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Measurement of Small Photon Numbers in Circuit QED Resonators.
Juan Atalaya1, Alex Opremcak1, Ani Nersisyan1
1Google Quantum AI, Santa Barbara, California 93111, USA.
Physical Review Letters
|June 3, 2024
Summary
This study measures low intracavity photon numbers using qubit dephasing. The Carr-Pucell-Meiboom-Gill technique accurately quantifies thermal and coherent photon populations in resonators.
Area of Science:
- Quantum optics
- Superconducting circuits
- Cavity quantum electrodynamics
Background:
- Photon-induced qubit dephasing is a known phenomenon.
- Measuring low photon numbers in resonators is challenging.
- Existing methods lack precision for small photon populations.
Purpose of the Study:
- To develop a precise method for measuring small average numbers of intracavity photons.
- To quantify both coherently and thermally driven photon populations.
- To validate a theoretical model for photon-induced dephasing.
Main Methods:
- Utilizing the off-resonant interaction between fluctuating photons and a qubit.
- Applying a Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence to the qubit.
- Analyzing qubit dephasing rates with derived formulas for non-Gaussian noise.
Main Results:
- Demonstrated accurate measurement of thermal and coherent photon populations.
- Achieved sensitivity down to a few 10^{-4} average photons.
- Showed excellent agreement between CPMG dephasing rate formulas and experimental data.
Conclusions:
- The CPMG technique is effective for measuring low intracavity photon numbers.
- The developed dephasing rate formulas accurately describe the experimental observations.
- This method provides a new tool for characterizing quantum systems and resonators.
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