118 / 168
Abstracts
P4.6
Competition of Triangular and Square Vortex-Lattice in
Two-Component Bose-Einstein Condensates
Toshiaki Kanai, Makoto Tsubota
Department of Physics, Osaka City University, Japan
Quantum vortex-lattice formulation in two-component BECs has been studied
theoretically[1] and experimentally[2]. In two-component BECs, there are some
behaviour which do not appear in one-component BEC. Change of structure
of quantum vortex-lattice is one of the most clear behaviours. The structure
of vortex-lattice is triangle, square, vortex-sheet et al[1], and depend on some
parameters. We study numerically the competition of triangular and square
vortex-lattice around the boundary of triangular lattice phase and square lattice
phase. Around the boundary , because of the competition, the relaxation time
will get longer. So, we pay attention to the relaxation time.
[1]K.Kasamatsu, M.Tsubota, and M.Ueda, Phys. Rev. Lett. 91, 150406 (2003)
[2]V.Schweikhard et al, Phys. Rev. Lett. 93, 210403 (2004)
P4.7
A novel multi-frequency lock-in technique to probe superfluid
helium-4 using quartz tuning forks.
Bradley D.I., Haley R.P., Kafanov S., Noble M.T., Pickett G.R., Tsepelin V.,
Vonka J., Wilcox T.
Lancaster University, Faculty of Science and Technology, Department of Physics,
Lancaster, LA1 4YB, UK
We report on a novel new technique to measure the resonance of linear oscillators
by exciting and measuring the response over many frequencies simultaneously.
By using a multi-frequency lock-in analyser we can measure the resonance curve
much quicker than by using a conventional single frequency lock-in amplifier
technique. We use multi-frequency lock-in and a standard Standford Research
Systems SR830 Lockin Amplifier to measure the frequency response of two 25
µ
m
wide quartz tuning forks and show that both instruments yield identical results.
We further confirm this by measuring the resonance frequency and width of the
forks over temperatures between 4.2K and 1.5K.
118