## Silicon spin qubits

Spin qubits are one of the prospective types of qubit for future scalable quantum computers. However, reliable fabrication of these basic quantum elements is challenging and requires nearly perfect materials and nanometer precision owing to their small size and sensitivity to the electromagnetic environment. Silicon, which has been the material of choice for classical computing for many years, also has highly desirable properties for the fabrication of spin qubits.

Individually confined electron and hole spins in silicon-based quantum dots have been shown to have exceptionally long lifetimes, up to seconds or longer for electrons in isotopically purified 28Si. Thanks to the tremendous advancement of silicon technology in recent years, reliable fabrication of silicon quantum dots has come within reach. Some of the silicon transistor devices in the latest technology nodes can actually be used directly as spin qubits.

## Why Quantum Computing

Technological progress goes hand in hand with incessant advances in computing power. Modern personal electronic devices have the computational power of a supercomputer from just two decades ago. Computer-aided designs, logistics, data analysis and cognitive computing have become an essential part of modern life. However, current progress in down-scaling transistors reaches physical limits when approaching atomic scales, and heat dissipation becomes a severe issue with increasing transistor densities.

Above all, certain complex physical problems such as computing energy spectra, correlations or time dynamics in molecular and condensed matter systems are beyond the reach of classical computers. These computations require exponential resources. The reason for this is the exponential growth of state space with the number of particles, preventing the computation of systems with more than a modest number of 50 particles. With a few more particles, even future supercomputers are destined to fail in performing exact calculations.

In contrast, a quantum computer has the potential to compute ground-state energies, energy spectra, time dynamics and correlations of such systems efficiently. Moreover, it is expected that certain types of optimization problems with application in logistics, time-scheduling and others can be solved more efficiently with the help of quantum effects.

## Spin qubit fabrication

The cleanroom of the Binnig and Rohrer Nanotechnology Center gives us an ideal environment to explore new materials and fabrication methods and to develop chip designs for a scalable quantum computing architecture.