1971 atomic clock experiment

Hafele-Keating experiment

The hafele-keating experiment: a groundbreaking test of time dilation, a brief overview of time dilation, designing the hafele-keating experiment, results and implications, impact on modern physics, applications in technology, concluding thoughts.

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Airborne Atomic Clocks to Test Einstein Time Theory

By Harold M. Schmeck Jr. Special to The New York Times

Oct. 2, 1971

WASHINGTON, Oct. 1—Two scientists and four atomic clocks will fly around the world next week to test one of the crucial implications of Einstein's theory of relativity.

The purpose of the flight is to test the so‐called clock paradox, which holds that a clock moving at high velocity will lose time relative to a clock standing still. In effect the passage of time would be slowed.

Because of this effect, it has been argued that a space traveler covering immense distances at extreme speeds would return to the earth younger than his twin who stayed home.

At ordinary speeds the effect would be so small as to defy measurement. However, Dr. Joseph C. Hafele, an assistant professor of physics at Washington University in St. Louis, has made some calculations showing theta the test is feasible with commercial jet airliners and the United States Naval Observatory's highly sophisticated cesium clocks.

The time consequences of Einstein's theories have been tested indirectly in the past by astronomical observations and by studies of the behavior of subatomic particles moving at extremely high velocities. All these tests have confirmed the Einstein predictions.

First Direct Test

Dr. Hafele said there had not been a previous experiment, to his knowledge, that used a clock, and therefore this could be called a direct test of the prediction. He expects the time effects to be borne out, but the physicist said there were some scientists who argued that there would be no effect on the measurement of time.

Dr. Hafele's calculations have persuaded scientists at the observatory to go ahead with the experiment. They are lending him four atomic clocks and the necessary auxiliary equipment and are sending an astronomer, Richard Keating, along on the flight.

The Navy will pay the bill, which amounts to about $3,700 in airline fares at the rate the Government pays commercial carriers.

The expedition will leave Dulles International Airport at 7:45 P.M. Monday on Pan American World Airways Flight 106, a Boeing 747 bound for London. Four seats will be occupied in the tourist cabin—two for the scientists and two for the clocks.

In an interview by telephone Dr. Hafele said the eastward flight around the world would be followed by a second trip in the opposite direction.

On each flight the time readings of the four clocks will be averaged, and the average will be compared with the Naval Observatory's reference clock.

A spokesman for the observatory said the operating characteristics of all the clocks were known and that none of the four to be used in the flight gains or loses more than 26 billionths of a second day.

Furthermore, it was explained that the rates at which they “drift” from the theoretically perfect time‐keeping were also known and could be taken into account in the calculations.

The clocks measure the pas sage of time by extremely regular pulses of electricity emitted by oscillating crystals. These crystal oscillators are in turn kept at an even more regular rate by the radioactive decay of cesium atoms.

These high‐precision atomic disintegrations act as a governor, so to speak, on the oscillator. The clocks also have small clock faces with conventional hour, minute and second hands, but these serve only to give a rough approximation of the time.

The calculations to test the effects of velocity on time must take into account not only the measured time but also the rotation of the earth and the slight diminution of gravity at the flight altitudes above 30,000 feet.

On the eastward trip, the airplane's speed will be added to the earth's rotational speed, which is about 1,000 miles an hour at the equator.

If this were the only effect, the clocks should lose time slightly relative to the observatory's reference clock. But Dr. Hafele said today that his latest calculations show the gravitational effect might offset this.

The relativity prediction holds that time would pass more slowly in a strong gravitational field than in a weak one. The stay‐at‐home clock in Washington will he subject to stronger gravity than the four airborne clocks because of the altitude difference.

Dr. Hafele said his calculations show that the airborne clocks should gain about 50 billionths of a second over the reference clock during the trip because of this factor.

On the westward global flight later this month, the airplane speed will have to be subtracted from the earth's rotation. Thus, to a hypothetically neutral observer in space, the clock in Washington will be moving at a higher velocity than the four in flight. The reference clock on the ground, therefore, will be losing time. Dr. Hafele estimates the difference at about 300 one‐billionths of a second for the entire trip.

The flight will be the physicist's first trip around the world, but it will hardly qualify as a pleasure junket. He and his colleague will change planes in London, picking up another Pan Am flight that will take them to Frankfurt, Istanbul, Beirut. Tehran, New Delhi, Bangkok, Tokyo, Honolulu and Los Angeles. They, will take an American Airlines flight on the final leg back to Dulles.

The whole trip will take about 60 hours. The longest planned stop is two hours in Honolulu.

Tru Physics

Hafele-Keating Experiment

Table of Contents

Introduction

The Hafele-Keating experiment was a test of the theory of relativity. In October 1971, Joseph C. Hafele, a physicist, and Richard E. Keating, an astronomer, took four cesium-beam atomic clocks aboard commercial airliners. They flew twice around the world, first eastward, then westward, and compared the clocks against others that remained at the United States Naval Observatory.

Basics of the Experiment

The experiment was designed to investigate the effects of both special and general relativity. According to special relativity, moving clocks are measured to be ticking more slowly than stationary ones (time dilation), while general relativity predicts that clocks closer to a massive object will tick slower than those located further away (gravitational time dilation).

Calculations Involved

The predicted time dilation due to velocity (special relativity) and gravitational potential (general relativity) is given by:

Results of the Experiment

The results of the experiment were consistent with the predictions of relativity. The time difference of the traveling clocks was in agreement with relativistic predictions, thus providing confirmation of the time dilation effects as predicted by the theory of relativity.

Conclusion and Impact

The Hafele-Keating experiment was one of the first empirical tests of the predictions of both special and general relativity. By showcasing time dilation effects in a real-world setting, it provided a significant confirmation of Einstein’s theories, and paved the way for further explorations of relativistic effects, such as those necessary for the accurate operation of the Global Positioning System (GPS).

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The hafele–keating experiment.

In 1971, time dilation, predicted by the special (and the general) theory of relativity, was experimentally verified in a particularly convincing manner. The brilliant idea for that experiment was concocted by Hafele and Keating , who used scheduled flights to carry two very precise atomic clocks around the earth close to the equator, one in eastbound flights and the other one in westbound flights (Fig. 3.1)…

The Hafele–Keating experiment was a test of the theory of relativity. In October of 1971, J. C. Hafele and Richard E. Keating took four cesium-beam atomic clocks aboard commercial airliners and flew twice around the world, first eastward, then westward, and compared the clocks against those of the United States Naval Observatory.

