Faster gates and reduced crosstalk on a new 2D QPU architecture
A simple and scalable architecture can achieve high operation accuracy using faster entangling gates.
The Science:
Fixed-frequency transmon qubits connected by fixed-frequency couplers possess long lifetimes. However, the entangling gates on this architecture take longer durations compared to those with flux tunable couplers. One major issue is the always-on ZZ interaction, which prohibits further increasing the coupling strength enabling faster gates. To solve this problem, we develop a simple scheme where a constant-amplitude drive is applied on the fixed-frequency resonator. The resulting dynamically induced qubit-qubit interaction cancels the stray coupling, allowing us to further increase the coupling strength. We numerically demonstrate much faster cross-resonance gates (~40 ns), which with realistic parameters brings the gate error below 10-4.
The Impact:
A fully functional quantum computer relies on sufficiently accurate gates among its processing units. The current state-of-the-art gate fidelities are still below the threshold for performing many useful applications. This work proposes a new way to achieve higher gate fidelities on superconducting qubits, helping SQMS advance toward the goal of building a useful quantum computer in the near term.
Summary:
The transmon qubit is the most widely used design among superconducting qubits. To accurately entangle the quantum states of different transmon qubits in a multi-qubit quantum computer, two distinct pathways have been explored. One path prioritizes prolonged qubit lifetimes and incorporates no flux-tunable elements. In contrast, the other emphasizes tunability, albeit with the trade-off of lower qubit coherence times, enabling faster entangling gates. However, the challenge arises in achieving both long coherence times and tunability simultaneously, posing a roadblock toward achieving higher gate fidelities on transmon qubits.
In this study, we introduce a novel method to overcome this roadblock. Specifically, we address the issue of crosstalk between qubits, a significant factor slowing down gates on qubits whose frequencies are not tunable but have the longest coherence times. Our approach involves the use of a constant amplitude drive to generate a dynamic interaction, known as resonator-induced-phase, between qubits, effectively mitigating the undesired crosstalk. This allows for an increased coupling strength, facilitating faster entangling gates. Through simulations, we demonstrate a substantial tenfold reduction in errors compared to current standards.
Contact:
Ziwen Huang, zhuang@fnal.gov
Institutions:
Fermi National Accelerator Laboratory, Northwestern University
Focus Area:
Devices
Citation:
Ziwen Huang, Taeyoon Kim, Tanay Roy, Yao Lu, Alexander Romanenko, Shaojiang Zhu, and Anna Grassellino, Physical Review Applied 22, 034007 (2024), https://doi.org/10.1103/PhysRevApplied.22.034007
Funding Acknowledgment:
This material is based upon work supported by the U.S. Department of Energy, Office of Science, National Quantum Information Science Research Centers, Superconducting Quantum Materials and Systems Center (SQMS) under Contract No. DE-AC02-07CH11359.