A quantum receiver is an essential element of quantum illumination (QI), which outperforms its classical counterpart, called classical illumination. However, there are only few proposals for realizable quantum receiver, which exploits nonlinear effects leading to increasing the complexity of receiver setups. To compensate this, in this paper, we design a quantum receiver with linear optical elements for Gaussian QI. Rather than exploiting nonlinear effect, our receiver consists of a 50:50 beam splitter and homodyne detection. Using double homodyne detection after the 50:50 beam splitter, we analyze the performance of the QI in different regimes of target reflectivity, source power, and noise level. We show that our receiver has better signal-to-noise ratio and is more robust against noise than the existing simple-structured receivers.

Quantum-enhanced sensing has a goal of enhancing a parameter sensitivity with input quantum states, while quantum illumination has a goal of enhancing a target detection capability with input entangled states in a heavy noise environment. Here we propose a concatenation between quantum-enhanced sensing and quantum illumination that can take quantum advantage over the classical limit. First, phase sensing in an interferometry is connected to a target sensing via quantum Fisher information. Second, the target sensitivity is investigated in noisy quantum-enhanced sensing. Under the same input state energy, for example, $N$-photon entangled states can exhibit better performance than a two-mode squeezed vacuum state and a separable coherent state. Incorporating a photon-number difference measurement, finally, the noisy target sensitivity is connected to a signal-to-noise ratio which is associated with a minimum error probability of discriminating the presence and absence of the target. We show that both the target sensitivity and the signal-to-noise ratio can be enhanced with increasing thermal noise.

Coherent conversion from microwave to optical wave opens new research avenues towards a long distance quantum network covering quantum communication, computing, and sensing out of the laboratory. Especially a multimode enabled system is essential for practical applications. Here we experimentally demonstrate coherent multimode conversion from the microwave to optical wave via collective spin excitation in a single crystal yttrium iron garnet (YIG, ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$) which is strongly coupled to a microwave cavity mode in a three-dimensional rectangular cavity. Expanding a collective spin excitation mode of our magnon-cavity hybrid system from Kittel to multimagnetostatic modes, we verify that the size of the YIG sphere predominantly plays a crucial role for the microwave-to-optical multimode conversion efficiency at resonant conditions. We also find that the coupling strength between multimagnetostatic modes and a cavity mode is manipulated by the position of a YIG inside the cavity. It is expected to be valuable for designing a magnon-hybrid system that can be used for coherent conversion between microwave and optical photons.

The development of quantum photonic information technology demands high-quality photon sources. Here we demonstrate a low-noise and high-speed photon source generated by the spontaneous four-wave mixing process in a micro/nanofiber (MNF). The pair generation in a MNF is tailorable by controlling its diameter and designed for creating signal and idler photons in the silicon-based detector wavelength range, yielding high detection efficiency and coincidence count rate. This MNF photon source can be coupled to other fiber systems with negligible coupling loss and can be efficiently exploited as fiber-based quantum light sources for quantum information applications.

In this paper, we propose a quantum-secured single-pixel imaging method that utilizes non-classical correlations of a photon pair. Our method can detect any attempts to deceive it by exploiting a non-classical correlation of photon pairs while rejecting strong chaotic light illumination through photon heralding. A security analysis based on polarization-correlation has been conducted, demonstrating that our method has improved security compared to existing quantum-secured imaging. More specifically, a partial deceiving attack, which sends a mixture of a true and a false signal, can be detected with our proposed analysis, while currently employed methods cannot. We also provide proof-of-principle demonstrations of our method and trustworthy images reconstructed using our security analysis. Our method can be developed using matured techniques used in quantum secure communication, thus offering a promising direction for practical applications in secure imaging.

Imaging with non-classically correlated photon-pairs takes advantages over classical limits in terms of sensitivity and a signal-to-noise ratio. However, it is still a challenge to achieve a strong resilience to background noise and losses for practical applications. In this work, we present heralded single-pixel imaging that is remarkably robust against bright background noise and severe signal losses. Using a strong temporal correlation between a photon-pair and joint measurement-based imaging method, we achieve the suppression of noise up to 1000 times larger than the signal and also demonstrate the correlation-induced SNR enhancement factor of over 200 against 70 times larger noise and a 90% signal loss compared to non-time-gated classical imaging. Our work enables correlated imaging with a highly scalable photon capacity.