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@ARTICLE{Hell:171952,
      author       = {Hell, Michael and Wegewijs, Maarten Rolf and DiVincenzo,
                      David},
      title        = {{C}oherent back action of quantum dot detectors: {Q}ubit
                      spin precession},
      journal      = {Physical review / B},
      volume       = {89},
      number       = {19},
      issn         = {1098-0121},
      address      = {College Park, Md.},
      publisher    = {APS},
      reportid     = {FZJ-2014-05506},
      pages        = {195405},
      year         = {2014},
      abstract     = {A sensitive technique for the readout of the state of a
                      qubit is based on the measurement of the conductance through
                      a proximal sensor quantum dot (SQD). Here, we theoretically
                      study the coherent backaction of such a measurement on a
                      coupled SQD-charge-qubit system. We derive Markovian kinetic
                      equations for the ensemble-averaged state of the SQD-qubit
                      system, expressed in the coupled dynamics of two
                      charge-state occupations of the SQD and two qubit isospin
                      vectors, one for each SQD charge state. We find that aside
                      from introducing dissipation, the detection also
                      renormalizes the coherent evolution of the SQD-qubit system.
                      Basically, if the electron on the detector has time to probe
                      the qubit, then it also has time to fluctuate and thereby
                      renormalize the system parameters. In particular, this
                      induces torques on the qubit isospins, similar to the spin
                      torque generated by the spintronic exchange field in
                      noncollinear spin-valve structures. Second, we show that for
                      a consistent description of the detection, one must also
                      include the renormalization effects in the next-to-leading
                      order in the electron tunneling rates, especially at the
                      point of maximal sensitivity of the detector. Although we
                      focus on a charge-qubit model, our findings are generic for
                      qubit readout schemes that are based on spin-to-charge
                      conversion using a quantum dot detector. Furthermore, our
                      study of the stationary current through the SQD, a test
                      measurement verifying that the qubit couples to the detector
                      current, already reveals various significant effects of the
                      isospin torques on the qubit. Our kinetic equations provide
                      a starting point for further studies of the time evolution
                      in charge-based qubit readout. Finally, we provide a
                      rigorous sum rule that constrains such approximate
                      descriptions of the qubit isospin dynamics and show that it
                      is obeyed by our kinetic equations.},
      cin          = {PGI-2 / JARA-FIT},
      ddc          = {530},
      cid          = {I:(DE-Juel1)PGI-2-20110106 / $I:(DE-82)080009_20140620$},
      pnm          = {422 - Spin-based and quantum information (POF2-422)},
      pid          = {G:(DE-HGF)POF2-422},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000335560500004},
      doi          = {10.1103/PhysRevB.89.195405},
      url          = {https://juser.fz-juelich.de/record/171952},
}