Microwave spectroscopy of a Cooper pair beam splitter

This article discusses how to demonstrate the entanglement of the split Cooper pairs produced in a doublequantum-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.