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Previous work showed that thermal light with a blackbody spectrum cannot be decomposed into a mixture of independent localized pulses. However, we find that in the weak-source limit and under the assumption of a flat spectrum, the first nonvacuum term in the state expansion does form a mixture of such pulses. This decomposition is essential for quantum-enhanced astronomical interferometry, which typically operates on localized pulses even though stellar light is inherently continuous-wave. We present a quantum derivation of the van Cittert–Zernike theorem that incorporates finite bandwidth, thereby justifying the operations on localized pulses while processing continuous-wave thermal light. For general spectra in the weak-source limit, we establish a criterion under which correlations between pulses can be safely neglected. When this criterion is not met, we provide a corrected strategy that accurately accounts for both the spectral profile and the detector-defined pulse shape. 

We propose a method to build an astronomical interferometer using continuous-variable quantum teleportation to overcome transmission loss between distant telescopes. The scheme relies on two-mode squeezed states shared by distant telescopes as entanglement resources, which are distributed using continuous-variable quantum repeaters. We find the optimal measurement on the teleported states, which uses beam splitters and photon-number-resolved detection. Compared to prior proposals relying on discrete states, our scheme has the advantages of using linear optics to implement it without wasting stellar photons, and making use of multiphoton events, which are regarded as noise in previous discrete schemes. We also outline the parameter regimes in which our scheme outperforms the direct detection method, schemes utilizing distributed discrete-variable entangled states, and local heterodyne techniques. 

We simulate Λ-type quantum memory in atomic ensembles with the addition of a high-lying sensor state in the continuous dynamical decoupling regime. We find order-of-magnitudes memory lifetime enhancement and explore the dressing-field parameter space. 

Developing a quantum light source that carries more than one bit per photon is pivotal for expanding quantum information applications. Characterizing a high-dimensional multiple-degree-of-freedom source at the single-photon level is challenging due to the large parameter space as well as limited emission rates and detection efficiencies. Here, we characterize photon pairs generated in optical fiber in the transverse-mode and frequency degrees of freedom by applying stimulated emission in both degrees of freedom while detecting in one of them at a time. This method may be useful in the quantum state estimation and optimization of various photon-pair source platforms in which complicated correlations across multiple degrees of freedom may be present. 

In the realm of quantum information processing, harnessing high-dimensional photonic systems provides a pathway to overcome limitations of traditional two-level systems. Orbital angular momentum (OAM) of light has emerged as a powerful tool for creating and manipulating high-dimensional entanglement, promising increased information capacity and enhanced security in quantum communication protocols. However, conventional methods like spontaneous parametric downconversion encounter challenges due to non-uniform production rates of Laguerre–Gaussian modes. This study explores the potential of spontaneous four-wave mixing in ring-core fibers (RCFs) as a viable platform for generating OAM photon pairs with tailored spectral and spatial properties. We show that by controlling the topological charge of pump photons, correlated, uncorrelated, and anti-correlated photon pairs can be engineered across arbitrary spectral ranges, essential for diverse quantum applications. Experimental noise characterization of the RCF-based source demonstrates a high coincidence-to-accidental ratio exceeding 4000, and a low heralded second-order correlation function (g_H⁽²⁾<0.005), which confirms its operation well into the single-photon regime. This work demonstrates the potential of RCFs as a versatile platform for generating structured photon pairs, paving the way for future high-dimensional quantum communication and information processing applications. 

Broadband quantum memory is critical to enabling the operation of emerging photonic quantum technology at high speeds. Here we review a central challenge to achieving broadband quantum memory in atomic ensembles—what we call the ‘linewidth-bandwidth mismatch’ problem—and the relative merits of various memory protocols and hardware used for accomplishing this task. We also review the theory underlying atomic ensemble quantum memory and its extensions to optimizing memory efficiency and characterizing memory sensitivity. Finally, we examine the state-of-the-art performance of broadband atomic ensemble quantum memories with respect to three key metrics: efficiency, memory lifetime, and noise.