  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.
