Fault-tolerant parity readout on a shuttling-based trapped-ion quantum computer

TL;DR

This paper demonstrates a fault-tolerant parity check measurement in a trapped-ion quantum computer, using a flag qubit to detect errors, achieving high fidelity and generating multi-qubit entanglement, advancing scalable quantum error correction.

Contribution

The work introduces a fault-tolerant weight-4 parity measurement scheme with a flag qubit in a shuttling-based ion trap system, enabling reliable error detection and multi-qubit entanglement.

Findings

Achieved 93.2% fidelity in flag-conditioned parity measurement.

Successfully intercepted injected bit and phase-flip errors.

Generated genuine six-qubit multi-partite entanglement.

Abstract

Quantum error correction requires the detection of errors by reliable measurements of suitable multi-qubit correlation operators. Here, we experimentally demonstrate a fault-tolerant weight-4 parity check measurement scheme. An additional 'flag' qubit serves to detect errors occurring throughout the parity measurement, which would otherwise proliferate into uncorrectable weight-2 errors on the qubit register. We achieve a flag-conditioned parity measurement single-shot fidelity of 93.2(2)\%. Deliberately injecting bit and phase-flip errors, we show that the fault-tolerant protocol is capable of reliably intercepting such faults. For holistic benchmarking of the parity measurement scheme, we use entanglement witnessing to show that the implemented circuit generates genuine six-qubit multi-partite entanglement. The fault-tolerant parity measurement scheme is an essential building block in a broad class of stabilizer quantum error correction protocols, including topological color codes. Our hardware platform is based on atomic ions stored in a segmented microchip ion trap. The qubit register is dynamically reconfigured via shuttling operations, enabling effective full connectivity without operational cross-talk, which provides key capabilities for scalable fault-tolerant quantum computing.