The task of ab initio optical phase measurement — the estimation of a completely unknown phase —has been experimentally demonstrated with precision scaling like the ultimate bound, the Heisenberg limit (HL), but with an overhead factor. This limit is defined in terms of N, the number of photon passes through the phase shift, or, in quantum computing language, the number of applications of a single-qubit phase gate encoding the unknown phase. However, existing approaches have not been able, even in principle, to achieve the best possible precision, i.e. saturating the HL exactly. Here we demonstrate a scheme to achieve true HL phase measurement, using a combination of three techniques: entanglement, multiple samplings of the phase shift, and adaptive measurement. Our experimental demonstration of the scheme, with photonic qubits and N = 3 photon-passes, achieves a precision that is within 4% of the HL, and which clearly surpasses the best precision theoretically achievable with simpler techniques. This work represents a fundamental achievement of the ultimate limits of metrology, and the scheme can be extended to higher N and other physical systems.
By Florian Marquardt
By Gary Steele
By Hendrik Bluhm
By Jean-Michel Raimond
By Alain Sarlette
By Sylvain Schwartz
By Sophia Economou
By Klaus Mølmer
By Howard M. Wiseman
By Michel Devoret
By Akira Furusawa
By Yanhong Xiao
By Alex Retzker
By Nicolas Didier
By Ivan Deutsch
By Mankei Tsang
By Aashish Clerk
By Valentina Parigi
By Rebing Wu
By Michael Biercuk
By Thomas Ayral
By Yassine Hamoudi
By Yassine Hamoudi
By Nana Liu
By Nana Liu
