Despite the inherent incompatibility of low-disorder carbon nanotubes and low-loss microwave resonators, researchers at the University of Basel and ETH Zurich, Switzerland, have found a way to construct a superconducting impedance-matching circuit that allows these two entities to be coupled with a significant increase in bandwidth and signal-to-noise ratio for the development of efficient nanodevices in future electronic circuits. [Nature Commun, DOI: 10.1038/ncomms8165]
The quest for increasingly compact electronic components that can pack more and more functionality or computing power into a smaller volume has perhaps been with us since the invention of the first electrical circuit. With the advent of the concept of nanotechnology in which components just a few dozen nanometers across can be constructed or self-assembled, there is now an urgency in finding stable and workable ways to hook components on this scale together without stumbling over the limitations of the laws of physics.
At the forefront of developments lie the carbon nanotubes, among other materials. Nanotubes offer unique heat conduction, can withstand strong currents and can be used as conductors or semiconductors depending on the precise nature of their implementation. More importantly, in some sense, carbon nanotubes have recently demonstrated their potential as low-disorder one-dimensional electron systems that can be used to probe the physics of spin-orbit and electron-phonon coupling. Additionally, they can also perform initialization and manipulation of spin qubits, making them potential components of a future quantum computer.
However, there is a significant limitation to current efforts to use carbon nanotubes - signal transmission between a carbon nanotube and a much larger electrical conductor component is not truly viable as a large proportion of the electrical signal carried by a component is lost through reflections. Antireflective coatings might work to prevent light bouncing off a sheet of glass, but how does one avoid signal reflections at the nanoscale.
The team used a mechanical transfer method to couple a nanotube to a gigahertz superconducting matching circuit which allows them to interconnect nanotube quantum dots with pristine transport characteristics between them. The transfer approach used by the team allows them to assemble a complex radio frequency device deterministically as well as to choose and use carbon nanotubes with particular properties, metallic or semiconducting, for a particular experiment and then to use the same circuit again with a different set of nanotubes.
The near matching the team has achieved is, they conclude, a "step forward promising high-bandwidth noise correlation measurements on high impedance devices such as quantum dot circuits."
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the bestselling science book "Deceived Wisdom".