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arXiv:2407.21415

In situ Qubit Frequency Tuning Circuit for Scalable Superconducting Quantum Computing: Scheme and Experiment

Jiang, Lei, Yu Xu, Li, Shaowei, Zhiguang Yan, Ming Gong, Rong Tao, Sun, Chenyin, Tianzuo Sun, Jiang, Tao, Deng, Hui, Chen Zha, Jin Lin, Fusheng Chen, Qingling Zhu, Yangsen Ye, Hao Rong, Kai Qi Yan, Sirui Cao, Yuan Li, Shaojun Guo, Qian, Haoran, Yisen Hu, Yulin Wu, Yuhuai Li, Gang Wu, Xueshen Wang, Shijian Wang, Wenhui Cao, Yeru Wang, Jinjin Li, Cheng-Zhi Peng, Zhu, Xiaobo, Jian-Wei Pan

Published Jul 31, 2024• 1 citation
arXivHTMLPDF

Abstract

Frequency tunable qubit plays a significant role for scalable superconducting quantum processors. The state-of-the-art room-temperature electronics for tuning qubit frequency suffers from unscalable limit, such as heating problem, linear growth of control cables, etc. Here we propose a scalable scheme to tune the qubit frequency by using in situ superconducting circuit, which is based on radio frequency superconducting quantum interference device (rf-SQUID). We demonstrate both theoretically and experimentally that the qubit frequency could be modulated by inputting several single pulses into rf-SQUID. Compared with the traditional scheme, our scheme not only solves the heating problem, but also provides the potential to exponentially reduce the number of cables inside the dilute refrigerator and the room-temperature electronics resource for tuning qubit frequency, which is achieved by a time-division-multiplex (TDM) scheme combining rf-SQUID with switch arrays. With such TDM scheme, the number of cables could be reduced from the usual $\sim 3n$ to $\sim \log_2{(3n)} + 1$ for two-dimensional quantum processors comprising $n$ qubits and $\sim 2n$ couplers. Our work paves the way for large-scale control of superconducting quantum processor.

DOI
10.48550/arxiv.2407.21415

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Frequency tunable qubit plays a significant role for scalable superconducting quantum processors. The state-of-the-art room-temperature electronics for tuning qubit frequency suffers from unscalable limit, such as heating problem, linear growth of control cables, etc. Here we propose a scalable scheme to tune the qubit frequency by using in situ superconducting circuit, which is based on radio frequency superconducting quantum interference device (rf-SQUID). We demonstrate both theoretically and experimentally that the qubit frequency could be modulated by inputting several single pulses into rf-SQUID. Compared with the traditional scheme, our scheme not only solves the heating problem, but also provides the potential to exponentially reduce the number of cables inside the dilute refrigerator and the room-temperature electronics resource for tuning qubit frequency, which is achieved by a time-division-multiplex (TDM) scheme combining rf-SQUID with switch arrays. With such TDM scheme, the number of cables could be reduced from the usual ∼3n\sim 3n∼3n to ∼log⁡2(3n)+1\sim \log_2{(3n)} + 1∼log2​(3n)+1 for two-dimensional quantum processors comprising nnn qubits and ∼2n\sim 2n∼2n couplers. Our work paves the way for large-scale control of superconducting quantum processor.
Abstract Here we consider a tunable superconducting cavity that can be used either as a tunable coupler to a qubit inside the cavity or as a tunable low noise, low temperature, RF filter. Our design consists of an array of radio-frequency superconducting quantum interference devices (rf SQUIDs) inside a superconducting cavity. This forms a tunable metamaterial structure which couples to the cavity through its magnetic plasma frequency. By tuning the resonant frequency of the metamaterial through an applied magnetic flux, one can tune the cavity mode profile. This allows us to detune the cavity initially centered at 5.593 GHz by over 200 MHz. The maximum quality factor approaches that of the empty cavity, which is 4.5 × 106. The metamaterial electromagnetic response is controlled via a low-frequency or dc magnetic flux bias, and we present a control line architecture that is capable of applying sufficient magnetic flux bias with minimal parasitic coupling. Together this design allows for an in-situ tunable cavity which enables low-temperature quantum control applications.
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Recent advances in solid-state qubit technology are paving the way to fault-tolerant quantum computing systems. However, qubit technology is limited by qubit coherence time and the scaling of quantum processors is limited by the complexity of coupling quantum systems with a classical electronic infrastructure. Hence, the proposed approach is to use CMOS at cryogenic temperatures, in order to ensure physical proximity to the quantum bits, thus reducing thermal gradients and increasing compactness. In this thesis, several RF circuits designed using commercial CMOS technology have been shown to be working at cryogenic temperatures. Such circuits could be easily interfaced (or integrated, in the future) with a qubit processor. The performance of the circuits is comparable to the state-of-the-art systems, currently used as control units for qubits. Moreover, these circuits have a much smaller form factor and could be made to work inside a dilution refrigerator where the qubits are operational, hence providing the first demonstration of a scalable solution.
The advancement of scalable quantum information processing relies on the accurate and parallel manipulation of a vast number of qubits, potentially reaching into the millions. Superconducting qubits, traditionally controlled through individual circuitry, currently face a formidable scalability challenge due to the excessive use of wires. This challenge is nearing a critical point where it might soon surpass the capacities of on-chip routing, I/O packaging, testing platforms, and economically feasible solutions. Here we introduce a multiplexed control scheme that efficiently utilizes shared control lines for operating multiple qubits and couplers. By integrating quantum hardware-software co-design, our approach utilizes advanced techniques like frequency multiplexing and individual tuning. This enables simultaneous and independent execution of single- and two-qubit gates with significantly simplified wiring. This scheme has the potential to diminish the number of control lines by one to two orders of magnitude in the near future, thereby substantially enhancing the scalability of superconducting quantum processors.