Markus Müller

Realizing Lattice Surgery on Two Distance-Three Repetition Codes with Superconducting Qubits

  1. Ilya Besedin,
  2. Michael Kerschbaum,
  3. Jonathan Knoll,
  4. Ian Hesner,
  5. Lukas Bödeker,
  6. Luis Colmenarez,
  7. Luca Hofele,
  8. Nathan Lacroix,
  9. Christoph Hellings,
  10. François Swiadek,
  11. Alexander Flasby,
  12. Mohsen Bahrami Panah,
  13. Dante Colao Zanuz,
  14. Markus Müller,
  15. and Andreas Wallraff
Quantum error correction is needed for quantum computers to be capable of fault-tolerantly executing algorithms using hundreds of logical qubits. Recent experiments have demonstrated
subthreshold error rates for state preservation of a single logical qubit. In addition, the realization of universal quantum computation requires the implementation of logical entangling gates. Lattice surgery offers a practical approach for implementing such gates, particularly in planar quantum processor layouts. In this work, we demonstrate lattice surgery between two distance-three repetition-code qubits by splitting a single distance-three surface-code qubit. Using a quantum circuit fault-tolerant to bit-flip errors, we achieve an improvement in the value of the decoded ZZ logical two-qubit observable compared to a similar non-encoded circuit. By preparing the surface-code qubit in initial states parametrized by a varying polar angle, we evaluate the performance of the lattice surgery operation for non-cardinal states on the logical Bloch sphere and employ logical two-qubit tomography to reconstruct the Pauli transfer matrix of the operation. In this way, we demonstrate the functional building blocks needed for lattice surgery operations on larger-distance codes based on superconducting circuits.
arxiv pdf

Realizing Repeated Quantum Error Correction in a Distance-Three Surface Code

  1. Sebastian Krinner,
  2. Nathan Lacroix,
  3. Ants Remm,
  4. Agustin Di Paolo,
  5. Elie Genois,
  6. Catherine Leroux,
  7. Christoph Hellings,
  8. Stefania Lazar,
  9. Francois Swiadek,
  10. Johannes Herrmann,
  11. Graham J. Norris,
  12. Christian Kraglund Andersen,
  13. Markus Müller,
  14. Alexandre Blais,
  15. Christopher Eichler,
  16. and Andreas Wallraff
Quantum computers hold the promise of solving computational problems which are intractable using conventional methods. For fault-tolerant operation quantum computers must correct errors
occurring due to unavoidable decoherence and limited control accuracy. Here, we demonstrate quantum error correction using the surface code, which is known for its exceptionally high tolerance to errors. Using 17 physical qubits in a superconducting circuit we encode quantum information in a distance-three logical qubit building up on recent distance-two error detection experiments. In an error correction cycle taking only 1.1μs, we demonstrate the preservation of four cardinal states of the logical qubit. Repeatedly executing the cycle, we measure and decode both bit- and phase-flip error syndromes using a minimum-weight perfect-matching algorithm in an error-model-free approach and apply corrections in postprocessing. We find a low error probability of 3% per cycle when rejecting experimental runs in which leakage is detected. The measured characteristics of our device agree well with a numerical model. Our demonstration of repeated, fast and high-performance quantum error correction cycles, together with recent advances in ion traps, support our understanding that fault-tolerant quantum computation will be practically realizable.
arxiv pdf