Single-photon detectors on the one hand and optical fibers for telecommunication on the other are technical fields of high importance in science and daily life. With the advent of fiber-based quantum communication and fiber metrology applying single-photon detectors, a direct link has been established. The work presented in this thesis is devoted to new techniques and developments in this environment.
Single-photon detectors on the one hand and optical fibers for telecommunication on the other are technical fields of high importance in science and daily life. With the advent of fiber-based quantum communication and fiber metrology applying single-photon detectors, a direct link has been established. The work presented in this thesis is devoted to new techniques and developments in this environment.
Quantum Communication is a groundbreaking technology that promises to revolutionize our current telecommunication systems. However, being a relatively new field, many challenges are yet to be confronted. This Doctoral thesis is dedicated to the advancement of Quantum Communications for fundamental studies and applications. Here, satellite-based, free-space and optical-fiber links are exploited to test and develop different Quantum Communication protocols. Different technologies, in particular free-space optics, fiber-based components and silicon photonic integrated circuits, are adopted to manipulate the quantum states of light. Different types of studies are performed ranging from fundamental tests of physics, to technological advancements, up till the development of fully-functioning Quantum Key Distribution systems. The work described in this thesis, I hope, represents a substantial contribution in the effort to transition Quantum Communications from the laboratories to a wide-spread deployment in future telecommunication infrastructures.
We will present our current efforts on single photon quantum metrology using high-efficiency superconducting detectors and high-efficiency single-photon sources based on spontaneous parametric downconversion. Optical power measurements based on single photon counting could establish a quantum standard for optical power calibration in the future. At NIST we are pursuing the development of single photon sources and single photon detectors for metrology, quantum and classical applications. As part of these efforts, we are pursuing the establishment of a measurement service for the calibration of single photon detectors. We present how our calibration is tied to the calibration of our transfer standard optical fiber power meters. Using the beamsplitter method, we have implemented a fiber-coupled and free-space measurement system. Also, we have developed testbeds and measurement protocols for the characterization of single photon sources and single photon detectors. We will review several methods, which allow for the characterization of the spatial and spectral degree of freedom in spontaneous parametric downconversion.
Optical quantum systems are ideal for testing quantum mechanical laws, but they also find many uses into possible applications to our everyday life related to quantum information science, such as quantum key distribution (QKD) or, in general, quantum communication. Nonlinear and quantum optics and their applications both to quantum communication and to tests of fundamental physics are described in this Thesis. In particular, we have developed and characterised heralded single photon sources at telecommunication wavelengths (1550 nm), based on nonlinear interactions of the second order between electric fields in dielectric materials. This is the starting point for the preparation of single photon entangled states, that we used as a resource for heralded amplification of photonic qubits, with a direct application in Device Independent Quantum Key Distribution (DIQKD) protocols, but also for testing fundamental questions in quantum physics, demonstrating the presence of entanglement in a state that counts a macroscopic number of particles, 500 photons.
Industrial technologies based on the production, manipulation, and detection of single and entangled photons are emerging, and quantum key distribution via optical fibre is one of the most commercially-advanced. The National Physical Laboratory is developing traceable performance metrology for the quantum devices used in these technologies. This is part of a broader effort to develop metrological techniques and standards to accelerate the development and commercial uptake of new industrial quantum communication technologies based on single photons. This presentation will give an overview of the work carried out at NPL and within the wider European community, and highlight plans for the future.
A growing number of technologies employ quantum properties in order to produce solutions that surpass the performance of conventional devices, or to execute operations that are fundamentally impossible with classical systems alone. In the field of optical quantum information science, photons are utilized to encode, communicate and manipulate information, making them vitally important. While photon production always constitutes the first step in any optical experiment, in the field of quantum information science, the recording of data through the process of photon detection is an equally crucial final step. This thesis deals with both the single photons generation (based on diamond color defects) and their detection, utilizing a novel type of superconducting detectors. In particular, part one of this thesis is devoted to the construction of custom designed microscope setup, and the development of laboratory experiments, to enable the generation of single photons as well as the investigation of the optical and spin properties of diamond color centers. Confocal microscopy is used for this purpose, as it allows for the identification and addressing of individual color centers that emit only single photons. This microscope also feature an integrated self-built microwave and magnetic hardware setup, which allows for a wide range of spin environment spectroscopy studies. Single photon emission is demonstrated through both photon anti-bunching and Rabi oscillations at room temperature. The second part of the thesis offers an exploration of superconducting single photon detectors through experiment. Since electronics are an essential part of these detectors, the possibility of using a novel alternative scheme based on capacitive readout combined with fast gating to enable simplified readout is demonstrated. This scheme overcomes the limitations of conventional readout schemes, which require large bandwidth amplification and complex counting electronics. Besides photon detection, the capabilities of these detectors are also expanded to include high-energy particles in the MeV energy range, and the detectors are demonstrated to not only detect single α- and β-particles, but to do so with near unity efficiency. Finally, a multipurpose testing station for superconducting detectors is demonstrated with a central objective of optimizing the coupling efficiency of light to the active area of the detector, as well as to allow for a fast exchange of the optical fiber, thereby facilitating an efficient characterization of the detector. The optimization of this coupling efficiency was demonstrated through proof-of-principle experiments.