The quantum world defies common sense at every turn. Shaped over hundreds of thousands of years by biological evolution, our modern human brain struggles to understand things outside of our familiar naturalistic context. It is easy to understand a predator chasing prey across a grassy plain; understanding most anything that happens at subatomic scales can take years of intense scholarship and gnarly piles of math. It’s no surprise, then, that every year physicists deliver mind-boggling new insights and discoveries from the deep foundations of reality, far beyond the frontiers of our perception. Right here, American scientist highlights some of our 2022 favorites.
The universe is a little unreal
This year’s Nobel Prize in Physics was awarded to researchers who have spent decades proving that the universe isn’t locally real – a feat that, to quote comedian Douglas Adams, “set a lot of people very angry and was widely seen as a bad decision”. “Local” here means that any object – an apple, for example – can only be influenced by its immediate environment, not by events on the other side of the universe. “Real” means that every object has definite properties, regardless of how it is observed – no amount of squinting will turn an apple from red to green. Except that careful and repeated experimentation with entangled particles has shown conclusively that such seemingly reasonable restrictions do not always apply to the quantum realm, the most fundamental level of reality we can measure. If you’re not sure what exactly the disappearance of local realism means for life, the universe, and, well, everythingDon’t worry: you’re not alone: physicists are also perplexed.
Lasers create time crystals and portals to higher dimensions
Though they sound like plot elements from a cult classic sci-fi movie, two independent papers published earlier this year describe non-fictional ways to harness light at the quantum frontier. In one study, researchers reported the first-ever construction of laser-based time crystals, quantum systems that exhibit crystal periodic structures not in space but in time. In the other, a team detailed how precise patterns of laser pulses caused chains of ions to behave like a novel phase of matter occupying two time dimensions. The first study could lead to cheap, robust microchips for making time crystals outside of labs. The latter proposes a method to improve the performance of quantum computers. For most of us, though, these studies can go a long way toward looking smart at cocktail parties.
Quantum telepathy conquers unbeatable game
The Mermin-Peres Magic Square Game (MPMS) is the kind of competition you can only win by not playing. This gloomy relative of Sudoku involves two participants taking turns adding the value +1 or -1 to the cells of a three-by-three grid to collaboratively fulfill a victory condition. Although players must coordinate their actions to succeed, they are not allowed to communicate. And even if each correctly guesses the other’s move, the pair can still only win eight of the game’s nine tricks, unless they play a quantum version. If qubits (which can swap values between +1 and -1) are used to fill each cell, two players can, in theory, complete a perfect run avoiding conflicting moves for all nine rounds. In practice, however, the chances of guessing every move correctly are extremely slim. Yet by carefully exploiting the entanglement between qubits, each turn players can guess each other’s actions without actually communicating – a vexing technique known as quantum pseudotelepathy. In July, researchers published a paper reporting their successful real-world demonstration of this strategy to achieve flawless performance. Nor is it all fun and games: such work probes the fundamental limits of how information can be shared between entangled particles.
Testing the Intestable Unruh Effect
According to the principles of quantum field theory – an uneasy union between Einstein’s special theory of relativity and quantum mechanics used to model the behavior of subatomic particles – empty space is not actually empty. Instead, what we perceive as emptiness is filled with overlapping energy fields. Fluctuations in these fields can produce photons, electrons and other particles essentially out of “nothing”. Of the various bizarre phenomena expected to arise from such curious circumstances, the strangest might be the Unruh Effect, a hot shroud of ghostly particles summoned by any accelerating object in a vacuum. Named after theorist Bill Unruh, who described it in 1976, this effect is so subtle that it has yet to be observed. That may soon change if a tabletop experiment proposed in April is successfully completed. The experiment involves accelerating a single electron through an intense and carefully configured electromagnetic field. This configuration should lower the acceleration threshold for the Unruh effect to manifest visibly, increasing the chances of catching a glimpse of its elusive quantum glow, according to the authors.
A new angle on quantum spin
Not all of the counterintuitive quirks of quantum physics have to do with natural causes. Some are arguably more self-inflicted, resulting from researchers’ questionable choices in how they name and describe certain phenomena. Consider the case of quantum “spin”, the label affixed to the intrinsic angular momentum of elementary particles. The term is confusing because such particles can not physically rotate – if they were simply whirling subatomic gyroscopes, their rotation would be incredibly fast, far exceeding the speed of light. But quantum spin is crucial in accounting for the observed behavior of electrons and other particles: although they may not physically spin, the particles clearly do Something. What exactly this “something” is can be captured most accurately by mathematical equations, but its causal physical basis remains murky. A relatively new (and highly controversial) hypothesis appeals to quantum field theory for an explanation. In this proposal, particles (which result from fluctuations in quantum fields) derive their spin (angular momentum) from their original fields, much like a turbine driven by the wind. “If this is where the angular moment lies”, American scientistThe article on the idea noted that “the problem of an electron spinning faster than the speed of light disappears; the region of the field carrying an electron’s spin is much larger than the so-called point electron itself.
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