  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.
