arXiv: Programming quantum circuits in a complex medium

Experimental setup and results for a five-dimensional discrete Fourier gate

In a recent paper on the arXiv, we show how high-dimensional quantum optical circuits can be programmed inside a commercial multi-mode fibre through the use of inverse-design techniques. Using these methods, we were able to demonstrate the transport, manipulation, and measurement of high-dimensional photonic entanglement by using the transmission channel itself!

We also present numerical results on the scalability of our approach, showing how the resource of a high-dimensional mode-mixer allows perfect and lossless circuits to be realised in principle. By harnessing something as simple as light scattering inside a multi-mode fibre, our work serves as a new, yet practical alternative to integrated photonic platforms.

This work was done in collaboration with our QuantERA project partners Claudio Conti (La Sapienza, Rome) and Pepijn Pinkse (Uni Twente, Netherlands). We look forward to many more exciting collaborations in the future!

Journal of Optics : Entangled ripples and twists!

Artist’s depiction of entangled Laguerre-Gaussian modes in 43 dimensions

In a recent article published in IOPscience Journal of Optics (Emerging Leaders Special Issue) we demonstrate the full-field entanglement of radial (ripples) and azimuthal (twists) Laguerre-Gaussian modes of light. While the azimuthal degree-of-freedom has attracted a lot of interest over the past two decades, the radial degree-of-freedom presents some unique challenges to experimentalists.

By carefully tuning our optical system parameters and adopting some recently developed techniques for precise spatial mode measurement, we generated and measured entanglement in a 43-dimensional radial and azimuthal LG mode space. We also studied two-photon quantum correlations between 9 LG mode groups, which are of significant interest in the field of fibre optics.

Science Advances: Quantum Conference Key Agreement

Most of us have spent an inordinate amount of time over the past year in online conference calls, which are sure to become a regular feature in our lives. Recent events such as the ransomware attacks on US energy firms have highlighted more than ever the need for information security in such electronic forms of communication.

In a collaboration with the Mostly Quantum Lab at Heriot-Watt, we demonstrated the first quantum-secure conference call between four users. Using a multi-photon entangled GHZ state distributed over fiber-optic cables with a combined length of 50km, we built a secure key between four parties and used it to share an image of the Cheshire cat. It won’t be long before the first quantum-secure Zoom call!

See the original publication in Science Advances or media coverage in the journal Nature and Physics World magazine for more details.

Congrats Euan and Dylan!

We’d like to congratulate Euan Mackay and Dylan Danese, who recently finished their senior undergraduate projects in our research group.

Euan is going on to do his MSc in Theoretical Physics at the University of Edinburgh, while Dylan is continuing onto the integrated MSc in Physics at Heriot-Watt.

Best of luck to you both!

Quantum Journal: Pixel Entanglement

Twas the night before Christmas, when all through the lab,
Not a creature was stirring, not even a browser tab,
The laser was focused on the crystal with care,
In the hope that pixel entanglement soon would be there!

In our recent paper published in the journal Quantum, we demonstrate high-dimensional entanglement of “pixels” of light with a record dimensionality, quality, and measurement speed! We achieved entangled state fidelities of up to 94.4% in a 19-dimensional state-space, entanglement in up to 55 local dimensions, and an entanglement-of-formation of up to 4 ebits. We were also able to improve upon the time taken by previous techniques for measuring entanglement by more than two orders of magnitude! This work was done in collaboration with our friends in Vienna and the Czech Republic.