Dephasing of a superconducting qubit induced by photon noise.
We have studied the dephasing of a superconducting flux qubit coupled to a dc-SQUID based oscillator. By varying the bias conditions of both circuits we were able to tune their effective coupling strength. This allowed us to measure the effect of such a controllable and well-characterized environment on the qubit coherence. We can quantitatively account for our data with a simple model in which thermal fluctuations of the photon number in the oscillator are the limiting factor. In particular, we observe a strong reduction of the dephasing rate whenever the coupling is tuned to zero. At the optimal point we find a large spin-echo decay time of .
Bertet
P
P
Quantum Transport Group, Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg, Delft, The Netherlands.
Chiorescu
I
I
Burkard
G
G
Semba
K
K
Harmans
C J P M
CJ
DiVincenzo
D P
DP
Mooij
J E
JE