Physicists first recorded a negative time for photons

An international group of physicists recorded a phenomenon that was considered impossible for a long time: the photon can be in an excited state of the atom in negative time. The results published in the journal APL Quantumthey do not give the opportunity to travel in time, but open up new prospects for quantum sensors and studies of the interaction of light and matter

The experiment conducted under the leadership of Efraim Steinberg from the University of Toronto is based on the passage of the photon through the cloud of atoms. It is usually believed that when the photon excites the electron, it loses part of its energy and dissipates. But the researchers found that the average time spent by a photon in a state of excitation of the atom may be negative.

In other words, the peak of excitement seems to manifest before the photon is generally entering the cloud-an illusion that occurs due to the fact that the pulse front comes earlier, and the peak remains inside, scattering.

To “catch” this strange phenomenon, they used the method of a weak probe. Imagine an invisible probe that carefully measures whether an atom is in an excited state without interfering with the process. Integrating the data on time, scientists received the averaged time of the photon in excited state. For a narrow -lane pulse, it amounted to (–0.82 ± 0.31) θ₀, and for broadband – (0.54 ± 0.28) θ₀, where θ₀ is the average positive excitation time. These numbers show that the negative time is not just abstract mathematics, but a physically measurable effect.

To check the observations, two oncoming laser beams were sent to a cloud from Rubidia-85 atoms chilled to 60–70 μC. One bundle created excitement, the other fixed it through a weak dimension of the phase. The results confirmed the predictions: The photon could remain in a state of excitement “before”, as it would seem, had to achieve it.

Theorists from the Massachusetts Institute of Technology, the University of Griffith and India explain that the negative time here does not mean the reverse course of the watch. It reflects contextuality – a quantum property in which the measurement result depends on the observation method.

“Imagine that you look at the stage at different angles: the same action may seem premature or belated depending on the position,” the authors of the study explain

Howard Wizman from the University of Griffith explains that the negative averaged time of excitation of the photon is associated with a group delay: the pulse front comes earlier, and the peak remains inside the cloud.

“This creates the illusion that the photon is leaving the environment earlier than it enters there,” he says.

“This phenomenon emphasizes unusual quantum effects and potential advantages in calculations and sensors, where classical methods are powerless,” adds Jonte Hans, co -author of the study

Steinberg notes that earlier negative values ​​were simply ignored as purely mathematical and impossible to fix

“Now we see that they have a physical meaning, and we want to better understand what“ negative time ”is. Similarly, as if the clock sometimes whispered to us not about the past or future, but about the hidden processes taking place right here and now. ”He admits.

Thus, the discovery does not violate causal relationships, but puts a new challenge to scientists-to understand how the quantum world turns over time and what opportunities it opens for technology. The study demonstrates unusual aspects of the interaction of light and matter and shows that even such seemingly fundamental concepts, as a flow of time, behave differently on a quantum scale.

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on 2025-09-24 07:38:00.
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