---
res:
  bibo_abstract:
  - 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.@eng
  bibo_authorlist:
  - foaf_Person:
      foaf_givenName: Johannes M
      foaf_name: Johannes Fink
      foaf_surname: Fink
      foaf_workInfoHomepage: http://www.librecat.org/personId=4B591CBA-F248-11E8-B48F-1D18A9856A87
    orcid: 0000-0001-8112-028X
  - foaf_Person:
      foaf_givenName: M
      foaf_name: Göppl, M
      foaf_surname: Göppl
  - foaf_Person:
      foaf_givenName: Matthias
      foaf_name: Baur, Matthias P
      foaf_surname: Baur
  - foaf_Person:
      foaf_givenName: R
      foaf_name: Bianchetti, R
      foaf_surname: Bianchetti
  - foaf_Person:
      foaf_givenName: Peter
      foaf_name: Leek, Peter J
      foaf_surname: Leek
  - foaf_Person:
      foaf_givenName: Alexandre
      foaf_name: Blais, Alexandre
      foaf_surname: Blais
  - foaf_Person:
      foaf_givenName: Andreas
      foaf_name: Wallraff, Andreas
      foaf_surname: Wallraff
  bibo_doi: 10.1038/nature07112
  bibo_issue: '7202'
  bibo_volume: 454
  dct_date: 2008^xs_gYear
  dct_publisher: Nature Publishing Group@
  dct_title: Climbing the Jaynes-Cummings ladder and observing its √n nonlinearity
    in a cavity QED system@
...