---
_id: '1763'
abstract:
- lang: eng
  text: The field of cavity quantum electrodynamics (QED), traditionally studied in
    atomic systems, has gained new momentum by recent reports of quantum optical experiments
    with solid-state semiconducting and superconducting systems. In cavity QED, the
    observation of the vacuum Rabi mode splitting is used to investigate the nature
    of matter-light interaction at a quantum-mechanical level. However, this effect
    can, at least in principle, be explained classically as the normal mode splitting
    of two coupled linear oscillators. It has been suggested that an observation of
    the scaling of the resonant atom-photon coupling strength in the Jaynes-Cummings
    energy ladder with the square root of photon number n is sufficient to prove that
    the system is quantum mechanical in nature. Here we report a direct spectroscopic
    observation of this characteristic quantum nonlinearity. Measuring the photonic
    degree of freedom of the coupled system, our measurements provide unambiguous
    spectroscopic evidence for the quantum nature of the resonant atom-field interaction
    in cavity QED. We explore atom-photon superposition states involving up to two
    photons, using a spectroscopic pump and probe technique. The experiments have
    been performed in a circuit QED set-up, in which very strong coupling is realized
    by the large dipole coupling strength and the long coherence time of a superconducting
    qubit embedded in a high-quality on-chip microwave cavity. Circuit QED systems
    also provide a natural quantum interface between flying qubits (photons) and stationary
    qubits for applications in quantum information processing and communication.
acknowledgement: This work was supported by SNF and ETHZ. P.J.L. was supported by
  the EU with an MC-EIF. A.B. was supported by NSERC, CIFAR and FQRNT
author:
- first_name: Johannes M
  full_name: Johannes Fink
  id: 4B591CBA-F248-11E8-B48F-1D18A9856A87
  last_name: Fink
  orcid: 0000-0001-8112-028X
- first_name: M
  full_name: Göppl, M
  last_name: Göppl
- first_name: Matthias
  full_name: Baur, Matthias P
  last_name: Baur
- first_name: R
  full_name: Bianchetti, R
  last_name: Bianchetti
- first_name: Peter
  full_name: Leek, Peter J
  last_name: Leek
- first_name: Alexandre
  full_name: Blais, Alexandre
  last_name: Blais
- first_name: Andreas
  full_name: Wallraff, Andreas
  last_name: Wallraff
citation:
  ama: Fink JM, Göppl M, Baur M, et al. Climbing the Jaynes-Cummings ladder and observing
    its √n nonlinearity in a cavity QED system. <i>Nature</i>. 2008;454(7202):315-318.
    doi:<a href="https://doi.org/10.1038/nature07112">10.1038/nature07112</a>
  apa: Fink, J. M., Göppl, M., Baur, M., Bianchetti, R., Leek, P., Blais, A., &#38;
    Wallraff, A. (2008). Climbing the Jaynes-Cummings ladder and observing its √n
    nonlinearity in a cavity QED system. <i>Nature</i>. Nature Publishing Group. <a
    href="https://doi.org/10.1038/nature07112">https://doi.org/10.1038/nature07112</a>
  chicago: Fink, Johannes M, M Göppl, Matthias Baur, R Bianchetti, Peter Leek, Alexandre
    Blais, and Andreas Wallraff. “Climbing the Jaynes-Cummings Ladder and Observing
    Its √n Nonlinearity in a Cavity QED System.” <i>Nature</i>. Nature Publishing
    Group, 2008. <a href="https://doi.org/10.1038/nature07112">https://doi.org/10.1038/nature07112</a>.
  ieee: J. M. Fink <i>et al.</i>, “Climbing the Jaynes-Cummings ladder and observing
    its √n nonlinearity in a cavity QED system,” <i>Nature</i>, vol. 454, no. 7202.
    Nature Publishing Group, pp. 315–318, 2008.
  ista: Fink JM, Göppl M, Baur M, Bianchetti R, Leek P, Blais A, Wallraff A. 2008.
    Climbing the Jaynes-Cummings ladder and observing its √n nonlinearity in a cavity
    QED system. Nature. 454(7202), 315–318.
  mla: Fink, Johannes M., et al. “Climbing the Jaynes-Cummings Ladder and Observing
    Its √n Nonlinearity in a Cavity QED System.” <i>Nature</i>, vol. 454, no. 7202,
    Nature Publishing Group, 2008, pp. 315–18, doi:<a href="https://doi.org/10.1038/nature07112">10.1038/nature07112</a>.
  short: J.M. Fink, M. Göppl, M. Baur, R. Bianchetti, P. Leek, A. Blais, A. Wallraff,
    Nature 454 (2008) 315–318.
date_created: 2018-12-11T11:53:53Z
date_published: 2008-07-17T00:00:00Z
date_updated: 2021-01-12T06:53:03Z
day: '17'
doi: 10.1038/nature07112
extern: 1
fulldoi: https://doi.org/10.1038/nature07112
intvolume: '       454'
issue: '7202'
main_file_link:
- open_access: '1'
  url: http://arxiv.org/abs/0902.1827
month: '07'
oa: 1
page: 315 - 318
publication: Nature
publication_status: published
publisher: Nature Publishing Group
publist_id: '5358'
quality_controlled: 0
status: public
title: Climbing the Jaynes-Cummings ladder and observing its √n nonlinearity in a
  cavity QED system
type: journal_article
volume: 454
year: '2008'
...