Solid State Quantum Optics

In many cases even a very detailed numerical simulation cannot model faithfully enough a quantum device that has to be optimized. In such cases, measurement feedback is needed in order to design control pulses that steer the device with the desired precision. Together with our experimental collaborators, we use the open-source software Quantum Optimal Control Suite (QuOCS) for measurement-based, closed-loop, pulse optimization.

From a theoretical point of view, we study and design measurement protocols tailored to the experimental setup in order to obtain the most efficient closed-loop optimization protocols.

Various control pulses acting on the system and/or its environment allow to tune the system-environment interaction. The efficient description of these driven open systems typically requires approximations tailored to the regime of interest (i.e., certain constraints on the drive or assumptions on the environment). For quantum sensing, we consider a system (sensor) that interacts with the environment in a desired (signal) and undesired, deleterious (noise) way.

To operate the quantum sensor, the effect of the noise, e.g., from neighboring spins, has to be suppressed and the effect of the signal (typically external to the sensor device) has to be extracted. For this aim we apply methods of optimal control, measurement-induced control, and dynamical decoupling to engineer the system-environment interactions. For quantum computing applications, instead, understanding and characterizing the interactions of the system with the environment is crucial to design high-fidelity gates in the presence of noise.

Color Centers are atomic defects in crystals, such as nitrogen vacancy (NV) centers in diamond, where two carbon atoms of the diamond crystal are replaced by one nitrogen atom and one vacancy, are a unique platform for the control of single electron and nuclear spins - even at room temperature - in solid-state devices. A free electron of the colour centre and surrounding nuclear spins can be manipulated with lasers and electromagnetic fields in the radio-frequency and microwave domain.

NV centers in nanodiamonds are a leading platform in quantum sensing. Due to the good optical properties, especially group-IV defects like germanium or tin vacancy centres are also studied for applications in quantum communications, such as quantum repeater devices. Such optical links could also be a pathway to build scalable quantum computing devices based on colour centres.