The status of Johnson noise thermometry

Abstract

Since Johnson's experimental observations of thermal noise in 1927, and Nyquist's explanation of the phenomenon shortly afterwards in 1928, thermal noise has attracted interest as a means of measuring temperature. The independence of the thermal noise from the material nature of the sensor makes it particularly attractive for metrological applications. However, the noise signals are extremely small and some ingenuity is required to make accurate measurements. This paper reviews the foundations of Johnson noise thermometry and the various techniques that have been employed to measure temperature via Johnson noise. Emphasis is placed on key developments in noise thermometers for metrological applications. The review includes the current activities of teams involved in noise thermometry research.

Review of temperature measurement

“…The type of circuitry used depends on the temperature range and was reviewed by Kamper, 101 by Blalock and Shepard, 102 and by White et al 103 For low temperature measurements, at less than 1 K, two types of absolute noise thermometers have proved useful according to Soulen et al 104 Both measure the noise voltage generated by a resistor using a superconducting quantum interference device ͑SQUID͒. In one type the resistor is inductively coupled to the SQUID.…”

Development of high frequency and wide bandwidth Johnson noise thermometry

“…Temperature is measured by passively monitoring fluctuations of the conducting components within the nanoscale device without current excitations. Difficulties in measuring low level voltage noise 5 have limited the applications of JNT to metrology 9,10 and extreme environments such as nuclear reactors 11 and ultralow temperatures. 5 Recently, considerable progress has been made in the measurement of noise on mesoscopic devices by applying radiometry techniques, 4,7,12 opening up the possibility of using JNT to study a wide range of mesoscopic phenomena.…”

“…9,17 Johnson noise from the sample is added to the unwanted Johnson noise from these lossy components. Cross-correlation techniques can mitigate this problem by amplifying the Johnson noise signal of interest independently via two separate measurement lines [17][18][19][20] and discarding uncorrelated noise between the two channels.…”

“…3(b) and 3(c) plot the standard deviation of 1000 temperature measurements for 28 MHz and 328 MHz correlation bandwidth, respectively, as a function of integration time. In both auto-and cross-correlation experiments, the sensitivity follows an inverse square root power law described by the Rice relation: 9,22 dT…”

A novel on-chip three-dimensional micromachined calorimeter with fully enclosed and suspended thin-film chamber for thermal characterization of liquid samples

“…The resolution of temperature measurement with RTD is limited by the Johnson-Nyquist thermal noise. 40,41 From calculated thermal noise, 8.17 Â 10 À6 C resolution for the temperature measurement with bandwidth of 28.5 Hz for fabricated device is expected. However, the measurement noise of the preamplifier and source meter far exceeds this noise floor and results in a measurement temperature resolution of 2 Â 10 À3 C. An 1 mA DC is used as excitation current of the sensor with a 4-wire measurement configuration to minimize the effects of contacts and connecting wires on temperature measurements.…”