… As published in Nature today, my colleagues and I have established a world-first in this area. We’ve demonstrated a quantum bit (or qubit) based on the nucleus of a single atom in silicon, promising dramatic improvements for data processing in the ultra-powerful quantum computers of the future.
…What determines the size of the atom is the orbit of the electron. The core of the atom is the nucleus, which contains the positive charge and is about a million times smaller than the electron orbit.
The nucleus itself has a spin, but its magnetic dipole is a thousand times weaker than that of the electron. Our breakthrough consists in the demonstration of a fully functional, readable and writable, quantum bit based on the nuclear spin of a single phosphorus atom.
This was an extraordinary challenge, but it came with big rewards.
Animation and explanation of how we wrote quantum information into the nucleus of an atom in silicon. Credit: UNSWTV
The nucleus is very well isolated from the outside world, and that means a delicate quantum state – the superposition of 0 and 1 – can remain undisturbed for very long time.
We managed to preserve it for 0.06 seconds, which in the quantum world is an eternity. We were able to read out the state of the nucleus with fidelity better than 99.8% – a result comparable with ions trapped in vacuum.
We even succeeded in observing “quantum jumps” (abrupt changes from one energy level to another) of the nuclear spin, something that even Erwin Schroedinger – one of the founding father of quantum mechanics – was sceptical about.
The electron and the nucleus of an atom represent two independent qubits – and that’s a lot of quantum resources in such a small volume. Since they are naturally coupled to each other, we are currently exploring the option of using the nucleus as a “quantum memory” for the state of the electron, which would otherwise decay more quickly.
There is still a long way to go before a large-scale quantum computer becomes available. But now we know silicon can be used to host coherent and high-fidelity qubits, the future looks rosier than ever.
Andrea Morello receives funding from the Australian Research Council and the U.S. Army Research Office.
It is fun to imagine what we would do with computers millions of times more powerful than today’s supercomputers. Perhaps we could simulate a reality to a degree where we could not tell if we were in one.