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!

PRL: Genuine High-Dimensional Quantum Steering

Theory and experiment coming together to demonstrate genuine high-dimensional quantum steering.

Our new paper “Genuine High-Dimensional Quantum Steering” has been published in Physical Review Letters. Collaborating along with the Quantum Information Theory Group at the University of Geneva, we formulated simple two-setting steering inequalities, the violation of which certifies a lower bound on the dimension of entanglement in a one-sided device-independent setting.

We experimentally certified 15-dimensional steering in dimension d = 31. It is the highest dimension of entanglement ever certified in a one-sided device-independent setting, which unlocks the potential of high-dimensional entanglement in several applications such as semi-device-independent quantum information protocols. More generally, this represents an important step towards the realization of noise-robust, high-capacity quantum networks in the near future.

arXiv: Entangled ripples and twists!

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

In a recent preprint on arXiv, 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.

Check out the preprint here: https://arxiv.org/abs/2104.04506

npj Quantum Info: Flexible semi-device-independent randomness

A Europe-wide collaboration: With colleagues in Czech Republic, Slovakia, Austria, Poland and Spain, theory and experiment came together for the development of a quantum random number generation framework that can be applied in a wide range of physical scenarios.

Our new paper “Semi-device independent random number generation with flexible assumptions” has been published in npj Quantum Information. Working along with theorists all over Europe, we formulated a framework for semi-device-independent quantum random number generation, and demonstrated the protocol with an experiment in the BBQ Lab. Our approach works with flexible assumptions and different levels of trust, allowing it to be implemented over a large number of practical situations.

This work was the result of an international collaboration that involved people in 6 different countries. Even though some of the co-authors haven’t even met in person, we developed theoretical methods and showed their experimental realisation. This is the power of science: joining people together, even during these difficult times!