A mini–arms race is unfolding in the supposed field of quantum radar, spurred by press reports in 2016 that China had built one—potentially threatening the ability of stealthy military aircraft to hide from conventional radars. Governments around the world have tasked physicists to look into the idea. Whereas a conventional radar searches for objects by detecting pulse of microwaves reflected from them, quantum radar would utilize pulses of microwaves linked by a quantum connection called entanglement. The system would retain one pulse and measure it in concert with the one reflected from the object. Correlations between the two would make it easier to spot an object through the glare of the surroundings. Or so researchers hoped. Groups have demonstrated elements of a quantum radar, but only in limited experiments that a nonquantum system can still match. And fundamental physical limits suggest the scheme can't beat ordinary radar for long-range detection. Even one of the inventors the basic concept thinks it won't work when applied to radar.