Background-free detection of trapped ions

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 2S1/2 to 2P1/2 transition as usual, but repump via the 2P3/2 level. By filtering out light on the cooling transition and detecting only the fluorescence from the 2P_3/2 to 2S1/2 decays, we suppress the scattered laser light background count rate to 1 per second while maintaining a signal of 29000 per second 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

Trapped-ion quantum computing: Progress and challenges

“…A first step in this direction was implemented via strong excitation (using 250 mW of laser power) on the quadrupole transition at 729 nm in 40 Ca + , followed by additional laser excitation at 854 nm to the 4P 3/2 state, which allowed background-free collection of the 393-nm photons emitted as the ion returns to the ground state [214]. This was followed by experiments which achieved higher detection rates by using a more tightly-focused 729-nm beam [215], or using multi-stage excitation to the same 4P 3/2 state in 40 Ca + by first-stage excitation to the P 1/2 state via 397-nm light and applying multiple IR beams at 850 nm, 854 nm and/or 866 nm [216]. In all three of these experiments, however, the 3D 5/2 state-which is the |0 qubit state in 40 Ca + -formed an intermediate state in the excitation chain.…”

Heating rate and electrode charging measurements in a scalable, microfabricated, surface-electrode ion trap

“…This gave approximately 50,000 counts/s for a single ion cooled on the S 1/2 −P 1/2 transition by one saturation intensity of resonant 397 nm light, and repumped on both the D 3/2 −P 3/2 (850 nm) and D 5/2 −P 3/2 (854 nm) transitions. Background scatter was ∼100 counts/s at this 397 nm power (2.0 μW in a spot with 1/e 2 radius w = 30 μm) [8]. Using a multi-element diffraction-limited fibre output collimator (CVI-Melles Griot GLC-14.5-8.0-405) and quartz optics for the 397 nm beam path were important in achieving this low background.…”

Focusing characteristics of a 4 πparabolic mirror light-matter interface

“…In contrast to our previous studies [13], we measure the response of the ion at a wavelength different to the one used for excitation. This approach is standard in fluorescence microscopy and has also been used in experiments with trapped ions [14]. It renders unnecessary a spatial separation of focused light and light scattered by the ion, thus lifting the limitation of focusing only from half solid angle as in Ref.…”