Ion Trapping: Technology and Techniques
Ion-Trajectory Analysis for Micromotion Minimization and the Measurement of Small Forces
For experiments with ions confined in a Paul trap, minimization of micromotion is often essential. In order to diagnose and compensate micromotion we have implemented a method that allows for finding the position of the radio-frequency (rf) null reliably and efficiently, in principle, without any variation of direct current (dc) voltages. We apply a trap modulation technique and focus-scanning imaging to extract three-dimensional ion positions for various rf drive powers and analyze the power dependence of the equilibrium position of the trapped ion. In contrast to commonly used methods, the search algorithm directly makes use of a physical effect as opposed to efficient numerical minimization in a high-dimensional parameter space. Using this method we achieve a compensation of the residual electric field that causes excess micromotion in the radial plane of a linear Paul trap down to 0.09 V/m. Additionally, the precise position determination of a single harmonically trapped ion employed here can also be utilized for the detection of small forces. This is demonstrated by determining light pressure forces with a precision of 135 yN. As the method is based on imaging only, it can be applied to several ions simultaneously and is independent of laser direction and thus well suited to be used with, for example, surface-electrode traps.
State selective detection of hyperfine qubits
In order to faithfully detect the state of an individual two-state quantum system (qubit) realized using, for example, a trapped ion or atom, state selective scattering of resonance fluorescence is well established. The simplest way to read out this measurement and assign a state is the threshold method. The detection error can be decreased by using more advanced detection methods like the time-resolved method or the π-pulse detection method. These methods were introduced to qubits with a single possible state change during the measurement process. However, there exist many qubits like the hyperfine qubit of +Yb171 where several state change are possible. To decrease the detection error for such qubits, we develop generalizations of the time-resolved method and the π-pulse detection method for such qubits. We show the advantages of these generalized detection methods in numerical simulations and experiments using the hyperfine qubit of +Yb171. The generalized detection methods developed here can be implemented in an efficient way such that experimental real time state discrimination with improved fidelity is possible.
A Planar Ion Trap Chip with Integrated Structures for an Adjustable Magnetic Field Gradient
We present the design, fabrication, and characterization of a segmented surface ion trap with integrated current-carrying structures. The latter produce a spatially varying magnetic field necessary for magnetic-gradient-induced coupling between ionic effective spins. We demonstrate trapping of strings of 172Yb+ ions and characterize the performance of the trap and map magnetic fields by radio frequency-optical double-resonance spectroscopy. In addition, we apply and characterize the magnetic gradient and demonstrate individual addressing in a string of three ions using RF radiation.
Thick-Film Technology for Ultra High Vacuum Interfaces
We adopt thick-film technology to produce ultra high vacuum compatible interfaces for electrical signals. These interfaces permit voltages of hundreds of volts and currents of several amperes and allow for very compact vacuum setups, useful in quantum optics in general, and in particular for quantum information science using miniaturized traps for ions or neutral atoms. Such printed circuits can also be useful as pure in-vacuum devices. We demonstrate a specific interface which provides 11 current feedthroughs, more than 70 dc feedthroughs and a feedthrough for radio frequencies. We achieve a pressure in the low 10-11 mbar range and demonstrate the full functionality of the interface by trapping chains of cold ytterbium ions, which requires the presence of all of the above mentioned signals. In order to supply precise time-dependent voltages to the ion trap, a versatile multi-channel device has been developed.