded Oxford Quantum Technology
Hub for Networked Quantum Information Technolo-
gies NQIT. MMK acknowledges a postdoctoral re-
search fellowship funding from the Higher Education
Commission of the Government of Pakistan. GW ac-
knowledges financial support from the NSF of China
(Grant No. 11405026) and Government of China
through a CSC (Grant No. 201506625070 ).
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