According to special relativity, the speed of a clock is greatest according to an observer who is not in motion with respect to the clock. In a frame of reference in which the clock is not at rest, the clock runs slower, and the effect is proportional to the square of the velocity. In a frame of reference at rest with respect to the center of the earth, the clock aboard the plane moving eastward, in the direction of the earth's rotation, is moving faster than a clock that remains on the ground, while the clock aboard the plane moving westward, against the earth's rotation, is moving slower.

According to general relativity, another effect comes into play: the slight increase in gravitational potential due to altitude that speeds the clocks back up. Since the aircraft are flying at roughly the same altitude in both directions, this effect is more "constant" between the two clocks, but nevertheless it causes a difference in comparison to the clock on the ground.

The results were published in Science in 1972:[1][2]

	predicted			measured
	nanoseconds gained
	gravitational (general relativity)	kinematic (special relativity)	total	measured
eastward	144±14	−184 ± 18	−40 ± 23	−59 ± 10
westward	179±18	96±10	275±21	273±7

The published outcome of the experiment was consistent with special relativity, and the observed time gains and losses were reportedly different from zero to a high degree of confidence.

That result was contested by Dr. A. G. Kelly who examined the raw data: according to him, the final published outcome had to be averaged in a biased way in order to claim such a high precision.[3] Also, Louis Essen, the inventor of the atomic clock, published an article in which he discussed the (in his opinion) inadequate accuracy of the experiment.[4]; however, neither of these publications are in peer-reviewed sources.

One notable approximate repetition of the original experiment took place on the 25th anniversary of the original experiment, using more precise atomic clocks, and the results were verified to a higher degree of accuracy.[5]. Nowadays such relativistic effects have been incorporated into the calculations used for the GPS system[6].

The equations and effects involved in the experiment are:

Total time dilation

Τ = Δτ v + Δτ g + Δτ s

Gravitation

Sagnac effect

Where h = height, v = velocity, ω = Earth's rotation and τ represents the duration/distance of a section of the flight. The effects are summed over the entire flight, since the parameters will change with time.

* Twin paradox * Time dilation * GPS Time Dilation

Retrieved from "http://en.wikipedia.org/" All text is available under the terms of the GNU Free Documentation License

September 23, 2010

How Time Flies: Ultraprecise Clock Rates Vary with Tiny Differences in Speed and Elevation

Newly developed optical clocks are so precise that they register the passage of time differently at elevations of just a few dozen centimeters or velocities of a few meters per second

By John Matson

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If you're enjoying this article, consider supporting our award-winning journalism by subscribing . By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

If you have ever found yourself cursing a noisy upstairs neighbor, take solace in the fact that he or she is aging faster than you are. Albert Einstein's theory of general relativity predicts that clocks at different gravitational potentials will tick at different rates—a clock at higher elevation will tick faster than will a clock closer to Earth's center. In other words, time passes more quickly in your neighbor's upstairs apartment than it does in your apartment. To complicate matters, the theory of special relativity, which preceded general relativity by a decade, predicts a similar effect for clocks in motion— a stationary clock will tick faster than a moving clock . This is the source of the famous twin paradox: Following a round-trip journey on a spaceship traveling at some exceptionally high velocity, a traveler would return to Earth to find that her twin sibling is now older than she is, because time has passed more slowly on the moving ship than on Earth. Both of these so-called time dilation effects have been verified in a number of experiments throughout the decades, which have traditionally depended on large scales of distance or velocity. In one landmark 1971 test Joseph Hafele of Washington University in Saint Louis and Richard Keating of the U.S. Naval Observatory flew cesium atomic clocks around the world on commercial jet flights, then compared the clocks with reference clocks on the ground to find that they had diverged, as predicted by relativity . But even at the speed and altitude of jet aircraft, the effects of relativistic time dilation are tiny—in the Hafele–Keating experiment the atomic clocks differed after their journeys by just tens to hundreds of nanoseconds. Thanks to improved timekeeping, similar demonstrations can now take place at more mundane scales in the laboratory. In a series of experiments described in the September 24 issue of Science , researchers at the National Institute of Standards and Technology (NIST) in Boulder, Colo., registered differences in the passage of time between two high-precision optical atomic clocks when one was elevated by just a third of a meter or when one was set in motion at speeds of less than 10 meters per second. Again, the effects are minuscule: It would take the elevated clock hundreds of millions of years to log one more second than its counterpart, and a clock moving a few meters per second would need to run about as long to lag one second behind its stationary counterpart. But the development of optical clocks based on aluminum ions, which can keep time to within one second in roughly 3.7 billion years, allows researchers to expose those diminutive relativistic effects. "People usually think of it as negligible, but for us it is not," says lead study author James Chin-wen Chou , a postdoctoral research associate at NIST. "We can definitely see it." The NIST group's optical clocks use lasers to probe the quantum state of aluminum ions held in radio-frequency traps. When the laser's frequency is just right, it resonates with a transition between quantum states in the aluminum ion whose frequency is constant in time. By constantly tuning the laser to drive that aluminum transition, an interaction that only occurs in a tiny window near 1.121 petahertz (1.121 quadrillion cycles per second), the laser's frequency can be stabilized to an exquisitely sensitive degree, allowing it to act as the clock's pendulum. "If we anchor the frequency of the oscillator—in our case, laser light—to the unchanging, stable optical transition in aluminum, the laser oscillation can serve as the tick of the clock," Chou explains. To put the sensitivity of the optical clocks in perspective, Chou notes that the two timekeepers in the study differed after a height change of a mere step on a staircase—never mind the entire floor separating you from your noisy neighbor—or with just a few meters per second of motion. "If you push your daughter on a swing, it's about that speed," he says. In the past, such relativistic experiments have involved either massive scales of distance or velocity, or else oscillations so fast that their ticks cannot be reliably counted for timing purposes, says Holger Müller , an atomic physicist at the University of California, Berkeley. "It's an enormous achievement that you can build optical clocks so good that you can now see relativity in the lab," he says. Müller has used atom interferometry to make precision measurements of relativistic effects, measurements that rely not on counting individual oscillations but on tracking the interference between two waves. (The frequencies of such waves, which oscillate tens of billions of times faster than the petahertz laser in an aluminum clock, are simply too high to monitor and count.) It is a process akin to striking two tuning forks to listen to the pulsations of their interference, without actually measuring how many times each fork vibrates. In that sense atom interferometers are pendulums without clockwork, so although they can make physical measurements with great precision, they cannot be used to keep time. "The new work operates on familiar scales of distance and velocity, with clocks that can be used for universal timing applications," Müller says. "They see the effects of general and special relativity, and that makes relativity something you can kind of see and touch."

