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

Electron spins confined to phosphorus donors in silicon are promising candidates as qubits 1 because of their long coherence times, exceeding seconds in isotopically purified bulk silicon 2 . With the recent demonstrations of initialization, readout 3 and coherent manipulation 4 of individual donor electron spins, the next challenge towards the realization of a Si:P donor-based quantum computer is the demonstration of exchange coupling 1 , 5 , 6 in two tunnel-coupled phosphorus donors. Spin-to-charge conversion 3 , 7 via Pauli spin blockade 8 , 9 , an essential ingredient for reading out individual spin states, is challenging in donor-based systems due to the inherently large donor charging energies (∼45 meV), requiring large electric fields (>1 MV m –1 ) to transfer both electron spins onto the same donor 10 . Here, in a carefully characterized 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. Exchange coupling can be observed in a two-donor system in silicon, opening the way to operations involving two qubits