Magnonic Analog of Black- and White-Hole Horizons in Superfluid ${}^3\mathrm{He}\text{−}B$

We report on the theoretical model and experimental results of the experiment made in a limit of absolute zero temperature ($\sim 600\mu \mathrm{K}$) studying the spin wave analog of black- and white-hole horizons using spin (magnonic) superfluidity in superfluid ${}^3\mathrm{He}\text{−}B$. 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.

Figure 1

Schematic 3D cross section of the experimental cell and concept of the experiment. Channel dimensions: the width is 3 mm, the height is 0.4 mm, and the channel length is 2 mm.

Figure 2

Voltage signals corresponding to spin-precession waves: the source domain (red), the detection domain (blue). The rectangular signal shows the time window when eight sinusoidal excitation pulses were applied in order to excite the spin-precession waves. Inset: the picture of the experimental cell on the bench before rf-shield installation.

Figure 3

The power spectral density of the free decay signals as a function of the phase difference measured from the source domain (upper) and the detection domain (bottom). Insets show a schematic illustration of the spin wave dynamics in channel.

Figure 4

The cross-correlation power spectral density of the source and detector free decay signals as a function of the phase difference $\mathrm{\Delta }{\alpha }_{\mathrm{rf}}$.