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Hafele–Keating experiment (1971)

In our previous article Gravitational redshift Part III - Experiments , we have mentionned the Pound–Rebka experiment , proposed in 1959 by Robert Pound and his graduate student Glen A. Rebka Jr, to test the gravitational redshift or Einstein effect, predicted as soon as 1907 in Einstein's paper On the relativity Principle and the conclusions drawn from it" .

This experiment, as successfull as it was - the result confirmed that the predictions of general relativity were borne out at the 10% level, still had two limitations:

- it only tested gravitational time dilation

- it was not measured with macroscopic clocks

In October 1971, Hafele and Keating flew cesium beam atomic clocks [1] around the world twice on regularly scheduled commercial airline flights, once to the East and once to the West.

In the opening statement of the first of two papers on the subject, the authors refer to the debate surrounding the "twins paradox" and how an experiment with macroscopic clocks might provide an empirical resolution.

In this experiment, both gravitational time dilation and kinematic time dilation are significant - and are in fact of comparable magnitude. Their predicted and measured time dilation effects were as follows:

Let us see how to calculate these relativistic predictions.

Kinematic effects (Special Relativity)

First let us consider as inertial referential the so called ECI ( Earth Centered Inertial ) with the center of Earth as origin but which does NOT rotate with the Earth [2] . In this non-rotating referential, we will note +v the speed with respect to the earth of the plane flying eastwards and -v the speed with respect to the earth of the plane flying westwards.

Consequently, a plane will fly with the velocity RΩ+v (respectively RΩ-v ) with respect to the ECI referential , R being the earth's radius at the equator and Ω the rotational speed of earth. We can use the Newton's addition of speed law there as we ignore the terms in higher order than v 2 /c 2 .

The ratio of the proper time interval (as mesured between two beats of the on-board clock) and the time interval as measured in ECI is then given by the usual Lorentz factor, as the consequence of the Transverse Doppler Effect

Therefore the relative shift of frequency between a flying clock and another one at rest in the ECI is given by:

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Old News, Vintage Photos & Nostalgic Stories

Hafele–keating experiment – two atomic clocks flew twice around the world, eastward and westward. back at home, they each showed different times.

Strangeness

The Hafele–Keating experiment was a test of the theory of relativity. In October 1971, Joseph C. Hafele, a physicist, and Richard E. Keating, an astronomer, took four cesium-beam atomic clocks aboard commercial airliners. They flew twice around the world, first eastward, then westward, and compared the clocks against others that remained at the United States Naval Observatory. When reunited, the three sets of clocks were found to disagree with one another, and their differences were consistent with the predictions of special and general relativity.

“During October 1971, four cesium atomic beam clocks were flown on regularly scheduled commercial jet flights around the world twice, once eastward and once westward, to test Einstein’s theory of relativity with macroscopic clocks. From the actual flight paths of each trip, the theory predicted that the flying clocks, compared with reference clocks at the U.S. Naval Observatory, should have lost 40+/-23 nanoseconds during the eastward trip and should have gained 275+/-21 nanoseconds during the westward trip … Relative to the atomic time scale of the U.S. Naval Observatory, the flying clocks lost 59+/-10 nanoseconds during the eastward trip and gained 273+/-7 nanosecond during the westward trip, where the errors are the corresponding standard deviations. These results provide an unambiguous empirical resolution of the famous clock “paradox” with macroscopic clocks.”

One of the actual HP 5061A Cesium Beam atomic clock units used in the Hafele–Keating experiment. By Binarysequence - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=24592511

In his original 1905 paper on special relativity, Einstein suggested a possible test of the theory: “Thence we conclude that a spring-clock at the equator must go more slowly, by a very small amount, than a precisely similar clock situated at one of the poles under otherwise identical conditions.” Because he had not yet developed the general theory, he did not realize that the results of such a test would, in fact, be null, since the surface of the earth is a gravitational equipotential, and therefore the effects of kinematic and gravitational time dilation would precisely cancel.

Since the Hafele–Keating experiment has been reproduced by increasingly accurate methods, there has been a consensus among physicists since at least the 1970s that the relativistic predictions of gravitational and kinematic effects on time have been conclusively verified. Criticisms of the experiment did not address the subsequent verification of the result by more accurate methods and have been shown to be in error.

Historical photos and information about the Hafele-Keating experiment

Ben Crowell

I teach physics, and I love the Hafele-Keating experiment as a way to introduce relativity. Because the experiment has a lot of charisma, it's cool to be able to show students photos of the men and the clocks aboard the plane. I've obtained and scanned copies some of these and posted them here. Below each low-resolution photo is a link to a full-resolution version.

In the course of digging up the photos, I ended up compiling some other links and information. Below the photos I've presented some of these items that might be of historical or pedagogical interest.

Hafele and Keating with clocks

[ Full resolution ]

This photo is from Time Magazine, October 18, 1971, where it appeared with "AP" written above the upper right corner. Georgina Brenner, who works for the BBC, has contacted The Associated Press and says, "they have confirmed they do not hold the copyright for that photo. We are now trying to get in touch with Time Magazine and Popular Mechanics, but this is proving difficult." Based on this information, it seems likely to me that Hafele and Keating just took a camera with them, and after being allowed to board early, they rounded up a crew member to take some snapshots. The photos would then be in the public domain because the photographer would not have renewed their copyright as required in that era. In the event that this photo is still copyrighted, it is reproduced here under the fair use exception to U.S. copyright law. Article (paywalled). I have retouched the photo, but that retouching is not copyrightable under U.S. law.

