A microwave transmission line can be tapered from millimetre to nanometre sizes to deliver an oscillating magnetic field to a single-spin quantum bit. The group’s work shows how properties such as impedance, transmission modes, discontinuities and dimensions, can significantly hinder the behaviour of the line at frequencies above 10 GHz if they are not appropriately addressed in the design. The study also highlights important considerations when modelling these types of structures using electro-magnetic simulation software.

Early rewards

These guidelines for nanoscale microwave antenna design have recently been used to operate an electron spin qubit based on a single phosphorus atom in silicon. The team successfully applied coherent excitations at frequencies as high as 50 GHz to write quantum information on the atom.

This experiment is the first milestone in an ambitious project that aims to combine quantum information processing with industry-standard silicon nanofabrication, to deliver a revolutionary quantum computer that can be produced using the same technological platform as modern CPUs – plus some careful microwave design.

More information on the study can be found in the journal Nanotechnology.