A newly developed atomic clock measures time based on the mass of a single atom. “This is the first clock based on a single particle,” says Holger Müller, a physicist at the University of California. “Its ticking rate is determined only by the particle’s mass.”
The idea for creating the clock originated in a study of the quantum principle that particles also behave as waves, & vice versa. In particular, Müller & his team wanted to determine how frequently the wave form of a single atom oscillates, a quantity that in quantum mechanics is linked directly to the atom’s mass. Then the researchers could use those oscillations like a pendulum to create a clock.
The problem with Müller’s goal was that it’s impossible to directly measure the oscillation frequency of waves of matter. The frequency of these waves is about 1025 hertz, 10 orders of magnitude higher than that of visible light. So Müller & his colleagues came up with an apparatus that creates two different sets of waves, the first one based on a cesium atom at rest & the second on the same atom in motion. The team measured the frequency difference between the waves & then used that number (around 100,000 hertz) to calculate the much larger oscillation frequency of cesium at rest.
Working like this, Müller was able to use the wave frequency of the cesium atom to create a clock that would gain (or lose) a second over an 8 year period. That’s better than a decent wristwatch but about a hundred million times less accurate than the best atomic clocks, which count the frequency of light emissions from an atom as its electrons release small bursts of energy.
Physicists not involved with Müller’s research are impressed by his technique but are more than sceptical about its potential for timekeeping. Some other researchers have a more “conceptual” objection: because there is nothing at this frequency actually oscillating within the atom, they say it is not a clock at all. “It may be a clock numerically, but it’s not a physical clock,” says Christian Bordé, a physicist at the Paris Observatory. Müller contends that the clock’s simplicity is its best feature, he is measuring an intrinsic quantum property of an atom, one that depends only on the atom’s mass. (OK, I’m sure that made sense somehow, somewhere, but not here….. Or to put it another way “WTF?”)
In fact, the establishment of the relationship between frequency & mass means Müller’s technique may well prove most useful as a scale for measuring mass, rather than as a clock. Scientists define the kilogram, the base unit of mass, with a lump of metal stored in a French vault. The international General Conference on Weights & Measures, led by Bordé (remember him, “It may be a clock numerically, but…..”?), wants to replace this artifact with a “kilogram standard” based on fundamental physical constants. Using Müller’s technique sit may be possible to do that by measuring the frequency of matter waves & so accurately determine an atom’s mass. Once he finds the mass of one atom, he says, it is straightforward to relate it to the masses of other atoms.
To think I used to find all this quantum stuff so confusing…….I’m embarrassed.
ThursdayAgain 
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