Precision lifetime measurements of a single trapped ion with ultrafast laser pulses

Abstract

We report precision measurements of the excited state lifetime of the 5p 2 P 1/2 and 5p 2 P 3/2 levels of a single trapped Cd + ion. The ion is excited with picosecond laser pulses from a mode-locked laser and the distribution of arrival times of spontaneously emitted photons is recorded. The resulting lifetimes are 3.148 ± 0.011 ns and 2.647 ± 0.010 ns for 2 P 1/2 and 2 P 3/2 respectively. With a total uncertainty of under 0.4%, these are among the most precise measurements of any atomic state lifetimes to date. Here we report excited state lifetime measurements using a time-correlated single photon counting technique on a single atom. This method, designed especially to eliminate common systematic errors, involves selective excitation of a single trapped ion to a particular excited state (lifetime of order nanoseconds) by an ultrafast laser pulse (duration of order picoseconds). Arrival of the spontaneously-emitted photon from the ion is correlated in time with the excitation pulse, and the excited state lifetime is extracted from the distribution of time delays from many such events.By performing the experiment on a single trapped ion, we are able to eliminate prevalent systematic errors, such as: pulse pileup that causes multiple photons to be collected within the time resolution of the detector, radiation trapping or the absorption and re-emission of radiation by neighboring atoms, atoms disappearing from view before decaying, and subradiance or superradiance arising from coherent interactions with nearby atoms. By using ultrafast laser pulses, we eliminate potential effects from applied light during the measurement interval.With this setup, at most one photon can be emitted following an excitation pulse. While this feature is instrumental in eliminating the above systematic errors, it would appear that this signal would require large integration times for reasonable statistical uncertainties. However, with a lifetime of only a few nanoseconds, millions FIG. 1: The experimental apparatus. (a) A picosecond mode locked Ti:Saph laser is tuned to four times the resonant wavelength for either the 5p 2 P 1/2 or the 5p 2 P 3/2 level of Cd + . Each pulse is then frequency-quadrupled through non-linear crystals, filtered from the fundamental and second harmonic, and directed to the ion. An amplified cw diode laser is also frequency quadrupled and tuned just red of the 2 P 3/2 transition for Doppler cooling of the ion within the trap. Acoustooptic modulators (AOM) are used to switch on and off the lasers as described in the text. Photons emitted from the ion are collected by an f /2.1 imaging lens and directed toward a photon-counting photo multiplier tube (PMT). The output of the PMT provides the start pulse for the time to digital converter (TDC), whereas the stop pulse is provided by the reference clock of the mode-locked laser. of such excitations can be performed each second, thus potentially allowing sufficient data for a statistical error of under 0.1% to be collected in a matter of minutes [6].A diagram of th...

Ab initiorelativistic many-body calculation of hyperfine splittings ofC113d+

“…The most reliable experimental results are presented by Moehring et al [21] to date with a total uncertainty of 0.4%. We can see from table I, our calculated lifetime for 5P fine structure states of 113 Cd + are in excellent agreement with the recent measured result [21] and highly correlated MBPT calculations [22]. Table II presents the computed values of the hyperfine energy splittings for ground state and few low-lying excited states of 113 Cd + .…”

“…f a Time-resolved laser-induced fluorescence [17] b Hanle-theory [18] c Beam-laser, beam foil (ANDC) [19] d Phase-shift method [20] e Ultrafast laser pulses [21] f Many-body third order perturbation theory [22] g Hanle [23] We report our lifetime results along with the other calculated and measured results in table I.…”

Precision measurement of the branching fractions of the 4p 2P3/2 decay of Ca II

“…[23] which are all about 4% higher, a discrepancy much bigger than for the relative decay strengths. From this point of view, it might be of interest to use a single trapped ion for a measurement of its excited state lifetime [36] or its absolute oscillator strengths.…”

Quantum interference of photon pairs from two remote trapped atomic ions

“…The periodic ultrafast excitation of the single ion leads to peaks at multiples of the pulse separation time. As the ion is excited on a timescale much faster than the excited-state lifetime, the spontaneously emitted photons have an exponential envelope 24 . Therefore, the peaks in the autocorrelation function have a two-sided exponential decay where the 1/e half width is given by the 8 ns lifetime of the excited state.…”