Fig. 1
From: Two-electron spin correlations in precision placed donors in silicon
Two qubit 2P−1P device with independent sequential readout. a An STM micrograph of a precision placed two spin-qubit donor device showing the lighter coloured lithographic outline where the hydrogen mask has been removed. Two spin-qubits, L and R, are separated by 16 ± 1 nm and sit equidistant at 19 ± 1 nm away from a larger readout structure which serves as both an electron reservoir and single-electron-transistor (SET) charge sensor with source (S) and drain (D) reservoirs and gates {GL, GM, GR, GS}; the scale bar is 20 nm. The insets show close-up STM micrographs of L and R where the green (blue) circles show fully (half) desorbed silicon dimers. White lines indicate the silicon dimer rows and the scale bars are 2 nm. b Current through the SET charge sensor as a function of VGL and VGR at the (1,1)–(2,0) charge transition. Electron spin readout is performed at the SET breaks (solid white lines, where tunnelling of qubit electrons to or from SET can occur) at the red and blue circles for L and R respectively. The approximate wait position for spin relaxation measurements is shown by the green square and the detuning axis between (1,1)–(2,0), \(\epsilon\), is indicated by the white arrow. The dashed white line indicates where electrons can tunnel between qubit sites, i.e. where \(\epsilon\) = 0. c The relevant electrochemical potentials in a magnetic field for spin readout of L (red arrows) and R (blue arrows). d A schematic representation of the controllable exchange interaction in a 2P−1P donor spin-qubit system. For detuning \(\epsilon \ll 0\) the electrons are in the (1,1) charge configuration and the spins are independent. For \(\epsilon\) > 0 the ground state (2,0) charge configuration is the two-electron singlet state. e, f Independent spin readout of L (R) demonstrated by spin relaxation, when the electron on R (L) is deterministically loaded with \(\left| \downarrow \right\rangle\). In each case the qubit initially prepared as spin down shows no decay behaviour indicating that the readout is independent at this detuning position, i.e. the exchange is negligible at the readout positions. All measurements were performed with Bz = 2.5 T
