Limits and opportunities of the quantum radar

From the field of inference and sensing with quantum systems, and quantum hypothesis testing in particular, we find the concepts of quantum radar. By exploiting entanglement to yield an advantage over classical setups, quantum radar has made headlines within the community and industries working with conventional radar. While it is generally understood that this advantage is not universal, the application space for a hypothetical device realizing it is actually severely restricted. In this work, we clarify the setting of a quantum radar in the context of quantum illumination and quantify the performance of such a device, in terms of radar operation in the microwave regime, compared to existing radar systems. Additionally, we discuss possible non-traditional, short-range applications to microwave radar. Our principal result is that it is unlikely a quantum radar based on quantum illumination will ever compete on equal footing with a conventional system for reasons fundamental rather than technological. To emphasize this result, we also comment on various technological possibilities and challenges in constructing a microwave quantum radar.