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    • Scientists Are Building the World’s Most Accurate Clock. It Could Be a Turning Point for Humanity.
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    Scientists Are Building the World’s Most Accurate Clock. It Could Be a Turning Point for Humanity.

    Harry Posted on

    Sundials that follow the sunwalking in the sky From hourglasses that show sand passing between glass bulbs, humans have long wrestled with how best to measure time. This year, scientists made rapid strides towards producing humanity’s most accurate clock ever: the nuclear clock.

    nuclear clocks It could boost our most advanced, state-of-the-art atomic clocks by a factor of ten, meaning they would potentially drop by one second every 300 billion years. Compared to optical power atomic clocksThis difference, which is estimated to decrease by just one second every 30 billion years, does not seem to be significant. But real-world impacts alone, including improved earthquake detection and satellite navigation systems, would be enormous. Beyond improving our daily lives, these more precise clocks could also help reveal the fundamental workings of our universe.

    But nuclear clock It’s not just a more accurate watch. This system works because of certain processes in the nuclear cores of atoms, “and these are fundamentally different processes from the processes in the electron shell that drive all atomic clocks,” says physicist Thorsten Schumm, an associate professor at the University of Vienna who studies nuclear clocks. Technology.

    Nuclei, located deep in the heart of an atom (where they occupy an area less than one ten-trillionth the size of the atom), are less sensitive to changes in their environment, such as stray electric and magnetic fields. This makes nuclear clocks more stable than modern atomic clocks, which rely on the outermost electron of the atom. Nuclear clocks are potentially much more portable, as they do not need to be kept in a vacuum or supercooled to minimize atomic motion.

    All modern clocks rely on an oscillator that moves in regular, repeatable cycles and a method of counting those cycles. Then it’s a matter of calibrating how many cycles correspond to one second (say, two pendulum swings for a Grandfather clock), a power source to direct the clock’s movement, and a housing to encompass it all.

    By 1949 scientists The National Institute of Standards and Technology was developing the first atomic clocks. The Cesium-133 clock came on the scene in the mid-1950s and is still used today to define seconds. This technology represented a major improvement in precision (how repeatable a measurement is) and accuracy (how close a measurement is to its true value). This is because the oscillator of this atomic clock is the electromagnetic radiation required to knock the outermost electron of an atom into a higher orbit or shell. For cesium, this is a microwave beam with a frequency of exactly 9,192,631,770 cycles per second.

    3D representation of cubic lattice structure with colored spheres showing atomic interactions

    TU Wien, O. Diekmann

    An artist’s drawing showing laser excitation of the atomic nucleus of a crystal.

    D., Ph.D., a physicist at the University of Colorado Boulder and head of one of the teams that first put all the experiments together. Jun Ye says this higher number of cycles is very important. ingredients Consider two pendulums in a future nuclear clock; One oscillates a billion times per second, the other a million times per second. “You know a billion swings will be more accurate because missing one cycle in 10⁹ is a one in a billion error versus a one in a million error,” Ye says.

    Coupling the oscillator to the atom also makes clocks easier to calibrate. The energy required to bring an atom of a particular element into an excited state is a fundamental property of that element. For example, the electrons of all strontium atoms that are part of the latest generation optical systems atomic clocks—make this transition when light waves with a frequency of 429 trillion cycles per second hit them. This means that clocks lose one second every 40 billion years; This is approximately three times the age of the universe.

    Now scientists are after an even bigger (and elusive) prize: the nucleus. Like electrons, the nucleus of an atom can move to a higher energy state. “But because the nucleus is small, the forces involved are very, very strong and the energy scales are much higher,” says Schumm, who frequently collaborates with Ye. higher frequency radiation gamma rays They are required and have thousands to millions of times more energy than the energy required by radiation electron transitions. Although this would mean more precise clocks, lasers in this energy range are not yet available.

    But in 1976, scientists discovered that: isotope The 229-Th of thorium has an extremely low excitation energy compared to other atomic nuclei due to a happy accident of nature. “It’s been a very long journey since then to narrow this down to a factor between zero and 10 electron volts and then get as close to an accurate measurement as possible,” says Schumm.

    However, the technology to produce the necessary radiation even at this “low” nuclear excitation energy had not yet been developed until recently. “There have been a number of quantum engineering technology developments over the past few decades that have allowed us to really push the performance of these watches forward,” Ye says. And over the past few years, that search has intensified, with groups around the world determining with increasing precision the energy needed to achieve this nuclear transition.

    a transparent spherical object and a metallic rod with blue light on top

    TU Wien, LTDCol

    Photograph of the Thorium-doped crystal that scientists used in the first laser excitation of the atomic nucleus.

    A collaboration at CERN in 2023 observed transition from the other side of the equation. They waited for 229-Ac (the excited state of the target Thorium isotope) to decay to 229-Th and measured the energy of the photon emitted as a result (8.338 eV). The following year scientists Germany and Austria And United States improved this number even further. They used broadband lasers to directly trigger this excitation in 229-Th atoms embedded in a crystal and watched for an afterglow as the nuclei returned to their ground state.

    “The work of the CERN group was very important for our research. Eric Hudson, a professor at the University of California at Los Angeles, said it narrowed down the nuclear transition energy and confirmed that the inclusion of Thorium atoms in the crystals could detect a clear signal. His team first proposed looking for the Thorium transition. crystals.

    Armed with these predictions, Ye and his colleagues then measured this number to a precision a million times higher than the previous best figure using an optical frequency comb, a multicolor laser that allows scientists to scan a target range of potential frequencies at extremely high speed. high resolutions.

    So when can we expect the nuclear clock to be in our pocket? “Not yet,” Ye says. He predicts that the next five years will see many advances toward more powerful, more precise lasers and other infrastructure needed to build an independent nuclear clock. “But I can’t tell you right now what day you’ll have a portable system running a nuclear clock on your phone. “That is the vision, but it will probably take some time.”

    Headshot of Connie Chang

    Connie Chang is a freelance writer covering science, parenting, and health in the Bay Area. She is a recovering scientist, avid knitter, and fanfiction enthusiast.

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