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@ARTICLE{Simm:1038602,
      author       = {Simm, Alexander and Machnes, Shai and Wilhelm-Mauch, Frank},
      title        = {{T}wo qubits in one transmon -- {QEC} without ancilla
                      hardware},
      publisher    = {arXiv},
      reportid     = {FZJ-2025-01574},
      year         = {2023},
      abstract     = {We show that it is theoretically possible to use higher
                      energy levels for storing and controlling two qubits within
                      a superconducting transmon. This is done by identifying
                      energy levels as product states between multiple effecitve
                      qubits. As a proof of concept we realise a complete set of
                      gates necessary for universal computing by numerically
                      optimising control pulses for single qubit gates on each of
                      the qubits, entangling gates between the two qubits in one
                      transmon, and an entangling gate between two qubits from two
                      coupled transmons. The optimisation considers parameters
                      which could make it possible to validate this
                      experimentally. With these control pulses it is in principle
                      possible to double the number of available qubits without
                      any overhead in hardware. The additional qubits could be
                      used in algorithms which need many short-living qubits such
                      as syndrom qubits in error correction or by embedding
                      effecitve higher connectivity in qubit networks.},
      keywords     = {Quantum Physics (quant-ph) (Other) / FOS: Physical sciences
                      (Other)},
      cin          = {PGI-12},
      cid          = {I:(DE-Juel1)PGI-12-20200716},
      pnm          = {5221 - Advanced Solid-State Qubits and Qubit Systems
                      (POF4-522) / Verbundprojekt: German Quantum Computer based
                      on Superconducting Qubits (GEQCOS) - Teilvorhaben:
                      Charakterisierung, Kontrolle und Auslese (13N15685)},
      pid          = {G:(DE-HGF)POF4-5221 / G:(BMBF)13N15685},
      typ          = {PUB:(DE-HGF)25},
      doi          = {10.48550/ARXIV.2302.14707},
      url          = {https://juser.fz-juelich.de/record/1038602},
}