QFS2016 Book of Abstracts

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.

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