New techniques for quantum information with trapped ions

Quantum information processing with trapped ions is so far the most advanced scalable technology for quantum logic. Still many difficulties have to be surmounted before a device dapable of solving worthwhile computational problems, like the factoring of a large integer number into their primes, can be realized. The proposed work aims to tackle some of the most urgent problems that presently block the way towards this goal. A number of self sustainded experiments are proposed that aim to explore the poteintial of new concepts connected to quantum information with trapped ions. A new generation of ion traps that utilizes the possibilities of micro- engineering will be developed. These `trap chips` will integrate part of the electronics and can be manufacrured with very low geometrical errors. In a second step they will be used to check the practical feasibility of a new concept for individual addressing of qubits. Micro-engineering is also the key to the ralization of a competely new concept of ion trap quantum logic featuring a two dimension array of independent traps, each holding one ion. An additional ion is moved as a head over the plane of the array. A laser beam imposes a state dependent pushing force onto the head and one ion in the array, thus mediating a quantum phase gate between the two. Such a gate will ease the demands on laser cooling since the motional state of the coupled ions does not affect the gate and is more readily scalable than a linear trap. Cooling of ions is a prerequsite for all types of quantum logic, so we plan to characterize several methods of sup- Doppler cooling that promise to be conceptually simpler and more efficient than resolved sideband cooling. Especially Sysiphus cooling, polarization gradient cooling and new hybrid thechniques that combine Raman cooloing with conventional Doppler cooling techniques will be considered. Cooling of ions by collisional exchange with a cloud of ultracold neutrals promises lower equilibriun temperatrures than Doppler cooling with a substantial population in the ground states of all motional degrees of freedom. Since this method does not depend on the ion species it might open an avenue to cool all sorts of ions, even if they are not suitale for laser cooling. Influene of the proposed work on the development of the field The present situation in the field of quantum information is that a well developed theory is still waiting for experiments to realize some of the concepts. In this sense very advance towards practical realization of devises that can handle quantum informateion is a real breakthrough in the field. Three of the main experimental obstacles for quantum inrofmation with trappes ions are to bild suitable traps, ground state cooling of several (more than two) ions and individual addressing. The proposed program attacks all three problems. Micro-engineered traps have the potential to transform the design of ion traps from an art to engineering. Voltage controlles addressing would be a great simplification in the individual addressing problem and the use of new simple cooling methods could reduce the technical overhead presently used for ground state cooling. Quantum logic with an array of individual traps is a completely new concept that might set new standards in the field. It is not restricted by some of the problems mentioned above, but will depend on solving a new set of problems. The proposal eyplores the very frontier of quantum information with ion traps and any results we will find, will help to define the cutting edge of this field.