Transversal CNOT gate with multi-cycle error correction
A scalable and programmable quantum computer holds the potential to solve
computationally intensive tasks that classical computers cannot accomplish
within a reasonable time frame, achieving quantum advantage. However, the
vulnerability of the current generation of quantum processors to errors poses a
significant challenge towards executing complex and deep quantum circuits
required for practical problems. Quantum error correction codes such as
Stabilizer codes offer a promising path forward for fault-tolerant quantum
computing, however their realisation on quantum hardware is an on-going area of
research. In particular, fault-tolerant quantum processing must employ logical
gates on logical qubits with error suppression with realistically large size
codes. This work has implemented a transversal CNOT gate between two logical
qubits constructed using the Repetition code with flag qubits, and demonstrated
error suppression with increasing code size under multiple rounds of error
detection. By performing experiments on IBM quantum devices through cloud
access, our results show that despite the potential for error propagation among
logical qubits during the transversal CNOT gate operation, increasing the
number of physical qubits from 21 to 39 and 57 can suppress errors, which
persists over 10 rounds of error detection. Our work establishes the
feasibility of employing logical CNOT gates alongside error detection on a
superconductor-based processor using current generation quantum hardware.
Younghun Kim Martin Sevior Muhammad Usman