Phonon Squeezing in a Superconducting Molecular Transistor

TL;DR

This paper demonstrates that Josephson transport through a molecular or nanotube junction can induce quantum squeezing of local phonon modes, revealing entangled charge and phonon states influenced by superconducting phase and junction asymmetry.

Contribution

It provides an exact ground-state solution in the large-gap limit and a variational extension, showing how Josephson current can generate and control phonon squeezing and non-classical states.

Findings

Josephson current induces phonon squeezing.

Phonon squeezing is controlled by phase difference and junction asymmetry.

Non-classical phonon states can be probed optically.

Abstract

Josephson transport through a single molecule or carbon nanotube is considered in the presence of a local vibrational mode coupled to the electronic charge. The ground-state solution is obtained exactly in the limit of a large superconducting gap, and is extended to the general case by variational analysis. Coherent charge fluctuations are entangled with non-classical phonon states. The Josephson current induces squeezing of the phonon mode, which is controlled by the superconducting phase difference and by the junction asymmetry. Optical probes of non-classical phonon states are briefly discussed.