Distinguishing coherent and thermal photon noise in a circuit quantum electrodynamical system

In the cavity-QED architecture, photon number fluctuations from residual cavity photons cause qubit dephasing due to the ac Stark effect. These unwanted photons originate from a variety of sources, such as thermal radiation, leftover measurement photons, and cross talk. Using a capacitively shunted flux qubit coupled to a transmission line cavity, we demonstrate a method that identifies and distinguishes coherent and thermal photons based on noise-spectral reconstruction from time-domain spin-locking relaxometry. Using these measurements, we attribute the limiting dephasing source in our system to thermal photons rather than coherent photons. By improving the cryogenic attenuation on lines leading to the cavity, we successfully suppress residual thermal photons and achieve T1-limited spin-echo decay time. The spin-locking noise-spectroscopy technique allows broad frequency access and readily applies to other qubit modalities for identifying general asymmetric nonclassical noise spectra.

Campbell, Daniel LMassachusetts Institute of Technology (MIT) (author)
Krantz, Philip,1984Massachusetts Institute of Technology (MIT)(Swepub:cth)philipk (author)
Kjaergaard, MortenMassachusetts Institute of Technology (MIT) (author)
Kim, DavidMIT Lincoln Laboratory (author)
Yoder, Jonilyn LMIT Lincoln Laboratory (author)
Hover, DavidMIT Lincoln Laboratory (author)
Sears, AdamMIT Lincoln Laboratory (author)
Kerman, Andrew JMIT Lincoln Laboratory (author)
Orlando, Terry PMassachusetts Institute of Technology (MIT) (author)
Gustavsson, Simon,1978Massachusetts Institute of Technology (MIT)(Swepub:cth)simong (author)
Oliver, William DMassachusetts Institute of Technology (MIT) (author)
Massachusetts Institute of Technology (MIT)MIT Lincoln Laboratory (creator_code:org_t)

By the author/editor: Yan, Fei; Campbell, Daniel ...; Krantz, Philip, ...; Kjaergaard, Mort ...; Kim, David; Yoder, Jonilyn L; show more...; Hover, David; Sears, Adam; Kerman, Andrew J; Orlando, Terry P; Gustavsson, Simo ...; Oliver, William ...; show less...

About the subject

NATURAL SCIENCES: NATURAL SCIENCES; and Physical Science ...; and Subatomic Physic ...

ENGINEERING AND TECHNOLOGY: ENGINEERING AND ...; and Nano technology; and Nano technology

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