Researchers Proved the “Quantum Time Flip” Can Go Backward
Input/output is the term for time before and after a particular physical moment or scenario, and in certain quantum scenarios, those ‘befores’ and ‘afters’ can be interchangeable.
Researchers have recently developed a brand-new way to verify if the input/output ports of a quantum computer do in fact express this property—one that involves a “quantum time flip.”
The team is hopeful that this particular quantum property could someday lead to the development of a unified theory of quantum gravity.
It’s been 35 years since Cher first wanted to turn back time, but it turns out that quantum mechanics might have allowed for this wild reversal all along. In new research, scientists from China and Hong Kong show that—in certain quantum systems—the time variable can be reversed by creating a double superposition (one each in opposite directions) and still bear out valid results. What results from this little bit of quantum trickery is both an input and output that are considered indefinite, meaning that either one can be the input or the output. Basically, the after can go before the before. The peer-reviewed research appears in the journal Physical Review Letters.
In our day-to-day lives, we perceive time as marching inexorably forward, and that means many processes aren’t easily reversible. You can’t put the toothpaste back in the tube, so to speak—it’s a lot more difficult to reset an object back to its original state than it is to change it in the first place. This is called time’s arrow, and we believe it’s partly caused by the fact that our universe has been ever-expanding since the Big Bang.
Measurements and calculations of the physics of our universe must account for how space itself is expanding, and you can’t run the same calculations without the things affected by time—let alone with those factors reversed. But quantum mechanics is underpinned by the notion that these factors can be reversed on the nano scale, known as the CPT theorem—Change, Parity, and Time reversal symmetry.
“The theorem,” the researchers explain in the paper, “implies that, at the fundamental level, the roles of past and future are symmetric: while we normally treat systems at earlier times as the inputs and systems at later times as the outputs, the dynamical laws of quantum mechanics are indifferent to the direction of time.”
In this case, input and output are also terms that relate to quantum machines like computers. Inputs include things like your keyboard, mouse, and microphone, while outputs include your monitor, printer, and speakers. In a quantum machine, both the inputs and outputs are instead entangled qubits (quantum bits), or other particles in superposition. They’re microscopic blips that act in coordination to represent information, the same way binary and its associated micro-fast electrical zaps work in traditional computers.
What’s new here is not the idea of switchable input/output ports itself—the fundamentals of quantum mechanics indicated that this was possible. But the scientists behind this new paper have laid out a way to verify that everything is entangled correctly, its all in superposition, and the overall device is working with its input/output ports reversible as intended.
To do this, the scientists built a virtual model of something called a quantum time flip. This is a recently discovered theoretical device that moves light both forward and backward in time. It uses just one photon, so it will likely need to scale up in some way in order to jump into real life applications. Much like quantum computers themselves, these paradigms must be built from scratch.
The researchers conclude their paper with the idea that indefiniteness of this type, where inputs and outputs can be reversed, may be key to a unifying theory of quantum gravity for our universe. In the meantime, working through examples of these devices may help scientists codify them. “While an explicit physical model for scenarios with indefinite time direction has yet to be proposed,” the authors wrote, “the availability of a mathematical framework for their study and an experimental platform for their simulation represent valuable tools for understanding their operational implications.”
You Might Also Like
