Demonstrating contextuality with superconducting quantum systems

An international team of researchers has produced one of the most comprehensive demonstrations of quantum contextuality to date. 

Contextuality is a quantum phenomenon that contradicts classical physics and everyday intuition.

Lead author Dr Markus Jerger, member of the Superconducting Quantum Devices Laboratory at the ARC Centre of Excellence for Engineered Quantum Systems, describes the phenomenon by painting a picture of Christmas Day.

“Imagine you and your family are gathered together to open gifts. You would be surprised if the contents of your gift were different depending on whether it is your son who is opening his present or your daughter who is opening her present at the same time as you.”

“In the same way the joint opening of different pairs of gifts affects their contents, a measurement of a quantum system affects the outcome of other measurements, even if they seem to be totally independent from each other. This is known as quantum contextuality.”

Contextuality has previously been shown in systems using trapped ions, photons and spins, but experimental loopholes remained in those experiments. This new experiment used superconducting circuits specifically to close those loopholes.

“By closing the loopholes, we demonstrated contextuality in the most convincing way without using additional assumptions and excluding explanations of the experimental results by other quantum properties.”

As contextuality is closely linked to the power of a quantum information processing, this experiment also confirms that superconducting quantum circuits are well set to build a quantum computer.

The study, titled “Contextuality without nonlocality in a superconducting quantum system”, was published in Nature Communications.