A.B. Mundt

Coupling a single atomic quantum bit to a high finesse optical cavity.

The quadrupole S(1/2)-D(5/2) optical transition of a single trapped Ca+ ion, well suited for encoding a quantum bit of information, is coherently coupled to the standing wave field of a high finesse cavity. The coupling is verified by observing the ions response to both spatial and temporal variations of the intracavity field. We also achieve deterministic coupling of the cavity mode to the ions vibrational state by selectively exciting vibrational state-changing transitions and by controlling the position of the ion in the standing wave field with nanometer precision.

Experimental Demonstration of Ground State Laser Cooling with Electromagnetically Induced Transparency

Ground state laser cooling of a single trapped Ca(+)on is achieved with a technique which tailors the absorption profile for the cooling laser by exploiting electromagnetically induced transparency. Using the Zeeman structure of the S(1/2) to P(1/2) dipole transition we achieve up to 90% ground state probability. The new method is robust, easy to implement, and proves particularly useful for cooling several motional degrees of freedom simultaneously, which is of great practical importance for the implementation of quantum logic schemes with trapped ions.

Speed of ion-trap quantum-information processors

We investigate theoretically the speed limit of quantum gate operations for ion trap quantum information processors. The proposed methods use laser pulses for quantum gates which entangle the electronic and vibrational degrees of freedom of the trapped ions. Two of these methods are studied in detail and for both of them the speed is limited by a combination of the recoil frequency of the relevant electronic transition, and the vibrational frequency in the trap. We have experimentally studied the gate operations below and above this speed limit. In the latter case, the fidelity is reduced, in agreement with our theoretical findings. // Changes: a) error in equ. 24 and table III repaired b) reference Jonathan et al, quant-ph/ 0002092, added (proposes fast quantum gates using the AC-Stark effect)

Laser cooling with electromagnetically induced transparency: application to trapped samples of ions or neutral atoms

A novel method of ground state laser cooling of trapped atoms utilizes the absorption profile of a three (or multi-) level system which is tailored by a quantum interference. With cooling rates comparable to conventional sideband cooling, lower final temperatures may be achieved. The method was experimentally implemented to cool a single Ca

Experiments towards quantum information with trapped calcium ions

^+

Quantum information processing and cavity QED experiments with trapped Ca' ions

ion to its vibrational ground state. Since a broad band of vibrational frequencies can be cooled simultaneously, the technique will be particularly useful for the cooling of larger ion strings, thereby being of great practical importance for initializing a quantum register based on trapped ions. We also discuss its application to different level schemes and for ground state cooling of neutral atoms trapped by a far detuned standing wave laser field.

Precision measurement and calculation of the 3d /sup 2/D-level lifetimes of /sup 40/Ca+

Summary form only given. Ground state cooling and coherent manipulation of ions in a rf-(Paul) trap is the prerequisite for quantum information experiments with trapped ions. In our experiments a single /sup 40/Ca/sup +/ ion in a conventional Paul trap has been cooled to the ground state of vibration with 99.9% (98%) probability in the axial (radial) trap direction. We use a continuous resolved sideband method where we drive the S/sub 1/2/-D/sub 5/2/ quadrupole transition (@ 729nm) and repump the ion to the ground state via the D/sub 5/2/-P/sub 3/2/ dipole transition. Efficient cooling is achieved on the timescale of a few ms.

Experimental and theoretical study of the3dD2–level lifetimes ofCa+40

Single trapped Ca+ ions, stored in a linear Paul trap and laser-cooled to the ground state of their harmonic quantum motion are used for quantum information processing. As a demonstration, composite laser pulse sequences were used to implement phase gate and CNOT gate operation. For this, Stark shifts on the qubit transitions were precisely measured and compensated. With a single ion stored inside a high-finesse optical cavity, a cavity mode can be coherently coupled to the qubit transition.

Experimental and theoretical study of the 3d {sup 2}D-level lifetimes of {sup 40}Ca{sup +}

Int this paper, a measurement technique based on deterministic coherent excitation to the D/sub 5/2/ state or incoherent shelving in the D/sub 3/2/ state is introduced, followed by a waiting period with free spontaneous decay and finally a measurement of the remaining excitation by high-efficiency quantum state detection.

New experimental and theoretical approach to the 3d D-level lifetimes of 40Ca+

We report measurements of the lifetimes of the 3d