QUROPE Quantum Information Processing and Communication in Europe

K. Saeedi, S. Simmons, J. Z. Salvail, P. Dluhy, H. Riemann, N. V. Abrosimov, P. Becker, H.-J. Pohl, J. L. Morten and M. L. W. Thewalt
Science 342, 830-833 (2013)

A recurring problem in attempts to implement quantum algorithms is decoherence, which refers to the
uncontrolled coupling of quantum bits (qubits) to surrounding noise. One of the most promising techniques
to eliminate this unwanted coupling is to encode qubits onto the spin state of magnetically isolated atomic
nuclei, which have a very small coupling to external fields because of their low charge-to-mass ratio.

In their work, Saeedi and colleagues show that the lifetime of phosphorous nuclei within an ultra-pure
sample of silicon can be extended almost indefinitely. A coherence time of 39 minutes was a lower bound,
due to imperfections in the 250 radio-frequency pulses used to correct for inhomogeneities across the
sample. Furthermore, this extraordinary coherence time was measured in a solid-state system, and at roomtemperature. This result is an exciting indication that decoherence can be all-but eliminated in the right
material. The outstanding challenge is now to introduce an architecture for coupling individual qubits in a
controlled way.