I am aiming to put together a Majorana qubit with a superconducting qubit, and use the coupling between them to read the state of the Majorana qubit from the microwave frequency response of the resonator in the superconducting qubit. This device paves the way to future generation of quantum computers and is the beginning of many studies to exploit Majorana fermions and their unique topological features.
Each elementary particle has an antiparticle, following Dirac’s equation. In a superconductor, the creation operator, γ†, and the annihilation operator, γ, for quasiparticles at energy E obey the following relation: γ(E) = γ†(−E). In the middle of the superconducting gap, where E = 0 (Fermi level) there can exist a quasiparticle for which γ = γ†, the annihilation and creation of a particle are the same operation and hence this particle is its own antiparticle – Majorana fermion. To create Majorana modes one needs a ballistic semiconductor nanowire with strong spin-orbit interaction that is in the proximity of a conventional superconductor, and the Majorana modes can be realized at the ends of the nanowire.
A pair of Majorana bound state forms a two-level system and hence a quantum bit (qubit). In qubits encoded in Majorana fermions, the information is stored in a topological property of the system. This protects the information from decoherence. The very same fact also makes it very challenging to control and coherently transfer the information into and out of the system once we need it. Superconducting qubits (solid state electrical circuits based on Josephson junctions), on the other hand, are easy to control, read out, and couple together. A fascinating idea is to put together a superconducting qubit with Majorana fermions and form a two-qubit hybrid quantum system that leverages the advantages of both qubits via their coupling. The superconducting qubit is used to read out the Majorana states, while the other qubit may act as a local quantum memory. Hence, this hybrid system can be used as a building block for a full-scale quantum computer which demands a physical qubit that is scalable, has a well-defined initial state, and brings together coherence with reliable control and read-out.