Quantum illumination radars rely on quantum sources of two-mode squeezing vacuum to produce signals with quantum-enhanced correlations. The recent demonstration of quantum radar transmitters in the laboratory has shown promising progress in the technology. Amplification of the faint quantum signals is however necessary in order to make quantum radars practical. Here we discuss the possibility of amplifying quantum signals while preserving a quantum advantage. We find that amplifying both signals equally cannot beat an ideal source of classically correlated signals, but does provide a quantum advantage over noisy classical sources. We also briefly discuss other amplifications scheme that may provide further enhancements.
Quantum illumination radars rely on quantum sources of two-mode squeezing vacuum to produce signals with quantum-enhanced correlations. The recent demonstration of quantum radar transmitters in the laboratory has shown promising progress in the technology. Amplification of the faint quantum signals is however necessary in order to make quantum radars practical. Here we discuss the possibility of amplifying quantum signals while preserving a quantum advantage. We find that amplifying both signals equally cannot beat an ideal source of classically correlated signals, but does provide a quantum advantage over noisy classical sources. We also briefly discuss other amplifications scheme that may provide further enhancements.
Recently, a quantum-enhanced radar transmitter operating at microwave frequencies, called a quantum two-mode squeezing radar (QTMS radar), was demonstrated in the laboratory. Inspired by this, we discuss the possibility of building an array of quantum radars. In order for quantum radars to be practically relevant, it is important that an array can be built. We find that it is indeed possible to build such an array, but that the details matter. A quantum illumination radar array may not be very effective, but a QTMS radar array is quite amenable to array signal processing. We also briefly discuss the practical aspects of building a quantum radar array.
We propose a protocol for quantum illumination: a quantum-enhanced noise radar. A two-mode squeezed state, which exhibits continuous-variable entanglement between so-called signal and idler beams, is used as input to the radar system. Compared to existing proposals for quantum illumination, our protocol does not require joint measurement of the signal and idler beams. This greatly enhances the practicality of the system by, for instance, eliminating the need for a quantum memory to store the idler. We perform a proof-of-principle experiment in the microwave regime, directly comparing the performance of a two-mode squeezed source to an ideal classical noise source that saturates the classical bound for correlation. We find that, even in the presence of significant added noise and loss, the quantum source outperforms the classical source by as much as an order of magnitude.
Quantum radar has emerged as a promising sensing paradigm that exploits quantum resources, including entanglement and quantum correlations, to enhance target detection in noisy and lossy environments. Although entanglement generated by superconducting devices such as Josephson parametric amplifiers, Josephson parametric converters, and Josephson traveling-wave parametric amplifiers is rapidly degraded under realistic propagation conditions, the remaining quantum correlations can still provide a measurable detection advantage through the principles of quantum illumination. This review presents a comprehensive engineering perspective on quantum radar, covering the theoretical foundations of quantum illumination, microwave entanglement generation, electro-optomechanical quantum transducers, atmospheric channel effects, cryogenic receiver architectures, and digital signal-processing techniques. Recent microwave experimental demonstrations are also reviewed, highlighting the transition from theoretical concepts to laboratory-scale implementations. Collectively, these developments demonstrate that microwave quantum radar is evolving toward practical sensing architectures while emphasizing the engineering challenges that must be addressed before real-world deployment.
We compare the performance of a quantum radar based on two-mode squeezed states with a classical radar system based on correlated thermal noise. With a constraint of equal number of photons NStransmitted to probe the environment, we find that the quantum setup exhibits an advantage with respect to its classical counterpart of √2 in the cross-mode correlations. Amplification of the signal and the idler is considered at different stages of the protocol, showing that no quantum advantage is achievable when a large-enough gain is applied, even when quantum-limited amplifiers are available. We also characterize the minimal type-II error probability decay, given a constraint on the type-I error probability, and find that the optimal decay rate of the type-II error probability in the quantum setup is ln(1 + 1/NS) larger than the optimal classical setup, in the NS<; <; 1 regime. In addition, we consider the Receiver Operating Characteristic (ROC) curves for the scenario when the idler and the received signal are measured separately, showing that no quantum advantage is present in this case. Our work characterizes the trade-off between quantum correlations and noise in quantum radar systems.
Quantum illumination has been suggested as a way to improve the sensitivity of remote target detection by taking advantage of quantum entanglement between a traveling electromagnetic beam of light interrogating the target, and a second beam kept in the lab. In the microwave domain, superconducting quantum circuit utilizing superconducting Josephson tunnel junctions can be used as quantum-limited amplifiers of faint microwave signals, as well as bright sources of quantum entangled signals. These Josephson parametric amplifiers (JPAs) are poised to become fundamental building block in a future quantum illumination radar operating in the microwave domain. Demonstrating a practical advantage of quantum illumination with ambient temperature signals is, however, challenging. Indeed, current quantum protocols are not practical as they require a complex receiver with stringent phase-matching conditions, which cannot be met in the field. Notably, it is also not currently known how one can transfer faint microwave signals out of cryogenic systems without destroying their fragile entanglement. In this article, we discuss the recent progress and challenges regarding the development of an all-microwave quantum illumination radar using the recently developed and implemented quantum-enhanced noise radar protocol. This quantum illumination protocol is simpler to implement and procures a quantum enhancement over its classical analog. Finally, we discuss different strategies that may resolve the issue of transmitting microwave entanglement under ambient conditions. We, thus, conclude that successful transmission of entangled microwaves can be done in the near future, with possible demonstrations of practical quantum advantage over short distances.
We have built and evaluated a prototype quantum radar in the laboratory which operates at microwave frequencies. Because the signal generation process relies on quantum mechanical principles, the system is considered to contain a quantum-enhanced radar transmitter. This transmitter generates a pair of entangled microwave signals and transmits one of them through free space, where the one-way signal is measured using a simple and rudimentary receiver. The type of entanglement used is called two-mode squeezed vacuum (TMSV), so we may call our radar a quantum two-mode squeezing radar (QTMS radar). At the heart of the transmitter is a device called a Josephson parametric amplifier (JPA), which generates the entangled microwave beams; these are then sent through a chain of amplifiers. One beam passes through 0.5 m of free space; the other is measured directly. The two measurement results are correlated in order to distinguish noise from signal. We compare this quantum-enhanced transmitter to a similar one using only conventional components, and find that there is a significant gain when the two systems broadcast signals at approximately the same power.