Three Special Sessions on Quantum Radar at IEEE Radar Conferences

Abstract

Quantum radar is a hot topic for several reasons, especially because of the two recent experiments at X-band reported in [2] and [3]. The second reason is the story that microwave quantum radar was used in the real world by Chinese to track aircraft and missiles at 100-km range [5]. The third reason is the assertion that microwave quantum radar can defeat stealthy aircraft and missiles [5]. Such claims have been published by highly respected peerreviewed archival journals, such as Popular Mechanics, but most experts say that these assertions are highly dubious [7]. The fourth reason is that the taxpayers of China, Canada, Sweden, the United Kingdom, the United States, Italy, Austria, and other countries have apparently spent a significant amount of money for research on quantum radars. Consequently, a special session on quantum radar was held (virtually) at the IEEE International Radar Conference on April 30, 2020, which did not occur in Washington, DC. The five talks varied widely in perspective: Three were upbeat, but two were rather negative. Marco Frasca and Alfonso Farina presented a new idea to entangle atoms with photons, rather than the boring old method of entangling pairs of photons; the purpose here is to allow a greater number of photons to be usefully entangled for microwave quantum radar. Marco Frasca is a real physicist who deeply understands quantum mechanics, and Alfonso Farina is a famous expert in real radar systems. Han Liu, Amr Helmy, and Bhashyam Balaji explained how to use temporal correlation of photons rather than boring old polarization entanglement to improve quantum radar performance by roughly 10–20 dB relative to a classical radar. A crucial point in this comparison is that the classical radar was not optimized, which is an important theme throughout all three special sessions. The third talk analyzed the benefits of using multiple quantum transmit devices in parallel; Marco Lanzagorta, who literally wrote the book on quantum radar [6], is the physicist on this team, and Jeff Uhlmann (who invented the unscented Kalman filter) is the engineer in this collaboration. All three of these talks were upbeat about the potential for quantum radar. In contrast, J erôme Bourassa and Chris Wilson showed that a certain important class of quantum radars cannot beat the optimal classical radar if the transmit signal and the so-called “idler” (i.e., the other partner in the entangled photon pair) are amplified equally. This negative result is useful to know. Of course one wonders what happens with asymmetrical amplification of the transmitted signal and the idler, and this important question was answered at the special session on quantum radar at the IEEE Radar Conference in Florence, Italy (September 2020), which we shall review later. Both Wilson and Bourassa are real physicists who have quantum mechanics for breakfast. The fifth talk, by Daum (not to be confused with the author of this note), was also rather negative. Daum showed that the cost of X-band quantum radars is roughly 10 orders of magnitude more than the corresponding classical radar with today’s technology. In the future, with the most optimistic assumptions, the relative cost can be reduced to only five orders of magnitude. During the chat for this special session Professor Ravi Advi (the organizer of this special session) said that he was in tears after learning about this cost analysis, and these were not tears of joy. But one could put a positive spin on the huge cost of quantum radars, because companies typically make a profit of 10%–20% on sales, and hence, quantum radars would put them in clover. The chat was continuously active throughout the entire 2-h session. This allows for 10 timesmore questions from people around the world than is typical at face-toface meetings. Many participants said that virtual meetings were much better than face-to-face sessions, because they avoid the cost and time and inconvenience of travel, hotels, and parking. Michael Zatman, the Chairman of the IEEE Radar Conference, asked some good technical questions, and he said that this chat was probably the best at the whole conference. Zatman asked about the assumptions used to compute 10–20 dB of improvement in performance for quantum radar relative to classical radar; as we shall see ahead, this is a recurring crucial question for all three special sessions. The second special session on quantum radar was held virtually at the IEEE Radar Conference on September 22, Author’s current address: Fred Daum, Department of Quantum Information, Raytheon, Woburn MA 01801 USA (e-mail: [email protected]). Manuscript received June 8, 2020; accepted June 11, 2020, and ready for publication January 29, 2021. Review handled by Peter Willett. 0885-8985/21/$26.0