Catapulting towards massive and large spatial quantum superposition

TL;DR

This paper proposes a method to rapidly generate large spatial quantum superpositions of nano-crystals using magnetic field gradients, enabling tests of quantum mechanics and gravity at macroscopic scales.

Contribution

It introduces a novel approach to create large superpositions within seconds by accelerating spin states with magnetic fields, applicable to various materials.

Findings

Superpositions of size 1-10 μm achieved in 1-2 seconds.

Magnetic field gradient control is critical for coherence.

Method applicable to nano-crystals with embedded spins like NV centers.

Abstract

Large spatial quantum superposition of size ${\cal O}(1-10)~{\rm \mu \text{m}}$ for mass $m \sim 10^{-17}-10^{-14}~\text{kg}$ is required to probe the foundations of quantum mechanics and testing classical and quantum nature of gravity via entanglement in a laboratory. In this paper, we will show that it is possible to accelerate the two spin states of a macroscopic nano-crystal sourced by the inhomogeneous nonlinear magnetic field in the Stern-Gerlach type setup. We will assume that the electronic spin can be embedded at the centre of the nano-crystal, such as the nitrogen-vacancy (NV) centre of diamond. Our analysis will be generic to any dopant or any material. We will show that we can create a desired superposition size within $1-2$ seconds by catapulting the trajectories of the two spin states with a modest magnetic field gradient and then recombine the trajectories for a coherent interference. We will show the demanding nature of the precision required in the magnetic field to recover $99\%$ spin coherence confidence level at the moment of interference.