Driven Superconducting Qubits Exhibit Lower-Than-Expected Quasiparticle Generation Rates up to 300GHz

Superconducting qubits represent a leading technology for building powerful quantum computers, yet their performance can be limited by unwanted energy loss within the circuits. Byoung-moo Ann from the Korea Research Institute of Standards and Science, Sang-Jun Choi from Kongju National University, and Hee Chul Park from Pukyong National University, working with colleagues including Sercan Deve and Robin Dekker from Delft University of Technology, now demonstrate that energy loss caused by drive-induced quasiparticle generation across the crucial Josephson junctions within these qubits is significantly lower than previously feared. The team applied intense microwave signals to superconducting circuits and carefully measured the resulting energy dissipation, finding rates far below those predicted by standard models. This discovery prevents overestimation of a key error source in quantum processors and, crucially, suggests new avenues for materials science and device design to further enhance qubit stability and performance.

Transmon and Charge Qubit Stability Research

This research focuses on superconducting qubits, addressing issues related to qubit stability, readout accuracy, and the impact of quasiparticles and driving fields. It covers core qubit technologies, including transmon, charge, and flux qubits, and explores various coupling architectures and fabrication materials. Scientists investigate methods to improve qubit performance and scalability through innovative designs and materials. A major theme is qubit stability and decoherence, with numerous studies addressing factors limiting qubit coherence, such as quasiparticle poisoning, charge noise, and flux noise. Investigations also explore structural instabilities in driven Josephson circuits and methods to prevent them.

Lower Quasiparticle Generation Rates Observed in Qubits

Scientists have achieved a breakthrough in understanding and mitigating drive-induced quasiparticle generation (QPG) in superconducting quantum circuits, a critical challenge for building fault-tolerant quantum computers. Their work demonstrates that QPG rates in strongly driven superconducting qubits are substantially lower than previously predicted by theoretical models. Experiments revealed that even when conservatively attributing all measured dissipation to QPG, the observed energy loss rates were far lower than those predicted. Researchers discovered that incorporating high-frequency cutoffs in the QPG conductance accurately explained the experimental data, reducing predicted QPG rates by several orders of magnitude.

Quasiparticle Generation Limited by High Frequencies

Researchers have demonstrated that energy loss from superconducting quantum circuits, caused by quasiparticle generation (QPG) from microwave drives, is significantly lower than previously predicted. Applying intense microwave signals to superconducting qubits, the team quantified energy dissipation and found that observed rates of QPG were several orders of magnitude smaller than expected. This discrepancy arises because the standard model for QPG does not account for high-frequency cutoffs in the conductance, which limit the generation of these quasiparticles. By incorporating these high-frequency cutoffs into their calculations, researchers successfully explained the experimental data, revealing a more accurate understanding of QPG rates.