Our joint paper with the QuTech DiCarlo Lab at TU Delft and QuantWare has been published in the Physical Review Letters (APS).
Study of spectator effects during repeated parity checks. (a) Simplified schematic of the device with color coding to identify data qubits (Q_1 and Q_2, red), ancilla (Q_0, blue), and spectator (Q_4, purple). (b) Quantum circuit realizing the indirect measurement of X_2 X_1 parity using Q_0 as ancilla. A X_π pulse is applied to Q_1 and Q_2 during readout of Q_0. To study spectator effects, a X_π pulse is applied to Q_4, toggling it between ground and first-excited state in every round. (c) Error-detection probability measured over 100 rounds at different C_04 frequencies (represented by the color scale), keeping spectator Q_4 in the ground state. (d) Error-detection probability measured now toggling Q_4 at every round. (e) Common plot of the error-detection probability at round 100 for data in (c) and (d). Vertical lines mark the ξ_ZZ^04=0, J_1^04=0 and J_2^04=0 coupler bias points.
About the paper
The publication, Optimizing the Frequency Positioning of Tunable Couplers in a Circuit QED Processor to Mitigate Spectator Effects on Quantum Operations, examines how the frequency positioning of tunable couplers influences the performance of superconducting quantum processors.
In multi-qubit systems, residual interactions between qubits, often referred to as spectator effects, can introduce errors during operations such as single-qubit gates, two-qubit gates, and readout. This study investigates how these effects depend on the configuration of flux-tunable couplers in a circuit QED architecture.
Using a five-transmon device with tunable couplers, the researchers map how interaction terms, including ZZ and exchange couplings, vary as a function of the coupler frequency. The results show that these interactions can be individually minimized, but not simultaneously at a single operating point.
The experiments further indicate that the optimal coupler configuration depends on the type of quantum operation. For example, suppressing exchange interactions reduces errors during readout, while minimizing ZZ coupling improves performance in two-qubit gates and repeated parity measurements.
Overall, the findings suggest that dynamically adjusting the coupler frequency for different operations could improve system performance, taking advantage of the fast tunability of the coupler design.
The publication demonstrates OrangeQS’s expertise in characterizing and optimizing quantum hardware and showcases how industrial tools and academic exploration can mutually benefit when addressing key challenges for scalable quantum computing.
About Physical Review Letters
Physical Review Letters (PRL) is a leading journal in physics published by the American Physical Society. It features short reports on significant developments and influential ideas across fundamental, applied, and interdisciplinary physics.
PRL publishes concise, high-quality research that is intended to advance the field and inform ongoing work across a broad range of physics disciplines. The journal is edited by researchers and is designed to serve the needs of the scientific community.
Find the paper here: https://journals.aps.org/prl/abstract/10.1103/wdfj-4nbt
