Quantum Density Fluctuations in Classical Liquids

Abstract

We discuss the density fluctuations of a fluid due to zero point motion. These can be regarded as density fluctuations in the phonon vacuum state. We assume a linear dispersion relation with a fixed speed of sound and calculate the density correlation function. We note that this function has the same form as the correlation function for the time derivative of a relativistic massless scalar field, but with the speed of light replaced by the speed of sound. As a result, the study of density fluctuations in a fluid can be a useful analog model for better understanding fluctuations in relativistic quantum field theory. We next calculate the differential cross section for light scattering by the zero point density fluctuations, and find a result proportional to the fifth power of the light frequency. This can be understood as the product of fourth power dependence of the usual Rayleigh cross section with the linear frequency dependence of the spectrum of zero point density fluctuations. We give some estimates of the relative magnitude of this effect compared to the scattering by thermal density fluctuations, and find that it can be of order 0.5% for water at room temperature and optical frequencies. This relative magnitude is proportional to frequency and inversely proportional to temperature. Although the scattering by zero point density fluctuation is small, it may be observable.

7 pages

References in corpus (4)

• "Cosmological" quasiparticle production in harmonically trapped superfluid gases
• Casimir forces between defects in one-dimensional quantum liquids
• Casimir-like force arising from quantum fluctuations in a slow-moving dilute Bose-Einstein condensate
• Calculations of liquid helium and neon VUV emission spectra, self-absorption and scattering for a neutrino detector

Cited by in corpus (11)

• Analogue Gravity
• Analog model for quantum gravity effects: phonons in random fluids
• A Fluid Analog Model for Boundary Effects in Field Theory
• Quantum Brownian motion in an analog Friedmann-Robertson-Walker geometry
• Space and Time Averaged Quantum Stress Tensor Fluctuations
• Large Zero Point Density Fluctuations in Fluids
• Stochastic motion in an expanding noncommutative fluid
• Quantum Fluctuations of Fields and Stress Tensors
• Vacuum Radiation Pressure Fluctuations on Electrons
• Zero Point Density Fluctuations and Electron Brownian Motion
• Possible Frictionless Regime for Ultra-High Temperature Amorphous Matter