Microwave spectroscopy of a Cooper pair beam splitter

TL;DR

This paper proposes using microwave spectroscopy to demonstrate entanglement in a Cooper pair beam splitter by observing nonmonotonic current responses caused by microwave irradiation, revealing coherence effects.

Contribution

It introduces a method to detect entanglement in a CPS through microwave spectroscopy and analyzes the current response to microwave irradiation.

Findings

Current peaks vary nonmonotonically with microwave amplitude.

The effect is due to subradiance caused by pair coherence.

The effect is measurable with realistic parameters.

Abstract

This article discusses how to demonstrate the entanglement of the split Cooper pairs produced in a double-quantum-dot based Cooper pair beam splitter (CPS), by performing the microwave spectroscopy of the CPS. More precisely, one can study the DC current response of such a CPS to two on-phase microwave gate irradiations applied to the two CPS dots. Some of the current peaks caused by the microwaves show a strongly nonmonotonic variation with the amplitude of the irradiation applied individually to one dot. This effect is directly due to a subradiance property caused by the coherence of the split pairs. Using realistic parameters, one finds that this effect has a measurable amplitude.