Silicon Qubit Interface

An optical interface to single solid-state qubits will provide a promising path towards distributed quantum computing. Control and coupling of single electron or nuclear spins via photons not only offers high addressability but also allows for long distance transfer of quantum information even through optical fibres. High read-out sensitivity and fidelity required for quantum computing can be achieved with nanotransistor charge sensing.

As a first milestone, hybrid optical–electrical access to single spins of individual Er ions in a nanotransistor (Figure 1a) has been demonstrated [1], and is applicable to other defects in solids. This hybrid approach with sensitive electrical read-out (Figure 1d) and high energy resolution (Figure 2) opens a new way to the optical addressing and manipulation of the electron and nuclear spin states of individual defects in a solid, other than NV centres in diamond.
The following steps include optical control and electrical read-out of single spins of individual Er ions, and optically coupling individual qubits in optical cavities linked by waveguides. Besides, we also work on other solid-state qubit candidates (e.g. P:Si) and towards combining this hybrid method with real-space scanning tunneling spectroscopy.
Recent output in this area includes:

[1] C.M. Yin, M. Rancic, G.G. de Boo, N. Stavrias, J.C. McCallum, M.J. Sellars, and S. Rogge, “Optical addressing of an individual erbium ion in silicon”. Nature 497, 91-94 (2013).

[2] S. Rogge, M. J. Sellars, C. M. Yin, J. C. McCallum, G. G. de Boo, M. Rancic, and N. Stavrias, “Optical addressing of individual targets in solids”, Australian pre.patent AU2012905400 (2012).

Figure 1. Photoionization spectroscopy of an individual Er3+ ion. a, Coloured scanning electron micrograph of a typical SET device used in this study and a band structure of Er3+ ions in silicon. CB, conduction band; VB, valence band. Top, schematic cross-section of the SET showing the optical addressing of individual Er3+ ions. b, The SET charge-sensing scheme. The loss of an electron due to photoionization induces a transient shift of the current (I)/gate voltage (VG) curve towards lower gate voltages, causing a change in current from I(q0) to I(q+). c, d, The current–time traces recorded for a fixed gate voltage (VM) under non-resonant (c) and resonant (d) illumination. e, The histogram of current–time traces as a function of the photon energy detuning. The photon energy of the illumination is detuned with respect to the centred wavelength of 1,537.9 nm. [1].

Figure 2. The photoionization spectrum of a single 167Er3+ ion and a contour plot of the photoionization spectra showing evolution of the hyperfine interaction. [1]