Using thermal light sources to take accurate distance measurements

June 29, 2017, University of Portsmouth
Simplified scheme of the sensing technique published in Optics Express. Credit: University of Portsmouth

New research has made it possible for the first time to compare the spatial structures and positions of two distant objects, which may be very far away from each other, just by using a simple thermal light source, much like a star in the sky.

This sensing technique, introduced by Dr Vincenzo Tamma at the University of Portsmouth in collaboration with the University of Bari in Italy and the University of Maryland, Baltimore County in the US in the recent publication in Optics Express, enables the comparison of the of a remote object with a reference object, paving the way for important .

The technique builds on the famous Hanbury Brown and Twiss effect, originally employed to measure the angular size of a distant star, which gave birth to the novel field of quantum optics. The reported new research has now taken the physics behind this effect an important step further.

Dr Tamma said: "These results not only deepen our understanding of the interesting physics behind multiphoton but are also of interest in the development of quantum technologies for remote sensing, biomedical imaging and information processing."

The multiphoton interference phenomenon at the heart of this novel sensing technique was first predicted by Dr Tamma and his student Johannes Seiler in 2014 and reported as a Fast Track Communication in the journal New Journal of Physics. The counterintuitive nature of this phenomenon made it difficult to accept by part of the scientific community. Nonetheless, it has already led to three independent verifications (here,here and here) in three different experimental scenarios in US, Italy and South Korea.

In the recent publication in Scientific Reports in collaboration with the University of Bari, this technique has been experimentally employed for the spatial characterization of two remote objects, namely two double-pinhole masks, at distances that, in principle, could be arbitrarily large.

In the experimental setup, thermal light impinges on a balanced beam splitter and then reaches the two remote double-pinhole masks through the two beam splitter output channels.

Dr Tamma said: "In the experiment reported here, the distance between the two pinholes is large enough that there is no coherence between the light passing through them. The classic Young's double-slit experiment teaches us that in this case no single-photon interference can be measured behind each mask separately. Nonetheless, multiphoton interference is observed by performing correlation measurements with two detectors, one placed behind each of the two masks. Even more interesting, the measured interference pattern allows us to retrieve information about the position and spatial structure of both masks.

"Remarkably, this sensing technique allows the measurement, via multiphoton interference, of the relative shrinking/stretching of one object with respect to the other. Furthermore, if both detectors are moved, symmetrically, farther away from the optical axis it is even possible to increase the measurement sensitivity to the changes in the spatial structures. Similar analysis can be performed to determine the relative position of the two different objects."

The application of this to sensing of arbitrary remote objects could pave the way to a broad spectrum of applications in . Furthermore, the extension of this scheme to the use of entangled photons may lead to applications in high-precision metrology beyond any classical capability.

The physics of multipath correlations at the heart of this effect has been already demonstrated to be crucial in the simulation of quantum logic gates with a thermal source. This has potentially important applications in information processing and the development of novel optical algorithms.

Explore further: A twist on Hanbury Brown—Twiss interferometry offers new approach for remote sensing

More information: Michele Cassano et al. Spatial interference between pairs of disjoint optical paths with a single chaotic source, Optics Express (2017). DOI: 10.1364/OE.25.006589

Milena D'Angelo et al. Characterization of two distant double-slits by chaotic light second-order interference, Scientific Reports (2017). DOI: 10.1038/s41598-017-02236-8

Tao Peng et al. Experimental controlled-NOT gate simulation with thermal light, Scientific Reports (2016). DOI: 10.1038/srep30152

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