An online listing of errata for early editions of the textbook by Hartle says that the photo (below) of Luther and Dabney had been published with an erroneous caption describing them as Hafele and Keating. Hartle says, "A correct picture of Hafele and Keating [the one shown above] on their initial flight is below. Thanks to Robert Nelson of the Satellite Engineering Research Corporation for pointing out this error and supplying the correct picture." It is therefore possible that the photo was taken by Nelson, or it may be that Nelson simply supplied Hartle with a copy.

Hafele and Keating with clocks and stewardess

From Popular Mechanics, January 1972, p. 30. Article in Google Books. I don't know the copyright status of this photo. This issue of Popular Mechanics does not give specific photo credits for almost any of the photos in it. If this was a snapshot taken by the crew or another passenger, then it is now in the public domain due to its publication without notice before 1977. If it was taken by a photographer as a work for hire, then it is (c) 1971 Hearst Corporation. If it was taken by an employee of the U.S. Naval Observatory, then it is a public-domain product of the U.S. government. In the event that it is copyrighted, I am reproducing it here under the fair use exception to U.S. copyright law. I have retouched the photo, but that retouching is not copyrightable under U.S. law.

Luther and Dabney boarding plane

This photo, from the same era as the Hafele-Keating experiment, shows U.S. Naval Observatory technicians George Luther and Bill Dabney boarding a commercial plane with an atomic clock. It is a public-domain product of the U.S. government.

Navy plane and clock used for Alley's Chesapeake Bay experiment

These photos show a plane and set of atomic clocks used in a 1975-6 experiment by Alley et al., which was basically a higher-precision repeat of the Hafele-Keating experiment. Inside the sealed box are three Cs clocks and three Rb clocks. The plane's motion was measured accurately by radar so that the kinematic time dilation could be eliminated. A pulsed laser system was used in order to get a real-time comparison of the flying clocks with an identical set on the ground, thereby measuring the gravitational time dilation at the plane's 9000 m elevation. I'm guessing that the top photo might be public domain, since the plane is a Navy plane. I don't know the copyright status of the bottom one.

Other contemporary accounts in the popular press

Scientific papers describing the hafele-keating experiment, papers by alley et al..

A group at the University of Maryland led by C. Alley did clock-on-plane experiments similar to Hafele and Keating's, improving the precision and measuring the relativistic effects to about 1% and testing the dependence on variables such as latitude.

Other scientific papers of historical or pedagogical interest

Modern hobbyist Tom Van Baak has done a truly amazing mountain-valley experiment of this flavor with a second-hand atomic clock in the family minivan. There is a web site and mailing list (Time Nuts) for people who do high-precision timing experiments for fun, and they have a museum with old photos and documentation.

I would be grateful to anyone who could e-mail me with any of the following:

50th Anniversary of 1971 Hafele-Keating Experiment

Archive photos, anniversary photos (october 2021 / bellevue, wa), 50 years ago today, time magazine, october 18, 1971.

Hafele-Keating Experiment Reassessed

September 2020

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The Time Dilation Experiment: How Physicists Prove Its Real

As a team of physicists, we are fascinated by the concept of time dilation. It is a fundamental aspect of Einstein's Theory of Relativity that describes how time can appear to pass differently for two observers in different frames of reference. This theory has been proven experimentally time and time again, and today we want to take you through some of the most compelling experiments that have been conducted to demonstrate this phenomenon.

The first thing we need to understand is what time dilation actually means. In simple terms, it refers to the fact that time appears to move slower for an observer who is moving relative to another observer who is stationary. This may sound counterintuitive, but it has been demonstrated repeatedly through carefully designed experiments. These experiments not only help us better understand the nature of our universe but also have practical implications in fields such as GPS technology and space travel. So let's dive into the exciting world of physics and explore some fascinating examples of how physicists prove that time dilation is real!

Understanding Time Dilation Theory

[the concept of time dilation experiment, the first time dilation experiment, recent time dilation experiments, atomic clock experiment, gravitational time dilation experiment, results and analysis, implications of time dilation, applications in space travel, theoretical implications, future research and development, frequently asked questions, how does time dilation theory relate to einstein's theory of relativity, are there any potential drawbacks or limitations to performing time dilation experiments, how do physicists account for the effects of time dilation in practical applications, such as gps systems, can time dilation be observed in everyday life, or is it only detectable in extreme conditions, what are some current areas of research or future applications for time dilation theory.

Understanding the mind-bending theory of time dilation is essential for grasping the intricacies of Einstein's theory of relativity. In simple terms, time dilation can be defined as the difference in elapsed time between two events that occur at different distances from a gravitational mass or relative to each other's motion. This means that time passes slower for an object in motion or near a massive object than it does for an observer who is stationary and far away.

To understand this concept better, let's take an example. Imagine two synchronized clocks placed at different altitudes - one on top of Mount Everest and another at sea level. According to the theory of general relativity, because gravity is weaker at higher altitudes, the clock on Mount Everest would tick faster than the one at sea level. This phenomenon can be explained mathematically using equations such as Lorentz transformations and special relativity formulas.

With this understanding of time dilation, we can now delve into the concept of time dilation experiment without missing any crucial details.

](/blog/time-travel-theories/time-dilation/time-dilation-experiment-physicists-prove-real)As we delve deeper into the concept of measuring time in different ways, a mind-bending realization starts to take shape. The theory of relativity suggests that time is not constant and can be influenced by various factors, such as gravity and motion. To prove this theory, physicists have conducted numerous experiments over the years using advanced measurement techniques and observational evidence.

To further illustrate the concept of time dilation, here are some key points to consider:

According to the theory of relativity, time passes more slowly in strong gravitational fields or at high velocities.
This means that if two individuals were traveling at different speeds or in different gravitational fields, they would experience time differently.
The first experimental evidence for time dilation came from the famous Hafele-Keating experiment in 1971, which involved atomic clocks being flown around the world on commercial airliners.

With these ideas in mind, let us explore how physicists were able to conduct their first time dilation experiment.

You will delve into the first demonstration of time's non-constant nature through an experiment using advanced measurement techniques and observational evidence. The first time dilation experiment was conducted by two physicists, Joseph Hafele and Richard Keating, in 1971. They flew atomic clocks on separate commercial airplanes that traveled around the world in opposite directions. This experimental setup allowed them to compare the elapsed time of one clock with respect to another.

