Nonlinear atom interferometer surpasses classical precision limit

TL;DR

This paper demonstrates that nonlinear atom interferometry with Bose-Einstein condensates can surpass classical precision limits by generating entangled states and spin squeezing, enhancing phase sensitivity in quantum measurements.

Contribution

It introduces a nonlinear atom interferometer using controlled interactions and Feshbach resonance, achieving phase sensitivity beyond classical limits with entangled atomic states.

Findings

15% phase sensitivity enhancement over classical measurement

Detection of -8.2dB spin squeezing

Entanglement of 170 atoms within the interferometer

Abstract

Interference is fundamental to wave dynamics and quantum mechanics. The quantum wave properties of particles are exploited in metrology using atom interferometers, allowing for high-precision inertia measurements [1, 2]. Furthermore, the state-of-the-art time standard is based on an interferometric technique known as Ramsey spectroscopy. However, the precision of an interferometer is limited by classical statistics owing to the finite number of atoms used to deduce the quantity of interest [3]. Here we show experimentally that the classical precision limit can be surpassed using nonlinear atom interferometry with a Bose-Einstein condensate. Controlled interactions between the atoms lead to non-classical entangled states within the interferometer; this represents an alternative approach to the use of non-classical input states [4-8]. Extending quantum interferometry [9] to the regime of large atom number, we find that phase sensitivity is enhanced by 15 per cent relative to that in an ideal classical measurement. Our nonlinear atomic beam splitter follows the "one-axis-twisting" scheme [10] and implements interaction control using a narrow Feshbach resonance. We perform noise tomography of the quantum state within the interferometer and detect coherent spin squeezing with a squeezing factor of -8.2dB [11-15]. The results provide information on the many-particle quantum state, and imply the entanglement of 170 atoms [16].