Silicon Qubit Environment

Electronic and nuclear spin of dopants in macroscopic samples of bulk silicon have recently been shown to have exceptional coherence properties. This program seeks to develop an understanding of the physical behaviour of dopants as functional elements in a nanostructured environment envisioned for nanoelectronics and quantum computation.

This includes developing methods to gain control over the electronic wavefunctions of single donors near interfaces which render them manifestly different from bulk dopants, examining associated valley-orbit effects, and observing the consequences for electronic coherence. It also includes developing an understanding of coherent coupling and exchange among dopants necessary to exert external control over multi-electron quantum states. Such problems are of central importance to both for pair-wise (mutual) entanglement as well as coherent transport of spin in current proposals for quantum computation.

Figure 1 (A) Schematic of FinFET device in which control of the wavefunction of a single donor bound electron has been achieved enabling, for example, tunable hyperfine coupling between the donor electron and nuclear spin as envisioned in the Kane proposal. (B) The current signal used to probe the wavefunction. (C) An applied electric field on a gate controls a transition of the electron wavefunction between the donor nucleus and a nearby interface.

Figure 2 (A) Schematic of two-qubit system of proximate donor spins, which under control of external gates A and J can be used to entangle the qubits. (B) Measured real-space coupled-hole transition density using cryogenic scanning tunnelling spectroscopy. Hole spin qubits are of interest because of the possibility to perform qubit operations using dynamical electric fields and because of the relative insensitivity of their coherence to the spin of the host silicon nuclei.  Rich pseudospin physics is imparted by the complex valence band structure.

Recent output in this area includes:

[1] Verduijn, J., Tettamanzi, G. C., & Rogge, S. (2013). Wave Function Control over a Single Donor Atom. Nano Letters, 13(4), 1476.
[2] Verduijn, J., Agundez, R. R., Blaauboer, M., & Rogge, S. (2013). Non-local coupling of two donor-bound electrons. New Journal of Physics, 15(3), 033020.
[3] Mol, J. A., Salfi, J., Miwa, J. A., Simmons, M. Y., & Rogge, S. Interplay between quantum confinement and dielectric mismatch for ultra-shallow dopants. Accepted for publication in Physical Review B.
[4] Mol, J. A., Salfi, J., Rahman, R, Miwa, J. A., & Rogge, S. Interface-split Kramers doublets for acceptor-based qubits. Submitted.
[5] Mol, J. A., Salfi, J., Rogge, S. Quantum Computing with Acceptor-based Qubits, Australian Provisional Patent Application 2013900975 (2013)