Manipulating Fock states of a harmonic oscillator while preserving its linearity

  1. Kristinn Juliusson,
  2. Simon Bernon,
  3. Xin Zhou,
  4. Vivien Schmitt,
  5. Hélène le Sueur,
  6. Patrice Bertet,
  7. Denis Vion,
  8. Mazyar Mirahimi,
  9. Pierre Rouchon,
  10. and Daniel Esteve
We present a new scheme for controlling the quantum state of a harmonic oscillator by coupling it to an anharmonic multilevel system (MLS) with first to second excited state transition frequency on-resonance with the oscillator. In this scheme that we call „ef-resonant“, the spurious oscillator Kerr non-linearity inherited from the MLS is very small, while its Fock states can still be selectively addressed via an MLS transition at a frequency that depends on the number of photons. We implement this concept in a circuit-QED setup with a microwave 3D cavity (the oscillator, with frequency 6.4 GHz and quality factor QO=2E-6) embedding a frequency tunable transmon qubit (the MLS). We characterize the system spectroscopically and demonstrate selective addressing of Fock states and a Kerr non-linearity below 350 Hz. At times much longer than the transmon coherence times, a non-linear cavity response with driving power is also observed and explained.
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