Fig. 1: Experimental set-up for the accuracy test of the PQCG.
From: A primary quantum current standard based on the Josephson and the quantum Hall effects
a The PQCG is composed of PJVS1 and QHRS1 connected through a triple connection (red lines 1, 2, 3) ensured via the windings of N1 turns of a new CCC, which are used to measure and amplify the quantized current I1. The shields at ground potential of the high and low potential cables are not shown on the scheme. The SQUID detector of the CCC feedbacks on an external current source (VCCS) which maintains the current IPQCG into the series connection of QHRS2 and of the winding of N2 turns. To reduce the finite gain error of the SQUID, a voltage source of the programmable Josephson bias source (PJBS) drives the VCCS and preadjusts the output current, such that the SQUID feedbacks only on a small fraction of IPQCG (see Uncertainties section in Methods). The voltage drop at QHRS2 is measured in a quantum voltmeter configuration made of PJVS2 and a null detector, ND (EM Electronics Model N11). The frequency of the Josephson microwave signals are referenced to a 10 MHz frequency standard linked to an atomic clock time base. Both PJVS are controlled and synchronized using the same PJBS. For measurements performed with n1 = 4096, a decoupling stage ensures the electrical isolation between the two PJVS so that the PQCG and the quantum voltmeter can each be grounded. For n1 = 1920, no decoupling stage is used implying that only PJVS1 is grounded. Four different cryostats are used to cool down quantum devices (represented by purple, blue gray, cyan and light blue colors). b ND recordings, ΔV, for frequencies f2 + Δ f (red circle) and f2 − Δf (blue circle) as a function of time τ while the current IPQCG is periodically switching on and off (I+ measurement protocol).
