Towards optical Raman quantum memories with colour centres in diamond

Thesis

Quantum memories are a key technology enabling arbitrarily-scalable optical quantum information processing architectures via active synchronisation and multiplexing of quantum information. Optically active confined impurities, called colour centres, in a spin-free and highly transparent diamond host material are promising systems to realise such devices in the solid-state, suitable for integration in a scalable guided-wave on-chip photonic platform.

In this thesis, the transition from optical Raman quantum memories in atomic vapours to solid-state systems is prepared, exploring two diamond-based systems:

On the basis of ensembles of neutrally charged nitrogen vacancy centres, desirable properties and criteria of solid-state systems used for optical quantum memories are developed. These include non-vanishing off-resonant Raman coupling, variable acceptance bandwidth for broadband pulses and cross-linear polarised optical transitions to prevent the generation of noise during the Raman memory protocol, which have been realised experimentally by applying external uniaxial stress to the system. However, attempts to measure the very short orbital ground state lifetime affirmed unfavourable theoretical estimations, rendering this centre unsuitable for memory applications.

As a potential alternative, the negatively charged silicon vacancy centre has been investigated, which offers a large ground state splitting with extended life and coherence times and narrow inhomogeneous spectral lines due to its inversion symmetry. In an ensemble of silicon vacancy centres, the ground state lifetime is measured and coherent manipulation via resonant Ramsey interference and Hahn echo is demonstrated. In a second step, off-resonant two-photon transitions are achieved implementing stimulated Raman adiabatic passage between the orbital ground states. Finally, strong light-matter interaction of a weak signal field with the ensemble via phase-sensitive four-wave mixing is shown forming the basis for integrated Raman-based memories and single photon nonlinearities in ensembles of silicon vacancy centres and closely related defects.

Authors: Weinzetl, C

• DOI: 10.5287/ora-erwj48jj8
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford