There is, of course, a wide difference between a claim of a laboratory "proof of concept" and the deployment of an actual working quantum radar. Indeed, US defense contractor Lockheed Martin has been attempting to build its own quantum radar for long range detection since 2007, with no public reports of deployment. A number of hurdles have to be overcome not just in making the system work, but also truly useful. A major obstacle towards an operational quantum radar is the problem of quantum decoherence; as a quantum system like entangled particles spends more time in the environment, the longer exposure to the outside environment will cause the quantum system to 'decay' (to lose its quantum behavior). This imposes range limitations on current quantum radar prototypes, since longer range equals more time spent exposed to its surroundings. While a 100km-range quantum radar may seem impressive by scientific research standards, the demands of air defense against stealth bombers or missiles would require a much greater range to be of optimal military use.