Latest / The Last Observer: Science and Beyond / World’s First Nuclear Clock Starts Ticking in Vienna

Transcript

World’s First Nuclear Clock Starts Ticking in Vienna · The Last Observer: Science and Beyond

• 0:00
  Speaker 1: Welcome to The Last Observer, a journey through science, history,
• 0:04
  Speaker 1: and the universe's greatest mysteries. From ancient enigmas to the
• 0:08
  Speaker 1: deepest questions at the frontiers of reality, we explore the discoveries, ideas,
• 0:13
  Speaker 1: and mysteries that challenge what we think we know. Stay curious,
• 0:18
  Speaker 1: keep questioning, and let's search for the truth beyond the known.
• 0:27
  Speaker 2: Welcome to The Last Observer Podcast. Today we will talk
• 0:31
  Speaker 2: about the world's first self-stabilizing nuclear clock that scientists just
• 0:35
  Speaker 2: got ticking in a laboratory in Vienna.
• 0:38
  Speaker 3: Nuclear clock. That phrase alone is interesting. We have all
• 0:42
  Speaker 3: heard of atomic clocks. They are the reason GPS works,
• 0:45
  Speaker 3: and the second is defined so. Precisely. What changes when
• 0:49
  Speaker 3: you move from the atom to the nucleus?
• 0:52
  Speaker 2: Atomic clocks lock onto the energy jumps of electrons orbiting
• 0:55
  Speaker 2: the nucleus. Those jumps are extremely regular, but the electrons
• 0:59
  Speaker 2: sit far out and can be nudged by stray electric
• 1:02
  Speaker 2: or magnetic fields. A nuclear clock uses a transition inside
• 1:06
  Speaker 2: the nucleus itself. The nucleus is thousands of times smaller
• 1:10
  Speaker 2: and much more tightly bound, so it should be less
• 1:12
  Speaker 2: sensitive to the outside world.
• 1:14
  Speaker 3: Less sensitive sounds good for a clock, but it also
• 1:17
  Speaker 3: makes the transition harder to reach. Most nuclear energy levels
• 1:20
  Speaker 3: sit at high energies that require gamma rays. Gamma rays
• 1:24
  Speaker 3: are not practical for a precision laser.
• 1:27
  Speaker 2: That is why Thorium-229 is special. It has one nuclear
• 1:31
  Speaker 2: transition that sits unusually low in energy, only about 8
• 1:34
  Speaker 2: electron volts. That is still ultraviolet light, but it is
• 1:38
  Speaker 2: laser accessible. Researchers have known about this transition for decades,
• 1:42
  Speaker 2: yet measuring its exact frequency and then building a usable
• 1:45
  Speaker 2: laser took a long time.
• 1:47
  Speaker 3: So the Vienna team doped a crystal of calcium fluoride
• 1:50
  Speaker 3: with Thorium-229 nuclei and shone a continuous ultraviolet laser through it.
• 1:56
  Speaker 3: When the laser frequency matches the nuclear resonance, the nuclei
• 2:00
  Speaker 3: absorb some of the light.
• 2:02
  Speaker 2: They monitor the amount of light that gets through the crystal.
• 2:05
  Speaker 2: If the absorption weakens that means the laser has drifted
• 2:08
  Speaker 2: slightly off the resonance. An electronic feedback loop then adjusts
• 2:12
  Speaker 2: the laser frequency to bring it back to the peak absorption.
• 2:15
  Speaker 2: The clock stabilizes itself.
• 2:18
  Speaker 3: Self-stabilizing is the key phrase. Earlier experiments could excite the
• 2:22
  Speaker 3: nuclear transition, but they still needed an ordinary atomic clock
• 2:25
  Speaker 3: as an external reference to keep everything locked. This version
• 2:29
  Speaker 3: runs without that external reference in the loop.
• 2:32
  Speaker 2: They kept it running stably for more than 24 hours
• 2:35
  Speaker 2: without anyone intervening. That demonstration moves nuclear timekeeping from a
• 2:39
  Speaker 2: spectroscopic curiosity into an actual functioning clock.
