On the Detection of Quantum Noise and Low-Temperature Dephasing

David R. Reichman, R. Silbey, Alberto Suárez

The nonperturbative treatment of the pure dephasing problem studied by Osad’ko and Skinner and Hsu is reexamined. It is found that these treatments are inadequate for very low temperatures in the case of Ohmic friction. New nonperturbative methods are used to expose interesting pure dephasing behavior at very low temperatures in this case. The methods are shown to coincide with the previous theories at higher temperatures. The experimental detection of such phenomena is discussed.

Roland Jung, Gert‐Ludwig Ingold, Peter SCHRAMM +1 more

Anonymous

Trevis A. Crane

Low-frequency noise caused by critical-current fluctuations in Josephson junctions can lead to substantial, measurement-induced dephasing in superconducting qubits. The purpose of this work is to measure this noise as a function of temperature and to simulate its effect on the measurement dynamics associated with superconducting qubits. In Nb trilayer junctions we measure the noise power at 1 Hz down to 10 mK and verify a T2 dependence for T > 1 K, below which we observe a flattening of the noise magnitude versus temperature. In Al trilayer junctions we measure the critical-current noise power at 1 Hz from 10 mK to 1.4 K and find no dependence on temperature over this range. Possible reasons for the deviation from a T2 dependence are explored, including heating and sample quality. Simulations of the effect of 1/f noise are performed to examine the consequence of using different qubit sampling methods on expected dephasing times. Using the two sampling methods, we can probe the spectral nature and possible source of the dominant noise in a qubit.

E. S. R. Gopal

Chee‐Kong Lee, L. C. Kwek, Jianshu Cao

We study the stochastic resonance of quantum discord (``discord resonance'') in coupled quantum systems and make a comparison with the stochastic resonance of entanglement (``entanglement resonance''). It is found that the discord resonance is much more robust against dephasing noise and thermal effects than the entanglement resonance. We also show that, unlike the entanglement resonance, the level of dissipation at which the discord resonance occurs is not sensitive to dephasing noise. These results suggest that it is easier to detect the discord resonance in actual experiments, where the dephasing noise and temperature are difficult to control.