QTube · Synthesising a macroscopic quantum superposition of a nanotube

One major quest in physics is to extend quantum superposition states from the microscopic to the macroscopic world. To achieve this, we need to explore innovative approaches for synthesizing macroscopic quantum superpositions of massive objects. While recent advancements have demonstrated quantum non-Gaussian states of motion in mechanical oscillators, the delocalization achieved has been only marginally larger than the zero-point motion. QTube aims to address this limitation by quantum delocalizing a nanotube mechanical resonator, an object composed of approximately 106 atoms, to a length scale greater than its diameter.QTube will tackle several key challenges with significant scientific impact: (i) developing a nanotube double quantum dot qubit with record-breaking coherence rate; (ii) detecting the mechanical vibrations of the nanotube in the quantum ground state using a quantum nondemolition approach with a superconducting resonator (iii) observing quantum jumps of phonons, an unprecedented milestone in quantum physics; (iv) demonstrating, for the first time, a double-well potential for nanomechanical vibrations, thereby entering an extreme regime in nonlinear mechanics; and (v) synthesizing a macroscopic quantum superposition of a nanotube. This macroscopic quantum superposition will be achieved by utilizing a novel squeezing protocol with the double-well potential to enhance the anti-squeezed quadrature without parametric drive and create Wigner negativity when the anti-squeezed quadrature is large. The double quantum dot qubit will certify the macroscopic quantum superposition state through Wigner tomography.If successful, QTube will extend the frontier of macroscopic quantum superposition states and unlock new possibilities in macroscopic quantum tunneling, precise quantum sensing of forces, and entanglement between mechanical systems.