Abstract
The ability to control and measure the temperature of propagating microwave modes down to very low temperatures is indispensable for quantum information processing and may open opportunities for studies of heat transport at the nanoscale, also in the quantum regime. Here, we propose and experimentally demonstrate primary thermometry of propagating microwaves using a transmon-type superconducting circuit. Our device operates continuously, with a sensitivity down to and a bandwidth of 40 MHz. We measure the thermal occupation of the modes of a highly attenuated coaxial cable in a range of 0.001 to 0.4 thermal photons, corresponding to a temperature range from 35 mK to 210 mK at a frequency around 5 GHz. To increase the radiation temperature in a controlled fashion, we either inject calibrated, wideband digital noise, or heat the device and its environment. This thermometry scheme can find applications in benchmarking and characterization of cryogenic microwave setups, temperature measurements in hybrid quantum systems, and quantum thermodynamics.
3 More- Received 31 March 2020
- Accepted 15 October 2020
DOI:https://doi.org/10.1103/PhysRevX.10.041054
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by Bibsam.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Propagating modes of microwave waveguides play a key role in quantum information processing with superconducting circuits, connecting the quantum processor with the classical electronics controlling it. These modes, which provide a way to prepare and stabilize the quantum states, must operate at the lowest possible temperature to minimize the introduction of errors in the quantum bits. Beyond quantum computing, these modes can also provide heat baths in experiments in quantum thermodynamics. In either case, measuring the temperature of microwave modes with good accuracy and temporal resolution is of paramount importance. Here, we report on a novel type of thermometer designed for this purpose.
Our thermometry concept relies on the interplay between coherent and incoherent scattering from a quantum emitter driven at resonance. The emitter is strongly coupled to the end of the waveguide under test. Thermal photons in the waveguide lead to a measurable drop in the coherently scattered signal, which is continuously recorded. Our implementation, which uses a superconducting circuit operated at gigahertz frequencies, features simplicity, large bandwidth, high sensitivity, and negligible power dissipation.
We expect this thermometer to enable a range of experiments in thermodynamics at the nanoscale and in the quantum regime. For example, it can monitor in real time the temperature of a mesoscopic electron reservoir or measure the scattering of thermal microwaves from a circuit acting as a quantum heat engine or refrigerator. It also provides a way to benchmark the cryogenic environment in quantum computing and quantum sensing experiments.