The data collection process involved comparing the readings of the clocks after they returned from their journeys. The results showed that the clock traveling westward experienced a slower passage of time than the stationary clock on Earth, whereas the clock flying eastward experienced a faster passage of time than its counterpart on Earth. This finding provided strong evidence for Einstein's theory of relativity and proved that time dilation is not just a theoretical concept but a real phenomenon that occurs in our universe.

This groundbreaking experiment paved the way for further research into understanding how gravity affects space-time and led to more recent time dilation experiments exploring new frontiers such as black holes and neutron stars.

In recent years, there have been several groundbreaking experiments that further prove the existence of time dilation. One such experiment involved atomic clocks, which are incredibly precise timekeeping devices. By measuring the differences in time between two identical atomic clocks (one stationary and one in motion), scientists were able to observe time dilation effects predicted by Einstein's theory of relativity.

Another experiment involved observing gravitational time dilation, which occurs when an object is located near a massive body causing it to experience slower time than an observer farther away from the massive body. Scientists observed this effect by using extremely sensitive atomic clocks placed at different heights above sea level.

The results and analysis of these experiments provide even more evidence for the reality of time dilation and its importance in our understanding of physics.

You'll feel the ticking of an atomic clock in your bones as you imagine the precision and accuracy required for this experiment. Atomic clocks are the standard for measuring time with extreme accuracy, relying on the natural vibrations of cesium atoms to keep incredibly precise time. The recent atomic clock experiment conducted by physicists tested whether or not time dilation occurs at different altitudes above Earth's surface.

The test involved comparing two identical atomic clocks: one kept on the ground and another taken up to a high altitude via airplane. The results confirmed that time dilation does indeed occur, with the higher altitude clock running slightly faster than its grounded counterpart due to gravitational differences. This level of atomic clock accuracy is essential for measuring even the smallest differences in time dilation, providing crucial data for theories like Einstein's theory of relativity.

Now, let's move on to the next step where we explore how physicists conduct experiments that prove gravitational time dilation is real.

Get ready to feel the thrill of discovery as we delve into the fascinating world of gravitational time differences and how they can be measured with incredible precision. The gravitational time dilation experiment involves measuring the difference in time between two clocks placed at different altitudes in a gravitational field. As Einstein's theory of general relativity predicted, time moves slower closer to a massive object due to the curvature of space-time caused by gravity.

Experimental evidence for this effect was first observed in 1962 when atomic clocks on board airplanes flew around the Earth and were found to be out of sync with identical clocks on the ground. More recent experiments have used highly precise atomic clocks flown on airplanes or launched into space satellites to measure these effects even more accurately. These experiments have also been able to detect other factors that can affect time dilation, such as changes in velocity and gravitational waves. With this technology, physicists are able to confirm that general relativity is indeed an accurate description of our universe.

As we move onto discussing results and analysis, it's important to note that these experiments have not only provided evidence for Einstein's theory but also opened up new avenues for research into fundamental physics, including investigations into dark matter and quantum gravity.

Now we can finally see the fascinating and groundbreaking results that confirm Einstein's theory of general relativity. The gravitational time dilation experiment has provided evidence that time slows down in stronger gravitational fields, which is consistent with the predictions made by the theory. By using precision measurement techniques to compare atomic clocks at different altitudes, scientists have demonstrated that time passes more slowly closer to massive objects.

The results obtained from this experiment are statistically significant and provide strong support for Einstein's theory. They indicate that gravity affects not only space but also time, which is a fundamental concept in physics. These findings have important implications for our understanding of the universe and its behavior. As we move on to discussing the implications of time dilation, we must keep in mind how crucial these experimental results are for advancing our knowledge of physics.

So now that we understand the basics of time dilation and how it has been experimentally proven, let's look at some of its implications. First, there are practical applications for space travel: as objects near the speed of light experience less time than those at rest, astronauts on long space missions could age slower than their counterparts on Earth. Secondly, time dilation has theoretical implications for our understanding of the nature of time itself and its relationship to space. Finally, continued research and development in this area could lead to new technologies and a deeper understanding of fundamental physics.

You'll be fascinated to learn that space travel could become more efficient and faster with the use of time dilation, as demonstrated by the fictional spacecraft in the movie Interstellar. The concept behind this is simple: if astronauts travel at a speed close to the speed of light, their time will slow down relative to those on Earth. This means that they can effectively age slower than their counterparts back home, allowing them to spend more time exploring and less time aging.

This has huge implications for astronaut travel, as it means that we can potentially send humans on long-duration missions without worrying about the effects of prolonged exposure to zero gravity. Furthermore, it also opens up possibilities for interstellar travel and even time travel (in theory). Of course, there are still many technical challenges that need to be overcome before we can realize these dreams, but it's an exciting prospect nonetheless. With all of this in mind, let's delve deeper into the theoretical implications of time dilation.

We can hardly contain our excitement as we explore the mind-boggling theoretical implications of time slowing down at high speeds. Philosophical considerations arise when we ponder how this phenomenon challenges our understanding of the nature of time itself. Our traditional view of time as an absolute and constant entity is shattered by the reality that it can warp and distort depending on relative motion.

The practical implications are equally fascinating. Time dilation has been observed in experiments involving atomic clocks, which have shown that even fractions of a second can make a significant difference over long distances or high velocities. This has important implications for GPS systems, where precise timing is critical for accurate location tracking. As we continue to unravel the mysteries of time dilation, future applications in fields such as space travel and telecommunications may become possible. But first, more research and development is needed to fully harness this incredible phenomenon.

You're about to discover the exciting possibilities that lie ahead in the field of researching and developing new technologies that can harness the incredible effects of time distortion at high speeds. With the confirmation of time dilation through experiments, scientists are now exploring ways to apply this phenomenon in innovative timekeeping devices and space travel. One potential application is using atomic clocks on spacecraft to accurately measure time in space, where the effects of gravity and velocity can distort time.

Technological advancements in quantum mechanics and nanotechnology are also paving the way for more precise measurements of time dilation. Researchers are experimenting with using quantum entanglement to create ultra-precise clocks that could be used for navigation or even detecting gravitational waves. As we continue to uncover more about this fascinating aspect of physics, it's clear that there are countless possibilities for future research and development in this field.

