Quantum physics in one spatial dimension is peculiar and remarkably rich, yet even with strong interactions and disorder, surprisingly tractable. This is due to the fact that the lowenergy physics of nearly all 1D systems can be cast in terms of the Luttinger liquid, a key concept that parallels that of the Fermi liquid in higher dimensions. Although there have been many theoretical proposals to use linear chains and ladders of Josephson junctions to create novel quantum phases and innovative electronic devices, for example, quantum systems with topologically protected states, only modest progress has been made experimentally. One major roadblock has been understanding the role of disorder in such systems.

I will present recent experiments from our lab that shed light on the competition between the Mott insulator and Bose glass, and strongly confirm the quantum theory of onedimensional disordered bosonic systems. The Bose glass phase is thought to describe helium-4 in porous media, cold atoms in disordered optical potentials, disordered magnetic insulators, and thin superconducting films. The ubiquity of such an electronic glass in Josephson-junction chains has important implications for their proposed use as a fundamental current standard, which is based on synchronisation of coherent tunnelling of flux quanta (quantum phase slips). We have also recently extended our measurements to SQUID chains and ladders, finding quite unexpected and tantalising behaviour.

Contact : Tim Duty