"This opens up the possibility of truly long-term coherent information storage at room temperature," said Mike Thewalt (Simon Fraser University), the lead researcher in this study.
The team began with a sliver of silicon doped with small amounts of other elements, including phosphorus. They then encoded quantum information in the nuclei of the phosphorus atoms: each nucleus has an intrinsic quantum property called 'spin', which acts like a tiny bar magnet when placed in a magnetic field. Spins can be manipulated to point up (0), down (1), or any angle in between, representing a superposition of the two other states.
The team prepared their sample at -269 C, just 4 degrees above absolute zero, and placed it in a magnetic field. They used additional magnetic field pulses to tilt the direction of the nuclear spin and create the superposition states. When the sample was held at this cryogenic temperature, the nuclear spins of about 37 per cent of the ions a typical benchmark to measure quantum coherence remained in their superposition state for three hours. The same fraction survived for 39 minutes when the temperature of the system was raised to 25 C.
"These lifetimes are at least ten times longer than those measured in previous experiments," says Stephanie Simmons (University of Oxford), who collaborated in the study. "We've managed to identify a system that seems to have basically no noise. They're high-performance qubits."
There is still some work ahead before the team can carry out large-scale quantum computations. The nuclear spins of the 10 billion or so phosphorus ions used in this experiment were all placed in the same quantum state. To run calculations, however, physicists will need to place different qubits in different states.
The technology also has potential
|Contact: Oli Usher|
University College London