A team led by Professor Andrea Morello has just demonstrated the operation of a new type of quantum bit, called 'flip-flop' qubit, which combines the exquisite quantum properties of single atoms, with easy controllability using electric signals, just as those used in ordinary computer chips.
A deliberate target: electrical control of a single-atom quantum bit
"Sometimes new qubits, or new modes of operations, are discovered by lucky accident. But this one was completely by design," says Prof. Morello. "Our group has had excellent qubits for a decade, but we wanted something that could be controlled electrically, for maximum ease of operation. So we had to invent something completely new."
Prof. Morello's group was the first in the world to demonstrate that using the spin of an electron as well as the nuclear spin of a single phosphorus atom in silicon could be used as 'qubits' – units of information that are used to make quantum computing calculations. He explains that while both qubits perform exceptionally well on their own, they require oscillating magnetic fields for their operation.
"Magnetic fields are difficult to localise at the nanometre scale, which is the typical size of the individual quantum computer components. This is why the very first proposal for a silicon quantum bit envisaged having all the qubits immersed in a uniform oscillating magnetic field, applied across the whole chip, and then using local electric fields to select which qubit gets operated."
A few years ago, Prof. Morello's team had a realisation: by defining the qubit as the combined up-down / down-up orientation of the electron and the nucleus of the atom would permit controlling such qubit using the electric fields alone. Today's result is the experimental demonstration of that visionary idea.
"This new qubit is called 'flip-flop' because it's made out of two spins belonging to the same atom – the electron and the nuclear spin – with the condition that they always point in opposite directions," says Dr Rostyslav Savytskyy, one of the lead experimental authors of the paper, published in Science Advances.
