No abstract

Ultra-high sensitivity temperature sensing and stable thermal control are crucial for many science experiments testing fundamental theories to high precision. Here we report the first pico-kevin scale thermometer operating at room temperature with an exceptionally low theoretical noise figure of ~70pK/Hz at 1 Hz and a high dynamic range of ~500 K. We have experimentally demonstrated a temperature sensitivity of <3.8nK/Hz at 1 Hz near room temperature, which is an order of magnitude improvement over the state of the art. We have also demonstrated an ultra-high stability thermal control system using this thermometer, achieving 3.7 nK stability at 1 s and ∼ 120 pK at 10⁴ s, which is 10-100 times more stable than the state of the art. With some upgrades to this proof-of-principle device, we can expect it to be used for very high resolution tests of special relativity and in critical point phenomena.

Charges as small as 1 pC degrade the performance of high precision inertial reference instruments when accumulated on their test masses (TM). Non-contact charge management systems are required for the most sensitive of these instruments, with the TM charges compensated by photoelectrons in a feedback loop with a TM charge measurement system. Three missions have successfully demonstrated this technique: GP-B, the LISA Pathfinder, and the UV-LED mission, launched in 2004, 2015, and 2014 respectively; with the first two using the 254 nm Hg line and the last one a set of 255 nm UV-LEDs. UV-LEDs represent a significant improvement over the discharge sources, in terms of reliability, lifetime, switching speeds, power consumption, weight, and volume. Charge management techniques that eliminate the charge measurement and feedback systems, referred henceforth as passive, reduce the complexities and disturbance effects introduced by these systems, and are thus the subject of active research and development work. Passive charge management depends critically on the stability and reproducibility of the photoemission properties of a given system. In support of this work, we present comprehensive flight characterization data for a suite of 16 UV-LEDs in various configurations and 255 ± 1 nm center wavelength. We back up our results with ground-based measurements performed in configurations comparable to the flight one between September 4, 2020, and October 8, 2020. Results confirm the reliability of the UV LEDs in space environment and are fully consistent with the findings of ground studies. We find that the equilibrium potential of the TM, under illumination by the 255 nm LEDs, is independent of the UV intensity and reproduceable to about ± 6 mV, or ± 6 fC/pF, over periods of up to six months. The value of the equilibrium potential is dependent on the geometry of the electric field between TM and enclosure.