A paradox at the heart of quantum physics has been tested in an extraordinary fashion, pushing the boundaries of human intuition beyond breaking point by measuring a pulse of light in 37 dimensions.
Led by scientists from the University of Science and Technology of China, a team of researchers developed a method of testing a type of Greenberger-Horne-Zeilinger (GHZ) paradox according to strict criteria using a fiber-based photonic processor.
Their findings clarify how quantum weirdness operates on a fundamental level, potentially informing future applications in quantum technology. Not to mention reaffirming just how useless our brains are at understanding the operations manual for our Universe’s engine.
If you want to know if there is any mail inside your mailbox, you merely need to walk out and take a look. From that one, simple observation you can deduce the postal service has been and popped a belated birthday card from Aunt Judy in through the slot. Thanks Aunt Judy!
This intuitive system can be described as local realism. You can imagine a chain of events from Aunt Judy to yourself taking place, each moving through a series of connected locations from Aunt Judy’s kitchen table, to the post office, to your address.
For most things in science, local realism does a good enough job of describing how things are.
But then scientists had to come along and mess it all up with quantum physics, discovering the machine running reality operates by rules that make little sense. Arguably the most bizarre of which contradict local realism.
Accordingly, before you look inside the mailbox, the Universe has yet to settle on whether a card is inside, if a postal service has been by, or if Aunt Judy has remembered your birthday.
Physicists refer to these undecided objects and events as contexts, and their relationship to one another as entanglement. The only way to know if Aunt Judy sent a card is to look in the mailbox and check – before then, it was all a big shrug as far as reality goes.
This might all seem straightforward so far, but the GHZ paradox throws a mammoth spanner in the works by predicting outcomes to experiments that contradict localism, as if Aunt Judy’s card manifested inside your mailbox without the postal service’s assistance.
How far could this absurdity stretch? To push the paradox to breaking point, the researchers aimed to find the most extreme case of non-locality using just three contexts.
Swapping a coherent stream of photons for Aunt Judy’s card, and a system of fiber-optics and precise interference-measuring tools for a postal service and a mailbox, the researchers put their scenario through its paces, working backward from observed correlations to show that even with just three contexts, our expectations of local realism can be thrown into the bin.
To understand how this might happen, however, we need to add a few more dimensions outside of our up-and-down, back-and-forth, and side-to-side, and second-to-second. Like, another 33 dimensions.
Here, the team designed a set of relationships between the three contexts that could be solved with 37 states, each representing a different spatial dimension.
Philosophically this all poses some deep questions, like why do we only experience reality in classical terms? Do those extra dimensions have any physical meaning? And why did Aunt Judy forget your birthday?
For now, knowing just three quantum maybes is all it takes to create a GHZ-type paradox could lead to deeper explorations of reality’s foundations, while setting boundaries on what might be possible in developing faster, more robust quantum circuits.
This research was published in Science Advances.
