Takeshi Kuwamoto

Dynamics of Quadruply Quantized Vortices in 87Rb Bose–Einstein Condensates Confined in Magnetic and Optical Traps

We studied the dynamics of quadruply quantized vortices in 87 Rb Bose–Einstein condensates. Vortices were created in magnetically trapped condensates with hyperfine spin F = 2 by employing topological phase imprinting technique, wherein the direction of atomic spin is adiabatically reversed by applying a bias magnetic field. Vortices were observed for a holding time of up to 10 ms. Disappearance of the vortices was attributed to considerable expansion and excitation of the condensates, which were caused by the distortion of the magnetic potential. In order to observe the long-term behavior of the vortices, we transferred the condensates to a crossed-type optical dipole force trap after creating the vortices. In this case, the vortices were observed for a holding time of up to 22 ms. We also observed density profiles, which indicated the presence of split vortices.

Systematic Study of Fine and Hyperfine Structures in Pr I by Doppler-Free Atomic-Beam Laser Spectroscopy

Atomic spectra of neutral praseodymium (Pr I) have been measured by means of the atomic-beam laser spectroscopy. Hyperfine structures of 34 atomic transitions in the wavelength range from 544 nm to 596 nm were resolved and hyperfine constants A and B were determined for 57 levels. Out of them, 18 transitions were found to be new ones and the energies and the electronic total angular momenta of 11 fine structure levels were determined for the first time.

Possible application of PXR to the beam-divergence measurements

Abstract The effect of the beam divergence on the parametric X-radiation has been experimentally investigated at NPI, Tomsk, and at INS, Tokyo for the electron energies 600 and 800 MeV, respectively. It has been shown that the crystal-orientation dependence of PXR is sensitive to the beam divergence, suggesting that PXR can offer a simple means for determining the angular divergence of high energy charged particle beams.

Collective Excitation of Bose–Einstein Condensates Induced by Evaporative Cooling

We demonstrate novel methods for exciting the collective oscillations of Bose–Einstein condensates without directly deforming the confinement potential. The collective excitations were induced through the radio-frequency (rf) forced evaporative cooling of 87 Rb atoms confined in a magnetic trap. We studied two methods, the first involving a sinusoidal amplitude modulation of the rf field, and the other a fast sweep of the rf frequency, both performed during evaporation. An almost-pure low-energy quadrupole oscillation mode was observed with both methods. In the case of the rf-amplitude modulation (fast rf-frequency sweep), the collective excitations are likely to be induced by the periodic (bulk) emission of atoms from the trap. We also observed substantial loss of atoms from the trap when the rf amplitude was modulated with a frequency near the axial-trap frequency. This allows a precise determination of the magnetic-trap frequency.

Stark and Zeeman Spectroscopies of Sm \captionsize I from Metastable-State Atomic Beam Produced by Electric Discharge

Hyperfine structures, isotope shifts, Stark and Zeeman effects of 5 transitions in Sm \captionsizeI are investigated by means of atomic-beam laser spectroscopy. We measure the transitions from 10801.10- and 12313.11-cm -1 metastable levels with 4 f 6 5 d 6 s configuration to 27925.31-, 28704.25-, 29041.31- and 30753.65-cm -1 odd-parity levels, which are candidates in order to measure parity nonconserving effect in Sm. Hyperfine constants A and B for odd-mass isotopes 147 Sm and 149 Sm are obtained except for 30753.65-cm -1 level. Isotope shifts of the transitions are determined and specific mass shift and field shift are also derived by King-plot analysis. Stark splitting is resolved for the transition between 12313.11- and 30753.65-cm -1 levels, and the tensor polarizability of the upper level is determined to be α 2 = 535(12) kHz/(kV/cm) 2 . From Zeeman splitting, g -factors are precisely determined for 4 levels.

Density Dependence of Charge-4 Vortex Splitting in Bose–Einstein Condensates

We studied the axial-direction density dependence of the splitting of a charge-4 vortex created in 87Rb Bose–Einstein condensates. Vortices were generated by topological phase imprinting, and the axial density of the condensates was controlled by an optical potential. Linear and triangular arrangements of four single-charged vortices that emerged through the charge-4 vortex collapse were observed. The splitting of the charge-4 vortices was suppressed by maintaining the density outside the l = 2 unstable mode regions where linear arrangements were formed. In addition, we studied vortex dynamics in a high density region for which investigations have not been previously performed.