M. Kumakura

Spin squeezing via one-axis twisting with coherent light.

We propose a new method of spin squeezing of atomic spin, based on the interactions between atoms and off-resonant light which are known as paramagnetic Faraday rotation and fictitious magnetic field of light. Since the projection process, squeezed light, or special interactions among the atoms are not required in this method, it can be widely applied to many systems. The attainable range of the squeezing parameter is S^{-2/5}, where S is the total spin, which is limited by additional fluctuations imposed by coherent light and the spherical nature of the spin distribution.

Injection-Locking of Blue Laser Diodes and Its Application to the Laser Cooling of Neutral Ytterbium Atoms

We present a simple, laser-diode-based ultraviolet light source with sufficient power and narrow linewidth. In this scheme, an injection-locking technique was applied, for the first time to our knowledge, to a GaN blue laser diode (LD). By injecting ~5 mW output light of the external cavity laser diode (ECLD) into two free-running blue slave LDs, we could obtain an output power of over 30 mW from the injection-locked slave LDs. The characterisitics of the injection-locked slave LD were studied in detail. We also present an absolute frequency-locking scheme with about a 500 MHz locking bandwidth, where we achieved offset-locking of the frequencies of two ECLDs. As an interesting example of the application of these developments, we demonstrated laser cooling and trapping of ytterbium atoms.

Topological creation of a multiply charged quantized vortex in the Rb Bose-Einstein condensate

A quadruply-charged quantized vortex has been created successfully in the 87Rb Bose-Einstein Condensate (BEC). The condensate was confined in a cloverleaf magnetic trap, and the vortex was formed by the reversal of the axial magnetic field. The vortex could be observed only in a holding time of about 1 ms, which was much shorter than that reported in the Na BEC, and the vortex position was also unstable in the BEC. To overcome these experimental difficulties, we took the following two measures and improved the vortex formation: (i) axial confinement with a FORT, which prevents the BEC from axial expansion after the field reversal, and (ii) compensation of gravity with a blue-detuned laser beam, which removes the gravitational sag.

Fast polarimetry system for the application to spin quantum non-demolition measurement

We report the development of a fast pulse polarimeter for the application to quantum non-demolition measurement of atomic spin (spin QND). The developed system was tunable to the atomic resonance of a ytterbium atom and has narrow laser line width suitable for spin QND. Using the developed polarimeter, we successfully demonstrated the measurement of the vacuum noise, with 106 to 107 photon number per pulse.

Visible observation of metastable helium atoms confined in an infrared/visible double resonance trap

Using a visible probe laser exciting the 2p3P2→3d3D3 transition (λ=588 nm), we have demonstrated a visible observation of metastable He atoms magnetooptically trapped by an infrared laser resonant with the 2s3S1→2p3P2 transition (λ=1083nm). Detecting visible resonance fluorescence, only 104 atoms confined in a trap with a diameter of 1 mm have been sensitively observed even with the naked eye. It has been found that under a given condition the visible laser operates as a trapping laser and considerably extends the capture range of infrared laser detuning.

Paramagnetic Faraday rotation with spin-polarized ytterbium atoms

We report the observation of paramagnetic Faraday rotation of spin-polarized ytterbium (Yb) atoms. As the atomic samples, we used an atomic beam, released atoms from a magneto-optical trap (MOT), and trapped atoms in a far-off-resonant trap (FORT). Since Yb is diamagnetic and includes a spin-1/2 isotope, it is an ideal sample for spin physics, such as quantum non-demolition measurement of spin (spin QND), for example. From the results of the rotation angle, we confirmed that the atoms were almost perfectly polarized.

BOSE-EINSTEIN CONDENSATION OF YTTERBIUM ATOMS

We report the achievement of Bose-Einstein condensation of ytterbium (Yb) atoms by the all-optical method. The Yb atomic beam from an oven is first decelerated by the Zeeman slowing technique using the singlet transition and then captured by a magnetooptical trap using an intercombination transition. The evaporative cooling is performed in a novel crossed optical trap, which results in the formation of condensates of about 5 x 10 3 atoms of 174 Yb. We determine the scattering length of 174 Yb to be between 1 and 3 nm by combining the behavior of the condensate and the result of measuring photoassociation. The prospect of Yb condensates is also discussed.

Photoassociation of Laser-cooled Ytterbium Atoms

We report photoassociation of laser-cooled ytterbium (Yb) atoms. By detecting the trap loss of 174Yb atoms in the FORT due to the photoassociation beam, we could observe more than 90 photoassociation resonances of vibrational levels in the C; state which connects asymptotically to the SO+lPl atomic state in the dissociation limit. From the observed resonance frequencies we could precisely determine the atomic radiative lifetime of the 4 state to 5.464 f 0.005 ns. We have also observed linebroadening of photoassociation resonances, which is ascribed to the predissociation to the triplet states, and determined the transition probability to be 0.2. Furthermore, we have observed the decrease of the intensity of photoassiciation signal at 435 GHz detuning from the SO+Pl asymptote, from which the scattering length is estimated to be equal to or less than 3 nm.

Laser Cooling of a Helium Atomic Beam

The laser cooling of a helium atomic beam in the 2s3S1 metastable state has been demonstrated. Using a single-mode LNA (La1-xNdxMgAl11O19) laser resonant with the 2s3S1-2p3P2 transition, the metastable atoms are cooled by the Doppler cooling method combined with the Zeeman-tuning technique. To monitor the velocity distribution, the Doppler profile of the 2p3P2-3d3D3 transition is observed. As a result, the most probable velocity of the metastable helium atoms, which is initially 750 m/s, is decelerated to 90 m/s.