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Observing quantum state diffusion by heterodyne detection of fluorescence

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Abstract
A qubit can relax by fluorescence, which prompts the release of a photon into its electromagnetic environment. By counting the emitted photons, discrete quantum jumps of the qubit state can be observed. The succession of states occupied by the qubit in a single experiment, its quantum trajectory, depends in fact on the kind of detector. How are the quantum trajectories modified if one measures continuously the amplitude of the fluorescence field instead? Using a superconducting parametric amplifier, we perform heterodyne detection of the fluorescence of a superconducting qubit. For each realization of the measurement record, we can reconstruct a different quantum trajectory for the qubit. The observed evolution obeys quantum state diffusion, which is characteristic of quantum measurements subject to zeropoint fluctuations. Independent projective measurements of the qubit at various times provide a quantitative verification of the reconstructed trajectories. By exploring the statistics of quantum trajectories, we demonstrate that the qubit states span a deterministic surface in the Bloch sphere at each time in the evolution. Additionally, we show that when monitoring fluorescence field quadratures, coherent superpositions are generated during the decay from excited to ground state. Counterintuitively, measuring light emitted during relaxation can give rise to trajectories with increased excitation probability.
Keywords
RESONANCE FLUORESCENCE, JOSEPHSON RING MODULATOR, JUMPS, LIMIT, SYSTEMS, PHOTON, ATOM, SPIN

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Chicago
Campagne-Ibarcq, Philippe, Pierre Six, Landry Bretheau, Alain Sarlette, Mazyar Mirrahimi, Pierre Rouchon, and Benjamin Huard. 2016. “Observing Quantum State Diffusion by Heterodyne Detection of Fluorescence.” Physical Review X 6 (1).
APA
Campagne-Ibarcq, Philippe, Six, P., Bretheau, L., Sarlette, A., Mirrahimi, M., Rouchon, P., & Huard, B. (2016). Observing quantum state diffusion by heterodyne detection of fluorescence. PHYSICAL REVIEW X, 6(1).
Vancouver
1.
Campagne-Ibarcq P, Six P, Bretheau L, Sarlette A, Mirrahimi M, Rouchon P, et al. Observing quantum state diffusion by heterodyne detection of fluorescence. PHYSICAL REVIEW X. APS; 2016;6(1).
MLA
Campagne-Ibarcq, Philippe et al. “Observing Quantum State Diffusion by Heterodyne Detection of Fluorescence.” PHYSICAL REVIEW X 6.1 (2016): n. pag. Print.
@article{7244915,
  abstract     = {A qubit can relax by fluorescence, which prompts the release of a photon into its electromagnetic environment. By counting the emitted photons, discrete quantum jumps of the qubit state can be observed. The succession of states occupied by the qubit in a single experiment, its quantum trajectory, depends in fact on the kind of detector. How are the quantum trajectories modified if one measures continuously the amplitude of the fluorescence field instead? Using a superconducting parametric amplifier, we perform heterodyne detection of the fluorescence of a superconducting qubit. For each realization of the measurement record, we can reconstruct a different quantum trajectory for the qubit. The observed evolution obeys quantum state diffusion, which is characteristic of quantum measurements subject to zeropoint fluctuations. Independent projective measurements of the qubit at various times provide a quantitative verification of the reconstructed trajectories. By exploring the statistics of quantum trajectories, we demonstrate that the qubit states span a deterministic surface in the Bloch sphere at each time in the evolution. Additionally, we show that when monitoring fluorescence field quadratures, coherent superpositions are generated during the decay from excited to ground state. Counterintuitively, measuring light emitted during relaxation can give rise to trajectories with increased excitation probability.},
  articleno    = {011002},
  author       = {Campagne-Ibarcq, Philippe and Six, Pierre and Bretheau, Landry  and Sarlette, Alain and Mirrahimi, Mazyar and Rouchon, Pierre and Huard, Benjamin},
  issn         = {2160-3308},
  journal      = {PHYSICAL REVIEW X},
  keywords     = {RESONANCE FLUORESCENCE,JOSEPHSON RING MODULATOR,JUMPS,LIMIT,SYSTEMS,PHOTON,ATOM,SPIN},
  language     = {eng},
  number       = {1},
  publisher    = {APS},
  title        = {Observing quantum state diffusion by heterodyne detection of fluorescence},
  url          = {http://dx.doi.org/10.1103/PhysRevX.6.011002},
  volume       = {6},
  year         = {2016},
}

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