Measurements below the standard quantum limit in atomic interferometry

P. Hyllus, K. Eckert

Christian Groß

Alfredo Luis, Luis Lorenzo Sánchez-Soto

A. Kuzmich, N. P. Bigelow, L. Mandeļ

We show that the accuracy of atomic interferometry can be improved by using QND measurements of the atomic populations at the inputs to the interferometer. The accuracy of such a scheme surpasses the standard quantum limit of phase measurement δϕ SQL = 1/√ N and could reach the Heisenberg limit δϕ ∼ 1/ N . We propose to perform QND measurements of atomic populations with an off-resonant laser field. The conditions necessary for this kind of QND measurement could be fulfilled in a variety of ways with current experimental techniques, including magneto-optical traps and atomic cells.

Monika A. M. Marte, P. Zoller, Murray Holland +2 more

Massimiliano Rossi, David Mason, Junxin Chen +2 more

Interferometrie techniques to measure mechanical displacement are subject to constraints ultimately governed by quantum mechanics. In a "standard" measurement of a mechanically induced optical phase shift, there exists a trade-off between measurement imprecision and motion disturbance, known as standard quantum limit (SQL) [1]. For a mechanical resonator with susceptibility χm(Ω), this limit is SSQL(Ω) = ħ|χm(Ω)| (ħ reduced Planck constant), at any frequency Ω. In the last half-century, a number of systems, including advanced LIGO and ultracold atoms have progressed towards this limit, but excess sources of noise have yet prevented fully reaching the SQL. Here, we show measurements of an ultracoherent mechanical resonator performed at the SQL within 33% [2] and, for the first time, below the SQL by 1.5 dB[3]. The latter has been possible by a non-standard measurement scheme that explois quantum correlations between optical quadratures induced in the optomechanical device.