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Quantum Optics with Spins in Solid State: The Power of Ensembles

Final Report Summary - SOLIDSPINQOPT (Quantum Optics with Spins in Solid State: The Power of Ensembles)

Quantum optics with spin ensembles in solid state

For the field of quantum information science one of the key challenges is to transfer the quantum state of an electronic spin onto the quantum state of an optical pulse, and vice versa. The field of atomic physics showed that a spin-ensemble approach has very strong advantages for making this functionality robust against various technical imperfections that one has to deal with in practice. A central theme in the research group of Prof. van der Wal is to implement this spin-ensemble approach with semiconductor materials, where it can be implemented in micron-scale optical waveguides with the optically-active spin ensemble embedded in the waveguide material. This project is for the largest part based on an ERC Starting Grant, which was running from Feb. 2012 till Feb. 2017.

One key effect that was demonstrated with localized donor electrons in GaAs is the effect known as Electromagnetically Induced Transparency (EIT), which is fundamental to all further quantum information applications. Here, two lasers each address an optical transition from one of the electron spin states to a common optically excited state (a bound-exciton state). However, via electron spin coherence and quantum interference in the system’s dynamics, the lasers provide control on the spin while there is (in the ideal case) no optical excitation at all.

The team used this EIT effect for making quantum optical control of donor-spins in GaAs a self-improving effect. In relation to the important topic of a central spin controlling a nuclear spin bath, the team showed a two-laser control scheme that pumps away nuclear spin fluctuations. Suppressing these nuclear spin fluctuations is important since these limit the electron spin coherence time.

The team also got results from a research line aimed at exploring quantum optics with spin with new material systems. Here the focus was on silicon carbide (SiC). The approach used the electronic spin of Si-C divacancy defects (a system very similar to the famous NV-center in diamond, but potentially better for quantum applications). For this field, the team demonstrated the first all-optical control of these spin states, preparation of coherent spin superpositions, a pathway for removing ensemble inhomogeneity for the optical transitions, and (also for this material) the EIT effect.