• 2:44
  Speaker 3: How good is the precision right now? I saw numbers
• 2:47
  Speaker 3: around one second of error in 30 million years. That
• 2:50
  Speaker 3: is already impressive for a first prototype, but I know
• 2:53
  Speaker 3: the best atomic clocks do better.
• 2:55
  Speaker 2: Yes, the current fractional frequency instability is roughly 10 to
• 2:59
  Speaker 2: the minus 15. The record-holding optical atomic clocks reach far
• 3:04
  Speaker 2: higher stability. The point is that nuclei have a fundamental
• 3:07
  Speaker 2: advantage because external perturbations couple more weakly to them. With
• 3:12
  Speaker 2: engineering improvements, nuclear clocks are expected to catch up and
• 3:15
  Speaker 2: potentially surpass atomic clocks.
• 3:17
  Speaker 3: There is also a second nuclear clock that came online
• 3:20
  Speaker 3: at almost the same time in Beijing. They used a
• 3:23
  Speaker 3: different laser and a slightly different readout, but the same
• 3:26
  Speaker 3: thorium transition in a similar crystal.
• 3:29
  Speaker 2: Having two independent groups succeed in the same week is reassuring.
• 3:33
  Speaker 2: It shows the approach is robust. The Vienna clock is
• 3:36
  Speaker 2: the one that fully closes the feedback loop by itself,
• 3:39
  Speaker 2: so it is the first true standalone nuclear clock.
• 3:42
  Speaker 3: The crystal approach is interesting because most precision atomic clocks
• 3:45
  Speaker 3: use single ions or clouds of atoms held in vacuum
• 3:49
  Speaker 3: and cooled with lasers. Here you have a solid piece
• 3:52
  Speaker 3: of material sitting at room temperature containing a huge number
• 3:55
  Speaker 3: of nuclei.
• 3:56
  Speaker 2: Up to about a quadrillion thorium nuclei in the crystal.
• 4:00
  Speaker 2: That large number gives a strong absorption signal so the
• 4:03
  Speaker 2: feedback can work quickly. You do not need the elaborate
• 4:07
  Speaker 2: ion traps and ultra-high vacuum systems that atomic clocks require.
• 4:12
  Speaker 3: But the laser has to be at 148 nanometers, which
• 4:15
  Speaker 3: is deep in the vacuum ultraviolet. Ordinary air absorbs that light,
• 4:19
  Speaker 3: so the whole optical path has to be carefully designed.
• 4:22
  Speaker 3: Getting a continuous wave laser with enough power and a
• 4:25
  Speaker 3: narrow enough line width at that wavelength was a major
• 4:28
  Speaker 3: technical achievement by the German partners at PTB.
• 4:32
  Speaker 2: They used four-wave mixing and cadmium vapor to generate the
• 4:35
  Speaker 2: ultraviolet light and then locked everything carefully. Once that laser
• 4:39
  Speaker 2: was stable, the feedback loop could be closed for the
• 4:42
  Speaker 2: first time.
• 4:43
  Speaker 3: They compared the nuclear clock against a well-characterized ytterbium-ion optical
• 4:48
  Speaker 3: atomic clock. An optical fiber link transferred the frequency information
• 4:52
  Speaker 3: between the two laboratories so they could measure how the
• 4:55
  Speaker 3: nuclear clock behaved over a full day.
• 4:58
  Speaker 2: The comparison showed that the nuclear clock stayed within roughly
• 5:01
  Speaker 2: one second of error per 30 million years of operation.
• 5:05
  Speaker 2: For a brand new technology that has never existed before,
• 5:08
  Speaker 2: that is a strong first result.
• 5:10
  Speaker 3: The Beijing clock used a stronger laser, but the Vienna
• 5:13
  Speaker 3: crystals had higher thorium concentration and better optical quality. The
• 5:18
  Speaker 3: researchers already noted that combining the best elements of both
• 5:21
  Speaker 3: experiments should improve performance further.
• 5:24
  Speaker 2: Temperature stability of the crystal matters. They measured that the
• 5:27
  Speaker 2: nuclear transition frequency shifts only weakly with temperature, which is fortunate.
