Near perfect quantum bits demonstrated

This research was announced today by UNSW and Science in Public, read the original release by clicking here.


An Australian-led international team has created near-perfect silicon-based quantum computing components, reaching fidelities higher than 99%.
In doing so they’ve hit a critical fidelity threshold, a significant moment that demonstrates the viability of multi-qubit silicon devices.

The devices, which were made using ANFF NSW’s equipment at UNSW, achieved 1-qubit operation fidelities up to 99.95 per cent, and 2-qubit fidelity of 99.37 per cent with a three-qubit system comprising an electron and two phosphorous atoms, introduced in silicon via ion implantation.

“When the errors are so rare, it becomes possible to detect them and correct them when they occur. This shows that it is possible to build quantum computers that have enough scale, and enough power, to handle meaningful computation,” said Professor Andrea Morello of UNSW, who led the work, with partners in partners in the US, Japan, Egypt, UTS and the University of Melbourne.

The development of quantum components involves a fine balancing act of a number of required properties. Each qubit must preserve information for long enough for it to be used, and must be able to interact with other qubits within the system without the delicate quantum state collapsing. Success in one direction can mean compromising others: recent work by Morello and his team demonstrated that they could preserve information for as long as 35 seconds in a qubit – a relative eternity – but in doing so made it difficult for these long-life qubits to work well with others and errors would occur.

The paper published in Nature by Morello et al. describes how the team overcame this problem by using an electron encompassing two nuclei of phosphorus atoms.

“If you have two nuclei that are connected to the same electron, you can make them do a quantum operation,” says Dr Mateusz Mądzik, one of the lead experimental authors.

“While you don’t operate the electron, those nuclei safely store their quantum information. But now you have the option of making them talk to each other via the electron, to realise universal quantum operations that can be adapted to any computational problem.”

“This really is an unlocking technology,” says Dr Serwan Asaad, another lead experimental author. “The nuclear spins are the core quantum processor. If you entangle them with the electron, then the electron can then be moved to another place and entangled with other qubit nuclei further afield, opening the way to making large arrays of qubits capable of robust and useful computations.”

Looking forward

Excitingly, Morello’s paper is one of three published today in Nature that independently confirm that robust, reliable quantum computing in silicon is now a reality. A Delft team in the Netherlands led by Lieven Vandersypen, and a RIKEN team in Japan led by Seigo Tarucha have also demonstrated similar fidelities using silicon.

A number of base materials are being employed in the race to realise quantum technologies, but the use of silicon is incredibly appealing when considering widespread adoption and production of quantum tech.

Silicon is used heavily in the semiconductor industry, so silicon-based quantum components could be produced using existing manufacturing technologies without having to develop, build, and pay for new fabrication processes required for more exotic qubit foundations.

This promising alignment with conventional manufacturing purposes goes further still –Professor David Jamieson, leader of the University of Melbourne team involved in the Australian-led research published today, explained: “The phosphorous atoms were introduced in the silicon chip using ion implantation, the same method used in all existing silicon computer chips. This ensures that our quantum breakthrough is compatible with the broader semiconductor industry.”

Just last week, Professor Jamieson published research that demonstrated an elegant solution that allows for precise placement of single ions within the silicon in order to create entire arrays of qubits. The team’s technique was developed with assistance from ANFF Victoria’s flagship facility, the Melbourne Centre for Nanofabrication, and involves drilling out a hole in a cantilever used in atomic force microscopy – this allows for single phosphorous atoms to pass through and for them to be detected once in place by listening for a signature “click”.

World-class researchers working with the foresight to pursue approaches with feasible manufacturing options is placing Australia at the forefront of quantum developments. In providing open access to industry-relevant nanofabrication equipment and expertise, ANFF is proud to be able to assist.

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