Andreev qubits help lay the groundwork for quantum computer platforms
According to many computing experts, the future is quantum. Taking advantage of the fact that matter consists of both particles and waves, quantum computing offers vastly increased computation power. This boosted capacity could be applied to many complex global challenges, from cryptography for safer communication, to chemistry for more tailored pharmaceuticals. The challenge is in progressing from the conceptual stage to actually building functioning quantum hardware. In pursuit of such revolutionary rewards, many research groups around the world are dedicated to achieving this. The EU-funded AndQC project worked on a series of experimental and theoretical problems associated with developing a solid-state quantum platform. “Our work investigating semiconductor channels embedded in superconducting quantum circuits, is helping to lay the foundation for further applied research in this transformational field,” says project coordinator Attila Geresdi. The resulting 88 scientific publications are testament to this.
Andreev qubits
In the world of quantum computers, quantum bits, or ‘qubits’, take over the role of the classic binary ‘0’ or ‘1’ bits – the basic units of information that make current computations possible. AndQC was especially interested in particular qubits called ‘Andreev qubits’ because of their unprecedented functionality. Andreev qubits exhibit different ‘levels’ – occupied by zero, one or two electrons – each producing different superconducting properties. AndQC focused on the ‘Andreev spin qubit’, as it offers the possibility of directly coupling a single electron spin and the electronic current flowing around it. The recent Copenhagen Node breakthrough of depositing superconductors with clean interfaces on semiconductor nanostructures, holds out the prospect of building an Andreev qubit platform. In these devices, electrostatic gating could tune the qubit frequency, offering flexibility and scalability. The AndQC team demonstrated the ability to effectively control Andreev qubits, alongside various coupling concepts and combinations of materials. Results were benchmarked against established scalable solid-state quantum technologies, in particular semiconductor spin qubits and superconducting quantum circuits. Leveraging this for a solid-state platform will depend on high-quality semiconductor nanowires and two-dimensional semiconductor heterostructures, along with clean superconductor leads. “We significantly advanced the readiness level of quantum platforms based on Andreev qubits,” adds Geresdi. “But the challenge of the need for clean nanofabrication, as well as finding the right combination of semiconductor and superconductor materials, remains.” The team also investigated as yet unexplored fermionic quantum computation. Fermions are groups of particles with the same spin properties, including protons, neutrons, electrons, neutrinos and quarks. This approach could allow more efficient simulation of electrons (themselves fermions) in molecules and novel materials, overcoming some of the current barriers to the introduction of real-life quantum computing. The project produced a blueprint for the experimental realisation of fermionic quantum computation using Andreev quantum bits.
The quantum leap ahead
Quantum technologies, especially quantum computing, is a strategically important research field for the European Union, as evidenced by the Quantum Flagship initiative and the billions of euro available in funding for its development. “As our scope was limited to an initial demonstration of Andreev quantum bits, now we need to work on its practical implementation, bringing this research closer to the European market. Public-private partnerships could help facilitate this, perhaps supported by the European Innovation Council,” concludes Geresdi.
Keywords
AndQC, quantum, computing, qubit, nano, semiconductor