Best position for Silicon Atom Qubits to increase Atomic-based quantum processors

Atomic scale of two interacting silicon donors. Credit: CQC2T

Australian researchers have found a “sweet spot” for placing qubits in silicon to increase it atom– quantum based processors.

Researchers at the Center for Excellence in Quantum Computing and Communication Technologies (CQC)2T) Working with Silicon Quantum Computing (SQC) they have placed a ‘sweet spot’ for placing qubits in silicon to increase quantum processors based on atoms.

Generation of quantum bits or qubits by placing phosphorus atoms in silicon precisely – Method initiated by CQC2Professor Michelle Simmons Director T – is a global leader in the development of quantum silicon computers.

In the group’s study, published today Nature Communications, accurate placement has been shown to be essential for the development of strong interactions or couplings between qubits.

“We have positioned ourselves in the best position to create reproducible, strong and fast interactions between qubits,” says Professor Sven Rogge, head of research.

“We need these strong interactions to design a multi-qubit processor and ultimately a useful quantum computer.”

Two qubit gates – the central construction of a quantum computer – use interactions between qubit pairs to perform quantum operations. For qubits in the silicon atom, previous research has suggested that interactions between qubits at certain positions in the silicon crystal have an oscillation of components that can be difficult to slow down and control gate operations.

“For almost two decades, the potential oscillating nature of interactions has been predicted to be challenging to increase in scale,” says Professor Rogge.

“Now, with new measurements of qubit interactions, we have a deep understanding of the nature of these oscillations and proposed a strategy for accurately positioning them so that the interaction between qubits is strong. This is an outcome that many thought was impossible.”

Finding the ‘sweet spot’ in symmetrical crystals

Researchers say they have now found that exactly where you place your qubits is essential to creating strong, consistent interactions. This crucial approach has major implications for the design of large-scale processors.

“Silicon is an anisotropic crystal, which means that the direction in which atoms are placed can have a major impact on the interactions between them,” says Dr. Benoit Voisin, author of the study.

“Although we were aware of this anisotropy, no one studied in detail how it could be used to relieve the oscillating force of the interaction.”

“We found that there is a special angle or sweet spot within a given plane of silicon crystal where the interaction between qubits is resistant. It is important that this sweet spot can be obtained using existing scanning tunneling microscopy (STM) lithography techniques developed at UNSW.”

“In the end, both the problem and the solution arise directly from the crystal symmetries, so it’s a nice turn.”

Using STM, groups are able to map the wave function of atoms in 2D images and determine their spatial location in silicon crystal – first demonstrated in 2014 Materials of nature and advanced in 2016 Nanotechnology of Nature paper.

In recent research, the team used the same STM technique to observe details at the atomic scale about the interactions between double atoms.

“Using the imaging technique of our quantum state, we were able to see the anisotropy of the wave function and the effect of direct interference in the plane for the first time – this was the starting point for understanding how this problem behaves,” says Dr. Voisin.

“We first understood that we needed to work on the effect of each of these two components individually before examining the full picture to solve the problem – this is how we could find this sweet spot with the accuracy of an easily located atomic location provided by our STM lithography technique.”

Silicon quantum computer builds atom by atom

CQC UNSW scientists2They are leading the world in the race to build silicon-based quantum computers in silicon. CQC researchers2T, and its associated marketing company SQC, is the only team in the world with the ability to see the exact location in the solid state of qubits in the world.

In 2019, the Simmons team achieved an important milestone in its approach to accuracy – the team first began building the fastest two-qubit silicon gate, placing two-atom qubits next to each other, and then observing and measuring their spin conditions in real time. . The research was published in Nature.

Now, with the latest advances from the Rogge team, CQC researchers2These T and SQC interactions are positioned for use on larger scale systems to achieve scalable processors.

“Observing and accurately locating atoms on silicon chips continues to provide a competitive advantage for manufacturing quantum computers in silicon,” says Professor Simmons.

The combined Simmons, Rogge and Rahman teams are working with SQC to build the first useful and commercial quantum silicon computer. Located with CQC2At the UNSW Sydney campus, SQC aims to build the highest quality and most stable quantum processors.


B. Valley, J. Bocquel, A. Tankasala, M. Usman, J. Salfi, R. Rahman, MY Simmons, LCL Hollenberg, and S. Rogge’s “Valley interference and spin exchange in silicon on an atomic scale.” 2020, Nature Communications.
DOI: 10.1038 / s41467-020-19835-1

“Resolving Quantitative Interference in a Silicon in a Judge Spatially” by J. Salfi, JA Mol, R. Rahman, G. Klimeck, MY Simmons, LCL Hollenberg, and S. Rogge, April 6, 2014. Materials of nature.
DOI: 10.1038 / nmat3941

“Spatial metrology of dopants in silicon with precision of specific lattice sites” M. Usman, J. Bocquel, J. Salfi, B. Voisin, A. Tankasala, R. Rahman, MY Simmons, S. Rogge, and LCL Hollenberg, 6 June. 2016, Nanotechnology of Nature.
DOI: 10.1038 / nnano.2016.83

Y. He, SK Gorman, D. Keith, L. Kranz, JG Keizer, and MY Simmons, “Two-Qubit Gate Between Electrons of Silicon Phosphorus Donors,” July 17, 2019. Nature.
DOI: 10.1038 / s41586-019-1381-2

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