• 5:32
  Speaker 2: Two different crystals gave frequencies that agreed at the level
• 5:35
  Speaker 2: of about one part in 10 trillion.
• 5:38
  Speaker 3: Why should the nucleus be a better reference in principle?
• 5:41
  Speaker 3: The electrons that atomic clocks use feel the electromagnetic fields
• 5:44
  Speaker 3: of nearby atoms and of the laboratory environment. The nuclear
• 5:48
  Speaker 3: transition depends mainly on the strong force that holds the
• 5:51
  Speaker 3: protons and neutrons together. External electric and magnetic fields have
• 5:55
  Speaker 3: a much smaller effect on it.
• 5:57
  Speaker 2: That difference in sensitivity is exactly what makes the comparison
• 6:00
  Speaker 2: between a nuclear clock and an atomic clock scientifically powerful.
• 6:05
  Speaker 2: If the two clocks drift relative to each other over
• 6:07
  Speaker 2: long times, it could mean that a fundamental constant is
• 6:11
  Speaker 2: changing or that some new field is interacting differently with
• 6:14
  Speaker 2: nuclei and with electrons.
• 6:16
  Speaker 3: They already performed one such search. Using the Vienna nuclear clock,
• 6:20
  Speaker 3: they looked for fluctuations that might be caused by ultralight
• 6:23
  Speaker 3: dark matter coupling to the strong nuclear force. No variation
• 6:27
  Speaker 3: was seen, but the limits they obtained are already competitive
• 6:30
  Speaker 3: with earlier work done with atomic clocks.
• 6:32
  Speaker 2: The dark matter result is noteworthy because most clock-based searches
• 6:36
  Speaker 2: have only constrained how dark matter might couple to electromagnetism.
• 6:40
  Speaker 2: A nuclear frequency reference opens a window onto models that
• 6:44
  Speaker 2: interact with the strong force. Even a null result constrains
• 6:48
  Speaker 2: the possible mass and coupling strength of those particles.
• 6:51
  Speaker 3: It is striking that the first operating nuclear clock was
• 6:54
  Speaker 3: immediately put to use as a physics sensor rather than
• 6:57
  Speaker 3: just being celebrated as a timekeeping milestone. That shows the
• 7:01
  Speaker 3: community has been waiting for this tool.
• 7:04
  Speaker 2: The two Nature papers appeared in early October. One describes
• 7:07
  Speaker 2: the Vienna self-stabilizing clock with its feedback loop and the
• 7:11
  Speaker 2: dark matter search. The other reports the Beijing implementation. Together
• 7:15
  Speaker 2: they established that laser-addressed nuclei can serve as practical frequency references.
• 7:21
  Speaker 3: Physicists first proposed nuclear clocks nearly 50 years ago. The
• 7:25
  Speaker 3: thorium-229 isomer was identified as the only realistic candidate because
• 7:29
  Speaker 3: its excitation energy is so low. Narrowing down that energy
• 7:33
  Speaker 3: to the precision needed for a laser took decades of spectroscopy.
• 7:37
  Speaker 2: Once the frequency was known to high enough accuracy, the
• 7:40
  Speaker 2: remaining challenges were technical. Producing a suitable crystal with enough thorium,
• 7:45
  Speaker 2: building a narrow Lindwut continuous laser at 148 nanometres, and
• 7:50
  Speaker 2: closing a real-time feedback loop. All of those pieces came
• 7:54
  Speaker 2: together in the last couple of years.
• 7:56
  Speaker 3: The solid-state platform has practical advantages for the future. You
• 8:00
  Speaker 3: can imagine more compact devices that do not require the
• 8:03
  Speaker 3: full infrastructure of an ion trap laboratory. That could matter
• 8:07
  Speaker 3: for applications where you want a highly stable oscillator in
• 8:10
  Speaker 3: a less controlled environment.
• 8:12
  Speaker 2: For everyday timing, the existing atomic clocks are already more
• 8:15
  Speaker 2: than good enough. The near-term scientific payoff is the ability
• 8:19
  Speaker 2: to compare nuclear and electronic transitions over long periods. Those
• 8:23
  Speaker 2: comparisons can test whether the fine structure constant or other
• 8:26
  Speaker 2: parameters of the standard model are truly constant.
