New experiment dives into quantum physics in a liquid

A diagram illustrating the effects of laser light on sound waves in liquid helium.
The space between two optical fibers (yellow) is filled wth liquid helium (blue). Laser light (red) is trapped in this space, and interacts with sound waves in the liquid (blue ripples). (Image credit: Harris Lab)

For the first time, Yale physicists have directly observed quantum behavior in the vibrations of a liquid body.

A great deal of ongoing research is currently devoted to discovering and exploiting quantum effects in the motion of macroscopic objects made of solids and gases. This new experiment opens a potentially rich area of further study into the way quantum principles work on liquid bodies.

The findings come from the Yale lab of physics and applied physics professor Jack Harris, along with colleagues at the Kastler Brossel Laboratory in France. A study about the research appears in the journal Physical Review Letters.

We filled a specially designed cavity with superfluid liquid helium,” Harris explained. “Then we use laser light to monitor an individual sound wave in the liquid helium. The volume of helium in which this sound wave lives is fairly large for a macroscopic object — equal to a cube whose sides are one-thousandth of an inch.”

Harris and his team discovered they could detect the sound wave’s quantum properties: its zero-point motion, which is the quantum motion that exists even when the temperature is lowered to absolute zero; and its quantum “back-action,” which is the effect of a detector on the measurement itself.

The co-first authors of the study are Yale postdoctoral fellows Alexey Shkarin and Anya Kashkanova. Additional authors are Charles Brown of Yale and Jakob Reichel, Sébastien Garcia, and Konstantin Ott of the Kastler Brossel Laboratory.

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Jim Shelton: james.shelton@yale.edu, 203-361-8332