PRX: Loss and Noise-robust Quantum Steering

Our resident artist’s depiction of high-dimensional entanglement that is simultaneously robust to noise and loss (Credit: Vatshal Srivastav)

We are very excited to share our new publication, “Quick Quantum Steering: Overcoming Loss and Noise with Qudits,” which was published today in the leading APS journal Physical Review X!

Quantum steering is a phenomenon in quantum physics that occurs when two parties, say Joe and Rishi, share an entangled state—a state of two particles that is strongly correlated, no matter how far apart the particles are. By making specific measurements on his particle in London, Rishi can then “steer” the quantum state of Joe’s particle in Washington to behave a certain way. The physicist Erwin Schrodinger called this steering of the wavefunction “magic,” as it forces Joe to believe that Rishi can influence his particle from a distance (it is important to note that Rishi cannot transfer any information instantaneously to Joe in this manner).

However, this form of entanglement is also easily destroyed in a realistic environment that includes loss and noise, which limits its use in applied scenarios such as quantum communication. In this work, we develop a new theoretical test of quantum steering that not only works under massive amounts of loss and noise, but can also be performed very quickly. We were able to demonstrate it in the lab by harnessing the inherent high-dimensional nature of light—photons entangled in their spatial structure.

Our results are significant for the development of practical quantum communication technologies. Even the best optical fibres in the world suffer from a certain amount of loss, which puts strict limitations on the distance over which entanglement-based quantum communication can be carried out. Having a loss-tolerant method for steering entanglement opens a pathway towards practical quantum communication networks with the ultimate form of security. The simultaneous ability to withstand noise could also allow such networks to operate over our existing telecommunications links, which would carry noisy classical traffic at the same time.

This work received media coverage in 145 news outlets (a new BBQLab record!) and was done in collaboration with our close collaborators Prof. Nicolas Brunner, Dr. Roope Uola, and Sebastien Designolle at the University of Geneva, Switzerland. See selected coverage of our work in APS Physics Magazine, UKRI News, The Independent, London Evening Standard, and The Daily Mail.

HW Press release: Quantum leap for Heriot-Watt research into unhackable communications networks
Journal reference: V. Srivastav et al, “Quick Quantum Steering: Overcoming Loss and Noise with Qudits,” Physical Review X 12, 041023 (2022), DOI: 10.1103/PhysRevX.12.041023.

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