• 8:30
  Speaker 3: There is also interest in using nuclear clocks as sensors
• 8:33
  Speaker 3: for other phenomena. Because the nucleus responds differently to gravitational
• 8:37
  Speaker 3: fields or to possible new forces, the differential measurement against
• 8:41
  Speaker 3: an atomic clock can amplify small effects.
• 8:45
  Speaker 2: The current resonance is still relatively broad, on the order
• 8:48
  Speaker 2: of tens of kilohertz. Narrowing the line width by improving
• 8:52
  Speaker 2: crystal quality and laser stability should bring large gains in
• 8:55
  Speaker 2: short-term stability. Longer averaging times will then push the ultimate
• 8:59
  Speaker 2: accuracy higher.
• 9:01
  Speaker 3: The team has already shown that the frequency is reproducible
• 9:04
  Speaker 3: between different crystals and that it does not shift strongly
• 9:07
  Speaker 3: with temperature. Those are the kinds of systematic effects that
• 9:10
  Speaker 3: have to be controlled before you can claim record-breaking performance.
• 9:14
  Speaker 3: Looking further ahead, I wonder how quickly the precision can improve.
• 9:18
  Speaker 3: Optical atomic clocks took many years to reach their current level.
• 9:22
  Speaker 3: The nuclear clock community seems to be moving faster because
• 9:26
  Speaker 3: many of the supporting technologies already exist.
• 9:29
  Speaker 2: The laser systems, the frequency combs, and the comparison techniques
• 9:33
  Speaker 2: developed for atomic clocks can be adapted. The new element
• 9:37
  Speaker 2: is the nuclear reference itself. Once that reference is stable,
• 9:41
  Speaker 2: the rest of the infrastructure can be shared.
• 9:44
  Speaker 3: There is still work to do on the crystal. Higher
• 9:47
  Speaker 3: thorium doping, lower strain, and better understanding of any residual
• 9:51
  Speaker 3: frequency shifts will all help. The fact that two independent
• 9:54
  Speaker 3: crystals already agreed well is a positive sign.
• 9:58
  Speaker 2: If the stability improves by even two or three orders
• 10:01
  Speaker 2: of magnitude, the nuclear clock will become competitive with the
• 10:04
  Speaker 2: best atomic clocks for many purposes. Beyond that, it could
• 10:08
  Speaker 2: set new records and open previously inaccessible tests of fundamental physics.
• 10:13
  Speaker 3: The dark matter search they already performed is only the beginning.
• 10:17
  Speaker 3: With better clocks and longer integration times, the sensitivity to
• 10:20
  Speaker 3: ultralight dark matter will increase. Models that couple preferentially to
• 10:24
  Speaker 3: the strong force will be constrained more tightly than ever before.
• 10:28
  Speaker 2: Comparisons between nuclear and atomic clocks over months or years
• 10:32
  Speaker 2: could also look for slow drifts in the fundamental constants.
• 10:35
  Speaker 2: Those drifts, if they exist, would be a signal of
• 10:38
  Speaker 2: new physics beyond the standard model. The different dependence on
• 10:42
  Speaker 2: the strong force versus electromagnetism makes the comparison particularly clean.
• 10:48
  Speaker 3: I keep thinking about the practical side as well. A
• 10:51
  Speaker 3: more compact and environmentally robust clock could improve timing in
• 10:55
  Speaker 3: places where atomic clocks are hard to operate, for example
• 10:58
  Speaker 3: in space or in mobile applications. Even if the ultimate
• 11:02
  Speaker 3: accuracy is not needed every day, the robustness might matter.
• 11:06
  Speaker 2: For now, the excitement is mainly scientific. We finally have
• 11:10
  Speaker 2: a working clock that ticks according to the nucleus rather
• 11:13
  Speaker 2: than the electrons. It stabilizes itself for a full day,
• 11:17
  Speaker 2: and it has already been used to set new limits
• 11:19
  Speaker 2: on certain dark matter interactions.
• 11:22
  Speaker 3: That combination of a new technology and an immediate physics
• 11:25
  Speaker 3: result feels like a real turning point. The field of
• 11:28
  Speaker 3: nuclear clocks has moved from theory and spectroscopy into operational devices.
