New kind of echo from quantum black holes

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 particlelike and holelike 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.