Coupling a superconducting quantum bit to a superconducting resonator oers the opportunity
to investigate the interaction between light and matter with a unique exibility of design,
which allows to explore coupling regimes hardly accessible otherwise [1]. This research area,
referred to as Circuit-Quantum Electrodynamics (Circuit-QED), is also promising in terms of
on-chip quantum information processing. In this talk, we discuss the new eects arising when
the resonator in which the qubit is embedded is itself non-linear. In our experiment, the qubit
(a transmon [2]) is capacitively coupled to a resonator incorporating a Josephson junction that
provides a Kerr non-linearity.
First, taking advantage of the bistability provided by this anharmonicity, we demonstrate
a single-shot, high delity, low backaction and nearly Quantum Non Demolition readout [3].
Gathering all these features is critical for quantum computing. Then, we study the qubit spectrum
while the cavity is pumped by a microwave tone: the most striking feature is the presence
of asymetric sidebands around the transmon transition frequency. We interpret these spectra
through a simple model related to parametric amplication. These experiments illustrate the rich
physics at play in non-linear Circuit-QED, which might become a new playground for probing
the interaction of (articial) atoms with non classical states of light.
References
[1] A. Wallra, D. I. Schuster, A. Blais, L. Frunzio, R.-S. Huang, J. Majer, S. Kumar, S. M. Girvin and
R. J. Schoelkopf, Nature 431 162 (2004)
[2] J. Koch, T.M. Yu, J.M. Gambetta, A.A. Houck, D.I Schuster, J. Majer, A. Blais, M.H. Devoret,
S.M. Girvin, and R.J. Schoelkopf, Phys. Rev. A 76, 042319 (2007)
[3] F. Mallet, F.R. Ong, A. Palacios-Laloy, F. NGuyen, P. Bertet, D. Vion, and D. Estève, Nature
Physics 5, 791-795 (2009)