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CRC Press eBooks

Quantum Interferometric Communications in Free Space

F. J. Duarte

Published Jan 15, 2024• 0 citations
Publisher

Abstract

Free-space secure communications via interferometric characters generated by quantum N -slit interferometers, and ensembles of indistinguishable photons, is discussed quantitatively in detail. The highly sensitive ability of this interferometric methodology to detect attempts of third-party intrusion is highlighted.
DOI
10.1201/9781003398707-8

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N-slit interferometry has recently been applied to generate a series of interferometric characters that propagate, in free space, according to well established interference and optical propagation principles. Any attempt to intercept the interferometric character leads to detectable spatial distortions. Originally, experiments were reported at distances in the centimetre range. Here, successful communications, and enhanced detection sensitivity of optical interception, at distances of over 7 m is reported. Further, we discuss conceptual countermeasures and their inapplicability to intercept, undetected, the interferometric characters.
Quantum mechanics values highly its sovereignty and does not allow extraneous intrusions. In quantum mechanics processing we can only observe the input state and the output state. Attempts to intrude, or to ‘peek in between,’ are always successfully detected. This is the essence behind quantum cryptography and the principle of what provides robust security to quantum communications in general. Here we focus on quantum entanglement based cryptography. This methodology puts to work Bell's theorem to verify that no external intrusion has occurred. We also describe a more stringent all-quantum protocol entirely based on a measurements strategy. The chapter concludes with a description of the N -slit interferometric communications approach that reinforces understanding of the concepts that bring unprecedented security to quantum communications.
The history of the probability amplitude equation |ψ〉=(|x,y〉−|y,x〉) applicable to quanta pairs, propagating in different directions with entangled polarizations, is reviewed and traced back to the 1947–1949 period. The interferometric Dirac foundations common to |ψ〉=(|x,y〉−|y,x〉) and the generalized N-slit interferometric equation, for indistinguishable quanta, are also described. The results from a series of experiments on N-slit laser interferometers, with intra interferometric propagation paths up to 527 m, are reviewed. Particular attention is given to explain the generation of interferometric characters, for secure space-to-space communications, which immediately collapse on attempts of interception. The design of a low divergence N-slit laser interferometer for low Earth orbit-low Earth orbit (LEO-LEO), and LEO-geostationary Earth orbit (LEO-GEO), secure interferometric communications is described and a weight assessment is provided.
Optical communication via free-space channels is attractive for establishing long-range secure quantum networks, but is often hindered by deleterious effects on the transverse spatial mode profile of the beam, caused by propagation through the atmosphere. Additionally, interferometric measurement at the receiver becomes much more difficult with multimode profiles. This study presents a compact time-delay interferometer with high stability and interference visibility for single- and multimode spatial profiles. The results of this study are important for the future of quantum communication networks as well as a wide range of techniques for classical and quantum optical measurement.