the physicist persuaded Just as werewolves turn into humans and humans turn into werewolves, light particles undergo opposite transformations at the same time. In carefully designed circuits, photons behave as if time were flowing in a quantum combination of forward and backward directions.
“For the first time ever, it’s like having a machine that can travel in both directions,” said Sonya Franke-Arnold, a quantum physicist at the University of Glasgow in Scotland who was not involved in the study. rice field.
Unfortunately for science fiction fans, these devices have nothing in common with the 1982 DeLorean. Through experiments conducted by two independent teams in China and Austria, the laboratory clock kept ticking steadily. Also for photons, researchers debate whether the reversal of the arrow of time is real or simulated.
Either way, the puzzling phenomenon could lead to new kinds of quantum technology.
Giulia Rubino, a researcher at the University of Bristol, said: “You can imagine circuits in which information flows in both directions.
anything at once
Physicists first noticed ten years ago that the strange rules of quantum mechanics upend the common sense concept of time.
The essence of quantum strangeness is: When looking for particles, they are always found at a single point-like location. But before being measured, particles behave like waves. It has a “wave function” that spreads and spreads over multiple routes. In this undetermined state, the particles exist in a quantum blend of possible positions known as superposition.
In a paper published in 2013, Giulio Chiribella, now a physicist at the University of Hong Kong, and his co-authors propose a circuit that goes beyond the superposition of positions in space and puts events into a superposition of temporal order. bottom. Four years later, Rubino and her colleagues demonstrated this idea directly experimentally. They sent photons along the superposition of her two paths. One is the path through event A and then through event B, and the other is the path through B and then through A. called indeterminate causation.
Not content with merely disrupting the order of events in the flow of time, Chilibela and his colleague Zixuan Liu next took aim at the direction of time itself: the arrow. They sought a quantum device in which time enters a superposition that flows from the past to the future and vice versa: the infinite arrow of time.
To do this, Chiribella and Liu realized they needed a system that could produce opposite changes, like a metronome with an arm swinging from side to side. They envisioned placing such systems on top of each other, much like a musician flicking a quantum metronome left and right simultaneously. They described a scheme for setting up such a system in 2020.
Optical magicians began creating arrows of time that would soon face off in the laboratory. Two teams declared success last fall.
two timing game
Chiribella and Liu have come up with a game that only Quantum 2 timers are good at. To play the game with light, you need to shoot photons from two crystal gadgets, A and B. Passing through a gadget rotates the photon’s polarization by an amount depending on the gadget’s settings. Passing backwards through the gadget rotates the polarization in the opposite direction.
Before each round of the game, the referee secretly configures the gadget in one of two ways: The path forward through A and then backward through B is the path of the photon Shift the wavefunction relative to the time-reversal path (going backwards through A and then forwarding through B) or not. Players need to understand which one the referee chose. After the player arranges gadgets and other optical elements to their liking, sending photons through the maze, perhaps using a half-silver mirror, he splits them into two superimposed paths. Photons reach his one of two detectors. If the player has set up the maze in a clever enough way, clicking a detector with photons will reveal the referee’s choice.
