Conditions for anti-Zeno effect observation in free-space atomic radiative decay

Frequent measurements can modify the decay of an unstable quantum state with respect to the free dynamics given by Fermi's golden rule. In a landmark article, Nature 405, 546 (2000), Kofman and Kurizki concluded that in quantum decay processes, acceleration of the decay by frequent measurements, called the quantum anti-Zeno effect (AZE), appears to be ubiquitous, while its counterpart, the quantum Zeno effect, is unattainable. However, up to now there have been no experimental observations of the AZE for atomic radiative decay (spontaneous emission) in free space. In this work, making use of analytical results available for hydrogen-like atoms, we find that in free space, only non-electric-dipolar transitions should present an observable AZE, revealing that this effect is consequently much less ubiquitous than first predicted. We then propose an experimental scheme for AZE observation, involving the electric quadrupole transition between D 5/2 and S 1/2 in the heaviest alkali-earth ions Ca + and Sr +. The proposed protocol is based on the STIRAP technique which acts like a dephasing quasi-measurement

Ion transport in macroscopic RF linear traps

Efficient transport of cold atoms or ions is a subject of increasing concern in many experimental applications reaching from quantum information processing to frequency metrology. For the scalable quantum computer architectures based on the shuttling of individual ions, different transport schemes have been developed, which allow to move single atoms minimizing their energy gain. In this article we discuss the experimental implementation of the transport of a three-dimensional ion cloud in a macroscopic linear radiofrequency (RF) trap. The present work is based on numerical simulations done by molecular dynamics taking into account a realistic experimental environment. The deformation of the trapping potential and the spatial extension of the cloud during transport appears to be the major source of the ion energy gain. The efficiency of transport in terms of transfer probability and ion number is also discussed

Metastable level lifetimes from electron-shelving measurements with ion clouds and single ions

The lifetime of the 3d^2D_5/2-level in singly-ionized calcium has been measured by the electron-shelving technique on different samples of rf trapped ions. The metastable state has been directly populated by exciting the dipole-forbidden 4S_1/2 - 3D_5/2 transition. In ion clouds, the natural lifetime of this metastable level has been measured to be (1095+-27) ms. For the single-ion case, we determined a lifetime of (1152+-20) ms. The 1sigma-error bars at the 2%-level have different origins for the two kinds of experiments: data fitting methods for lifetime measurements in an ion cloud and control of experimental parameters for a single ion. De-shelving effects are extensively discussed. The influence of differing approaches for the processing of the single-ion quantum jump data on the lifetime values is shown. Comparison with recent measurements shows excellent agreement when evaluated from a given method

Crystallization of ion clouds in octupole traps: structural transitions, core melting, and scaling laws

International audienceThe stable structures and melting properties of ion clouds in isotropic octupole traps are investigated using a combination of semi-analytical and numerical models, with a particular emphasis at finite size scaling effects. Small-size clouds are found to be hollow and arranged in shells corresponding approximately to the solutions of the Thomson problem. The shell structure is lost in clusters containing more than a few thousands of ions, the inner parts of the cloud becoming soft and amorphous. While melting is triggered in the core shells, the melting temperature unexpectedly follows the rule expected for three-dimensional dense particles, with a depression scaling linearly with the inverse radius

Comment on "Prospect of optical frequency standard based on a 43Ca+ ion"

A recent evaluation of the frequency uncertainty expected for an optical frequency standard based on a single trapped $^{43}$Ca$^+$ ion was published in Phys. Rev. A {\bf 72} (2005) 043404. The paper contains some interesting information like systematic frequency shifts but fails to depict their uncertainty, leading to confuse accuracy and precision. The conclusions about the major contribution to the frequency shift are not consistent with the presented calculations and omit comparisons with data published previously

Diffraction phases in atom interferometers

Diffraction of atoms by laser is a very important tool for matter wave optics. Although this process is well understood, the phase shifts induced by this diffraction process are not well known. In this paper, we make analytic calculations of these phase shifts in some simple cases and we use these results to model the contrast interferometer recently built by the group of D. Pritchard at MIT. We thus show that the values of the diffraction phases are large and that they probably contribute to the phase noise observed in this experiment.Comment: v3 11/03/0

A double ion trap for large Coulomb crystals

While the linear radiofrequency trap finds various applications in high-precision spectroscopy and quantum information, its higher-order cousin, the linear multipole trap, is almost exclusively employed in physical chemistry. Recently, first experiments have shown interesting features by laser-cooling multipole-trapped ion clouds. Multipole traps show a flatter potential in their centre and therefore a modified density distribution compared to quadrupole traps. Micromotion is an important issue and will certainly influence the dynamics of crystallized ion structures. Our experiment tends to investigate possible crystallization processes in the multipole. In a more general way, we are interested in the study of the dynamics and thermodynamics of large ion clouds in traps of different geometry.Comment: 10th International Workshop on Non-Neutral Plasmas, Greifswald : Germany (2012

Heating rate in a linear quadrupole trap

In radio-frequency trap, the temperature of ion ensembles converges towards a hot equilibrium due to radio-frequency heating. This effect is detrimental to the stability of trapped ensembles and is the justification of cooling. The intensity of this radio-frequency heating increases with the amplitude of the radio-frequency field $q_x$. Using an analytical empirical formula, we show that the lifetime of the ion ensemble $t_0$ under cold condition increases with $q_x$ according to a power law $t_0\propto q_x^A$, and does not vary significantly for the several ion quantities $N$ tested. The temperature of the explosive onset $B$ decreases linearly with $q_x$. We also show that non-linear instabilities due to trapping parameters decreases $t_0$ and $B$, and produce a local increase of heating rate for certain temperature ranges.Comment: 6 pages including the 29 references, 4 figures, 2 tables. Research article intended to complete the previously published work at https://doi.org/10.1103/PhysRevA.108.01310

Fast and efficient transport of large ion clouds

The manipulation of trapped charged particles by electric fields is an accurate, robust and reliable technique for many applications or experiments in high-precision spectroscopy. The transfer of the ion sample between multiple traps allows the use of a tailored environment in quantum information, cold chemistry, or frequency metrology experiments. In this article, we experimentally study the transport of ion clouds of up to 50 000 ions. The design of the trap makes ions very sensitive to any mismatch between the assumed electric potential and the actual local one. Nevertheless, we show that being fast (100 $\mu$s to transfer over more than 20 mm) increases the transport efficiency to values higher than 90 %, even with a large number of ions. For clouds of less than 2000 ions, a 100 % transfer efficiency is observed