Readout scheme of the fullerene-based quantum computer by a single-electron transistor

We propose a potential scheme, based on the achieved technique of a single-electron transistor, to implement the readout of an electronic spin state inside a doped ${\mathrm{C}}_{60}$ fullerene by means of the magnetic dipole-dipole coupling and spin filters. In the presence of an external magnetic field, we show how to perform the spin state detection by transforming the information contained in the spin state into the tunneling current. The robustness of our scheme against sources of error is discussed.

Figure 1

Schematic diagram of our readout scheme, where the fullerene with inside spin is to be detected. The unfilled circles denote the electrons whose spins have been flipped by ESR pulses. The spin filter blocks spin-up electrons and only lets spin-down electrons pass. The way for the blocked electrons by the filter in the drain going to ground is omitted here.

Figure 2

Time evolution of the density-matrix elements for the case of ${\omega }_e={\omega }_0$ with the initial state $-i\cos (\alpha \pi ∕2)\mid \uparrow ⟩\mp \sin (\alpha \pi ∕2)\mid \downarrow ⟩$, where $1∕{\gamma }_p=25\mathrm{ns}$, the solid and dashed curves represent $\alpha =0.1$ and 0.2, respectively. P1, P2, and P3 correspond to ${\rho }_{2\uparrow \uparrow }$, ${\rho }_{2\uparrow \downarrow }$ (or ${\rho }_{2\downarrow \uparrow }$), and ${\rho }_{2\downarrow \downarrow }$, respectively.