Prof Andrew Steane

Abstract:

We demonstrate the use of dynamic decoupling techniques to extend the coherence time of a single memory qubit by nearly two orders of magnitude. By extending the Hahn spin-echo technique to correct for unknown, arbitrary polynomial variations in the qubit precession frequency, we show analytically that the required sequence of π-pulses is identical to the Uhrig dynamic decoupling (UDD) sequence. We compare UDD and Carr-Purcell-Meiboom-Gill (CPMG) sequences applied to a single ⁴³Ca⁺ trapped-ion qubit and find that they afford comparable protection in our ambient noise environment. © 2011 IOP Publishing Ltd.

Abstract:

We demonstrate a Doppler cooling and detection scheme for ions with low-lying D levels which almost entirely suppresses scattered laser light background, while retaining a high fluorescence signal and efficient cooling. We cool a single ion with a laser on the {Mathematical expression} transition as usual, but repump via the {Mathematical expression} level. By filtering out light on the cooling transition and detecting only the fluorescence from the {Mathematical expression} decays, we suppress the scattered laser light background count rate to 1 s -1 while maintaining a signal of 29000 s -1 with moderate saturation of the cooling transition. This scheme will be particularly useful for experiments where ions are trapped in close proximity to surfaces, such as the trap electrodes in microfabricated ion traps, which leads to high background scatter from the cooling beam. © 2011 Springer-Verlag.

Abstract:

We characterise the performance of a surface-electrode ion "chip" trap fabricated using established semiconductor integrated circuit and micro-electro-mechanical-system (MEMS) microfabrication processes, which are in principle scalable to much larger ion trap arrays, as proposed for implementing ion trap quantum information processing. We measure rf ion micromotion parallel and perpendicular to the plane of the trap electrodes, and find that on-package capacitors reduce this to ≲10 nm in amplitude. We also measure ion trapping lifetime, charging effects due to laser light incident on the trap electrodes, and the heating rate for a single trapped ion. The performance of this trap is found to be comparable with others of the same size scale. © 2011 Springer-Verlag.