Generating Entangled Microwave Radiation Over Two Transmission Lines

TL;DR

This paper demonstrates the first experimental creation of spatially separated two-mode squeezed microwave states using superconducting circuits, with measurable entanglement and high entanglement generation rate.

Contribution

It introduces a novel superconducting circuit setup with two Josephson mixers to generate and verify entangled microwave fields across separate transmission lines.

Findings

Successfully generated spatially separated entangled microwave states.

Measured output noise below vacuum level, confirming entanglement.

Achieved a rate of 6 Mebit.s$^{-1}$ in entanglement generation.

Abstract

Using a superconducting circuit, the Josephson mixer, we demonstrate the first experimental realization of spatially separated two-mode squeezed states of microwave light. Driven by a pump tone, a first Josephson mixer generates, out of quantum vacuum, a pair of entangled fields at different frequencies on separate transmission lines. A second mixer, driven by a $\pi$-phase shifted copy of the first pump tone, recombines and disentangles the two fields. The resulting output noise level is measured to be lower than for vacuum state at the input of the second mixer, an unambiguous proof of entanglement. Moreover, the output noise level provides a direct, quantitative measure of entanglement, leading here to the demonstration of 6 Mebit.s$^{-1}$ (Mega entangled bits per second) generated by the first mixer.