# Magnonic Analogue Black/White Hole Horizon in Superfluid $^3$He-B: experiment

## TL;DR

This experimental study demonstrates magnonic black/white hole horizons in superfluid helium-3, showing wave amplification and potential for observing spontaneous Hawking radiation at ultra-low temperatures.

## Contribution

First experimental realization of magnonic black/white hole horizons in superfluid helium-3 using spin superfluidity at near-zero temperature.

## Key findings

- White hole horizon blocks spin-precession wave propagation.
- Observed wave amplification upon reflection from the horizon.
- Estimated Hawking radiation temperature is significantly lower than background temperature.

## Abstract

We provide experimental details of the first experiment made in zero temperature limit ($\sim$ 600\,$\mu$K) studying the magnonic black/white hole horizon analogue using absolutely pure physical system based on the spin superfluidity in superfluid $^3$He-B. We show that spin precession waves propagating on the background of the spin super-currents in a channel between two Bose-Einstein condensates of magnons in form of homogeneously precessing domains mimic the properties of the black/white horizon. Once the white hole horizon is formed and blocks the propagation of the spin-precession waves between two domains, we observed an amplification effect, i.e. when the energy of the spin precession waves reflected from the horizon is higher than the energy of the excited spin precession waves before horizon was formed. Moreover, the estimated temperature of the spontaneous Hawking radiation in this model system is about four orders of magnitude lower than the system's background temperature what makes it a promising tool to study the effect of spontaneous Hawking radiation.