[fsh]

"Quantum radar" is a toy experiment with zero practical applications. The experiments achieved a "quantum advantage" by using entangled photons which only works in the single-photon regime. Since microwave photons are pretty small, this implies incredibly low transmission powers. With the typical return loss of an airplane (stealth or not) detected by a radar antenna, one would have to average for centuries to detect something (assuming the airplane stays there for said centuries). This assumes perfect entanglement with no other imperfections.

[verdverm]

We can probably remove the quantum hype and still arrive at the same circumstance. Stealth does not make you invisible, just insufficient for locking on. In theory, it is supposed to make the jet indistinguishable from a bird or similar small object, but it's a cat & mouse game like anything else. It could likely be possible to fire a loitering A2A into the general vicinity of a stealth craft and it thermally finds targets of opportunity.