Discrimination of Dephasing Sources by Continuous Dynamical Decoupling

Decoherence induced by the unwanted noise is one of the most important obstacles to be overcame in the quantum information processing. To do this, the noise power spectral density needs to be accurately characterized and then used to the quantum operation optimization. The known continuous dynamical decoupling technique can be used here as a noise probing method based on a continuous-wave resonant excitation field, followed by a gradient descent protocol. In this paper, we estimate the noise spectroscopy over a frequency range 0-530 kHz for both laser frequency and magnetic field noises by monitoring the transverse relaxation from an initial state |+sigma_x>. In the case of the laser noise, we also research into two dominant components centered at 81.78 and 163.50 kHz. We make an analogy with these noise components and driving lasers whose lineshape is assumed to be Lorentzian. This method is verified by the experimental data and finally helps to characterize the noise.