Full-field Coherent Quantum Imaging

Lead Research Organisation: University of Strathclyde
Department Name: Physics

Abstract

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Description This project was a collaboration between the Strathclyde group and the groups of Profs. Padgett and Buller. This was very much a joint experimental and theoretical project to which we contribued the theoretical work. This summary emphasises these theoretical contributions.

Our principal objective was to address the controversial question of whether or not ghost imaging is a quantum phenomenon or has a classical explanation. It is now clear that ghost imaging, although it does possess a classical analogue, is indeed a quantum phenomenon or, to be more precise, it is a phenomenon in which quantum effects can be manifest. To demonstrate this we designed ghost imaging experiments in which non-local phenomena were evident. This included, in particular, an experiment in which we were able to demonstrate quantum non-locality through the violation of a Bell inequality [Jack et al, Phys. Rev. Lett. 103, 08083602 (2009)].

In order to pursue our objective of gaining insight into the nature of quantum imaging we carried out an in-depth investigation of the entanglement properties of our down-converted photons. This included, in particular, using angular position/orbital angular momentum entanglement to study two-photon interference by passing our photons through apertures in the form of double angular slits [Jha et al, Phys. Rev. Lett. 104, 010501 (2010).]. In this way we were able to investigate and quantify the entanglement of effective qubits. As a demonstration of our ability to manipulate the quantum state we performed the first realisation of optical entanglement localized in three spatial dimensions [Romero et al, Phys. Rev. Lett. 106, 100407 (2011)].

For us, the highlight of our collaboration was the theoretical formulation and experimental confirmation of an Einstein-Podolsky-Rosen paradox for angle and angular momentum [Leach et al, Science 329, 662 (2010)]. This included deriving testable inequalities based on measured uncertainties and on information entropy, the violation of which constitutes the EPR paradox. The resulting correlations were found to violate the effective uncertainty principle by an order of magnitude, making our experiment the strongest realization on record.

As we enhance the precision of our experiments, the long-standing issue of how to separate the spin and orbital components of the total angular momentum becomes even more pressing. A major step in this direction was the realization that there exists a natural helicity in conventional electromagnetic theory [Barnett et al, Phys. Rev. A 86, 013845 (2012)]. This quantity is the analogue of the helicities appearing in particle physics, in plasmas and in fluid mechanics.

In total the project led to 23 journal papers. Including the ones mentioned above, there were 1 paper in Science and 5 in Physical Review Letters. These 23 included further theoretical and experimental studies of entanglement and a review article on orbital angular momentum [Yao and Padgett, Adv. Opt. Photonics 3, 161 (2011)].

Finally, I should mention the paper "Resolution of the Abraham-Minkowski Dilemma" Barnett; Phys. Rev. Lett. 104, 070401 (2010). In this paper I resolve the century-long dilemma of the correct form of optical momentum in a medium. This work, although not listed in the original objectives, was the completion of work initiated under an earlier EPSRC-funded proposal.
Exploitation Route It lead, in some ways, to the QuantIC Quantum Imaging Hub and to the associated links with the industrial sector.
Sectors Digital/Communication/Information Technologies (including Software),Security and Diplomacy
 
Description It led, in some sense, to the setting up of the QuantIC Quantum Imaging Hub, with its associated industrial contacts.
First Year Of Impact 2014
Sector Aerospace, Defence and Marine
Impact Types Economic
 
Description EPSRC
Amount £2,086,230 (GBP)
Funding ID EP/I012451/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 12/2010 
End 11/2014
 
Description Joint research with HERIOT-WATT UNIVERSITY 
Organisation Heriot-Watt University
Country United Kingdom 
Sector Academic/University 
PI Contribution University of Strathclyde researchers worked on this project with researchers from HERIOT-WATT UNIVERSITY
Start Year 2008