DEMETER · A scalable semiconductor quantum computation platform based on Ge hole spin-qubits in rhombic quadruple quantum dots in strained Ge/SiGe

A scalable semiconductor quantum computation platform based on Ge hole spin-qubits in rhombic quadruple quantum dots in strained Ge/SiGe

A quantum computer works fundamentally differently to a classical computer since quantum superposition takes advantage of the exciting ability of quantum particles to exist in more than one state at the same time. Because of quantum particle behaviour, some tasks such as superdense coding and teleporting unknown states, which are impossible to realize with classical resources, become possible. To achieve an advantage beyond the capabilities of any classical computer, quantum researchers and major national and international programmes such as the EU Quantum Technologies Flagship are focusing on speeding up common computational tasks including unsorted database searches and factorization. There are several proposed platforms for qubit realization, and quantum computation. Broadly they can be based on ion-traps, superconducting junctions, photonic circuits and semiconductor quantum dots, each of which can reach different clock speed and gate fidelity. While there has been great scientific progress and proof-of-concept demonstrations on all of these platforms, to address the challenge of scalability it makes sense to use all the machinery of traditional semiconductor integrated circuits which also opens the possibility of integrating classical computing with quantum accelerators. Semiconductor-based qubit platforms have gained significant traction and unlike superconducting qubits, which require highly complex control mechanisms, they offer natural scalability and compatibility with complementary metal-oxide-semiconductor (CMOS) technology. To this end, DEMETER employed a semiconductor materials platform and aimed at exploring qubits in electrostatically defined quantum dots by focusing on their fabrication, characterization, and integration with high-speed readout methodologies. The DEMETER project was conceived to push the boundaries of semiconductor-based quantum computing by exploring hole-spin qubits in germanium (Ge) quantum wells and its tin alloy (GeSn). The motivation behind this research stems from the need for scalable quantum computing architectures that leverage the mature fabrication techniques of semiconductor industries. The central idea was to develop rhombic quadruple quantum dot (RQQD) systems using strained Ge/SiGe heterostructures, providing a robust platform for high-fidelity qubit manipulation. Compared to spin qubits in silicon (Si), where unfavourable band alignment prevents strain engineering, low-disorder reproducible quantum wells for high-mobility holes can be realized in strained Ge/SiGe heterostructures. The exact relation between the electrically-tuneable spin-orbit coupling in Ge and the operation temperature is not well known but due to the low effective mass and high mobility it may be expected that holes in strained Ge/SiGe can operate at a temperature higher than 1.5K, which is state-of-the art for Si. This would allow integration of the driving cryo-electronics closer to the quantum circuit, further avoiding any sources of noise.

Data: CORDIS, © European Union