Magnonic Analog of Black- and White-Hole Horizons in Superfluid ^{3}He-B.

We report on the theoretical model and experimental results of the experiment made in a limit of absolute zero temperature (∼600  μK) studying the spin wave analog of black- and white-hole horizons using spin (magnonic) superfluidity in superfluid ^{3}He-B. As an experimental tool simulating the properties of the black- and white-hole horizons, we used the spin-precession waves propagating on the background of the spin supercurrents between two Bose-Einstein condensates of magnons in the form of homogeneously precessing domains. We provide experimental evidence of the white hole formation for spin precession waves in this system, together with the observation of an amplification effect. Moreover, the estimated temperature of the spontaneous Hawking radiation in this system is about 4 orders of magnitude lower than the system's background temperature which makes it a promising tool for studying the effect of spontaneous Hawking radiation.