  The representation of information within the spins of electrons and nuclei
has been powerful in the ongoing development of quantum computers. Although
nuclear spins are advantageous as quantum bits (qubits) due to their long
coherence lifetimes (exceeding seconds), they exhibit very slow spin
interactions and have weak polarisation. A coupled electron spin can be used to
polarise the nuclear spin and create fast single-qubit gates, however, the
permanent presence of electron spins is a source of nuclear decoherence. Here
we show how a transient electron spin, arising from the optically excited
triplet state of C60, can be used to hyperpolarise, manipulate and measure two
nearby nuclear spins. Implementing a scheme which uses the spinor nature of the
electron, we performed an entangling gate in hundreds of nanoseconds: five
orders of magnitude faster than the liquid-state J coupling. This approach can
be widely applied to systems comprising an electron spin coupled to multiple
nuclear spins, such as NV centres, while the successful use of a transient
electron spin motivates the design of new molecules able to exploit
photo-excited triplet states.

Quantum Physics