Free Nano-Object Ramsey Interferometry for Large Quantum Superpositions

TL;DR

This paper proposes a gravity-based interferometric method to create and detect large quantum superpositions of nano-objects, demonstrating immunity to motional noise and potential for testing quantum theory modifications.

Contribution

It introduces a novel spin-dependent free flight scheme for nano-objects that achieves macroscopic superpositions with high visibility and mass independence, enabling new quantum experiments.

Findings

High-visibility Ramsey fringes secured despite motional noise

Mass independence allows superposition of objects with varying masses

Potential to create 100 nm superpositions in 10^9 amu objects

Abstract

We propose an interferometric scheme based on an untrapped nano-object subjected to gravity. The motion of the center of mass (c.m.) of the free object is coupled to its internal spin system magnetically, and a free flight scheme is developed based on coherent spin control. The wavepacket of the test object, under a spin-dependent force, may then be delocalized to a macroscopic scale. A gravity induced dynamical phase (accrued solely on the spin state, and measured through a Ramsey scheme) is used to reveal the above spatially delocalised superposition of the spin-nano-object composite system that arises during our scheme. We find a remarkable immunity to the motional noise in the c.m. (initially in a thermal state with moderate cooling), and also a dynamical decoupling nature of the scheme itself. Together they secure a high visibility of the resulting Ramsey fringes. The mass independence of our scheme makes it viable for a nano-object selected from an ensemble with a high mass variability. Given these advantages, a quantum superposition with $100$ nm spatial separation for a massive object of $10^9$ amu is achievable experimentally, providing a route to test postulated modifications of quantum theory such as continuous spontaneous localisation.