Protecting quantum entanglement from leakage and qubit errors via repetitive parity measurements
C. C. Bultink (Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre, TU Delft - ALG/General)
T. E. O'Brien (Universiteit Leiden)
R. Vollmer (TU Delft - Business Development, Kavli institute of nanoscience Delft)
N. Muthusubramanian (Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre, TU Delft - QCD/DiCarlo Lab)
M. W. Beekman (Kavli institute of nanoscience Delft, TNO, Student TU Delft)
M. A. Rol (TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QCD/DiCarlo Lab)
X. Fu (TU Delft - QCD/Almudever Lab, TU Delft - QuTech Advanced Research Centre)
B. Tarasinski (TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QCD/DiCarlo Lab)
V. Ostroukh (Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre, TU Delft - QRD/Wimmer Group)
B. Varbanov (Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre, TU Delft - Applied Sciences)
A. Bruno (TU Delft - QCD/DiCarlo Lab, Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre)
L. DiCarlo (TU Delft - QCD/DiCarlo Lab, TU Delft - QN/DiCarlo Lab, Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre)
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Abstract
Protecting quantum information from errors is essential for large-scale quantum computation. Quantum error correction (QEC) encodes information in entangled states of many qubits and performs parity measurements to identify errors without destroying the encoded information. However, traditional QEC cannot handle leakage from the qubit computational space. Leakage affects leading experimental platforms, based on trapped ions and superconducting circuits, which use effective qubits within many-level physical systems. We investigate how two-transmon entangled states evolve under repeated parity measurements and demonstrate the use of hidden Markov models to detect leakage using only the record of parity measurement outcomes required for QEC. We show the stabilization of Bell states over up to 26 parity measurements by mitigating leakage using postselection and correcting qubit errors using Pauli-frame transformations. Our leakage identification method is computationally efficient and thus compatible with real-time leakage tracking and correction in larger quantum processors.
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