Herein, we develop a quantum voltage measurement system in a strong magnetic field. One of our goals is to conduct the quantum metrology triangle (QMT) experiment, which operate three electric quantum standards, a Josephson voltage standard (JVS), a quantized Hall resistance standard (QHRS) and a quantum current standard based on the single electron tunneling effect, in one dilution refrigerator [1]. To realize this system, with the strong magnetic field condition for the QHRS, it is necessary to reduce the magnetic field in the vicinity of the JVS device. A magnetic field shielding structure to reduce the magnetic field has been developed and the design of the structure was optimized by the numerical calculation with a finite element simulation, which lead us to the structure composed of a permalloy box covered by two superconducting layers [2]. In this study, we demonstrated an operation of the JVS device in the magnetic field shielding structure at a 4 K stage of the dilution refrigerator. At the bottom of the dilution refrigerator, about 50 cm below the JVS in the magnetic field shielding structure, a superconducting magnet with a cancelation coil was placed and generated a magnetic field. We measured the residual magnetic field inside of the magnetic field shielding structure with a Hall device [3] and evaluated the effect to the JVS operation [4]. The residual magnetic field was less than the geomagnetic field and the operating bias current margin of JVS was maintained, even under a generated magnetic field of 10.2 T. For the next step, the simultaneous operation of both the JVS and the QHRS devices in the refrigerator is planned.
[1] D. Matsumaru, et al., “Development of a Josephson voltage standard module for quantum metrology triangle measurements,” CPEM 2022 Conf. Digest, Nov 2022.
[2] D. Matsumaru, et al., “Simulation study of magnetic shielding effects for operation on a Josephson voltage standard device in a high magnetic field,” ISS2022 Conf. Digest, Nov. 2022.
[3] D. Matsumaru, et al., “Fabrication and evaluation of a superconducting shield for operating a Josephson voltage standard device in a high magnetic field,” ISS2023 Conf. Digest, Nov. 2023.
[4] D. Matsumaru, et al., “Operation of Josephson Voltage Standard with Superconducting Shield in Magnetic-Field Environment,” CPEM 2024 Conf. Digest, Jul. 2024.
This work was supported by JSPS KAKENHI Grant Number JP24K07616.
Keywords: magnetic shielding, magnetic field, Josephson effect, voltage standard