Physicists create algorithm to discover quantum cause-effect relations

In a paper published today, scientists at the University of Queensland have found a way to measure and understand cause and effect in the quantum world.

When we drop an egg and it cracks open the link between cause and effect is obvious. 

Not all situations are as clear-cut: establishing links for complicated networks of causal relations required inventing a new technique known as causal modelling.

However in the quantum world, these causal models fail because physical properties are not well-defined before they are measured.

The new study solved this problem by developing an algorithm that discovers complex causal networks for quantum systems.

Study author Dr Christina Giarmatzi said, “Our technique looks at the cause-and-effect relationships between the results of quantum measurements, making no assumptions of what is true before we have measured.” 

The algorithm uses data from quantum systems to identify a causal network that explains the experiment.

As co-author Dr Fabio Costa added, “A key feature is that our algorithm detects whether the cause-and-effect relations we find are solely responsible for the data that was measured, allowing us to identify hidden sources of errors in quantum devices.”

The algorithm could be used in future quantum technologies as they increase in size and complexity and contributes to foundational studies in quantum causality.

Published today in NPJ Quantum Information

Media contact: Dr Christina Giarmatzi,, +61 7 3346 7429 

Major funding support

Australian Research Council

The Australian Research Council Centre of Excellence for Engineered Quantum Systems (EQUS) acknowledges the Traditional Owners of Country throughout Australia and their continuing connection to lands, waters and communities. We pay our respects to Aboriginal and Torres Strait Islander cultures and to Elders past and present.