Imagine a clock that, even after one billion years of operation, ticks so precisely that it never misses a second. According to recent research, scientists are now more likely than ever to achieve that degree of timekeeping accuracy.
Such a device would be far more accurate than current state-of-the-art atomic
clocks, which measure time by defining a second through carefully timed energy
jumps in atoms' electrons. The signals that excite the atoms in atomic clocks
oscillate at a billion times per second.
A new method that researchers have created could improve this accuracy
by producing and monitoring oscillations in an even more difficult target: the nucleus
of an atom. To create this nuclear clock, the researchers excited the nuclear
particles in a solid-crystal thorium-229 atom using ultraviolet light. Then,
using an instrument known as an optical frequency comb, they counted the waves
in the UV signal to determine the frequency of the energy pulses that were
impacting the nucleus, which is comparable to a pendulum in a conventional clock.
A far higher frequency signal is needed to cause energy jumps in a
nucleus than is necessary for atomic clocks. This method should yield more precise
time measurements since it has more wave cycles per second.
Although their nuclear clock is still in development, if it is successful,
it has the potential to revolutionize not only timekeeping but also physics research
and even the way scientists probe the structure of the cosmos. According to
research that was published on September 4 in the journal Nature, the prototype
is already as accurate as an atomic clock, and future iterations are anticipated
to be even more accurate and stable.
As the scientists have demonstrated that these signals can be
generated and measured, "there are a lot of things that we can push to
further improve the accuracy," according to Chuankun Zhang, the lead study
author and graduate student at JILA, a collaborative research center supported by
the National Institute of Standards and Technology and the University of
Colorado Boulder.
Zhang explained that among the modifications might be adjusting the
lasers' alignment and frequency to better ping the nucleus.
Dr. Olga Kocharovskaya, a distinguished professor of physics at Texas
A&M University who was not involved in the research, stated, "This
work truly marks the dawn of a nuclear clock."
In 2023, scandium-45 atom nuclei were examined by Kocharovskaya and associates
as potential candidates for a nuclear clock. The energy transition and detectable
pulse those atoms produced at the time were the strongest ever seen in a
nucleus, but Kocharovskaya informed via email that the new findings from
thorium-229 produced a stronger signal and were more stable.
"The confidence this paper
provides in the reality of the nuclear clock is the broader significance,"
the speaker stated. "It is unequivocal that the construction of such a
clock is possible and imminent."
Repeatedly
Atomic clocks work by pinging an atom's electrons at particular frequencies
with electromagnetic radiation. The electrons are excited by energy bursts, which
cause them to move into a higher orbit around the atom. According to NASA,
oscillations that cause electrons to change states indicate the passage of
time.
Compared to common clocks that measure seconds in the vibrations of
quartz crystals, which are prone to going out of sync, atomic clocks are far more
reliable. Atomic clocks have been used for international timekeeping, space
exploration, and GPS technologies for many years.
Nevertheless, sync loss can also affect atomic clocks. According to Zhang,
electromagnetic disturbances have the potential to disrupt excited electrons
and compromise timekeeping accuracy.
On the other hand, nucleus particles in an atom are more difficult to disturb
than electrons. The strongest of all the fundamental forces, the strong nuclear force, firmly
holds protons and neutrons together. According to the researchers, more accurate
time measurements are made possible by wavelengths that oscillate at higher frequencies
and can cause a nucleus transition.
Prior to this study, numerous significant advancements in the field of
nuclear clock development had occurred. The first came about in 1976 when it was discovered that the
thorium nucleus was "uniquely low-energy" and that vacuum
ultraviolet, or VUV, laser light could be used to force it into an excited
state. According to the study, by 2003, scientists were suggesting that the
isotope thorium-229 would be a good candidate for nuclear clocks because
thorium required less energy to excite its nucleus than most other types of
atoms did.
Scientists developed a novel technique in 2023 to embed thorium-229
into crystals. This solid state system suppressed nuclear decay signals, facilitating
the tracking of desired signals. The wavelength of VUV light necessary to excite the nucleus
in thorium-229 was measured earlier this year by other researchers.
Zhang stated, "Our work builds on top of that." "This
crystal and our frequency comb light source allowed us to excite the various
transition energies and the nuclear transition." Zhang said that their findings
were approximately a million times more accurate than those of earlier measurements.
Dr. Shimon Kolkowitz, an associate professor and physics chair at the
University of California, Berkeley, described the paper as a "true tour de
force."
Kolkowitz, who was not involved in the research, said, "The quality
of the data and the speed with which they achieved the remarkable results in
this new manuscript is really amazing." "It marks a significant
advancement in the creation of nuclear clocks, a goal pursued by physicists for
many years.”
Transforming physics
Scientists have already benefited greatly from the accuracy and
stability of atomic clocks in their studies of space-time, gravitational
fields, and earthquakes. Nuclear clocks could provide "a major boost"
to these fields, according to Kocharovskaya. According to her, nuclear clocks
would be more accurate, simpler, and more portable than atomic clocks because
they wouldn't need strong magnetic and electric shielding, intense cooling, or
high vacuum conditions.
Zhang suggests that nuclear clocks combined with atomic clocks could transform
physics education itself. According to Zhang, scientists may be able to determine whether
fundamental physics constants are actually as constant as they appear to be or
whether they change at previously unmeasureable levels by tracking and
comparing frequency ratios in the two kinds of clocks over time.
He continued by saying that the study of dark matter, the enigmatic
material that makes up 80% of the universe but has never been directly
measured, may benefit greatly from the application of this paired clock
technique.
According to some scientists, dark matter interacts with quarks, gluons, and electrons in amounts that are currently undetectable.
Zhang stated that the goal is to determine whether dark matter interacts with the atomic nucleus in a manner that differs slightly from that of the atom's electron orbit. "New physics would be indicated if there was a change over time in the transition frequency ratio between the nuclear clock and the atomic clock."
These results suggest that the day when nuclear clocks outperform atomic clocks and eventually replace them is not too far off, according to Kolkowitz, even though there is still much work to be done in this regard.
"I expect that eventually some of the kinds of experiments we are currently doing in my lab to test relativity and search for new physics with atomic clocks will instead be performed with nuclear clocks as better UV laser sources are developed and as some of the mysteries and tricks of nuclear clocks get worked out," Kolkowitz stated.
Regarding nuclear clocks, what's next? Currently, only time will tell.
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