How Time Has Turned (and What It Hasn’t) Quantum Physicists

Physicists have convinced The particles of light go through opposite transformations simultaneously, such as the transformation of a human into a werewolf where a wolf turns into a human. In carefully designed circuits, photons act as if time flows in a quantum mixture of forwards and backwards.

“For the first time ever, we kind of have a time-travel machine that goes both ways,” he said. Sonya Frank Arnolda quantum physicist at the University of Glasgow in Scotland who was not involved in the research.

Unfortunately for sci-fi fans, the hardware has nothing in common with the 1982 DeLorean. Throughout the experiments, which were conducted by two independent teams in China and Austria, the lab hours kept ticking steadily forward. Only the photons flowing through the circuit suffer from time cheats. Even for photons, researchers debate whether flipping the arrow of time is real or a simulation.

Either way, the puzzling phenomenon could lead to new kinds of quantum technology.

“You can visualize circles in which your information can flow in both directions,” he said. Julia RubinoResearcher at the University of Bristol.

anything at any time in one go

Physicists first realized a decade ago that the strange rules of quantum mechanics were overturning logical notions of time.

The gist of quantum weirdness is this: When you look for a particle, you will always spot it in one point-like location. But before it can be measured, the particle behaves like a wave. It has a “wave function” that propagates and ripples through multiple paths. In this indeterminate state, the particle exists in a quantum jumble of possible sites known as a overlap.

in paper published in 2013, Julio Chiribella, a physicist now working at the University of Hong Kong, the co-authors proposed a circuit that would put events into a superposition of temporal orders, bypassing the step of superimposing locations in space. Four years later, Rubino and her colleagues directly empirically The idea. They sent a photon through a superposition of two paths: one where event A experienced event B then event B, and the other where B experienced then A. In a sense, each event seemed to cause the other, a phenomenon that came to be called Unspecified causation.

Not content with just fiddling with the order of events as time marched onward, Chiribella and his colleague Zexuan Liu aimed for the direction of march, or arrow, for time itself. They sought a quantum device in which time enters into a superposition flowing from the past into the future and back—an indefinite arrow of time.

To do this, Chiribella and Liu realized they needed a system that could undergo opposite changes, such as a metronome that could swing its arm left or right. They imagined putting such a system in a superposition, similar to a musician moving a quantum accelerator simultaneously left and right. they Scheme description To establish such a system in 2020.

The optics wizards immediately began building dueling arrows for time in the lab. Last fall, two teams reported success.

Two-time game

Chiribella and Liu create a game that only a two-quantum timer can beat. Playing the game with light involves shooting photons through two crystal tools, A and B. Passing forward through a tool rotates the photon’s polarization by an amount that depends on the device’s settings. Passing backwards through the instrument rotates the polarization in exactly the opposite direction.

Before each round of the game, the referee secretly adjusts the instruments in one of two ways: the path forward through A, then backward through B, will either transform the photon’s wave function relative to the time-reversed path (backward through A, then forward through B), or it will not do it. The player must know the choice made by the referee. After the player arranges the tools and other visual elements however they want, they send a photon through the maze, possibly splitting it into a two-path superposition using a half-silver mirror. The photon ends up in one of two detectors. If the player sets up their maze in a smart enough way, the flick of the detector containing the photon will reveal the judge’s choice.