Quantum Noise in the Josephson Charge Qubit
O. V. Astafiev, Yu. A. Pashkin, Yasunobu Nakamura, Tsuyoshi Yamamoto, J. S. Tsai · Physical Review Letters · 2004
We study decoherence of the Josephson charge qubit by measuring energy relaxation and dephasing with help of the single-shot readout. We found that the dominant energy relaxation process is a spontaneous emission induced by quantum noise coupled to the charge degree of freedom. Spectral density of the noise at high frequencies is roughly proportional to the qubit excitation energy.