New machine appears to defy the laws of physics by shattering the normal rules of light

What do you do when you want to break the laws of physics that define the movement and shape of light? Why, you build a ring-shaped device that forces pulses of light to orbit each other at very high speeds. As simple as it seems, this circular arrangement causes a light wave to lose its characteristic symmetry.

A normal light wave adheres to certain rules of physical symmetry. Two of the most important rules are time-reversal symmetry and polarization symmetry.

In time-reversal symmetry, light will stick to the same pattern of movement, be it going forward or backward. So if one records its movement and then plays it backward, the light would look and act the same way it did. The sole difference is that the light is now moving in the opposite direction.

The second rule of symmetry involves a property called polarization. Light is both a particle – called a photon – and a wave. As a light wave travels, it wobbles relative to the direction it is moving. This wobbling is called polarization.

In general, the polarization of light does not change. It stands as the second type of symmetry ascribed to normal light waves. (Related: Pulling off bandages could become less painful in the future, thanks to light.)

Light waves that travel in circles behave differently than normal

Those rules go out the metaphorical window once light enters the “optical ring resonator,” reported researchers from the National Physical Laboratory (NPL) and their counterparts at the Herriot-Watt University. Instead, light ditches both its time-reversal symmetry and its stable polarization.

In their experiment, light waves moved in circles within the chamber of the resonator. These trapped waves reverberated with each other, and their interactions generated phenomena that are extremely rare in nature.

Previous studies showed that light can lose its time-reversal symmetry in very specific circumstances. For example, a light wave can be forced to travel in a ring-like path, such as inside the aforementioned optical ring resonator.

During this constrained movement, the peak of the wave will not appear at the spot it normally should reach at that point in time. A backwards-played recording of the light wave will therefore look very different from the wave that is moving forward in time.

Likewise, a different process can remove the polarization symmetry of a wave by changing the way it oscillates. However, it was not known if a wave that loses its time-reversal symmetry will also lose its polarization symmetry.

Changing the properties of light by making its waves unsymmetrical

The NPL researchers demonstrated in their experiment that a light wave can lose both its time-reversal symmetry and its polarization symmetry at the same time. Their set-up calls for a laser to emit pulses of light into the optical ring resonator at precisely timed moments.

Inside the chamber, the pulses will follow circular paths and begin circling each other. Each light wave will peak at certain points, forming a pattern that can only apply in a particular direction in time. If a recording of these movements is played backward, it will not match the forward-moving patterns.

Furthermore, the waves abandon their strictly vertical movement. Instead of moving up and down, a wave forms ellipses – oval shapes that resemble squished circles. In summary, the waves lose their time-reversal and polarization symmetries.

The researchers published their findings in the science journal Physical Review Letters. They believe their discovery can lead to new ways of manipulating light. For example, if applied to optical circuits, the ability to modify the symmetry of light could potentially improve the accuracy of atomic clocks and make light-based quantum computers even more powerful than they already are.

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