Coherent Interaction Between Laser Photons and Single Spins in InAs Quantum Dots

This thesis focuses on coherent interactions between laser photons and single spins in two types of InAs quantum dots. Quantum dots are promising candidates for quantum information applications due the potential for on-demand emission of highly pure and indistinguishable photons. Achieving coherent interactions between photons and quantum dot spins is an important step towards complete control of a single spin, which is required for emerging quantum technology applications such as cluster states. Initially, the experimental concepts and techniques required for coherent spin control are demonstrated using the well-established platform of 900 nm InAs/GaAs quantum dots embedded in semiconductor micropillar cavities. In the first experiment, it is shown that a quantum dot spin can be used as a non-linearity to induce a photon phase shift. This is extended using spin-pumping techniques to create a single-photon phase switch, which is an important component for future quantum information networks. A quantum dot-micropillar system is also utilised to create time-bin encoded qubits with arbitrary phase, by controlling the phase of a laser driving a Raman spin-flip transition. This further emphasises the benefits of single-spin control in a quantum dot. Having demonstrated the above techniques, the second part of the thesis focuses on developing coherent control of spins in InAs/InP quantum dots emitting in the telecom C-band. These dots are embedded in a planar cavity, with a cubic zirconia solid immersion lens fixed to the sample surface. Correlation measurements were used to confirm good single photon statistics under continuous wave and pulsed resonant excitation, while indistinguishability measurements showed a visibility of 75%. These measurements indicate the presence of resonant Rayleigh scattered photons, which have not previously been observed at this wavelength. A Michelson interferometer allows for direct measurement of the coherence times of the photons. This confirms the emission of photons with coherence times exceeding the Fourier limit. Finally, resonance fluorescence is demonstrated for a negatively charged exciton in a Voigt geometry magnetic field. This is used as a first step towards coherent spin control of a quantum dot emitting at telecom wavelengths. Initial results indicating spin pumping, and therefore the feasibility of future spin control experiments, are introduced.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2022

Author dc:creator

• Wells, Louise

Advisors dc:contributor.advisor

• Ritchie, David
• Shields, Andrew

• Quantum dot
• Photonics
• Quantum optics

Licence

• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.89479

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/342063