The evolution of backward quantum processes on a quantum computer to damage information in the simulated past causes little change when it is returned to the “present”.
Using a quantum computer to simulate time travel, researchers have shown that there is no “butterfly effect” in the quantum realm. In research, information – qubits or quantum bits – “time travel” in the simulated past. One of these is therefore seriously damaged, like stepping on a butterfly, speaking metaphorically. Surprisingly, when all qubits return to the “present”
“On a quantum computer, there is no problem simulating the opposite evolution over time or simulating running a process backwards in the past,” said Nikolai Sinitsyn, theoretical physicist at the Los Alamos National Laboratory and co-author of the study. with Bin Yan, a post doc at the Center for Nonlinear Studies, also in Los Alamos. “So we can actually see what happens in a complex quantum world if we travel back in time, add little damage and return. We discovered that our world survives, which means there is no butterfly effect in quantum mechanics. “
In Ray Bradbury’s 1952 science fiction story, “A Sound of Thunder”, a character used a time machine to travel deep into the past, where he stepped on a butterfly. On his return to the present day, he found a different world. The history of the “butterfly effect” is often attributed to this story, which refers to the extreme sensitivity of a complex and dynamic system to its initial conditions. In such a system, at the beginning, small factors continue to strongly influence the evolution of the entire system.
Instead, Yan and Sinitsyn found that simulating a throwback to cause small local damage in a quantum system only leads to insignificant small local damage in the present.
This effect has potential applications in hardware that hides information and in testing quantum information devices. Information can be hidden from a computer by converting the initial state into a heavily entangled one.
“We have found that even if an intruder takes measurements that are harmful to the state in the heavily entangled state, we can still easily retrieve useful information because this damage is not amplified by a decoding process,” said Yan. “This justifies discussions about creating quantum hardware that will be used to hide information.”
“On a quantum computer, there is no problem simulating the opposite evolution over time or simulating running a process backwards in the past.” – Nikolai Sinitsyn
This new discovery could also be used to test whether a quantum processor works, in effect, according to quantum principles. Since the new no-butterfly effect is purely quantum, if a processor runs the Yan and Sinitsyn system and shows this effect, then it must be a quantum processor.
To test the butterfly effect in quantum systems, Yan and Sinitsyn used the theory and simulations with the IBM-Q quantum processor to show how a circuit could evolve a complex system by applying quantum gates, with cause and effect back and forth.
Soon, a quantum time machine simulator.
In the team’s experiment, Alice, a preferred stand-in agent used for quantum thought experiments, prepares one of her qubits in the present tense and runs it backwards through the quantum computer. In the deep past, an intruder – Bob, another favorite substitute – measures Alice’s qubit. This action disturbs the qubit and destroys all its quantum correlations with the rest of the world. Subsequently, the system runs up to the present moment.
According to Ray Bradbury, Bob’s small damage to the state and all those correlations in the past should be rapidly amplified during the complex evolution of forward-in-time. So Alice shouldn’t be able to retrieve her information eventually.
But that’s not what happened. Yan and Sinitsyn found that most of the information currently local was hidden in the deep past in the form of essentially quantum correlations that could not be damaged by minor tampering. They showed that the information returns to Alice’s qubit without much damage despite Bob’s interference. Counterintuitively, for deeper journeys into the past and for larger “worlds”, Alice’s final information returns it even less damaged.
“We found that the notion of chaos in classical physics and quantum mechanics has to be understood differently,” said Sinitsyn.
Reference: “Recovery of Damaged Information and Correlators Ordered Out of Time” by Bin Yan and Nikolai A. Sinitsyn, 24 July 2020, Physical review letters.
DOI: 10.1103 / PhysRevLett.125.040605
This work was supported by the United States Department of Energy.