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Title: Applications of coherent phonons in quantum optics : prospects for optically controlled ensemble quantum memories in the solid state
Author: Waldermann, Felix C.
ISNI:       0000 0001 3551 0981
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2009
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Quantum information processing (QIP) encompasses powerful methods of communication, cryptography and computation. For a successful deployment of quantum optics to QIP, quantum memories are necessary, i.e. devices that coherently store single photons. We here studied an off-resonant (Raman) type of quantum memories, and its possible realisation using solid state absorbers. A single photon is adiabatically absorbed by an ensemble of .absorbers with A-level structure, in a process mediated by a strong classical control field. Coherent retrieval is achieved by a second control pulse. The storage efficiency has been .calculated as a function of the ensemble optical depth, the absorber dipole moments, and the control field power. This scheme can be realised with a variety of quantum absorbers, e.g. atoms in a Brownian gas or semiconductor quantum dots. Absorbers in the solid state are advantageous because of their temporal stability, large dipole moments, and high densities. Two absorber types in the solid state have been analysed: the nitrogen vacancy (NV) centre in diamond, and delocalised optical phonon modes in Raman active solids. A review of the optical properties of the NV centre has been conducted, paying special attention to the attributes required for a quantum memory. A new, broadband quantum memory scheme has been introduced, using phonon sidebands for storage. An experimental analysis of a high energy ion irradiated, nitrogen-rich diamond sample created by high pressure and high temperature (HPHT) has been conducted to determine possible defect densities achievable. In order to achieve high fidelity storage, the photon-ens.emble interaction strength can be enhanced by a microcavity. Various types of microcavities have been created in single crystal diamond, and analysed using scanning electron microscopy (SEM) and micro-photoluminescence. Bulk phonon modes in diamond have also been investigated to asses their suitability for quantum memories and entanglement. Optical phonons can coherently be excited using Raman scattering with ultrafast laser pulses. This excitation type could be used for storage of broadband photons, if the optical retrieval (readout) of a phonon is possible. To analyse the storage lifetime, a novel technique for the decoherence measurement of optical phonons has been developed, using spectral interference of Stokes light. It allows to determine the lifetime of coherent phonons at the quantum level, i.e. in the regime relevant for quantum memories. We demonstrated this scheme with phonons in diamond. \Ve also present an experiment realising the detection of single optical phonons, which has been achieved using Anti-Stokes scattering. This allows for an ultrafast population· readout of optical phonon modes at the Brillouin zone centre.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available