When discussing time dilation theory, it's impossible not to mention Einstein's contributions to the field of physics. His theory of relativity revolutionized our understanding of space and time, showing that they are intertwined and not absolute. Time perception is a crucial aspect of this theory, as it suggests that time can appear differently depending on one's frame of reference. This idea has been tested and proven in various experiments, including the famous Hafele-Keating experiment where atomic clocks were flown around the world to measure differences in elapsed time due to changes in velocity and gravity. Overall, Einstein's work on relativity paved the way for further exploration into the nature of time and how it relates to our physical universe.

When it comes to performing time dilation experiments, there are certainly limitations and potential drawbacks to consider. One major limitation is the accuracy of the experiment itself. In order to measure time dilation accurately, physicists must use incredibly precise instruments and methods. Even small errors in measurement could lead to inaccurate results, which could have serious implications for our understanding of the universe. Another potential drawback is that time dilation experiments can be incredibly complex and difficult to carry out. They require a great deal of planning, resources, and expertise, which may not always be available. Despite these challenges, however, time dilation experiments remain an important tool for physicists seeking to better understand the nature of time and space.

When it comes to practical implications of time dilation, physicists have developed experimental methods that help account for its effects. For instance, GPS systems rely on precise timing to determine a user's location. However, the satellites that send signals to GPS devices are in motion relative to the Earth and therefore experience time dilation. To ensure accurate timing, scientists must adjust the clocks on the satellites based on calculations of their velocity and altitude. By doing so, they can correct for the effects of time dilation and provide users with reliable location data. Overall, while time dilation can pose challenges in certain applications, physicists have found ways to mitigate its impact through careful experimentation and analysis.

Everyday examples of time dilation can be observed in our daily lives. One example is the aging process, where time appears to pass more quickly for those who are moving at higher speeds relative to a stationary observer. Experimental methods have also been used to prove the existence of time dilation, such as high-speed particle accelerators and spacecraft traveling at high velocities. These experiments have shown that time dilation is not just a theoretical concept, but a real phenomenon that occurs in extreme conditions as well as everyday situations.

Future implications of time dilation theory are vast and exciting. Technological advancements in the field will allow for more precise measurements, leading to a deeper understanding of the universe's fundamental workings. To put this into perspective, consider that the world's most accurate atomic clock loses only one second every 15 billion years due to time dilation effects. This level of precision is necessary for research in areas such as space exploration, satellite communication, and GPS technology. As we continue to push the limits of our understanding of time and space, time dilation theory will undoubtedly play a crucial role in shaping our future discoveries and innovations.

So, there you have it – time dilation is not just a theory, but a proven fact. Through various experiments conducted over the years, physicists have demonstrated that time really does slow down when an object moves at high speeds or experiences intense gravitational forces.

But what does this mean for us? Well, it has implications for everything from our GPS systems (which rely on precise timing) to our understanding of the universe itself. It's mind-boggling to think about how much we've learned through these experiments and how much more we still have yet to discover. The possibilities are endless and truly exciting.

In conclusion, time dilation is one of those concepts that can seem too abstract and outlandish to be believed at first glance. But thanks to the hard work and ingenuity of countless scientists over the years, we now know that it's real – a verified phenomenon that shapes our world in ways we're only beginning to understand. It's proof that sometimes even the wildest theories can turn out to be true – a testament to human curiosity and perseverance if ever there was one.

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In a new experiment, physicists used a laser (shown) to probe a jump between two energy levels in thorium-229, which could serve as a nuclear clock.

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Major leap for nuclear clock paves way for ultraprecise timekeeping

by National Institute of Standards and Technology

The world keeps time with the ticks of atomic clocks, but a new type of clock under development—a nuclear clock—could revolutionize how we measure time and probe fundamental physics.

An international research team led by scientists at JILA, a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder, has demonstrated key elements of a nuclear clock. A nuclear clock is a novel type of timekeeping device that uses signals from the core, or nucleus, of an atom.

The team presents the results in the Sept. 4 issue of the journal Nature as a cover story.

The team used a specially designed ultraviolet laser to precisely measure the frequency of an energy jump in thorium nuclei embedded in a solid crystal. They also employed an optical frequency comb , which acts like an extremely accurate light ruler, to count the number of ultraviolet wave cycles that create this energy jump. While this laboratory demonstration is not a fully developed nuclear clock, it contains all the core technology for one.

Nuclear clocks could be much more accurate than current atomic clocks , which provide official international time and play major roles in technologies such as GPS, internet synchronization, and financial transactions.

For the general public, this development could ultimately mean even more precise navigation systems (with or without GPS), faster internet speeds, more reliable network connections, and more secure digital communications.

Beyond everyday technology, nuclear clocks could improve tests of fundamental theories for how the universe works, potentially leading to new discoveries in physics. They could help detect dark matter or verify if the constants of nature are truly constant, allowing for verification of theories in particle physics without the need for large-scale particle accelerator facilities.

Laser precision in timekeeping

Atomic clocks measure time by tuning laser light to frequencies that cause electrons to jump between energy levels . Nuclear clocks would utilize energy jumps within an atom's tiny central region, known as the nucleus, where particles called protons and neutrons cram together.

These energy jumps are much like flipping a light switch. Shining laser light with the exact amount of energy needed for this jump can flip this nuclear "switch."

A nuclear clock would have major advantages for clock precision. Compared with the electrons in atomic clocks, the nucleus is much less affected by outside disturbances such as stray electromagnetic fields. The laser light needed to cause energy jumps in nuclei is much higher in frequency than that required for atomic clocks.

This higher frequency—meaning more wave cycles per second—is directly related to a greater number of "ticks" per second and therefore leads to more precise timekeeping.

But it is very hard to create a nuclear clock. To make energy jumps, most atomic nuclei need to be hit by coherent X-rays (a high-frequency form of light) with energies much greater than those that can be produced with current technology. So scientists have focused on thorium-229, an atom whose nucleus has a smaller energy jump than any other known atom, requiring ultraviolet light (which is lower in energy than X-rays).

