Cooper pair splitting in parallel quantum dot Josephson junctions

Abstract

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.

Gate tunable parallel double quantum dots in InAs double-nanowire devices

“…In this study we repot on fabrication and characterization of InAs DNW junctions, where a quantum dot is formed in each NW, and evaluated the gate performances. The DNW devices are useful for making multiple spin qubits and topological circuits of non-local entangled electrons [15][16][17][18][19] or parafermions as well as majorana fermions 20 . We develop a fabrication technique for selectively placing DNW onto previously fabricated gate arrays and selectively contacting the two NWs.…”

Aharonov-Bohm and Aharonov-Casher effects in a double quantum dot Josephson junction

“…It is based on the measurement of the maximum Josephson current |I C |, as commonly done experimentally. Recent experiment by Deacon et al 9 has shown that it is possible to control experimentally the splitting of the Josephson current and to distinguish between local and nonlocal component of the Josephson current. The magnitude of the AC effect is directly related to the splitting efficiency of the experimental setup, since Rashba phase affects only the nonlocal Josephson current.…”

“…(8) and(9), only the local part of the Josephson current depends on φ AB , while the nonlocal component is affected by the Rashba phase. If both electrons of an entangled pair, being in the singlet state |S , travel through the same nanowire, their Rashba phases cancel due to opposite spins of the Cooper pair electrons, and the Josephson current only depends on the AB phase.…”

Nonlocal quantum state engineering with the Cooper pair splitter beyond the Coulomb blockade regime

“…Theoretical analysis of the branching currents and their crossed correlations was done in [18,19], and the subgap transport was studied in [20]. Only recently, measurements of the Josephson current flowing between superconducting contacts through two parallel QDs have demonstrated that the pairs are indeed entangled [21]. CPSs can also be used to probe the symmetry of the order parameter in unconventional superconductors [22,23], as a model system exhibiting unconventional pairing [24], to entangle mechanical resonators [25], or to engineer Majorana bound states which are not topologically protected [26].…”