Spin dynamical decoupling for generating macroscopic superpositions of a free-falling nanodiamond

TL;DR

This paper proposes a method to generate large spatial superpositions of a levitated nanodiamond with NV centers by combining spin dynamical decoupling and a long free-fall in a magnetic field, enabling macroscopic quantum states.

Contribution

It introduces a novel scheme integrating spin dynamical decoupling with a long free-fall to produce macroscopic superpositions in nanodiamonds.

Findings

Achieves a superposition with over 250 nm spatial separation.

Demonstrates a 2.4 m free-fall in a magnetic structure.

Maintains NV spin coherence during superposition generation.

Abstract

Levitated nanodiamonds containing negatively charged nitrogen-vacancy centers (${\text{NV}}^{-}$) have been proposed as a platform to generate macroscopic spatial superpositions. Requirements for this include having a long ${\text{NV}}^{-}$ spin coherence time, which necessitates formulating a dynamical decoupling strategy in which the regular spin flips do not cancel the growth of the superposition through the Stern-Gerlach effect in an inhomogeneous magnetic field. Here, we propose a scheme to place a $250$-nm-diameter diamond in a superposition with spatial separation of over $250$ nm, while incorporating dynamical decoupling. We achieve this by letting a diamond fall for $2.4$ m through a magnetic structure, including $1.13$ m in an inhomogeneous region generated by magnetic teeth.