Skip to main content
European Commission logo print header

Screening of an electron spin by an epitaxial superconducting island in a semiconductor nanowire

Project description

Tales of a superconducting island in a (nanowire) stream

Quantum computing capable of exponentially more computations in a second than classical computing has the potential to change the world with impact on fields from communications and artificial intelligence to security and medicine. The strength of quantum computers rests in the exotic quantum properties of its qubits (quantum bits) that are used to manipulate information. Majorana fermions, also called Majorana modes, are at the top of the most wanted list to act as qubits, but the scientific community is not certain the elusive and exotic quasiparticles have ever been seen. The most likely sighting was in a semiconductor nanowire attached to a superconductor. The EU-funded SpinScreen project will conduct advanced experimental investigations of this system with expected insight reaching far beyond its potential in quantum computing.


Europe’s leadership in quantum technologies can only be sustained by fundamental research. A challenge in this field is to choose the physical platform for qubits, the units of a quantum computer. Semiconductor nanowires coupled to superconductors offer a potential solution as a platform for a new type of qubit, which has the unique advantage of being inherently protected from decoherence.
The physical ingredients of this qubit are Majorana modes. A common device geometry used to investigate transport through these modes is a superconducting island coupled to a nanowire.
However, at this stage little is known about the interactions of islands with quantum dots, which are themselves commonplace near charge depletion. Whereas the interaction of a single dot strongly coupled to a superconductor lead at fixed potential is known to lead to anti-ferromagnetic screening by quasiparticles in the superconductor, the interaction of the dot with an isolated superconductor remains to be explored. If this gap in the knowledge is filled, we could learn to distinguish between subgap states related to screening of the dot, and those involving the island/nanowire hybrid. Crucially, only the latter ones are related to Majorana modes.
At QDev, I will investigate screening by an epitaxial superconducting Al island of a single quantum dot defined in an InAs nanowire. To do this, I will tune the coupling between the island and the dot with a gate voltage and obtain the quantum phase diagram.
While most of Majorana research is understandably focused on how to make a qubit, I will tackle three more fundamental questions, which will serve this purpose in the long run and go substantially beyond the state of the art. 1) How does a single quasiparticle in the island screen a spin? 2) How does screening occur when the island cannot accept quasiparticles? 3) Can novel non-Fermi liquid physics emerge when adding a superconducting lead to the dot-island system?


Net EU contribution
€ 207 312,00
Norregade 10
1165 Kobenhavn

See on map

Danmark Hovedstaden Byen København
Activity type
Higher or Secondary Education Establishments
Other funding
€ 0,00