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@ARTICLE{Hell:824045,
      author       = {Hell, Michael and Wegewijs, Maarten Rolf and DiVincenzo,
                      David},
      title        = {{Q}ubit quantum-dot sensors: {N}oise cancellation by
                      coherent backaction, initial slips, and elliptical
                      precession},
      journal      = {Physical review / B},
      volume       = {93},
      number       = {4},
      issn         = {2469-9950},
      address      = {Woodbury, NY},
      publisher    = {Inst.},
      reportid     = {FZJ-2016-06669},
      pages        = {045418},
      year         = {2016},
      abstract     = {We theoretically investigate the backaction of a sensor
                      quantum dot with strong local Coulomb repulsion on the
                      transient dynamics of a qubit that is probed capacitively.
                      We show that the measurement backaction induced by the noise
                      of electron cotunneling through the sensor is surprisingly
                      mitigated by the recently identified coherent backaction [M.
                      Hell, M. R. Wegewijs, and D. P. DiVincenzo, Phys. Rev. B 89,
                      195405 (2014)] arising from quantum fluctuations. This
                      indicates that a sensor with quantized states may be
                      switched off better than naively expected. This
                      renormalization effect is missing in semiclassical
                      stochastic fluctuator models and typically also in
                      Born-Markov approaches, which try to avoid the calculation
                      of the nonstationary, nonequilibrium state of the qubit plus
                      sensor. Technically, we integrate out the current-carrying
                      electrodes to obtain kinetic equations for the joint,
                      nonequilibrium detector-qubit dynamics. We show that the
                      sensor current response, level renormalization, cotunneling
                      broadening, and leading non-Markovian corrections always
                      appear together and cannot be turned off individually in an
                      experiment or ignored theoretically. We analyze the
                      backaction on the reduced qubit state—capturing the full
                      non-Markovian effects imposed by the sensor quantum dot on
                      the qubit—by applying a Liouville-space decomposition into
                      quasistationary and rapidly decaying modes. Importantly, the
                      sensor cannot be eliminated completely even in the simplest
                      high-temperature, weak-measurement limit since the qubit
                      state experiences an initial slip depending on the initial
                      preparation of qubit plus sensor quantum dot. The slip
                      persists over many qubit cycles, i.e., also on the time
                      scale of the qubit decoherence induced by the backaction. A
                      quantum-dot sensor can thus not be modeled as usual as a
                      “black box” without accounting for its dynamical
                      variables; it is part of the quantum circuit. We furthermore
                      find that the Bloch vector relaxes (rate 1/T1) along an axis
                      that is not orthogonal to the plane in which the Bloch
                      vector dephases (rate 1/T2), blurring the notions of
                      relaxation and dephasing times. Moreover, the precessional
                      motion of the Bloch vector is distorted into an ellipse in
                      the tilted dephasing plane.},
      cin          = {IAS-3 / PGI-2 / JARA-FIT},
      ddc          = {530},
      cid          = {I:(DE-Juel1)IAS-3-20090406 / I:(DE-Juel1)PGI-2-20110106 /
                      $I:(DE-82)080009_20140620$},
      pnm          = {144 - Controlling Collective States (POF3-144)},
      pid          = {G:(DE-HGF)POF3-144},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000368486600010},
      doi          = {10.1103/PhysRevB.93.045418},
      url          = {https://juser.fz-juelich.de/record/824045},
}