New developments in solid-state, spin-based quantum computing platforms are reported in a pair of papers published online this week in Nature. The studies report the creation of a programmable two-bit processor, and the strong coupling of a single electron spin and a single photon (which could enable isolated qubits, the building blocks of a quantum computer, to interact).
Much progress has been made in developing the individual components that might one day make up a spin-based quantum computing system. Thomas Watson and colleagues have taken this a leap further, producing a two-qubit device that can be programmed to perform two different quantum algorithms: the Deutsch-Jozsa algorithm - a test problem designed to be easier to solve using a quantum approach than a classical one - and Grover’s search algorithm - which could be used for searching through a database. The development paves the way to larger spin-based processors capable of more flexible applications.
An advantage of building a quantum computer based on semiconductor spin qubits is their long lifetimes in comparison with their superconducting counterparts. However, their weak interactions make them difficult to couple, which is necessary for a quantum processor to work. Existing coupling methods - the so-called exchange and dipole-dipole interactions - are relatively local in nature. To connect distant quantum bits, a ‘middle man’ is required, such as a microwave photon.
In the second study, Jason Petta and colleagues show that a photon confined in a microwave cavity can be strongly coupled to an electron spin trapped in a silicon double quantum dot. This set-up enables spin-photon coupling rates sufficient to ensure a coherent interface between the two components, bringing large-scale spin-based quantum processors another step closer.