• 11:33
  Speaker 2: It will be interesting to see how the precision evolves
• 11:36
  Speaker 2: over the next few years. If the improvements continue at
• 11:39
  Speaker 2: the present rate, we could soon have nuclear clocks that
• 11:42
  Speaker 2: not only match but exceed the performance of the best
• 11:44
  Speaker 2: atomic clocks.
• 11:46
  Speaker 3: And when that happens, the definition of the second itself
• 11:49
  Speaker 3: might eventually be revisited. More importantly, the new sensor will
• 11:53
  Speaker 3: give us another way to look for cracks in our
• 11:55
  Speaker 3: current understanding of the laws of physics.
• 11:57
  Speaker 2: A nuclear clock that keeps time by watching the heart
• 12:00
  Speaker 2: of the atom, and that can probe forces atomic clocks
• 12:03
  Speaker 2: cannot reach. That is the story that just arrived from
• 12:06
  Speaker 2: Vienna and from Beijing.
• 12:09
  Speaker 3: It is a quiet but profound advance. Timekeeping and fundamental
• 12:13
  Speaker 3: physics both gained a new instrument at the same moment.
• 12:16
  Speaker 3: I look forward to hearing what they measure next.
• 12:19
  Speaker 2: One thing that stands out is how the feedback loop
• 12:21
  Speaker 2: actually works in practice. The laser is shining continuously through
• 12:26
  Speaker 2: the crystal. A detector measures the transmitted intensity. That intensity
• 12:31
  Speaker 2: is highest when the laser is slightly off-resonance and drops
• 12:35
  Speaker 2: when the laser sits right on the nuclear transition, because
• 12:38
  Speaker 2: more light is absorbed.
• 12:39
  Speaker 3: So the system is looking for the point of maximum absorption.
• 12:43
  Speaker 3: If the intensity starts to rise, that means the laser
• 12:46
  Speaker 3: has drifted away from the resonance peak, and the controller
• 12:49
  Speaker 3: adjusts the laser frequency back toward the dip. It is
• 12:53
  Speaker 3: a classic servo loop, but the discriminator is the nuclear
• 12:56
  Speaker 3: absorption itself.
• 12:58
  Speaker 2: Because there are so many nuclei, the absorption signal is strong,
• 13:01
  Speaker 2: and the loop can respond within seconds. That is fast
• 13:05
  Speaker 2: enough to correct the ordinary drifts of a free-running laser.
• 13:09
  Speaker 3: They also had to make sure the crystal itself does
• 13:11
  Speaker 3: not introduce large shifts. Any strain or defects in the
• 13:15
  Speaker 3: calcium fluoride lattice can broaden the resonance or shift its
• 13:18
  Speaker 3: center frequency. The Vienna crystals turned out to be of
• 13:21
  Speaker 3: high enough quality that the resonance remained usable.
• 13:24
  Speaker 2: The Beijing group used a different method to generate their
• 13:27
  Speaker 2: ultraviolet light and a different detection scheme but reached a
• 13:30
  Speaker 2: similar level of stability. The fact that two quite different
• 13:34
  Speaker 2: technical implementations both worked is strong evidence that the underlying
• 13:38
  Speaker 2: nuclear transition is reliable.
• 13:41
  Speaker 3: I am curious about the long-term stability. Running for one
• 13:44
  Speaker 3: day is already useful, but many physics experiments need weeks
• 13:48
  Speaker 3: or months of continuous comparison. Do they expect the same
• 13:51
  Speaker 3: feedback loop to hold the frequency for much longer periods?
• 13:55
  Speaker 2: In principle, yes. The nuclear transition itself should be extremely stable.
• 14:00
  Speaker 2: The practical limits will come from residual temperature drifts, laser
• 14:03
  Speaker 2: power fluctuations, and any slow changes in the crystal. Those
• 14:07
  Speaker 2: are engineering problems that can be attacked systematically.
