All-optical Raman-based noise spectroscopy of a solid-state spin

The development of spin qubits with long coherence times for quantum information processing, communication and sensing requires sources of spin noise to be identified and mitigated. Although microwave-based spin control is typically used for noise spectroscopy of solid-state spin qubits, this approach becomes infeasible when high frequency noise components are stronger than the available microwave powers. Here, we introduce an all-optical approach for noise spectroscopy of spin qubits, which enables the characterization of spin systems for which microwave control is challenging. Our approach involves Raman-based spin rotations to optically implement the Carr-Purcell-Meiboom-Gill pulse sequences inspired by nuclear magnetic resonance spectroscopy. Analyzing the temporal dynamics of a spin of interest under the application of these sequences allows us to extract the spectral densities of the noise sources that interact with the spin and lead to its decoherence. To demonstrate the capabilities of our all-optical approach for noise spectroscopy, we use it to measure the noise spectral density of a single spin confined in an InAs/GaAs quantum dot. By leveraging the high bandwidths (over 100 MHz) provided by the all-optical approach, we extract the high frequency spectral density of the noise of a single spin interacting with a large ensemble of nuclear spins broadened by strain. Our measurements confirm previous theoretical modeling of such hyperfine interactions, and shed light on the ability to extend quantum dot coherence times utilizing dynamical decoupling sequences. As such, our Raman-based approach for noise spectroscopy provides insights for the development of optically-active semiconductor spin qubits with long coherence times for quantum information processing, communication and sensing.