New Kind of Echo from Quantum Black Holes

TL;DR

This paper introduces a new type of gravitational echo from quantum black holes, modeled as an Andreev reflector near the horizon, providing a potential way to probe black hole quantum states.

Contribution

It proposes a novel gravitational echo mechanism based on near-horizon Andreev reflection, linking echo signals to the quantum state of black holes.

Findings

Echoes exhibit a characteristic phase difference.

The near-horizon region acts as an Andreev reflector.

Echo signals encode information about the quantum state.

Abstract

We propose that a quantum black hole can produce a new kind of late-time gravitational echoes, facilitated by a near-horizon process analogous to Andreev reflection in condensed matter systems. In comparison to the traditional echo scenarios where the near-horizon region is treated as an ordinary reflector, we argue that, consequent to near-horizon gravitational scattering, this region is better described by an Andreev reflector. Such interactions lead to a novel contribution to gravitational echoes with a characteristic phase difference, an effect which is analogous to how Andreev reflections lead to propagating particle-like and hole-like components with a relative phase in certain condensed matter scenarios. Moreover, this novel contribution to the echo signal encodes information about the `near-horizon quantum state', hence offering a possible new window to probe the quantum nature of black holes.