• 14:11
  Speaker 3: They already measured the temperature coefficient and found it to
• 14:14
  Speaker 3: be small. That reduces one of the biggest worries. With
• 14:18
  Speaker 3: better thermal control, the day-long stability they demonstrated could extend
• 14:21
  Speaker 3: much further.
• 14:23
  Speaker 2: Another practical point is that the clock does not need
• 14:26
  Speaker 2: to be compared against an atomic clock in order to run.
• 14:29
  Speaker 2: The feedback keeps it locked to the nuclear resonance on
• 14:32
  Speaker 2: its own. The atomic clock comparison was only used afterward
• 14:36
  Speaker 2: to characterize how well it performed.
• 14:38
  Speaker 3: That independence is what makes it a true clock rather
• 14:41
  Speaker 3: than just a spectroscopic measurement. Once the loop is closed,
• 14:45
  Speaker 3: the device produces a stable frequency reference that can be
• 14:48
  Speaker 3: used for other experiments or for comparison with other clocks.
• 14:51
  Speaker 2: Thinking about the broader context, precision timekeeping has always driven
• 14:56
  Speaker 2: progress in both technology and fundamental physics. Atomic clocks enabled
• 15:00
  Speaker 2: GPS and also tested general relativity and the constancy of
• 15:05
  Speaker 2: the fine structure constant. Nuclear clocks add a new degree
• 15:09
  Speaker 2: of freedom because they respond differently to possible variations in
• 15:12
  Speaker 2: the strong force.
• 15:13
  Speaker 3: If the strong coupling constant were changing even slightly, the
• 15:17
  Speaker 3: nuclear clock would speed up or slow down relative to
• 15:20
  Speaker 3: an atomic clock. That differential measurement can be far more
• 15:24
  Speaker 3: sensitive than looking at either clock alone.
• 15:27
  Speaker 2: The same logic applies to certain dark matter models. Particles
• 15:30
  Speaker 2: that couple to the strong force would modulate the nuclear
• 15:33
  Speaker 2: transition frequency in a way that electronic transitions do not feel.
• 15:38
  Speaker 2: The Vienna team already set the first limits of this
• 15:41
  Speaker 2: kind with their new clock.
• 15:43
  Speaker 3: It is early days, so the limits are not yet
• 15:45
  Speaker 3: the tightest in every channel, but the method is now proven.
• 15:48
  Speaker 3: Future improvements in stability will translate almost directly into better sensitivities.
• 15:53
  Speaker 2: There is also the possibility of using nuclear clocks and networks.
• 15:57
  Speaker 2: If several nuclear clocks can be compared over long distances,
• 16:01
  Speaker 2: the common mode rejection of some noise sources becomes possible,
• 16:05
  Speaker 2: and the search for transient effects such as dark matter
• 16:08
  Speaker 2: waves or gravitational anomalies becomes more powerful.
• 16:12
  Speaker 3: The solid-state nature might eventually allow more compact or even
• 16:15
  Speaker 3: portable versions. That would open applications that current room-sized atomic
• 16:20
  Speaker 3: clock laboratories cannot easily support.
• 16:23
  Speaker 2: For the moment, the devices are still laboratory instruments, but
• 16:26
  Speaker 2: the path from the first atomic clocks of the 1950s
• 16:29
  Speaker 2: to the chip-scale atomic clocks of today shows how quickly
• 16:33
  Speaker 2: these technologies can move once the basic principle is demonstrated.
• 16:37
  Speaker 3: The nuclear clock has now crossed that threshold. Two groups
• 16:41
  Speaker 3: have operating devices, one of them is fully self-stabilizing, and
• 16:45
  Speaker 3: a first physics measurement has already been published. That is
• 16:48
  Speaker 3: a lot of progress in a short time.
• 16:51
  Speaker 2: I expect we will see rapid gains in the next
• 16:53
  Speaker 2: couple of years as the crystal quality improves and the
• 16:56
  Speaker 2: laser-lined wine narrows. The community is small but highly focused,
• 17:00
  Speaker 2: and the supporting technology from atomic clock research is already mature.
• 17:05
  Speaker 3: It is a good reminder that some of the most
• 17:07
  Speaker 3: interesting advances come from looking deeper into systems we thought
• 17:10
  Speaker 3: we already understood. The nucleus of thorium turns out to
• 17:13
  Speaker 3: be an excellent clock reference once you can address it
• 17:16
  Speaker 3: with a laser.
