A group of researchers led by Andreas Wallraff, Professor of Solid State Physics at ETH Zurich, has performed a loophole-free Bell test to disprove the concept of “local causality” formulated by Albert Einstein in response to quantum mechanics. By showing that quantum mechanical objects that are far apart can be much more strongly correlated with each other than is possible in conventional systems, the researchers have provided further confirmation for quantum mechanics. What’s special about this experiment is that the researchers were able for the first time to perform it using superconducting circuits, which are considered to be promising candidates for building powerful quantum computers.
Wallraff’s group can now confirm these results with a novel experiment. The work by the ETH researchers published in the renowned scientific journal Nature shows that research on this topic is not concluded, despite the initial confirmation seven years ago. There are several reasons for this. For one thing, the ETH researchers’ experiment confirms that superconducting circuits operate according to the laws of quantum mechanics too, even though they are much bigger than microscopic quantum objects such as photons or ions. The several hundred micrometre-sized electronic circuits made of superconducting materials and operated at microwave frequencies are referred to as macroscopic quantum objects.
For another thing, Bell tests also have a practical significance. “Modified Bell tests can be used in cryptography, for example, to demonstrate that information is actually transmitted in encrypted form,” explains Simon Storz, a doctoral student in Wallraff’s group. “With our approach, we can prove much more efficiently than is possible in other experimental setups that Bell’s inequality is violated. That makes it particularly interesting for practical applications.”