In 1976, scientists discovered this thorium energy jump, known as a "nuclear transition" in physics language. In 2003, scientists proposed using this transition to create a clock, and they only directly observed it in 2016. Earlier this year, two different research teams used ultraviolet lasers they created in the lab to flip the nuclear "switch" and measure the wavelength of light needed for it.

In the new work, the JILA researchers and their colleagues create all the essential parts of a clock: the thorium-229 nuclear transition to provide the clock's "ticks," a laser to create precise energy jumps between the individual quantum states of the nucleus, and a frequency comb for direct measurements of these "ticks."

This effort has achieved a level of precision that is one million times higher than the previous wavelength-based measurement. In addition, they compared this ultraviolet frequency directly to the optical frequency used in one of the world's most accurate atomic clocks, which uses strontium atoms, establishing the first direct frequency link between a nuclear transition and an atomic clock.

This direct frequency link and increase in precision are a crucial step in developing the nuclear clock and integrating it with existing timekeeping systems.

The research has already yielded unprecedented results, including the ability to observe details in the thorium nucleus's shape that no one had ever observed before—it's like seeing individual blades of grass from an airplane.

Toward a nuclear future

While this isn't yet a functioning nuclear clock, it's a crucial step towards creating such a clock that could be both portable and highly stable. The use of thorium embedded in a solid crystal, combined with the nucleus's reduced sensitivity to external disturbances, paves the way for potentially compact and robust timekeeping devices.

"Imagine a wristwatch that wouldn't lose a second even if you left it running for billions of years," said NIST and JILA physicist Jun Ye. "While we're not quite there yet, this research brings us closer to that level of precision."

The research team included researchers from JILA, a joint institute of NIST and the University of Colorado Boulder; the Vienna Center for Quantum Science and Technology; and IMRA America, Inc.

Journal information: Nature

Provided by National Institute of Standards and Technology

This story is republished courtesy of NIST. Read the original story here .

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Breakthrough: Scientists Create World's First Nuclear Clock Prototype

A huge breakthrough decades in the making was made just a few months ago , and already scientists are realizing its potential: A measurement of the gap between the quantum energy states of a thorium nucleus has been used to create the very first, rudimentary nuclear clock.

By coupling a strontium atomic clock with a crystal containing thorium nuclei, a team of physicists has successfully demonstrated the core technology that will lead us to the first fully realized and developed nuclear clock.

That milestone – still yet to be reached – will open up a whole new realm of ultra-precise timekeeping.

"With this first prototype, we have proven: Thorium can be used as a timekeeper for ultra-high-precision measurements," explains physicist Thorsten Strumm of the Vienna University of Technology.

"All that is left to do is technical development work, with no more major obstacles to be expected."

An atomic clock is one that relies on the very precise 'ticking' of atoms as they switch between energy states when stimulated by a laser, as determined by the states of the electrons that whirl about the nucleus at the atomic core.

This is a lot more difficult to achieve with the nucleus itself, however, since it takes a lot more energy to shift its energy state than it does to change the energy state of electrons.

A nuclear clock is highly desirable, though, since it would be a lot more stable and precise than an atomic clock. In turn, a nuclear clock would enable more precise measurements of the physical Universe – which has implications for everything from navigation to the search for dark matter .

A measurement of the energy jump – the difference between the energy states – of a thorium nucleus was announced earlier this year . And this has allowed Strumm and his colleagues to determine the precise energy required to create the change in energy states, the mechanism on which a nuclear clock would tick.

The next step was to demonstrate that they could create a clock from this ticking, and this is what Strumm and his colleagues have now done.

The clock they demonstrated is not the full nuclear clock experience, but the first steps in that direction. The strontium clock at JILA at the National Institute of Standards & Technology is operated using infrared light.

The team created a small calcium fluoride crystal containing thorium nuclei, the energy states of which are switched using vacuum ultraviolet light.

To couple the crystal to the atomic clock, the researchers needed to find a way to convert the infrared light to ultraviolet. They did this by creating a frequency comb of infrared wavelengths, and running it through xenon gas, which interacts with the infrared light to emit ultraviolet wavelengths.

The result was a combined frequency comb that could excite the transition of the thorium nuclei and synchronize it with the ticking of the strontium atoms.

The resulting nuclear ticking isn't any more precise than the strontium atomic clock, but now that the core concept has been demonstrated, the actual technology is in sight – and very close to full realization, the researchers say.

"Imagine a wristwatch that wouldn't lose a second even if you left it running for billions of years. While we're not quite there yet, this research brings us closer to that level of precision," says physicist Jun Ye of JILA.

The team ran their experiment many times; each time, they achieved results consistent with an atomic clock. The next step will be to refine it.

"When we excited the transition for the first time, we were able to determine the frequency to within a few gigahertz. That was already more than a factor of a thousand better than anything known before. Now, however, we have precision in the kilohertz range – which is again a million times better," Schumm says .

"That way, we expect to overtake the best atomic clocks in 2-3 years."

The research has been published in Nature .

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Published: 04 September 2024

Frequency ratio of the 229m Th nuclear isomeric transition and the 87 Sr atomic clock

Chuankun Zhang ORCID: orcid.org/0000-0001-5669-9082 1 , 2 , 3 ,
Tian Ooi ORCID: orcid.org/0009-0004-2738-0186 1 , 2 , 3 ,
Jacob S. Higgins 1 , 2 , 3 ,
Jack F. Doyle 1 , 2 , 3 ,
Lars von der Wense 1 , 2 , 3 nAff7 ,
Kjeld Beeks ORCID: orcid.org/0000-0002-8707-6723 4 nAff8 ,
Adrian Leitner ORCID: orcid.org/0009-0007-1156-1881 4 ,
Georgy A. Kazakov 4 ,
Peng Li 5 ,
Peter G. Thirolf 6 ,
Thorsten Schumm ORCID: orcid.org/0000-0002-1066-202X 4 &
Jun Ye ORCID: orcid.org/0000-0003-0076-2112 1 , 2 , 3

Nature volume 633 , pages 63–70 ( 2024 ) Cite this article

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Atomic and molecular physics
Nuclear physics
Optical physics
Quantum physics

