Using Frequency Combs to Detect the Decay of the Nucleus from the First Energy State of the Thorium-229

Now, optical physicist Jun Ye at JILA, a research institute in Boulder, Colorado, and his colleagues have built on these advances1. They succeeded in stimulating the transition with exquisite precision, but also hook the thorium to another timekeeper using a type of laser known as a Frequency comb. This device, which creates a spectrum of equally spaced frequency lines at higher energies than ever before, has been used for measurements since 20128. It was only when other groups had found ways to raise the thorium-229 signal in crystals that they were able to see the potential for driving a nuclear clock.

Finding this one meant looking at an enormous range of values, since theoretical models of the nucleus can’t accurately predict the energy of such transitions. thorium-229 decays slowly from its first energy state. The chance of seeing the decay from second to second is low with a half-life of around 30 minutes.

Identifying Dark Matter in Atomic Clocks with a High-Frequency Laser Frequency Comb: The Case of thorium-229

Atomic clocks currently hold the world record for most accurate timekeeping. The electrons jump between atomic energy levels, which causes them to be absorbed by light. Lasers that are locked give the read-out.

Any change in the forces would be amplified in the nuclear transition frequency, making nuclear clocks potentially about 100 million times more sensitive than atomic ones to the effects of this kind of dark matter. The latest result — which pinpoints the frequency with an accuracy of 13 decimal places — is already precise enough to narrow down the possible energy ranges in which light dark matter could exist, says Fuchs. Nuclear physics could also benefit from the more precise transition frequency, which could help scientists to distinguish betweendifferent possible shapes of the throrium-229 nucleus, she adds.

The JILA team looked for the transition frequency in trillions of thorium-229 atoms embedded in a crystal using a system known as a frequency comb. The comb is capable of releasing an array of laser frequency lines. It allows researchers to illuminate the crystal in many precise frequencies at once to look for a match more quickly than using a single-frequency laser.

The transition felt amazing, said study co-author Chuankun Zhang, a physicist at JILA. “We spent the entire night doing all the tests to check if this is actually really the signal that we were looking for,” he says.

honing is also required for the laser system. “Fortunately, this amazing technique has high potential,” says Olga Kocharovskaya, a physicist at Texas A&M University in College Station. She says that the source will be used in the future clock.