The New Quantum Era

Chapter 10. Man-Made Atoms

Mercury has passed into a new state, which on account of its extraordinary electrical properties may be called the superconductive state.

Heike Kamerlingh Onnes

The story of superconducting qubits begins with the phenomenon of superconductivity itself. When electrons travel through a material, they encounter resistance, a sort of friction against their forward movement that causes some energy to dissipate in the form of heat and other by-products. Resistance is why an electrical device will feel warm to the touch when plugged into a power supply. The phenomenon was discovered in 1911 by Dutch physicist Heike Kamerlingh Onnes, but finding an explanation for the behavior would take decades of effort. In the late 1950s, a trio of physicists at the University of Illinois Urbana-Champaign collaborated on research into the conditions under which resistance disappears and a material behaves as a superconductor. John Bardeen, Leon Cooper, and their grad student Robert Schrieffer were working with materials that, when cooled to very low temperatures using liquid helium, would cause electrons to be attracted to one another and form pairs. These are now called Cooper pairs, and once they have formed, all the pairs of electrons move in correlation with one another, with absolutely no resistance. A current flowing through a superconducting circuit will go on forever with no energy dissipation, even after the source of the current is disconnected, so long as the ...