• 17:18
  Speaker 2: And once you can lock a laser to it, the
• 17:20
  Speaker 2: whole apparatus becomes a new kind of sensor for the
• 17:23
  Speaker 2: fundamental constants and for possible new forces. That combination of
• 17:27
  Speaker 2: better timekeeping and new physics reach is what makes the
• 17:30
  Speaker 2: result significant.
• 17:32
  Speaker 3: I will be watching for the next round of results.
• 17:35
  Speaker 3: If the stability continues to improve, the nuclear clock could
• 17:38
  Speaker 3: become one of the most precise instruments we have for
• 17:40
  Speaker 3: testing whether the laws of physics are truly constant.
• 17:43
  Speaker 2: Putting the pieces together, the Vienna experiment shows that a
• 17:47
  Speaker 2: nuclear clock can operate autonomously. The feedback loop keeps the
• 17:51
  Speaker 2: laser locked to the thorium resonance without continuous human adjustment
• 17:56
  Speaker 2: or an external atomic reference running in real time.
• 17:59
  Speaker 3: The 24-hour demonstration is important because it proves the loop
• 18:03
  Speaker 3: remains stable over timescales that matter for actual measurements. Short
• 18:07
  Speaker 3: spectroscopic scans are one thing. Continuous operation is another.
• 18:12
  Speaker 2: The fractional frequency instability they achieved is already good enough
• 18:16
  Speaker 2: for some interesting physics. The dark matter limits they published
• 18:20
  Speaker 2: are competitive precisely because the nuclear reference responds to a
• 18:23
  Speaker 2: different interaction than the atomic clocks used in previous searches.
• 18:27
  Speaker 3: Future work will focus on narrowing the resonance further. A
• 18:31
  Speaker 3: narrower line means the feedback can lock more tightly and
• 18:34
  Speaker 3: the short-term stability improves. Longer averaging then reduces the uncertainty
• 18:39
  Speaker 3: even more.
• 18:40
  Speaker 2: Improvements in crystal growth, laser power, and thermal control are
• 18:44
  Speaker 2: all underway. The researchers have already indicated that combining the
• 18:48
  Speaker 2: best elements of the Vienna and Beijing setups should yield
• 18:51
  Speaker 2: a better clock quickly.
• 18:53
  Speaker 3: In the longer term, the solid-state platform may allow devices
• 18:56
  Speaker 3: that are smaller and more robust than traditional atomic clocks.
• 19:00
  Speaker 3: That could matter for applications in space or in field-deployed
• 19:03
  Speaker 3: sensors where size and environmental tolerance count.
• 19:07
  Speaker 2: Even if the ultimate accuracy remains a laboratory goal, The
• 19:11
  Speaker 2: existence of a working nuclear frequency reference changes what kinds
• 19:14
  Speaker 2: of experiments are possible. Differential measurements against atomic clocks become
• 19:19
  Speaker 2: a practical tool rather than a theoretical proposal.
• 19:23
  Speaker 3: The papers in Nature mark the transition from decades of
• 19:26
  Speaker 3: preparatory spectroscopy to operational clocks. That is a genuine milestone
• 19:31
  Speaker 3: for precision measurement.
• 19:33
  Speaker 2: We now have a clock that uses the nucleus of
• 19:35
  Speaker 2: thorium-229 as its reference, and that can stabilize itself for
• 19:39
  Speaker 2: a full day. It has already been used to constrain
• 19:42
  Speaker 2: certain models of dark matter. That combination of new technology
• 19:46
  Speaker 2: and new physics is what makes the result worth paying
• 19:49
  Speaker 2: attention to.
• 19:50
  Speaker 3: It will be fascinating to see how far the precision
• 19:52
  Speaker 3: can be pushed and what new limits or unexpected signals
• 19:55
  Speaker 3: appear as the clocks improve. For now, the first self-stabilizing
• 19:59
  Speaker 3: nuclear clock is ticking in Vienna, and the field has
• 20:02
  Speaker 3: a new instrument.