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Conference on Lasers and Electro-Optics

Studies of quantum jumps in a single /sup 25/Mg/sup +/ ion held in a Penning trap

H. Powell, William M. Irvine, Martijn A. van Eijkelenborg, D. M. Segal, Richard Claude Thompson

Published Aug 29, 2005• 0 citations
Publisher

Abstract

Summary form only given. We have performed a study of quantum jumps in single magnesium ions held in a Penning trap. This system is unusual in that quantum jumps may be observed using only a single laser frequency which serves to laser cool the ion (providing fluorescence for detection), shelve the ion in a metastable state (via an off-resonant Raman transition) and also to repump the ion from the metastable state back into the cooling cycle (again via a Raman transition). Single /sup 24/Mg/sup +/ ions have been studied in a Penning trap before but we have predicted and now observed a number of interesting effects that occur only in /sup 25/Mg/sup +/. We have also trapped single ions of /sup 26/Mg/sup +/ and confirmed that their quantum jump behaviour is similar to that of /sup 24/Mg/sup +/ as expected. The novel features in the behaviour of /sup 25/Mg/sup +/ are due to the presence of hyperfine structure in this ion.

DOI
10.1109/iqec.2000.907969

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•Nov 1, 2011•1 citation
Summary form only given. We have performed a study of quantum jumps in single magnesium ions held in a Penning trap. This system is unusual in that quantum jumps may be observed using only a single laser frequency which serves to laser cool the ion (providing fluorescence for detection), shelve the ion in a metastable state (via an off-resonant Raman transition) and also to repump the ion from the metastable state back into the cooling cycle (again via a Raman transition). Single /sup 24/Mg/sup +/ ions have been studied in a Penning trap before but we have predicted and now observed a number of interesting effects that occur only in /sup 25/Mg/sup +/. We have also trapped single ions of /sup 26/Mg/sup +/ and confirmed that their quantum jump behaviour is similar to that of /sup 24/Mg/sup +/ as expected. The novel features in the behaviour of /sup 25/Mg/sup +/ are due to the presence of hyperfine structure in this ion.
The quantum jump statistics for the three stable isotopes of Mg + have been studied experimentally. Single ions of magnesium were held and laser cooled in a Penning trap. Quantum jumps were observed by collecting the resonance fluorescence near 280 nm from the cooled ion. The jump rate was analysed to find ratios of the average time the ion spends fluorescing, `on' time, to the average time it spends in the dark state, `off' time: for both 24 Mg + and 26 Mg + this value was found to be 15.9±1.2, in agreement with a theoretical value of 16.0. The presence of hyperfine structure in 25 Mg + means that while the jump rate for 24 Mg + and 26 Mg + remains unaltered for both available cooling transitions, for the odd isotope the on to off ratio is predicted to be 11.8 and 22.8 for the lower and upper transitions respectively. Experimental values for these ratios were found to be 10.2 ± 0.7 and 22.0 ± 0.6. The occurrence of so-called nuclear jumps in 25 Mg + is investigated qualitatively. These rare jumps are produced as a result of the hyperfine splitting, which is only present in the odd isotope. Although the data indicate some evidence for this type of jump, it is not possible to draw any firm conclusions due to the small number of events observed.
Several experiments performed at NBS using a single (or few) trapped atomic ions are described. We recently observed the ‘‘quantum jumps’’ in the fluorescence from a single ion of Mg+ due to spontaneous Raman transitions between the energy levels of the ion. In this system, a single laser is used to induce transitions between Zeeman sub‐levels of the ion. As with other realizations of quantum jumps, the dynamics of the population evolution is governed by an effective two‐level rate equation. A novel coherence phenomenon between excited state sub‐levels makes this system ideally suited for quantitatively testing the quantum jump theory. Our data are consistent with theory to within the measurement precision of 2%. Images of two to four ions which have been laser‐cooled until they ‘‘crystallize’’ are displayed and several other recent single ion experiments are mentioned.
We have performed laser cooling of Mg+{}^{+}+ ions confined in a Penning trap. The externally produced ions were captured in flight, stored, and laser cooled. Laser-induced fluorescence was observed perpendicular to the cooling laser axis. Optical detection down to the single-ion level together with the electronic detection of the ion oscillations inside the Penning trap have been used to acquire information on the ion storage time, ion number, and ion temperature. Evidence for the formation of ion crystals has been observed. These investigations are an important prerequisite for the sympathetic cooling of simultaneously stored highly charged ions and the precision laser spectroscopy of forbidden transitions in these.
Summary form only given. Single ions in Paul traps are investigated for quantum information processing. Superpositions of the S/sub 1/2/ and the D/sub 5/2/ states are used to implement a qubit. Single /sup 40/Ca/sup +/ ions are either held in a spherical Paul trap or alternatively, in a linear Paul trap. The ions are optically cooled and fluorescence light at 397 nm on the S/sub 1/2/-P/sub 1/2/ transition is monitored for a state measurement by the electron shelving technique. The S/sub 1/2/-D/sub 5/2/ quadrupole transition at 729 nm is excited for sideband cooling and for quantum state preparation. Individual ions in a linear string are addressed by a tightly focused 729 nm laser beam. In the spherical Paul trap (4.5 MHz trap frequency) a single Ca/sup +/ ion has been cooled to the ground state of vibration with a probability of up to 99.9%. Starting from this Fock state |n=0> coherent quantum state manipulation on the S/sub 1/2/-D/sub 5/2/ transition is achieved.
This thesis presents work aimed towards achieving sideband cooling of 40Ca+ ions in a Penning trap. The observation of an increase in the number of quantum jumps as a function of the trapping magnetic field is first presented. This observation is explained by the ion falling into a long-lived D5/2 state, out of which the ion is not being re-pumped. The ion can fall into this state due to mixing of the fine structure components with the same mJ quantum number induced by the applied magnetic field. A calculation of the mixing and shelving rate as a function of magnetic field strength is presented. This theory matches well with the experimental results observed. This work has been presented in a publication in which a perturbative analysis was used. An alternative analysis is presented here in which the full Hamiltonian is diagonalised. The essential conclusions however remain unchanged. This ‘J-state mixing’ effect means re-pumping from each of the six D5/2 state sub-levels of our ion is required for efficient laser cooling. This is achieved by the addition of a system comprising an 854 nm laser and a fibre EOM to provide the radiation required to re-pump these levels. The same EOM is then used to re-pump out of the four sub-levels of the D3/2 state using a single 866 nm laser. This is a great simplification of the experimental setup required to cool a 40Ca+ ion in a Penning trap which would otherwise require ten separate lasers to independently address each of the D sub-states. Achieving efficient repumping leads to the ability to perform pulsed spectroscopy on the quadrupole S1/2 → D5/2 transition in 40Ca+ . Preliminary results of this spectroscopy in a radio-frequency trap are presented.