According to a news release from Louisiana State University, LSU researcher Mark Wilde has demonstrated the possibility of cloning quantum information from the past.

Some theorists have used the Grandfather paradox to suggest that it is actually beyond the bounds of possibility to alter the past. In the Grandfather paradox, a time traveler is unable to kill his grandfather back in time, because he himself would never be born, and as a consequence would never be able to travel through time to kill his grandfather.

“The question is, how would you have existed in the first place to go back in time and kill your grandfather?” Wilde asked.

David Deutsch, a physicist at Oxford, solved the Grandfather paradox suggesting that you could alter the past as long as you did so in a self-consistent manner.

“Meaning that, if you kill your grandfather, you do it with only probability one-half,” Wilde explained. “Then, he’s dead with probability one-half, and you are not born with probability one-half, but the opposite is a fair chance. You could have existed with probability one-half to go back and kill your grandfather.”

There are other problems associated with time travel. For example, there is the no-cloning theorem. This theorem, which is linked to the fact that one cannot copy quantum data at will, is a result of Heisenberg’s famous Uncertainty Principle, by which one can determine either the position of a particle or its momentum, but not both with unlimited precision. Thus, it is beyond the bounds of possibility to have a subatomic Xerox-machine that would take one particle and produce two particles with the same position and momentum — because then you would know too much about both particles simultaneously.

“We can always look at a paper, and then copy the words on it. That’s what we call copying classical data,” Wilde noted. “But you can’t arbitrarily copy quantum data, unless it takes the special form of classical data. This no-cloning theorem is a fundamental part of quantum mechanics – it helps us reason how to process quantum data. If you can’t copy data, then you have to think of everything in a very different way.”

However, Deutsch implied in a paper that it should be possible to violate the basic no-cloning theorem of quantum mechanics. The new method allows for a particle (or time traveler) to make multiple loops back in time.

“That is, at certain locations in spacetime, there are wormholes such that, if you jump in, you’ll emerge at some point in the past,” Wilde posited. “To the best of our knowledge, these time loops are not ruled out by the laws of physics. But there are strange consequences for quantum information processing if their behavior is dictated by Deutsch’s model.”

A single looping path back in time, acting according to Deutsch’s model, for instance, would have to allow for a particle entering the loop to remain the same each time it passed through a particular point in time.

“In some sense, this already allows for copying of the particle’s data at many different points in space,” Wilde explained, “because you are sending the particle back many times. It’s like you have multiple versions of the particle available at the same time. You can then attempt to read out more copies of the particle, but the thing is, if you try to do so as the particle loops back in time, then you change the past.”

In order to be consist with Deutsch’s model, Wilde had to conceive a solution that would allow for a looping curve back in time, as well as copying of quantum data based on a time travelling particle, without disturbing the past.

“That was the major breakthrough, to figure out what could happen at the beginning of this time loop to enable us to effectively read out many copies of the data without disturbing the past,” Wilde posited. “It just worked.”

However, the new method may actually point to complications with Deutsch’s original closed timelike curve model.

“If quantum mechanics gets modified in such a way that we’ve never observed should happen, it may be evidence that we should question Deutsch’s model,” Wilde noted. “We really believe that quantum mechanics is true, at this point. And most people believe in a principle called Unitarity in quantum mechanics. But with our new model, we’ve shown that you can essentially violate something that is a direct consequence of Unitarity. To me, this is an indication that something weird is going on with Deutsch’s model. However, there might be some way of modifying the model in such a way that we don’t violate the no-cloning theorem.”

The results of being able to copy quantum data from the past are significant. Systems for secure Internet communications, for instance, will probably soon depend on quantum security protocols that could be “hacked” if Wilde’s looping time travel methods were accurate.

“If an adversary, if a malicious person, were to have access to these time loops, then they could break the security of quantum key distribution,” Wilde explained. “That’s one way of interpreting it. But it’s a very strong practical implication because the big push of quantum communication is this secure way of communicating. We believe that this is the strongest form of encryption that is out there because it’s based on physical principles.”

Physicists and computer scientists are working on securing critical and sensitive communications utilizing the principles of quantum mechanics. This encryption would be unbreakable, unless hackers had access to Wilde’s looping closed timelike curves.

“This ability to copy quantum information freely would turn quantum theory into an effectively classical theory in which, for example, classical data thought to be secured by quantum cryptography would no longer be safe,” Wilde said. “It seems like there should be a revision to Deutsch’s model which would simultaneously resolve the various time travel paradoxes but not lead to such striking consequences for quantum information processing. However, no one yet has offered a model that meets these two requirements. This is the subject of open research.”

The study’s findings are described in greater detail in the journal Physical Review Letters.