Optically addressable spin qubits and their photonic interfacing
Prof. Dr. David Hunger (KIT (Karlsruher Institut für Technologie))

Optically addressable spins in the solid state are promising candidates for realizations of quantum networks and quantum computing nodes.

We study NV centers in diamond coupled to an optical microcavity to enhance the optical emission and get efficient access to the spin degree of freedom. Studying small ensembles, we observe collectively enhanced emission and non-trivial photon statistics, despite the presence of inhomogeneities and spatial separation between emitters [1].

As an alternative color center, we study SnV centers in diamond, which can possess superior optical coherence properties. We observe hour-long spectral stability and Fourier-limited emission linewidths of individual emitters. We leverage their spin degree of freedom by studying a strained diamond at mK temperature. To avoid Ohmic losses in the microwave line, we fabricate a superconducting coplanar waveguide on a diamond membrane. We demonstrate coherent manipulation of the electron spin and evaluate the decoherence properties for different magnetic field orientations at mK temperature [2]. We furthermore identify strongly coupled nuclear spins and achieve nuclear spin state preparation and coherent control. Prospects for integration into a microcavity for efficient spin-photon interfacing are discussed [3].
A complementary platform is rare earth ion-based materials. I will report investigations of molecular rare-earth-complexes with promising coherence properties for quantum applications [4] and efforts to study single ions coupled to a cavity as qubits [5].

References
[1] Pallmann et al., arxiv:2311.12723
[2] Karapatzakis et al., Phys Rev X 14, 031036 (2024)
[3] Körber et al., Phys Rev Appl. 19, 064057 (2023)
[4] Serrano et al., Nature 603, 241 (2022)
[5] Deshmukh et al., Optica 10, 1339 (2023)