When liquid helium-3 is cooled to millikelvin temperatures, it transitions into a state of matter called a superfluid. From the outside, superfluid helium-3 looks like a simple, transparent medium. Nevertheless, its internal structure is extremely rich and is often described as “the Universe in a droplet” [1]. In helium-3, some atoms collectively play the role of the quantum vacuum—the macroscopic quantum state with the lowest-possible energy—and others behave like matter, interacting through analogs of electromagnetic and gravitational forces. So far, researchers have learned how to “smell” this internal structure by probing the weak magnetic field surrounding the helium-3 nuclei, “touch” it by pushing external objects through the fluid and measuring the reaction force, and “hear” it by placing a speaker and microphone inside the fluid. Now, Theo Noble and colleagues at Lancaster University in the UK have brought in a fourth sense with a camera that can “see” the intrinsic details of the helium-3 universe [2]. This capability could allow researchers to better understand turbulence in quantum fluids and to detect topological structures that are predicted to be hiding in this superfluid world.
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