April 23, 2024

The solution to the operational speed/coherence tradeoff could be electron holes.

New research reveals holes in the solution to operational speed/coherence and possible scaling up of qubits into a mini-quantum computing system.

Quantum computers will be far more powerful and efficient than the ‘classical’ computer today.

A way to create a quantum bit is to use spin, an electron that can point up or down. We want quantum computers to be as efficient and fast as possible using only electric fields. Common electrodes are used to apply them.

Spin does not usually ‘talk’ with electric fields, but in certain materials, spins can interact indirectly with electric fields. These are the most exciting materials being studied in quantum computing.

The spin-orbit interaction is the interaction that allows spins to talk with electric fields. It can be traced back to Einstein’s theory of relativity.

Researchers in quantum computing have been concerned that if this interaction is vital, any increase in the speed of operation would be offset by a loss of coherence (essentially, how long can we preserve quantum information).

“If electrons begin to talk to the electrical fields we apply to the lab, then this means that they are also exposed (generally called noise’) to unwanted, fluctuating electric fields that exist in any matter (generally called ‘noise’). Those electrons’ fragile quantum info would be destroyed,” said A/Prof Dimi (UNSW/FLEET), the lead of the theoretical roadmap study.

“But our study shows that this fear is not justified.”

“Our theoretical studies have shown that holes can be used to solve the problem. These holes are considered an absence of electrons, acting like positively-charged electrons.

This protects a quantum bit against charge fluctuations arising from the solid background.

Furthermore, the qubit’s sensitivity to noise is minimized at the “sweet spot,” where it can operate the fastest.

Dimi says that the study has shown that such a point is possible in quantum bits made up of holes. It also provides guidelines for experimentalists in reaching these points in their labs.

The dephasing time, or how long the quantum information is retained, is plotted against the applied electrical field. This controls the properties and thereby indicates a maximum sweet spot’. 

These points will allow experimental efforts to preserve as much quantum information as possible. These will provide strategies for “scaling up” quantum bits, i.e., building an ‘array of bits that could work as a mini quantum computer.

“This theory is crucial for scaling up quantum processors, and the first experiments have been performed,” said Prof Sven Rogge, Centre for Quantum Computing and Communication Technology (CQC 2T).

A/Prof Joe Salfi, University of British Columbia, says, “our recent experiments on hole qubits using silicon acceptors already demonstrated longer coherence time than we expected.” It is encouraging to see these observations have a solid theoretical basis. The prospects for hole qubits look bright indeed.

Leave a Reply

Your email address will not be published. Required fields are marked *