Single photons exhibit quantum interference behaviors in novel experiments that extend previous characterization techniques, a key step for assessing the utility of single photons in future quantum networks.
Twin-field quantum key distribution (TF-QKD) is recognized as a promising approach to surpass the repeaterless key rate bound, playing a pivotal role in long-distance quantum communication. However, conventional TF-QKD implementations rely on laser coherence, where coherent-state sources differ fundamentally from the non-classical light sources required for future quantum networks. Recent advances demonstrate that quantum dot (QD) sources can generate high-purity coherent single-photon states on demand, exhibiting both perfect antibunching and long coherence times akin to laser source. Here, we propose a six-state TF-QKD protocol utilizing coherent single-photon states, which can be directly achieved through current experimental techniques. Simulation results indicate that our protocol achieves significantly enhanced key rates and extended transmission distances. Moreover, a data size on the order of 108 is sufficient to surpass the repeaterless key rate bound, demonstrating particular robustness against finite-size effects. Our work paves the way for the direct implementation of long-distance quantum key distribution utilizing future quantum network infrastructure.
Photon-mediated interactions between atoms can arise via coupling to a common electromagnetic mode or by quantum interference. Here, we probe the role of coherence in cooperative emission arising from two distant but indistinguishable solid-state emitters because of path erasure. The primary signature of cooperative emission, the emergence of "bunching" at zero delay in an intensity correlation experiment, is used to characterize the indistinguishability of the emitters, their dephasing, and the degree of correlation in the joint system that can be coherently controlled. In a stark departure from a pair of uncorrelated emitters, in Hong-Ou-Mandel-type interference measurements, we observe photon statistics from a pair of indistinguishable emitters resembling that of a weak coherent state from an attenuated laser. Our experiments establish techniques to control and characterize cooperative behavior between matter qubits using the full quantum optics toolbox, a key step toward realizing large-scale quantum photonic networks.
Today, quantum photonics is one of the leading platforms for the research and development of the quantum information sciences and technologies. It is also the most promising platform for quantum networking protocols. As such, the investigation and characterization of quantum light sources is vital to the future of quantum research. In this thesis document, titled “Multimode Statistical Photonics and Quantum State Tomography for Quantum Networks,” I present my research on the multi-mode statistical properties of classical light sources, with applications to quantum state tomography methods for use in quantum communications and networking protocols. During my time here at LSU, I have worked with my fellow researchers in the quantum photonics group to investigate the quantum dynamics which govern the classical statistical behaviors of stochastically-random light sources. By extracting the correlated multiphoton, multi-mode subsystems of such sources, we have discovered nontrivial, uniquely-quantum behaviors within sources of light which were previously thought to be only classical. I have also developed a robust theoretical framework for describing such sources, utilizing techniques from quantum field theory, which we have shown to be an excellent predictor of experimental measurements. I have then applied these innovations to projects concerning plasmonic nanostructures, quantum imaging, and quantum sensing. Additionally, in collaboration with the National Institute of Standards and Technology (NIST), I have performed an experiment utilizing weak-field interference to prove the correctness of a quantum state tomography method called weak-field homodyne detection, a low-noise procedure which is ideal for quantum communications and networking protocols. As a result, I was able to completely reconstruct a coherent quantum state within the interference mode, and also to obtain some limited information about the remaining modes of that state. Throughout all of this, my research has had a particular focus on multi-mode photonics and its applications to plasmonics and quantum networking, and I believe that the state-tomography protocols and the results concerning stochastically-random quantum light sources will be of use to the quantum information and photonics communities for years to come.