Researchers from the Moscow Institute of Physics and Technology, working with colleagues in the U.S. and Switzerland, managed to revert a quantum computer’s state by a fraction of a second. They also estimated the probability of an electron in the vacuum of interstellar space spontaneously returning to a previous state in its own timeline.
Lead author Gordey Lesovik explained, “This work is part of a broader series exploring the potential to challenge the second law of thermodynamics. That law is deeply connected to the concept of the arrow of time, which describes time’s one-way flow from past to future.”
Researchers Challenge Thermodynamics with Engineered Quantum Time Reversal
“Our first paper introduced a concept known as a local perpetual motion machine of the second kind. In December, we explored how Maxwell’s demon could be used to violate the second law. In this latest study, we approached the issue from a new angle—by artificially generating a state that moves in the opposite direction of the thermodynamic arrow of time.”
The team wanted to explore whether time could spontaneously reverse—even briefly—for a single particle. To investigate this, they focused on observing a lone electron in the emptiness of interstellar space.
Study co-author Andrey Lebedev, from MIPT and ETH Zurich, explained, “Let’s say we begin observing an electron that’s localized — meaning we have a fairly good idea of where it is in space. Quantum mechanics doesn’t allow us to pinpoint its exact position, but we can define a small area where it’s most likely located.”
“As time progresses, the electron’s state evolves according to Schrödinger’s equation. Although this equation doesn’t favor a direction in time, the electron’s position rapidly becomes more uncertain, causing its probability distribution to spread out. This increasing uncertainty mirrors the growing disorder—or entropy—in larger systems, like billiard balls scattering on a table, a hallmark of the second law of thermodynamics.”
Schrödinger’s Equation Suggests Time Reversal Is Theoretically Possible Under Rare Cosmic Conditions
Valerii Vinokur, another co-author from Argonne National Laboratory in the U.S., added, “Still, Schrödinger’s equation is reversible. That means, mathematically, if we apply a transformation known as complex conjugation, it would describe the reverse: a dispersed electron re-localizing into a small area in the same amount of time. While this doesn’t naturally occur, it’s theoretically possible through a random fluctuation in the cosmic microwave background that fills the universe.”
The team then calculated the chances of such a reverse, where a spread-out electron spontaneously regains its previous localized state. Their findings showed that even if 10 billion newly localized electrons were observed continuously for the entire 13.7-billion-year lifespan of the universe, this time-reversal would only occur once. And even then, the electron would only shift back in time by a mere ten-billionth of a second.
When applied to large-scale events—like aging or volcanoes erupting—the sheer number of particles and the much longer timescales involved make time reversal essentially impossible. That’s why we don’t witness people growing younger or ink separating from paper.
To explore this further, the researchers conducted a four-phase experiment to simulate time reversal—not with an electron, but using a quantum computer made up of two, and later three, superconducting qubits.
Stage 1: Order
The experiment begins with each qubit set to its ground state, or zero. This represents a highly ordered setup, similar to an electron confined to a small space or a neatly arranged rack of billiard balls before the game starts.
Stage 2: Degradation
Next, order breaks down. Like an electron’s position spreading out or the balls scattering on a pool table after the break, the qubit system becomes increasingly complex, forming a shifting pattern of zeros and ones. This is done by briefly running an evolution program on the quantum computer. Although a similar breakdown could naturally occur from environmental interactions, using a controlled program allows the researchers to eventually reverse it.
Stage 3: Time Reversal
At this stage, a special program alters the quantum computer’s state to make it evolve in reverse—from disorder back to order. This deliberate “kick” mimics the improbable cosmic fluctuation that might reverse an electron’s state, but here it’s intentionally programmed. In the billiard analogy, it’s like giving the table an exact nudge that sends the balls rolling back to their original triangle.
Stage 4: Regeneration
The same evolution program from Stage 2 is run again. If the reversal “kick” was accurate, the system doesn’t spiral further into chaos—it rewinds. The qubits return to their original state, much like an electron refocusing or billiard balls retracing their paths back into formation.
The results were promising: in about 85% of trials, the two-qubit system successfully reverted to its original state. When a third qubit was added, the success rate dropped to around 50%, mainly due to hardware imperfections. The researchers believe that as quantum computers improve, error rates will decrease.
Lebedev noted, “What’s exciting is that this time-reversal algorithm might also help enhance the precision of quantum computers. It could be adapted to test and debug quantum programs by identifying and correcting noise and errors.”
Read the original article on: TechExplorist
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