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A ratiometric method for Johnson noise thermometry using a quantized voltage noise source



Sae Woo Nam, Samuel Benz, John M. Martinis, Paul Dresselhaus, Weston L. Tew, David R. White


Johnson Noise Thermometry (JNT) involves the measurement of the statistical variance of a fluctuating voltage across a resistor in thermal equilibrium. Modern digital techniques make it now possible to perform many functions required for JNT in highly efficient and predictable ways. We describe the operational characteristics of a prototype JNT system which uses digital signal processing for filtering, real-time spectral cross-correlation for noise power measurement, and a digitally synthesized Quantized Voltage Noise Source (QVNS) as an AC voltage reference. The QVNS emulates a constant spectral density which is stable, programmable, and calculable in terms of known parameters using digital synthesis techniques. Changes in analog gain are accounted for by alternating the inputs between the Johnson noise sensor and the QVNS. The Johnson noise power at a known temperature is first balanced with a synthesized noise power from the QVNS. The process is then repeated by balancing the noise power from the same resistor at an unknown temperature. When the two noise power ratios are combined, a thermodynamic temperature can be derived where the scaling is accomplished by the ratio of the two QVNS spectral densities. We present preliminary results where the ratio between the gallium triple point and the water triple point is used to demonstrate the accuracy of the measurement system with a standard uncertainty of 0.04 %.
Proceedings Title
Proc., 8th Temp. Symp. (TS2002)
Conference Dates
October 21-24, 2002
Conference Location
Chicago, IL, USA


Josephson junctions, signal synthesis, standards, voltage standards, correlation, Johnson noise, noise


Nam, S. , Benz, S. , Martinis, J. , Dresselhaus, P. , Tew, W. and White, D. (2003), A ratiometric method for Johnson noise thermometry using a quantized voltage noise source, Proc., 8th Temp. Symp. (TS2002), Chicago, IL, USA, [online], (Accessed June 24, 2024)


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Created December 31, 2002, Updated October 12, 2021