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Adaptive Optics for Quantum Communication

Periodic Reporting for period 1 - ADOQ (Adaptive Optics for Quantum Communication)

Reporting period: 2019-06-01 to 2021-05-31

The project “ADOQ: Adaptive Optics for Quantum Communications” started in June 2020 for 24 months and was carried out by Dr. Hugo Defienne at University of Glasgow, UK. The overall aim of the project was develop adaptive optics for quantum light to increase communication distance and enhance information capacity of quantum communication systems.

Securing exchanges of information on a global scale represents a major challenge in our society today. The emerging field of quantum communication relies on the fundamental laws of physics to offer unconditional security. In this respect, encoding information on spatial properties of photons has recently demonstrated a strong potential for increasing security level and data rates of quantum communications. However, disturbances in the distribution of quantum states in free-space and aberrated channels (i.e. atmospheric turbulence or multimode fibers) are critical challenges that must be overcome to advance beyond laboratory proof-of-principle demonstrations and implement long-distance communications. The goal of this work was to enhance information capacity and enlarge distances of quantum communications by monitoring optical disturbances using adaptive optics. This ambitious goal will be achieved by combining the powerful techniques of the emerging field of quantum light shaping, with the speed of adaptive optics systems and the extreme sensitivity and high temporal resolution of quantum imaging sensors.

The overall objectives addressed during the fellowship were: (1) Transmission of spatially-structured quantum states through aberrating media; (2) Improving data rate with high-speed single-photon manipulation and detection techniques; (3) Distributing High-dimensional quantum entanglement though aberrating media.
Four experimental studies have been completed during the 24 months of the fellowship. These studies explored the interaction between quantum light and aberrated media by combining two cutting-edge technologies: fast adaptive optics and SPADs cameras.

A first study explores the transmission of spatially-entangled photons through optical aberrations. An experimental setup was built by combining a source of entangled photon pairs, a spatial light modulator, a thin scattering medium and an EMCCD camera for detection. Transmission of entangled photon is achieved in two steps. First, the transmission matrix of the scattering medium is measured quickly and efficiently using a classical source of light. Then, this matrix is re-used directly to control the propagation of entangled photon through the medium after replacing the classical source by a source of entangled photon pairs. Our results demonstrate the possibility to distribute partially entanglement through a scattering medium by a classical measurement of the transmission matrix.

A second study explores characterisation of entanglement between photon pairs using a fast single-photon detection technique. An experimental setup was built by combining a source of entangled photon pairs and a single-photon avalanche diode camera. Characterisation of entanglement between photon pairs at high-speed was achieved by imaging photons onto the SPAD camera in two different configurations (near-field and far-field). Our results demonstrate the possibility to certify high-dimensional entanglement at unprecedented speed, a key step in the establishment of a quantum communication protocol.

A third studies explores distribution of entanglement through a dynamic aberrated medium. An experimental setup was built by combining a source of hyper-entangled photon pairs, a spatial light modulator and a camera. I achieved distribution of entanglement through a thin dynamic scattering medium by exploiting a property of the space in which photon pairs evolve called decoherence-free subspace. Our results suggest that such a property can be used for distribution quantum entanglement and thus establishing quantum communication through dynamic aberrated media under certain conditions.

Finally, a fourth study explore the distribution of entanglement through a multimode fibre. Instead of sending photon through atmosphere, a multimode fibre has advantages such as keeping light confined and limiting losses when distances are in the order of kilometres. In term of aberrations, the mixing process performed by the fibre is similar to this happening through a turbulent atmosphere (linear scattering), but with a dynamic time much longer. Using fast spatial-light modulator and fast single-photon detector, we achieved distribution of high-dimensional entanglement through a commercial multimode fibre as part of a collaboration with researchers from Heriot-Watt University. Our results unlocked the possibility to implement a quantum communication protocol based on high-dimensional entangled state through complex media.

I have disseminated my results mainly through scientific publications, including 5 publications in peer-reviewed journals:
- H. Defienne and D. Faccio. Arbitrary spatial mode sorting in a multimode fiber. Physical Review A 101, 063830 (2020)
- B.Ndagano* H.Defienne* A.Lyons I. Strashynov, F. Villa, S. Tise and D. Faccio. Imaging entanglement correlations with a single-photon avalanche diode camera. npj Quantum information 6, 94 (2020); (*: equal contribution)
- H.Defienne* J.Zhao* E. Charbon and D. Faccio. Full-field quantum imaging with a single-photon avalanche diode camera. Physical Review A 103.4: 042608 (2021)
- H.Defienne B.Ndagano A.Lyons and D. Faccio. Polarization entanglement-enabled quantum holography. Nature Physics 17.5: 591-597 (2021)
- N. Valencia, S. Goel, W. McCutcheon, H. Defienne and M. Malik. Unscrambling entanglement though a complex medium. Nature Physics 16,1113-1116 (2020)
And 1 publication in a popular science journal: H.Defienne and D. Faccio. Towards real-time quantum imaging with single photon avalanche diode cameras. Photoniques 107: 36-39 (2021). In addition, I presented these results in 7 conferences through oral and poster presentations, including: ‘Quizco 2019’ , ‘Sensing with quantum light 2020’, ‘IQFA 2019’ , ‘COSI 2020’ , ‘Virtual Symposium on quantum technologies organised by the company Andor ‘ and two ‘Quantic meeting’ (via the Hub Quantic) in Bristol (UK) and in Glasgow (UK).
ADOQ has significant impacts in the domain of communications. More specifically, it offers new outcomes in the field of optical communications by exploring further the question: How can we established an ultra-secured optical communication protocol through atmosphere or optical fibres? Proposing solutions to this practical problem is particularly relevant in a fully interconnected world in which ensuring the security and privacy of transmitted data is central. In this respect, quantum technology is a very promising solution for creating ultra-secure communication networks and are in full expansion. ADOQ explored this solution in a very practical way by studying how quantum information can be transmitted through communication channels suffering from optical aberrations. Our results demonstrated for the first time that this was possible using wavefront shaping and adaptive optics methods, paving the way for the implementation of quantum communications in real-world conditions.
Distribution of entanglement through a complex communication channel by wavefront shaping