We developed a hybrid (superconductor/permalloy) magnetic shield for the operation of a Josephson voltage standard (JVS) device in high-magnetic field environments in a dilution refrigerator. The shield was employed for various applications, including general-purpose highly stable voltage referencing in low-temperature environments, arbitrary waveform generation for precise qubit operation, and quantum metrology triangle experiments [1]. These applications often require high-magnetic-field environments for the operation of the JVS devices. Previously, we operated a JVS device in the 4-K stage of a dilution refrigerator and achieved a highly stable reference voltage source operating at the same accuracy level as those of primary standards by generating quantized voltage and evaluating the uncertainty without a magnetic field [2]. Furthermore, we designed a triple-layered, hybrid magnetic shield using two superconductors (Nb and Pb) and a permalloy for the JVS device operation in a high-magnetic-field environment. Through computer simulations, we confirmed that the magnetic flux density near the Josephson device was reduced and it was less than that of the geomagnetic field [3].
Herein, we report the fabrication of a hybrid magnetic-shield structure based on the abovementioned design. Additionally, the evaluation results of the shielding effect of the structure in a cryogenic and high-magnetic-field environment are reported.
[1] N.-H. Kaneko, S. Nakamura and Y. Okazaki, “A review of the quantum current standard, “ Meas. Sci. Technol., vol. 27, no.3, pp. 1−20, Feb. 2016.
[2] D. Matsumaru, S. Nakamura, M. Maruyama and N.-H. Kaneko, “Stable Voltage Generation With a Josephson Voltage Standard Device Cooled at a 4 K Stage in a Dilution Refrigerator, “ IEEE Trans. Instrum. Meas., vol. 72, pp. 1−6, May 2023. Art. no. 1004706.
[3] D. Matsumaru, S. Nakamura, M. Maruyama, and N.-H. Kaneko, “Simulation study of magnetic shielding effects for operation on a Josephson voltage standard device in a high magnetic field,” ISS2022 Conf. Digest, pp. 1−1, Nov. 2022.