Journal of Physics B Atomic Molecular and Optical Physics

Deterministic cavity quantum electrodynamics with trapped ions

Matthias Keller, Birgit Lange, K. Hayasaka, Wulfhard K. Lange, HERBERT WALTHER

Published Jan 24, 2003• 28 citations

Abstract

We have employed radio-frequency trapping to localize a single 40 Ca + -ion in a high-finesse optical cavity. By means of laser Doppler cooling, the position spread of the ion's wavefunction along the cavity axis was reduced to 42 nm, a fraction of the resonance wavelength of ionized calcium (λ = 397 nm). By controlling the position of the ion in the optical field, continuous and completely deterministic coupling of ion and field was realized. The precise three-dimensional location of the ion in the cavity was measured by observing the fluorescent light emitted upon excitation in the cavity field. The single-ion system is ideally suited to implement cavity quantum electrodynamics under cw conditions. To this end we operate the cavity on the D 3/2 –P 1/2 transition of 40 Ca + (λ = 866 nm). Applications include the controlled generation of single-photon pulses with high efficiency and two-ion quantum gates.

DOI: 10.1088/0953-4075/36/3/318

Related papers

Deterministic ion-photon interaction in a cavity

Matthias Keller, Gerhard R. Guthöhrlein, Birgit Lange +3 more

Summary form only given. In a recent experiment, we have investigated the interaction between a single /sup 40/Ca/sup +/-ion stored in a radio-frequency trap and the field of an optical cavity. One mode of the cavity was tuned to the S/sub 1/2/ to P/sub 1/2/ transition of singly ionized calcium at a wavelength of /spl lambda/ = 397 nm. Using laser Doppler cooling in conjunction with the strong confinement of the ion in an effective harmonic potential (frequency 1.1 MHz), the extension of the ion's wave packet was reduced to 60 nm, corresponding to /spl lambda//7, in the direction of the cavity axis. The position of the ion in the cavity was determined by observing the fluorescent light emitted by the ion after excitation in the cavity field. A large fluorescent rate indicated a position of high intracavity intensity. An image of the standing wave pattern obtained in this way is shown. Note that throughout the measurement the ion remains stationary and the cavity is moved to scan the relative position of ion and field.

Quantum Electronics and Laser Science ConferenceJun 25, 20030 citations

Coupling a Single Atomic Quantum Bit to a High Finesse Optical Cavity

A.B. Mundt, Axel Kreuter, Christoph Becher +4 more

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 ion's response to both spatial and temporal variations of the intracavity field. We also achieve deterministic coupling of the cavity mode to the ion's 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.

arXiv:quant-ph/0202112Physical Review LettersAug 13, 2002304 citations

Stable long-term coupling of a single ion to a cavity mode

Matthias Keller, Birgit Lange, K. Hayasaka +2 more

With a single trapped calcium ion, strongly localized in an optical resonator, we have realized a cavity-QED system operating under continuous coupling conditions. Ion and field interact via cavity-assisted Raman pulses, applied between the S1/2 ground state and the metastable D3/2 state. We have studied the long-term stability of this interaction at the single-photon level by monitoring the emission from the cavity output and analysing its fluctuations on time-scales up to s. The small Allan variances we find confirm that ion and cavity mode are continuously coupled in a deterministically controlled way. Applications include the generation of single photons on demand and an atom–photon interface for optical quantum networks.

Journal of Modern OpticsDec 19, 200614 citations

Ion-trap cavity QED system for probabilistic entanglement

Nicolas Seymour-Smith

Laser systems and a linear radiofrequency (rf) Paul trap with an integrated co-axial cavity have been developed for experiments in cavity QED and probabilistic entanglement. Single 40Ca+ ions and large Coulomb crystals have been trapped routinely and laser cooled with long trapping lifetimes. A technique to achieve precise overlap of the pseudopotential minimum of the rf-field with the cavity mode has been implemented through variable capacitors in the resonant rf-circuit used to drive the trap. Three-dimensional micromotion compensation has been implemented. An 894 nm laser has been frequency stabilised to a Pound-Drever-Hall cavity which is in turn stabilised to atomic Cs using polarisation spectroscopy. The Allan variance of the error signal has been reduced to less than a kilohertz on timescales greater than a second. A novel implementation of the scanning cavity transfer lock has been developed to transfer the stability of the 894 nm laser to the 397 nm ion cooling and 866 nm repumping lasers. The bandwidth of the system has been increased to 380 Hz and the Allan variance of the error signal has been reduced to less than ten kilohertz on timescales of greater than a second. The pseudopotential minimum of the rf field has been overlapped optimally with the optical cavity mode through mapping of the fluorescence from cavity-field repumped ions as a function of their displacement. Coupling to the cavity mode has been confirmed by observation of resonant fluorescence into the cavity mode using the cavity-assisted Raman transition process. The thesis demonstrates that the setup is ready for the controlled production of single photons with pre-determined polarisation states, and progression onto new schemes to entangle multiple ions that are coupled to the optical cavity mode.

May 21, 20121 citation

A calcium ion in a cavity as a controlled single-photon source

Matthias Keller, Birgit Lange, K. Hayasaka +2 more

We present a single calcium ion, coupled to a high-finesse cavity, as an almost ideal system for the controlled generation of single photons. Photons from a pump beam are Raman-scattered by the ion into the cavity mode, which subsequently emits the photon into a well-defined output channel. In contrast with comparable atomic systems, the ion is localized at a fixed position in the cavity mode for indefinite times, enabling truly continuous operation of the device. We have performed numeric calculations to assess the performance of the system and present the first experimental indication of single-photon emission in our set-up.

New Journal of PhysicsJul 30, 200485 citations

Ion trap cavity system for strongly coupled cavity-QED

Elisabeth Brama

The combination of an ion trap with a high finesse optical cavity is an ideal system for the investigation of strong coupling cavity quantum electrodynamics, and allows the observation of a number of interesting quantum phenomena. To achieve the small mode volumes required without impairing the ion trapping small traps with a short ion electrode distance are needed. Two microscopic linear rf ion traps have been developed and built to accommodate experimental cavities of lengths of several 100 microns. The first trap design, the 'sandwich' trap, was successfully used to trap 40Ca+ - ions for several hours. It was characterised extensively including a measurement of the heating rates of the ions in the trap. Spectroscopy measurements of the cooling transition, as well as the two repumping transitions were carried out. The second trap design, the 'alumina' trap, also successfully trapped 40Ca+ - ions, and a full characterisation of this trap was made. The experimental cavity was installed at a preliminary cavity length distance of 3.7 mm. The cavity characteristics were examined. Finally the trapped ions were overlapped with the cavity mode by adjusting the trap minimum position along the trap axis via dc voltages and the vertical position of the cavity. To progress further a locking scheme for the cavity length as well as a single - photon detection setup are necessary. To achieve strong coupling a reduction of the cavity length will have to be made.

May 17, 20130 citations