In a paper published this week in the top international physics journal Nature Physics, the research team at the University’s Centre for Quantum Dynamics performed a series of new experiments on pairs of entangled particles, inspired by Einstein’s old idea, which he termed “spooky action at a distance”.
Entangled particles are a key resource for emerging quantum information technologies such as ultra-secure communication and ultra-fast computing.
Professor Howard Wiseman said a pair of particles could become entangled when they interacted.
“Like in a passionate romance, the individual particles lose their identity, even if they are separated into different laboratories, which are traditionally known as Alice’s lab and Bob’s lab,” Professor Wiseman said.
“But what if Alice claims to be making entangled pairs, but Bob doesn’t trust her? This is where Einstein’s idea comes in.”
What Einstein and co-workers discovered about entangled particles in 1935 is that if Alice makes a measurement on her particle, the result causes an instantaneous change in the properties of Bob’s particle, no matter how far away his lab is.
The sort of change depends on what sort of measurement Alice chooses to make, which is the spooky action Einstein described.
Associate Professor Geoff Pryde said the new paper showed that Einstein’s spooky action could be used to ensure that Alice dealt honestly with Bob.
“If Alice has the source of particle pairs in her lab, Bob would just have to trust her when she says that the particle she has sent to him is entangled with the one that she keeps,” Associate Professor Pryde said.
“However, Bob can confirm that Alice is not cheating by testing that she can affect his particle via Einstein’s effect.”
Professor Wiseman said they would be looking to apply this in quantum secret-key distribution, a commercially available technology that offered secure communication guaranteed by the laws of physics.
“Existing systems rely on the sender and receiver trusting each-others’ devices,” Professor Wiseman said.
“By developing new tests based on Einstein’s spooky action at a distance, we believe we will be able to make secure quantum communication possible even when Bob does not trust Alice.”
Tests similar to this on entangled photon pairs have been performed before, but they were based on a quantum effect discovered in 1964 (after Einstein’s death), and they were actually much stricter than necessary.
Associate Professor Pryde said the new tests gave a more accurate picture of whether Alice was cheating.
“What makes our experiment so much more powerful is that we allow Alice to use up to six different settings for her measurement device. Previous tests have only used two different settings,” he said.
The research was a collaboration between theorists – Professor Wiseman and his PhD student Steve Jones — and experimentalists – Dr Pryde and his PhD student Dylan Saunders, within Australia’s Centre for Quantum Computer Technology.