Matter clock links mass and time

Berkeley researchers have made a Compton clock based on the so-called Compton frequency of a matter wave (in a block of cesium).

Müller’s Compton clock is still 100 million times less precise than today’s best atomic clocks, which employ aluminum ions, improvements in the technique could boost its precision to that of atomic clocks, including the cesium clocks now used to define the second.

Müller can also turn the technique around to use time to measure mass. The reference mass today is a platinum-iridium cylinder defined as weighing one kilogram and kept under lock and key in a vault in France, with precise copies sparingly dispersed around the world. Using Müller’s matter wave technique provides a new way for researchers to build their own kilogram reference.

Müller’s proposal to make a mass standard based on time provides a new way to realize plans by the international General Conference on Weights and Measures to replace the standard kilogram with a more fundamental measure. It will involve an incredibly pure crystal of silicon, dubbed an Avogadro sphere, which is manufactured so precisely that the number of atoms inside is known to high accuracy.

And what about the question, What is time? Müller says that “I don’t think that anyone will ever have a final answer, but we know a bit more about its properties. Time is physical as soon as there is one massive particle, but it definitely is something that doesn’t require more than one massive particle for its existence. We know that a massless particle, like a photon, is not sufficient.”

Müller hopes to push his technique to even smaller particles, such as electrons or even positrons, in the latter case creating an antimatter clock. He is hopeful that someday he’ll be able to tell time using quantum fluctuations in a vacuum.

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