(Phys.org) A new study indicates holes the solution to operational speed/coherence trade-off, potential scaling up of qubits to a mini-quantum computer.
One way to make a quantum bit is to use the ‘spin’ of an electron, which can point either up or down. To make quantum computers as fast and power-efficient as possible we would like to operate them using only electric fields, which are applied using ordinary electrodes.
Although spin does not ordinarily ‘talk’ to electric fields, in some materials spins can interact with electric fields indirectly, and these are some of the hottest materials currently studied in quantum computing. The interaction that enables spins to talk to electric fields is called the spin-orbit interaction.
The fear of quantum-computing researchers has been that when this interaction is strong, any gain in operation speed would be offset by a loss in coherence (essentially, how long we can preserve quantum information).
“If electrons start to talk to the electric fields we apply in the lab, this means they are also exposed to unwanted, fluctuating electric fields that exist in any material (generically called `noise’) and those electrons’ fragile quantum information would be destroyed,” says A/Prof Dimi Culcer (UNSW/FLEET), who led the theoretical roadmap study.
“But our study has shown this fear is not justified.”
“Our theoretical studies show that a solution is reached by using holes, which can be thought of as the absence of an electron, behaving like positively-charged electrons.”
n this way, a quantum bit can be made robust against charge fluctuations stemming from the solid background.
Moreover, the ‘sweet spot’ at which the qubit is least sensitive to such noise is also the point at which it can be operated the fastest.

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