Abstract
Quantum channels in free-space, an essential prerequisite for fundamental tests of quantum mechanics and quantum technologies in open space, have so far been based on direct line-of-sight because the predominant approaches for photon-encoding, including polarization and spatial modes, are not compatible with randomly scattered photons. Here we demonstrate a novel approach to transfer and recover quantum coherence from scattered, non-line-of-sight photons analyzed in a multimode and imaging interferometer for time-bins, combined with photon detection based on a 8 × 8 single-photon-detector-array. The observed time-bin visibility for scattered photons remained at a high 95% over a wide scattering angle range of −450 to +450, while the individual pixels in the detector array resolve or track an image in its field of view of ca. 0.5°. Using our method, we demonstrate the viability of two novel applications. Firstly, using scattered photons as an indirect channel for quantum communication thereby enabling non-line-of-sight quantum communication with background suppression, and secondly, using the combined arrival time and quantum coherence to enhance the contrast of low-light imaging and laser ranging under high background light. We believe our method will instigate new lines for research and development on applying photon coherence from scattered signals to quantum sensing, imaging, and communication in free-space environments.
Highlights
1234567890():,; 1234567890():,; 1234567890():,; 1234567890():,; Introduction Quantum coherence is a key ingredient in many fundamental tests and applications of quantum mechanics including quantum communication[1], characterization of single-photon sources[2], generation of non-classical states[3], quantum metrology[4], quantum teleportation[5], quantum fingerprinting[6], quantum cloning[7], demonstrating quantum optical phenomena[8], and quantum computing[9] etc
We demonstrate that our system allows imaging a target that was illuminated with photons prepared with specific phase-signatures, that are recovered from the scattered photons with excellent phase coherence by the illuminated pixels
Quantum communication with scattered light we demonstrate the viability of freespace non-line-of-sight (NLOS) quantum communication experiments with ‘scattered photons’
Summary
As the scattered photons are imaged by the SPDA analyzer, the detected count pattern should follow the applied phase-signature. The coherent variation of intensity across the image in response to the applied phase is shown in Fig. 6 in Methods section. The observed pattern at the same two pixels (4,3) and (4,4) are included in Fig. 4d which shifted up due to the presence of high background photons, yet the correlation with the reference pattern is still visible. 8x8 SPDA other hand, as shown, visibility – the measure of coherence – stays fairly constant with decreasing signal intensity This means when the number of detected signal photon decreases, the relative amplitude of the count pattern decreases but the shape of the pattern stays fairly same. Finding a more sophisticated image-reconstruction method is out of this paper’s scope and will be presented elsewhere
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
