Spin blockade and exchange in Coulomb-confined silicon double quantum dots

Abstract

Electron spins confined to phosphorus donors in silicon are promising candidates as qubits due to their extremely long coherence times, exceeding seconds in isotopically purified bulk silicon. With the recent demonstrations of initialisation, read-out, and coherent manipulation of individual donor electron spins, the next challenge towards the realisation of a Si:P donor-based quantum computer is the demonstration of exchange coupling in two tunnel-coupled P donors. Spin-to-charge conversion via Pauli spin-blockade, an essential ingredient for reading out individual spin states, is challenging in donor based systems due to the inherently large donor charging energies (~45meV), requiring large electric fields (larger than 1MV/m) to transfer both electron spins onto the same donor. Here, in a carefully characterised double donor-dot device, we directly observe spin-blockade of the first few electrons and measure the effective exchange interaction between electron spins in coupled Coulomb-confined systems.