Chinese Physics Letters

Spectra of 4 2 S 1/2 →3 2 D 5/2 Transitions of a Single Trapped 40 Ca+ Ion

Shijie Gong, Fei Zhou, Haoyu Wu, Wei Wan, Liang Chen, Mang Feng

Published Jan 1, 2015• 2 citations

Abstract

We investigate the spectra of the electric quadrupole 4 2 S 1/2 →3 2 D 5/2 transitions in a single 40 Ca + ion confined in a home-built linear trap. We probe the transitions with an ultra-narrow bandwidth laser at 729 nm. In a weak magnetic field, the quadrupole transition splits into ten components with the maximal line strength proportional to their squared Clebsch—Gordan factors. In a magnetic field of the order of Gauss, the observed equidistant sideband reflects the Zeeman substructure modulated by the quantized oscillation due to the secular motion in the trap. The temperature of the trapped ion can be determined by the envelope of the sideband spectrum. We also demonstrate the Rabi oscillation in a carrier transition after the ion has been Doppler cooled, which can be fitted by the model with the thermal state of motion.

DOI: 10.1088/0256-307x/32/1/013201

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Chinese Physics Letters

Spectra of 4 2 S 1/2 →3 2 D 5/2 Transitions of a Single Trapped 40 Ca+ Ion

Shijie Gong, Fei Zhou, Haoyu Wu, Wei Wan, Liang Chen, Mang Feng

Published Jan 1, 2015• 2 citations

Publisher

Abstract

DOI: 10.1088/0256-307x/32/1/013201

Related papers

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A single

{}^{40}{\mathrm{Ca}}^{+}

ion is confined in a linear Paul trap and Doppler-cooled on the

{S}_{1/2}

{P}_{1/2}

dipole transition. Then the narrow quadrupole

{S}_{1/2}

{D}_{5/2}

transition at 729 nm is probed. The observed spectrum is interpreted in terms of the Zeeman substructure superimposed with oscillation sidebands due to the harmonic motion in the trap. The height of the motional sidebands provides a sensitive method to determine the ion's temperature and thus allows us to test sub-Doppler laser cooling schemes needed for quantum state preparation and quantum computation. We also observe the dynamics induced by Rabi oscillations on a carrier transition and interpret it in terms of the thermal state which is reached after Doppler cooling.

We report the laser cooling of a single

^{40}\text{Ca}^+

ion in a Penning trap to the motional ground state in one dimension. Cooling is performed in the strong binding limit on the 729-nm electric quadrupole

S_{1/2}\leftrightarrow D_{5/2}

transition, broadened by a quench laser coupling the

D_{5/2}

and

P_{3/2}

levels. We find the final phonon number to be

\bar{n}=0.014\pm0.009

. We measure the heating rate of the trap to be very low with

\dot{\bar{n}}=2.5\pm 0.3\textrm{s}^{-1}

and a scaled spectral noise density of

\omega S_{E}(\omega)\sim1.6^{-8}\textrm{V}^2\textrm{m}^{-2}\textrm{Hz}^{-1}\textrm{s}^{-1}

, which is consistent with the large ion-electrode distance. We perform Rabi oscillations on the sideband-cooled ion and observe a coherence time of

0.7\pm 0.1\textrm{ms}

, noting that the practical performance is currently limited by the intensity noise of the probe laser.

We experimentally demonstrate laser spectroscopy of the electric-quadrupole transition

6s{}^{2}{S}_{1/2}--5d{}^{2}{D}_{3/2}

of a single trapped

{}^{171}\mathrm{Yb}

ion. The probed transition has a natural linewidth of 3.1 Hz, and is at a wavelength of 435.5 nm. A

{}^{171}\mathrm{Yb}

ion is laser cooled to the range of the Doppler limit in a radio-frequency Paul trap. The $F=0--{F}^{\ensuremath{'}}=2,$ ${m}_{{F}^{\ensuremath{'}}}=0$ hyperfine component of the

{}^{2}{S}_{1/2}{--}^{2}{D}_{3/2}

transition is excited by a laser source whose frequency is controlled by an optical reference cavity of high intrinsic stability. The recoilless carrier component of the vibrational sideband spectrum is resolved with a minimum linewidth of approximately 80 Hz, corresponding to a fractional frequency resolution of $1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}.$ This resolution limit is attributed to laser frequency instability. The effective decoherence rates of the residual ion motion are inferred from the observation that the axial and two radial low-frequency first-order secular-vibration sidebands show minimum linewidths in the range of 0.2--1 kHz. Prospects for an optical frequency standard based on the investigated atomic system are discussed.