Landau Effective Interaction between Quasiparticles in a Bose-Einstein Condensate

Landau's description of the excitations in a macroscopic system in terms of quasiparticles stands out as one of the highlights in quantum physics. It provides an accurate description of otherwise prohibitively complex many-body systems, and has led to the development of several key technologies. In this paper, we investigate theoretically the Landau effective interaction between quasiparticles, so-called Bose polarons, formed by impurity particles immersed in a Bose-Einstein condensate (BEC). In the limit of weak interactions between the impurities and the BEC, we derive rigorous results for the effective interaction. They show that it can be strong even for weak impurity-boson interaction, if the transferred momentum/energy between the quasiparticles is resonant with a sound mode in the BEC. We then develop a diagrammatic scheme to calculate the effective interaction for arbitrary coupling strengths, which recovers the correct weak coupling results. Using this, we show that the Landau effective interaction in general is significantly stronger than that between quasiparticles in a Fermi gas, mainly because a BEC is more compressible than a Fermi gas. The interaction is particularly large near the unitarity limit of the impurity-boson scattering, or when the quasiparticle momentum is close to the threshold for momentum relaxation in the BEC. Finally, we show how the Landau effective interaction leads to a sizeable shift of the quasiparticle energy with increasing impurity concentration, which should be detectable with present day experimental techniques.Comment: 12 page

Pengaruh Suku Bunga Terhadap Aktivitas Perdagangan Saham (Studi Pada Bursa Efek Indonesia Periode 2005-2014)

The purpose of this study is to examine the effect of BI Rate and FED Rate partially and simultaneously on stock trading volume, stock trading value, and stock trading frequency by using multiple linear regression analysis. This study uses data quarter of 2005 to 2014 with 40 samples of data time series for each independent and dependent variables. Partial analyses result that; first, BI Rate affects on stock trading value and stock trading frequency negativelly, but does not affect on stock trading volume; second, FED Rate does not affect on stock trading volume, stock trading value, and stock trading frequency. Simoultan analyses result that BI Rate and FED Rate affect on stock trading value positively, but does not affect on stock trading volume and stock trading frequency. The findings in this study indicate the occurrence of asymmetric information to investors in receiving information about changes in BI Rate and FED Rate. It seems that investors tend to be more confident on self-assessment, ignoring changes in BI Rate and FED Rate, and more focus on the real return from the investments on selected stocks

Polaritons for testing the universality of an impurity in a Bose-Einstein condensate

Universality is a fundamental concept in physics that allows for the description of properties of systems that are independent of microscopic details. In this work, we show that polaritons in a Bose-Einstein condensate (BEC) are a suitable platform to probe in a non-demolition way the universal high-energy spectrum of an impurity strongly coupled to a BEC. Based on a field theory that includes the two-body correlations at the exact level we demonstrate that under appropriate conditions, the damping rate of slow-light propagation reveals the high-energy universal tail in the polaron spectrum.Comment: 4.5 + 2 pages