MULTIPHOTON INTERFEROMETRY


Read the full paper on the experiment here https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.263603 or scan the QR code


Scientists in the UK and Korea have undertaken breakthrough research that paves the way for new high precision sensing applications.


❱ ❱ Dr Vincenzo Tamma of Portsmouth University sees exciting applications over the horizon for multiphoton interferometry


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A Quantum of Precision


esearch scientists in the UK and Far East have succeeded in demonstrating experimentally how


multiphoton interference with thermal light can be observed beyond the coherence time. This is the first time that such demonstrations have been successful and it is paving the way towards achieving new levels of high precision sensing across a wide range of applications. The research was performed by a team of scientists based in Korea’s Pohang University of Science and Technology as well as the UK’s University of Portsmouth. They describe their observation as being a counter- intuitive phenomenon to what would be expected with multi-path correlation interferometry with thermal light.


DISTANCE INDEPENDENCE According to the researchers, “the intensity correlation between the outputs of two unbalanced Mach-Zehnder interferometers (UMZIs) with two classically correlated beams of thermal light at the input exhibits genuine second-order interference with the visibility of 1/3.” What came as a surprise in the research was that the second-order interference does not degrade at all regardless of how much the path length difference in each UMZI is increased beyond the coherence length of the thermal light. In addition, the second- order interference is dependent on the difference of the UMZI phases, independently of the distance between the two UMZIs. Since it is the interference that is


important in sensing and metrology, the independence of distance has important


❱ ❱ Fundamental research in quantum optics is providing the potential for greater precision in sensing and metrology


implications in terms of the possibility for applications involving high-precision measurements of remote phases. Dr Vincenzo Tamma, one of the researchers at the University of Portsmouth, who first predicted this effect theoretically with his student Johannes Seiler in New Journal of Physics, said: “This interferometric technique can be used in metrology and remote sensing to measure the relative phase between two remote spatial regions independently of their distances.”


SENSING APPLICATIONS More specifically, in terms of applications, the technique can be used for sensing the position and spatial structure of remote objects as well as measuring the difference in the pollution rate, for example, between two remote regions to provide a more precise understanding of the distribution of pollution. The results of the experiments


undertaken in Portsmouth and Pohang differ substantially from those of the established entangled-photon Franson interferometer which exhibits two- photon interference dependent on the sum of the UMZI phases and vanishing as the path length difference in each UMZI exceeds the coherence length of the pump laser. “This work offers deeper insight into


the interplay between interference and coherence in multi-photon interferometry,” explained Tamma. The Portsmouth based researcher went on to explain that this new and unexpected physical phenomenon, which was demonstrated for the first time experimentally in the laboratory of Professor Yoon-Ho Kim, will most likely have potential use for technological applications, including in high precision metrology and imaging, particularly sensing remote distant spatial structures. “Those working in engineering and technological development especially in metrology and imaging will be particularly interested, and the findings could inspire new technological schemes,” he says.


Recognising the potential benefits of such fundamental research at an academic level is the first step in bringing the resulting technology to engineering applications and gaining the benefits of ever-increasing levels of precision in remote sensing and metrology. The team of scientists from the UK and Korea have published their research, entitled “Second-order temporal interference with thermal light: Interference beyond the coherence time”, in Physical Review Letters. EE


DAQ, Sensors & Instrumentation Vol 1 No. 1 /// 5


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