An agile and stable optical system for high-fidelity coherent control of a single ⁸⁸Sr⁺ ion

  • Joseph Andrew Thom

Student thesis: Doctoral Thesis


This thesis describes experiments involving the coherent manipulation of a single ⁸⁸88Sr⁺ ion that is confined in a microfabricated trap. A stable and agile laser is constructed and used to perform rotations on an optical qubit that is encoded in the D₁/₂ (mj = -1/2) -D₅/₂(mj = -5/2) transition at 674 nm. After the excess micromotion is fully compensated in the microtrap, frequency-resolved optical pumping to the S₁/₂(mj = 1/2) qubit level is demonstrated with 99.8 % efficiency and resolved sideband cooling is used to reduce the mean vibrational number of the axial mode to n̄z~1. Deterministic ion transport between segments of the microtrap is also performed at frequencies up to 1 kHz. The agile laser permits fast, accurate and precise modulation of the optical phase, amplitude and frequency on a sub-microsecond timescale. Amplitude-shaped pulses are produced in near-perfect agreement with the desired functional form for durations ranging over 10⁶, which allows the frequency spectrum to be tailored in order to reduce off - resonant excitation. The agile system is stabilised in frequency by injection locking to an ultra-stable laser to yield a linewidth of < 10 Hz. Also, interrogation pulses are stabilised over a range of 10⁵ in optical power using a cascaded series of avalanche photodiodes, and the beam position at the ion is stabilised to < 0.4 % of the beam diameter. The complete system is capable of performing single qubit gate operations with an infidelity below a fault-tolerant limit. The agile laser is used to demonstrate that using Blackman rather than square shaped interrogation pulses offers an 11 dB reduction in off -resonant excitation. Also the phase agility of the system is verifed using Rabi and Ramsey spectroscopy. Finally, a spin-echo sequence is used to enhance the storage time of the optical qubit, and high resolution scans over the quadrupole transition are performed to measure a system coherence time of 1 ms.
Date of Award23 Feb 2016
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde & EPSRC (Engineering and Physical Sciences Research Council)

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