The first quantum revolution provided a microscopic understanding of nature and underpinned the development of transistors, originally made in germanium. The following assembly of silicon transistors into integrated circuits triggered the digital age, which completely changed our daily life. We are now in the midst of the second quantum revolution, in which quantum matter is engineered to develop disruptive technologies beyond the reach of classical understanding.

Quantum computing is considered by many the man on the moon goal of such second quantum revolution. How will we get there? In this talk I will discuss, from a materials perspective, how we are turning everyday silicon into the quantum computing wonder material by using quantum dots defined electrostatically in SiGe heterostructures.

Group-IV semiconductors Si and Ge offer several advantages for the realization of spin quantum bits. Si and Ge can be isotopically purified into a nuclear spin free materials, which allows long spin coherence time. A quantum dot defined by metallic gates in a strained Si/SiGe heterostructure can trap a single electron, such that the electron spin can be operated as a quantum bit, the elementary unit of quantum computation. Quantum dots in Si/SiGe heterostructure are promising because bear similarities from a materials and integration perspective to the transistors used in advanced semiconductor manufacturing. Advanced quantum control in Si qubits allows to run quantum algorithms on two qubit processors. Strong spin-photon coupling has been achieved in Si, a first step towards realizing large networks of quantum dot based spin qubit registers.[1] Additionally, SiGe heterostructures allows us to explore high mobility holes in strained Ge as a complementary option for fast quantum hardware due to the different band structure properties of Ge compared to Si. Recently, gate-controlled stable quantum dots were demonstrated in planar Ge, a first step towards Ge hole qubits.[2]

However, to deploy a qubit into high volume manufacturing in a quantum computer requires stringent control over substrate uniformity and quality. In this talk we will focus on carrier mobility and energetic valley splittings in SiGe heterostructures, which are two key electrical metrics of substrate quality relevant for qubits. To ensure rapid progress in quantum wells development we have implemented fast feedback loops from materials growth, to innovative heterostructure field effect transistor fabrication, and low temperature characterization. In this direction we show progress in developing a cryogenic platform for high-throughput magnetotransport measurements.

[1] N. Samkharadze, G. Zheng, N. Kalhor, D. Brousse, A. Sammak, U. C. Mendes, A. Blais, G. Scappucci, and L. M. K. Vandersypen, Science , eaar4054 (2018).

[2] N. W. Hendrickx, D.P. Franke, A. Sammak, M. Kouwenhoven, D. Sabbagh, L. Yeoh, R. Li, M. L. V. Tagliaferri, M. Virgilio, G. Capellini, G. Scappucci, M. Veldhorst, arXiv:1801.08869 (2018)