Quantum radar is a remote sensing technique for target detection that has extensively been explored in conjunction with entangled two-mode squeezed vacuum states. This work extends the existing protocol to a scheme that utilizes a three-mode squeezed state with genuine tripartite entanglement. The three entangled modes are divided into two signal modes and one idler mode. A numerical evaluation of the Chernoff bound shows that the proposed protocol has the potential to offer a higher quantum advantage in specific parameter regimes.
Quantum radar is a remote sensing technique for target detection that has extensively been explored in conjunction with entangled two-mode squeezed vacuum states. This work extends the existing protocol to a scheme that utilizes a three-mode squeezed state with genuine tripartite entanglement. The three entangled modes are divided into two signal modes and one idler mode. A numerical evaluation of the Chernoff bound shows that the proposed protocol has the potential to offer a higher quantum advantage in specific parameter regimes.
In recent years, quantum radar has focused entirely on using bipartite squeezed states of light as a mechanism for target detection. This paper studies the performance of a quantum radar that uses a tripartite squeezed state, whereby two signal beams are sent out towards the target which both correlate with the idler. It is found that for very low signal strengths, the bipartite has better performance. As the signal strength increases however, the tripartite becomes dominant. This result suggests that quantum radar (declared useful only in the low SNR regime) may possess more possibilities of increased performance at higher SNRs when different states are used for correlation. The bottleneck, of course, is the ability to generate transmit powers necessary to utilize.
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.
Entanglement is beneficial to enhancing a phase sensitivity beyond the classical limit that is given by a coherent state. The best performance is achieved with symmetric entangled states, which is enhanced further by sending more photons to the signal mode. We delve into which entanglement structure is valuable for quantum target sensing, such as a reflectivity parameter. We show that an asymmetric entangled state can approach the local joint measurement bound of a two-mode squeezed vacuum state which is a nearly optimal input state for quantum target sensing, whereas it cannot beat the performance of the coherent state for quantum phase sensing. The result is demonstrated with an asymmetric entangled coherent state whose performance is evaluated with quantum Fisher information and confirmed by the signal-to-noise ratio with an optimal observable. The best quantum advantage is achieved in the case of sending fewer photons to the signal mode and many more photons to the idler mode.
There has been a great interest in quantum metrology (e.g., quantum interferometric radar) due to its applications in sub-Rayleigh ranging and remote sensing. Despite interferometric radar has received vast amount of attentions over the past two decades, very few researches has been conducted on another type of quantum radar: quantum illumination radar, or more precisely quantum target detection. It is, in general, used to interrogate whether the low-reflectivity target in a noisy thermal bath is existed using quantum light. The entanglement properties of its emitted light source give it a unique detection advantage over the classical radar. Entangled coherent state (ECS), as a class of quantum states with high entanglement robustness in noisy environments, has been widely used in several fields of quantum science such as quantum informatics, quantum metrology . In this paper, we investigate the target detection performance of quantum illumination radar based on three different types of ECS states. We employ the two-mode squeezed vacuum state (TMSV) and the coherent state as benchmarks to compare and analyze the relationship between the entanglement strength of the three types of ECS states and their quantum illumination detection performance. We found that the detection performance of the three ECS states is better than that of the coherent state. However, it is inferior to that of the TMSV state when the target is of low reflectivity. The emitted photon number is much smaller than the background noise (we call this as “good” illumination conditions). On the contrary, quantum illumination radar has no obvious advantage over coherent state radar for target detection under other illumination conditions; further, the detection performance of these three types of ECS states is not evidently related to that of the TMSV state and the coherent state. Finally, we reveal that the target detection performance of quantum illumination for the first two types of ECS states can be determined by their entanglement strength under “good” illumination conditions by adjusting the inter-modal phase of these two ECS states while keeping the emitted photon number constant. Under other illumination conditions, there is no evidence to demonstrate the entanglement strength of ECS states being associated with their target detection performance.
A Microwave Quantum Radar (MQR) based on the Quantum Illumination (QI) protocol and using a Josephson traveling wave parametric amplifier (JTWPA) and a Phase-Coniugate Receiver is introduced for the first time. A JTWPA, operating as a two-mode squeezed vacuum state quantum source, emitting a microwave signal-idler entangled state is developed and experimentally characterised. A phase-conjugate receiver is used as a joint detecting unit for the entangled signal-idler pairs, and its corresponding receiver operating characteristic (ROC) curves are reported and compared to the optimal classic scheme. The proposed MQR scheme paves the way to a long-distance target detection.
In this paper, an explicit expression for the maximum detection range of an entangled quantum two-mode squeezed (QTMS) radar, in which a two-mode squeezed vacuum state of microwave electromagnetic fields is used, have been derived by considering both the quantum properties of the entangled microwave fields and radar parameters. By comparing this equation with that of traditional radars, we showed that one can though a QTMS radar as a traditional radar with a reduced threshold signal-to-noise ratio. By discussing the current limitations, it has been shown that the critical parameter to have both simultaneous quantum advantage and substantial radar range is increasing the bandwidth of the generated output signal in the quantum entangled source. It has been shown that by considering the current feasible system parameters, it is possible to implement a QTMS radar with maximum detection range up to the order of 2km, which is suitable for recognizing small unmanned aerial vehicles in urban distances. Moreover, based on the false alarm rate, we introduce two classes of early alarm and track QTMS radars. The present approach can be generalized to other quantum radars with different types of quantum sources like electro-opto-mechanical sources, and also may shed new light on investigating the quantum radar system toward practical applications. Finally, we have discussed the potential outlooks to improve and develop the quantum entangled radar systems to be practical from the engineering point of view.