Periodic Reporting for period 3 - TOPSQUAD (TOPOLOGICALLY PROTECTED AND SCALABLE QUANTUM BITS)
Reporting period: 2022-09-01 to 2023-08-31
1. Qubit fragility: current qubit architectures are too fragile to withstand interference from the environment (e.g. noise). This ‘quantum decoherence’ means destruction of the information of the qubits and thus poses a tremendous challenge to build a system of thousands of coherent logical quantum bits.
2. Qubit scalability: the qubit architecture is not scalable enough: the required number of qubits for a universal quantum computer is far out of reach for all proposed quantum systems, including superconducting qubits, ion trap qubits and spin qubits. Depending on the qubit type and architecture, the estimated minimum number of building blocks varies from 10 thousand up to 100 million. The most successful platforms can make between 10 and 100 quantum bits.
In TOSPQUAD, we studied two scalable platforms: germanium-silicon wires and Ge quantum wells. We addressed the qubit fragility by aiming to create topological states - stable states of matter with properties that are not destroyed by local perturbances. We addressed the qubit scalability by developing waferscale fabrication technology, using CMOS-compatible processes.
We successfully realized all necessary ingredients for an engineered topological protected qubit and gained significant insights in the study the underlying physics, such as Majorana or Andreev bound states.
The consolidation of results, novel findings and productive interactions between all the partners led to 16 articles published in high impact journals like Nature Nanotechnology, Nano Letters, Nature Review Materials and Physical Review Letters. Recently, another 2 manuscripts have been submitted and 7 are in preparation.
The potential of the two young high-tech SMEs, Basel Precision Instruments (BASPI) and nanoPHAB, the main suppliers of the TOPSQUAD technologies, has been boosted thanks to the exploitation activities that took place within the project. BASPI focusses on high-sensitivity experiments and nanoPHAB provides unprecedented nanophotonic technologies. At the final stage of the project, multiple categories of exploitation are foreseen: (1) nanofabrication services for quantum physics applications (lead nanoPHAB), (2) nanopatterning of silicon on germanium devices (lead nanoPHAB) (3) high precision instruments for quantum transport experiments - Gate Leakage Current Measurement Box and Low-Noise High-Stability Voltage Preamplifier (lead BASPI), and at longer term (4) proof of concept of topological qubits for quantum computing applications.
TOPSQUAD was exceptionally successful in terms of conquering new grounds, most notably proximity effect in Ge, fast electrical spin qubit control with sweet spots, gatemons and preparing the grounds for Andreev spin qubits. We delivered a major achievement in quantum computation by demonstrating gate tuneable transmon devices in both type-IV platforms: in Ge quantum wells and GeSi core-shell nanowires.