We could detect alien civilizations through their interstellar quantum communication

Since the mid-20th century, scientists have been looking for evidence of intelligent life beyond our solar system. For much of that time, scientists who are engaged in the search for extraterrestrial intelligence (SETI) have relied on radio astronomy surveys to search for signs of technological activity (aka "technosignatures"). With 4,375 exoplanets confirmed (and counting!) even greater efforts are expected to happen in the near future.