Interference and switching of Josephson current carried by nonlocal spin-entangled electrons in a SQUID-like system with quantum dots

Cooper pair splitting in parallel quantum dot Josephson junctions

Devices to generate on-demand non-local spin entangled electron pairs have potential application as solid-state analogues of the entangled photon sources used in quantum optics. Recently, Andreev entanglers that use two quantum dots as filters to adiabatically split and separate the quasi-particles of Cooper pairs have shown efficient splitting through measurements of the transport charge but the spin entanglement has not been directly confirmed. Here we report measurements on parallel quantum dot Josephson junction devices allowing a Josephson current to flow due to the adiabatic splitting and recombination of the Cooper pair between the dots. The evidence for this non-local transport is confirmed through study of the non-dissipative supercurrent while tuning independently the dots with local electrical gates. As the Josephson current arises only from processes that maintain the coherence, we can confirm that a current flows from the spatially separated entangled pair.

Spin-entangled electron pairs are one possible resource for future solid-state quantum information processing systems. Here, the authors directly prove spin entanglement between two electrons that had previously been a Cooper pair in a superconducting lead but were split using two quantum dots.