An international team of physicists has studied the controlled interaction of two spatially separated time crystals.
Experimental set-up. Quartz-glass sample container cylinder is filled partially with superfluid 3He-B, leaving a free surface of the superfluid approximately 3 mm above the centre of the surrounding coil system. The space above the free surface is vacuum due to the vanishing vapor pressure of 3He at sub-millikelvin temperatures. Magnons can be trapped in this configuration in two separate locations, in the bulk (colored blue) and touching the free surface (colored red). Transverse NMR coils are used both for RF pumping of magnons into the BECs, and for recording the induced signal from the coherently precessing magnetization M (light yellow arrow). The amplitude of the recorded signal is proportional to βM, the tipping angle of M, and its frequency corresponds to the precession frequency of the condensate. The condensates are trapped by the combined effect of the distribution of the orbital anisotropy axis of the superfluid (green arrows) via spin-orbit coupling, and a minimum of the external magnetic field created using a pinch coil (magenta wire loop). The external field H is oriented along the z axis of the sample container. Image credit: Autti et al, doi: 10.1038/s41563-020-0780-y.
Time crystals are different from a standard crystal, which is composed of atoms arranged in a regularly repeating pattern in space.
First theorized in 2012 by Nobel Laureate Frank Wilczek and identified in 2016, they exhibit the bizarre property of being in constant, repeating motion in time despite no external input.
Their atoms are constantly oscillating, spinning, or moving first in one direction, and then the other.
Time crystals have great potential for practical applications. They could be used to improve current atomic clock technology — complex timepieces that keep the most accurate time that we can possibly achieve.
They could also improve technology such as gyroscopes, and systems that rely on atomic clocks, such as GPS.
“Controlling the interaction of two time crystals is a major achievement,” said study lead author Dr. Samuli Autti, a researcher in the Department of Physics at Lancaster University and the Department of Applied Physics at Aalto University.
“Before this, nobody had observed two time crystals in the same system, let alone seen them interact.”
“Controlled interactions are the number one item on the wish list of anyone looking to harness a time crystal for practical applications, such as quantum information processing.”
Time crystal AC Josephson effect. Voltage recorded from the pick-up coils (NMR coils) after pre-amplification, analyzed with time-windowed Fourier analysis (fast Fourier transform, FFT). Two coexisting magnon-BEC time crystals, created with an RF drive pulse at t = 0, are seen as peaks in the Fourier spectrum. For clarity, the exciting pulse is left just outside the time window shown here. Here fL = 833 kHz is the Larmor frequency. The upper trace corresponds to the magnon-BEC time crystal in the bulk, and the lower trace to the time crystal touching the free surface. The bulk trap is the more flexible of the two, and the bulk time crystal frequency hence increases during the decay more than that of the surface crystal. Population oscillations between the time crystals result in amplitude oscillations of the two signals, seen as two side bands. Image credit: Autti et al, doi: 10.1038/s41563-020-0780-y.
Dr. Autti and colleagues observed time crystals by using helium-3, a rare isotope of helium with one missing neutron.
The physicists cooled superfluid helium-3 to within one ten thousandth of a degree from absolute zero (0.0001 K, or minus 273.15 degrees Celsius).
They then created two time crystals inside the superfluid, and allowed them to touch.
They observed the two time crystals interacting and exchanging constituent particles flowing from one time crystal to the other one, and back — a phenomenon known as the Josephson effect.
Their results were published in the journal Nature Materials.
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S. Autti et al. AC Josephson effect between two superfluid time crystals. Nat. Mater, published online August 17, 2020; doi: 10.1038/s41563-020-0780-y
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