  The size of silicon transistors used in microelectronic devices is shrinking
to the level where quantum effects become important. While this presents a
significant challenge for the further scaling of microprocessors, it provides
the potential for radical innovations in the form of spin-based quantum
computers and spintronic devices. An electron spin in Si can represent a
well-isolated quantum bit with long coherence times because of the weak
spin-orbit coupling and the possibility to eliminate nuclear spins from the
bulk crystal. However, the control of single electrons in Si has proved
challenging, and has so far hindered the observation and manipulation of a
single spin. Here we report the first demonstration of single-shot,
time-resolved readout of an electron spin in Si. This has been performed in a
device consisting of implanted phosphorus donors coupled to a
metal-oxide-semiconductor single-electron transistor - compatible with current
microelectronic technology. We observed a spin lifetime approaching 1 second at
magnetic fields below 2 T, and achieved spin readout fidelity better than 90%.
High-fidelity single-shot spin readout in Si opens the path to the development
of a new generation of quantum computing and spintronic devices, built using
the most important material in the semiconductor industry.
