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


Electron spins confined to phosphorus donors in silicon are promising candidates as qubits1 because of their long coherence times, exceeding seconds in isotopically purified bulk silicon2. With the recent demonstrations of initialization, readout3 and coherent manipulation4 of individual donor electron spins, the next challenge towards the realization of a Si:P donor-based quantum computer is the demonstration of exchange coupling1,5,6 in two tunnel-coupled phosphorus donors. Spin-to-charge conversion3,7 via Pauli spin blockade8,9, 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 donor10. 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.

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Figure 1: A few-donor double quantum dot.
Figure 2: Spectroscopy of a donor-based few-electron double quantum dot.
Figure 3: Comparison of measured binding energy spectra of few-donor double quantum dots with self-consistent atomistic TB calculations.
Figure 4: Observation of spin blockade.


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This research was conducted by the Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology (project no. CE110001027) and the US National Security Agency and US Army Research Office (contract no. W911NF-08-1-0527). Computational resources on, funded by the National Science Foundation (grant no. EEC-0228390), were used extensively. M.Y.S. acknowledges an ARC Laureate Fellowship.

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B.W. and T.F.W. carried out the fabrication. B.W. performed measurements. B.W., Y.H.M.T., S.M., T.F.W., H.R., R.R., L.H., G.K. and M.Y.S. analysed the data. Y.H.M.T., H.R. and R.R. carried out the calculations. M.Y.S. planned the project. G.K. planned the theoretical modelling approach. B.W. and M.Y.S. prepared the manuscript.

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Correspondence to Michelle Y. Simmons.

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Weber, B., Tan, Y., Mahapatra, S. et al. Spin blockade and exchange in Coulomb-confined silicon double quantum dots. Nature Nanotech 9, 430–435 (2014).

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