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Quantum Electronics and Laser Science Conference

Quantum information processing with trapped Ca/sup +/ ions

Ferdinand Schmidt‐Kaler, Christian F. Roos, H. J. Rohde, S. Gulde, A.B. Mundt, Dietrich G. Leibfried, Jürgen Eschner, R. Blatt

Published Nov 13, 2002• 0 citations
Publisher

Abstract

Summary form only given. 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 S/sub 1/2/-P/sub 1/2/ 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.

DOI
10.1109/qels.2001.962000

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DOI: 10.1007/s003400100721

Appl Phys Lasers

A novel method of ground-state laser cooling of trapped atoms utilizes the absorption profile of a three- (or multi-) level system that 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 + 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.

•Nov 21, 2007•0 citations
Summary form only given. 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 S/sub 1/2/-P/sub 1/2/ 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.
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.
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. 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 and manipulation. Individual ions in a linear string are addressed by a tightly focused 729 nm laser beam. A single Ca+ ion has been cooled in the spherical Paul trap 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. Starting from a Fock state |n=0> coherent quantum state manipulation on the S1/2-D5/2 transition is achieved. 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. The measured several decoherence time of a few ms 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.
Summary form only given. Single ions in Paul traps are investigated for quantum information processing. Superpositions of the S/sub 1/2/ and the D/sub 5/2/ states are used to implement a qubit. Single /sup 40/Ca/sup +/ 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 S/sub 1/2/-P/sub 1/2/ transition is monitored for a state measurement by the electron shelving technique. The S/sub 1/2/-D/sub 5/2/ 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. In the spherical Paul trap (4.5 MHz trap frequency) a single Ca/sup +/ ion has been cooled to the ground state of vibration with a probability of up to 99.9%. Starting from this Fock state |n=0> coherent quantum state manipulation on the S/sub 1/2/-D/sub 5/2/ transition is achieved.
For quantum information experiments we have cooled one and two 40 Ca + ions to the ground state of vibration with up to 99.9% probability, using resolved sideband cooling on the optical S 1/2 -D 5/2 quadrupole transition. Implementing a novel cooling scheme based on electromagnetically induced transparency on the S ↓/2 -P ↓/2 manifold we have achieved simultaneous ground state cooling of two motional sidebands 1.7 MHz apart. Coherent quantum state manipulation on the S 1/2 -D 5/2 quadrupole transition at 729 nm was demonstrated and up to 30 Rabi oscillations within 1.4 ms have been observed starting from the motional ground state and from the n=1 Fock state. In a linear rf-trap two ions were cooled to the ground state of motion and individual addressing of the ions with laser pulses is achieved.
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 (@729 nm) 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.
A novel method of ground-state laser cooling of trapped atoms utilizes the absorption profile of a three- (or multi-) level system that 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 + 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.