A project of the Theoretical Chemical and Quantum Physics Group

## Team

Ms. Kelly Walker, Mr. Samuel Wilkinson, Dr. Nicolas Vogt, A/Prof. Jared Cole

## Collaborators

M. Marthaler, G. Schön, A. Shnirman: Karlsruhe Institute of Technology

C. Müller: University of Queensland

## Brief Project Outline

Electrical circuits operating at sub-Kelvin temperatures display a range of effects, which can only be described by the laws of quantum mechanics. As these circuits can be fabricated "at will", they provide unique opportunities to study quantum effects where a circuit can be designed specifically to study a particular effect. Quantum circuits already find application in the detection of microscopic magnetic and electric fields, ultra-sensitive amplifiers and ultra-fast electronics. This project investigates the behaviour of quantum circuits for both applications in modern technology and to study fundamental physical principles.

These include:

- Quantum information processing – The generalisation of classical information theory and its use in the design of operation of quantum computers using quantum circuits.
- Quantum Metrology with Josephson junction arrays – The possible application of linear arrays of Josephson junction for providing a quantum definition of the unit of current, the ampere.
- Circuit quantum electrodynamics – Using quantum circuits to replicate effects and behaviour observed in conventional quantum optics experiments, including strong-coupling, coherent-incoherent interactions and single-atom/qubit effects.

## Recent Publications

P. Bushev, C. Müller, J. Lisenfeld, J. H. Cole, A. Lukashenko, A. Shnirman and A. V. Ustinov, *Multi-photon spectroscopy of a hybrid quantum system*, Phys. Rev. B **82**, 134530 (2010)

M. Marthaler, J. Leppäkangas and J. H. Cole, *Circuit-QED analogue of a single-atom injection maser: Lasing, trapping states and multistability*, Phys. Rev. B **83**, 180505 (2011)

K. A. Walker and J. H. Cole, *Correlated charge transport in bilinear tunnel junction arrays*, Physical Review B **88** 245101 (2013))

J. H. Cole, J. Leppakangas and M. Marthaler, *Correlated transport through junction arrays in the small Josephson energy limit: incoherent Cooper-pairs and hot electrons*, New Journal of Physics **16** 063019 (2014)

For more information about this project, please contact Jared Cole.