Single ion coupled to a high-finesse optical fibre cavity for cQED in the strong coupling regime

Kassa, Ezra (2017) Single ion coupled to a high-finesse optical fibre cavity for cQED in the strong coupling regime. Doctoral thesis (PhD), University of Sussex.

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Abstract

The research undertaken unites two distinct areas of quantum information processing: single ions stored in radio-frequency traps and single photons in optical fibres. Strings of ions are presently the most successful implementation of quantum computing, with elementary quantum algorithm and quantum simulations realised. The principal challenge in the field is to enhance the quantum processing power by scaling up current devices to larger systems. We pursue one of the most promising strategies: distributed quantum computation in which multiple small-scale ion processors are interlinked by exchanging photonic quantum bits via optical fibres. This requires a coherent quantum interface between ions and photons, mapping ionic to photonic quantum states and vice versa. To maximise fidelity and the success rate of the scheme, the interaction of ions and photons must take place in a microscopic optical cavity with high finesse. To this end, single 40Ca+ were trapped in a radio-frequency ion trap whose trapping electrodes are hollow cylinders. Optical fibres with mirrors machined on the facets are inserted into the electrodes to form a Fabry-Pérot cavity. Because the fibres are shielded by the electrodes the detrimental distortion of the trapping field due to their presence is suppressed and ions can be trapped for several hours. 40Ca+ has a -type energy level scheme wherein the ion is cooled on the 42P1/2 ⇔ 42S1/2 transition and the cavity is tuned to the 42P1/2 ⇔ 32D3/2 transition. This thesis reports the successful coupling of single ions to a high finesse optical fibre based cavity, with coupling strength g = 2π · 4:6 MHz. The cavity has length 367 μm, finesse of 40,000 and linewidth 2k = 2π · 9:4 MHz. In this coupling regime, the enhancement of the ion's emission rate through the Purcell effect was observed. Further, anti-correlation was observed in the emission rates between the P1/2 ⇔ D3/2 and P1/2 ⇔ S1/2 transitions with an effective emission rate suppression of up to 60% in the latter transition. The built system offers greater promises. Once the position in the cavity mode has been optimised we expect to reach the long-sought after strong coupling regime with (g, k, y) = 2π · (12:2; 4:7; 11:2) MHz.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QC Physics > QC0770 Nuclear and particle physics. Atomic energy. Radioactivity > QC0793 Elementary particle physics
Depositing User: Library Cataloguing
Date Deposited: 18 Jul 2017 09:26
Last Modified: 18 Jul 2017 11:33
URI: http://sro.sussex.ac.uk/id/eprint/69317

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