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University of Basel

25 March 2022

“Hot” spin quantum bits in silicon transistors

Schematic of the architecture of the silicon chips with hole spin qubits
The newly developed qubits are based on so-called holes (red) whose spin (arrow) in one or the other direction stores the information. They are arranged in an architecture based on silicon transistors. (Illustration: NCCR Spin)

Quantum bits (qubits) are the smallest units of information in a quantum computer. Currently, one of the biggest challenges in developing this kind of powerful computer is scalability. A research group at the University of Basel, working with the IBM Research Laboratory in Rüschlikon, has made a breakthrough in this area.

Quantum computers promise unprecedented computing power, but to date prototypes have been based on just a handful of computing units. Exploiting the potential of this new generation of computers requires combining large quantities of qubits.

It is a scalability problem which once affected classic computers, as well; in that case it was solved with transistors integrated into silicon chips. The research team led by Dr. Andreas Kuhlmann and Professor Dominik Zumbühl from the University of Basel has now come up with silicon-based qubits that are very similar in design to classic silicon transistors. The researchers published their findings in the journal Nature Electronics.

Building on classic silicon technology

In classic computers, the solution to the scalability problem lay in silicon chips, which today include billions of “fin field-effect transistors” (FinFETs). These FinFETs are small enough for quantum applications; at very low temperatures near absolute zero (0 kelvin or -273.15 degrees Celsius), a single electron with a negative charge or a “hole” with a positive charge can act as a spin qubit. Spin qubits store quantum information in the two states spin-up (intrinsic angular momentum up) and spin-down (intrinsic angular momentum down).

NCCR Spin

This work was conducted at the National Center of Competence in Research SPIN, which was launched in 2020 and is led by the University of Basel. The NCCR SPIN works on scalable spin qubits in semiconductor nanostructures of silicon and germanium, and is developing small, fast qubits for a universal quantum computer.

The SPIN network brings together research groups from the fields of experimental and theoretical physics, materials science, engineering, and computer science, spanning EPFL and ETH Zurich as well as the IBM Research – Zurich lab. In addition to research and development on its commercial superconducting quantum computers, IBM also carries out exploratory research into other qubit technologies, such as spin qubits, at its Zurich research center.

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