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Demonstration of Quantum Supremacy in A Photonic Device

Periodic Reporting for period 1 - QSUP (Demonstration of Quantum Supremacy in A Photonic Device)

Reporting period: 2017-03-01 to 2019-02-28

The overarching objective of this project was to demonstrate quantum supremacy using a photonic device. Our original intention was to focus on a time-bin approach based on a cavity loop architecture. However, a feasibility study proved this approach to be unfeasible and we adopted a spatially multiplex approach instead. We achieved a four photon source capability and are looking towards implementation of a 8 photon state in the near future.

The demonstration of quantum supremacy will be an important milestone in the history of quantum computers. It will provide great motivation for the many researchers who are aiming to build full scale quantum computers, and it will also ensure the public at large that their money is being spent on areas that will enable computation beyond what is possible using classical physics.
1.2.1 Work Package 1: Cavity loop architecture
A feasibility study on the cavity loop architecture gave results that were not conducive to building the system in full. However, the study allowed us to focus on an alternative approach to building a multi-photon source based on the ideas around the cavity loop architecture. The approach will allow us to translate from a 4 photon source to a 8 photon source without the need for additional electro-optic modulators.
1.2.2 Work package 2: Source engineering
We have build a room temperature setup for the testing of fibre taper coupling based on multi-axis precision alignment techniques. The fibre tapering will be paramount in the efficient coupling of single photons from chip-to-fibre.
We also developed an architecture for the coupling of two-photon entangled states from chip-to-fibre based on maintaining polarisation coherence of the entangled state. We realised that biexciton decay will naturally translate from polarisation entanglement to path, and converting back to polarisation entanglement is necessary for the ease of state manipulation. This realisation lead to the development of an interferometric technique for the coupling of entangled state from chip-to-fibre.
1.2.3 Work package 3: Implementation of BosonSampling
As the project was terminated before its completion, the implementation of BosonSampling is an outstanding goal. However, work is continuing to convert the four photon multiplex source to a eight photon system with the introduction of a cavity loop scheme. This will bring a photonic demonstration of boson sampling near 10 photons closer to realisation.
We have built a fully functional four photon source based on active temporal multiplexing of quantum emission from a quantum dot source. The source has been characterised using a range of quantum optics measurement techniques and improvements are being made accordingly.
We investigated the generation of entangled states of light by means of biexciton decay from IIIV semiconductor quantum dots coupled to photonic nanostructures. The generation of non-classical states of light is of paramount importance for the demonstration of quantum supremacy using a photonic device.