% IMPORTANT: The following is UTF-8 encoded.  This means that in the presence
% of non-ASCII characters, it will not work with BibTeX 0.99 or older.
% Instead, you should use an up-to-date BibTeX implementation like “bibtex8” or
% “biber”.

@ARTICLE{Saptsov:154994,
      author       = {Saptsov, R. B. and Wegewijs, M. R.},
      title        = {{T}ime-dependent quantum transport: {C}ausal superfermions,
                      exact fermion-parity protected decay modes, and {P}auli
                      exclusion principle for mixed quantum states},
      journal      = {Physical review / B},
      volume       = {90},
      number       = {4},
      issn         = {1098-0121},
      address      = {College Park, Md.},
      publisher    = {APS},
      reportid     = {FZJ-2014-04193},
      pages        = {045407},
      year         = {2014},
      abstract     = {We extend the recently developed causal superfermion
                      approach to the real-time diagrammatic transport theory to
                      time-dependent decay problems. Its usefulness is illustrated
                      for the Anderson model of a quantum dot with tunneling rates
                      depending on spin due to ferromagnetic electrodes and/or
                      spin polarization of the tunnel junction. This approach
                      naturally leads to an exact result for one of the
                      time-dependent decay modes for any value of the Coulomb
                      interaction compatible with the wideband limit. We
                      generalize these results to multilevel Anderson models and
                      indicate constraints they impose on renormalization-group
                      schemes in order to recover the exact noninteracting
                      limit.(i) We first set up a second quantization scheme in
                      the space of density operators constructing “causal”
                      field superoperators using the fundamental physical
                      principles of causality/probability conservation and
                      fermion-parity superselection (univalence). The
                      time-dependent perturbation series for the time evolution is
                      renormalized by explicitly performing the wideband limit on
                      the superoperator level. As a result, the occurrence of
                      destruction and creation superoperators are shown to be
                      tightly linked to the physical short- and long-time
                      reservoir correlations, respectively. This effective theory
                      takes as a reference a damped local system, which may also
                      provide an interesting starting point for numerical
                      calculations of memory kernels in real time. (ii) A
                      remarkable feature of this approach is the natural
                      appearance of a fermion-parity protected decay mode which
                      can be measured using a setup proposed earlier [Phys. Rev. B
                      85, 075301 (2012)]. This mode can be calculated exactly in
                      the fully Markovian, infinite-temperature limit by
                      leading-order perturbation theory, but surprisingly persists
                      unaltered for finite temperature, for any interaction and
                      tunneling spin polarization. (iii) Finally, we show how a
                      Liouville-space analog of the Pauli principle directly leads
                      to an exact expression in the noninteracting limit for the
                      time evolution, extending previous works by starting from an
                      arbitrary initial mixed state including spin and pairing
                      coherences and two-particle correlations stored on the
                      quantum dot. This exact result is obtained already in
                      finite-order renormalized perturbation theory, which
                      surprisingly is not quadratic but quartic in the field
                      superoperators, despite the absence of Coulomb interaction.
                      The latter fact we relate to the time evolution of the
                      two-particle component of the mixed state, which is just the
                      fermion-parity operator, a cornerstone of the formalism. We
                      illustrate how the super-Pauli-principle also simplifies
                      problems with nonzero Coulomb interaction.},
      cin          = {PGI-2},
      ddc          = {530},
      cid          = {I:(DE-Juel1)PGI-2-20110106},
      pnm          = {422 - Spin-based and quantum information (POF2-422)},
      pid          = {G:(DE-HGF)POF2-422},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000339445700008},
      doi          = {10.1103/PhysRevB.90.045407},
      url          = {https://juser.fz-juelich.de/record/154994},
}