Berlin 2001 – scientific programme
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AMPD: EPS AMPD
AMPD 6: Sitzung 6
AMPD 6.4: Talk
Wednesday, April 4, 2001, 10:55–11:20, H104
Quantum information processing with trapped ions — •R. Blatt, F. Schmidt–Kaler, C. Roos, H. Rohde, S. Gulde, A.B. Mundt, D. Leibfried, and J. Eschner — Institut für Experimentalphysik, Universität Innsbruck, A-6020 Innsbruck, Austria
Single ions in Paul traps are investigated for quantum information processing. Superpositions of the S1/2 and the D5/2 states are used to implement a qubit. Single 40Ca+ 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 S1/2 − P1/2 transition is monitored for a state measurement by the "electron shelving" technique. The S1/2 − D5/2 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 [1]. In the spherical Paul trap (4.5 MHz trap frequency) a single Ca+ ion has been cooled to the ground state of vibration with up to 99.9% probability. Cooling is achieved in all three dimensions simultaneously as well as ground state cooling of two ions. In the latter case all modes were cooled resulting in a ground state population of more than 96%.
Starting from a Fock state |n = 0> coherent quantum state manipulation on the S1/2 − D5/2 transition is achieved. More than 30 Rabi oscillations within 1.4 ms are observed on the blue motional sideband of this transition indicating the preserved coherence. A similar number of Rabi oscillations is obtained after preparation of the ion in the |n = 1> Fock state. The data show that decoherence is negligible on the time scale of a few oscillations, i.e. during the time required for a quantum gate operation [2]. The measured 1 ms decoherence time is attributed to residual laser and magnetic field fluctuations. Heating of the motional degrees of freedom has been measured directly and appears at a rate of 1 phonon per 190 ms (70 ms) at the secular frequencies ωaxial (ωradial).
A novel type of ground state laser cooling of a single trapped ion is achieved using a technique which tailors the absorption profile for the cooling laser by exploiting electromagnetically induced transparency in the Zeeman structure of the S1/2 − P1/2 dipole transition. This 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 [3].
[1] H.C. Nägerl, D. Leibfried, H. Rohde, G. Thalhammer, J. Eschner, F. Schmidt–Kaler, and R. Blatt, Phys. Rev. A 60, 145 (1999).
[2] Ch. Roos, Th. Zeiger, H. Rohde, H. C. Nägerl, J. Eschner, D. Leibfried, F. Schmidt–Kaler, and R. Blatt, Phys. Rev. Lett., 83, 4713 (1999).
[3] C. F.Roos, D. Leibfried, A. Mundt, F. Schmidt–Kaler, J. Eschner, R. Blatt, Phys. Rev. Lett., 85, 5547 (2000).