Optical atomic clocks 1 , 2 use electronic energy levels to precisely keep track of time. A clock based on nuclear energy levels promises a next-generation platform for precision metrology and fundamental physics studies. Thorium-229 nuclei exhibit a uniquely low-energy nuclear transition within reach of state-of-the-art vacuum ultraviolet (VUV) laser light sources and have, therefore, been proposed for construction of a nuclear clock 3 , 4 . However, quantum-state-resolved spectroscopy of the 229m Th isomer to determine the underlying nuclear structure and establish a direct frequency connection with existing atomic clocks has yet to be performed. Here, we use a VUV frequency comb to directly excite the narrow 229 Th nuclear clock transition in a solid-state CaF 2 host material and determine the absolute transition frequency. We stabilize the fundamental frequency comb to the JILA 87 Sr clock 2 and coherently upconvert the fundamental to its seventh harmonic in the VUV range by using a femtosecond enhancement cavity. This VUV comb establishes a frequency link between nuclear and electronic energy levels and allows us to directly measure the frequency ratio of the 229 Th nuclear clock transition and the 87 Sr atomic clock. We also precisely measure the nuclear quadrupole splittings and extract intrinsic properties of the isomer. These results mark the start of nuclear-based solid-state optical clocks and demonstrate the first comparison, to our knowledge, of nuclear and atomic clocks for fundamental physics studies. This work represents a confluence of precision metrology, ultrafast strong-field physics, nuclear physics and fundamental physics.

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Acknowledgements

We thank K. Kim, A. Aeppli, W. Warfield and W. Milner for building and maintaining the JILA 87 Sr optical clock; D. Lee, Z. Hu and B. Lewis for building and maintaining the JILA stable laser and the cryogenic Si cavity; the entire crystal growth team at TU Wien for preparation of the thorium-doped crystal; M. E. Fermann and J. Jiang for help in constructing the high-power infrared frequency comb; K. Hagen, C. Schwadron, K. Thatcher, H. Green, D. Warren and J. Uhrich for help in designing and building mechanical parts used in the detection setup; T. Brown and I. Rýger for help in designing and making electronics used in the experiment; M. Ashton, B. C. Denton and M. R. Statham for help in the shipment of radioactive samples; E. Hudson, E. Peik, J. Hur, J. Thompson, J. Weitenberg and A. Ozawa for helpful discussions; and IMRA America for collaboration. We acknowledge funding support from the Army Research Office (grant no. W911NF2010182), the Air Force Office of Scientific Research (grant no. FA9550-19-1-0148), the National Science Foundation (grant no. QLCI OMA-2016244), the National Science Foundation (grant no. PHY-2317149) and the National Institute of Standards and Technology. J.S.H. acknowledges support from a National Research Council Postdoctoral Fellowship. L.v.d.W. acknowledges funding from a Feodor Lynen fellowship from the Humboldt Foundation. P.G.T. acknowledges support from the European Research Council (Horizon 2020, grant no. 856415) and the European Union’s Horizon 2020 Programme (grant no. 664732). The 229 Th:CaF 2 crystal was grown in TU Wien with support from the European Research Council (Horizon 2020, grant no. 856415) and the Austrian Science Fund (grant DOI: 10.55776/F1004, 10.55776/J4834 and 10.55776/ PIN9526523). The project 23FUN03 HIOC (grant DOI: 10.13039/100019599) has received funding from the European Partnership on Metrology, co-financed from the European Union’s Horizon Europe Research and Innovation Programme and by the participating states. We thank the National Isotope Development Center of DoE and Oak Ridge National Laboratory for providing the Th-229 used in this work.

Author information

Lars von der Wense

Present address: Johannes Gutenberg-Universität Mainz, Institut für Physik, Mainz, Germany

Kjeld Beeks

Present address: Laboratory for Ultrafast Microscopy and Electron Scattering (LUMES), Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland

Authors and Affiliations

JILA, University of Colorado Boulder, Boulder, CO, USA

Chuankun Zhang, Tian Ooi, Jacob S. Higgins, Jack F. Doyle, Lars von der Wense & Jun Ye

NIST, Boulder, CO, USA

Department of Physics, University of Colorado Boulder, Boulder, CO, USA

Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien, Vienna, Austria

Kjeld Beeks, Adrian Leitner, Georgy A. Kazakov & Thorsten Schumm

IMRA America, Ann Arbor, MI, USA

Ludwig-Maximilians-Universität München, Garching, Germany

Peter G. Thirolf

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Contributions

C.Z., T.O., J.S.H., J.F.D., L.v.d.W., K.B., T.S. and J.Y. conceived and planned the experiment; K.B., A.L., G.A.K. and T.S. grew the thorium-doped crystal and characterized its performance; P.G.T. provided valuable insight and the parabolic mirror; and C.Z., T.O., J.S.H., J.F.D., L.v.d.W., P.L. and J.Y. performed the measurement and analysed the data. All authors wrote the manuscript.

Corresponding authors

Correspondence to Chuankun Zhang or Jun Ye .

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Extended data figures and tables

Extended data fig. 1 locking scheme used in our experimental setup..

A Yb-fiber oscillator is used to generate the fundamental frequency comb 40 . The light is amplified using a chirped pulse amplification scheme in a large mode area gain fiber. The output comb light (average power 40–50 W) is coupled to a femtosecond enhancement cavity with finesse ~600 to further enhance the peak power for efficient cavity-enhanced high harmonic generation. The 7 th harmonic is outcoupled using a grazing incidence plate 42 , 43 (GIP) and directed to the sample chamber. A portion of the pre-amplified comb light is picked off and focused to a highly nonlinear photonic crystal fiber (HNL PCF) for broadband supercontinuum generation. The light is also doubled using a periodically poled lithium niobate (PPLN) crystal. These two beams generate a beatnote that directly reports on f CEO ( f–2 f detection), which can be fed back to the pump current for f CEO locking. The supercontinuum light is beatnote locked against the Sr clock light at 698 nm through an auxiliary narrow linewidth Mephisto laser at 1064 nm. The beatnote f beat is mixed with a DDS output and is used to steer the Mephisto laser frequency. The Mephisto output is passed through a fiber acousto-optic modulator (AOM) to generate a frequency offset and is beat against a portion of the preamplified fundamental comb light. The control signal is fed back to the oscillator cavity length to close the loop for the f beat lock. We conduct our scans by changing the DDS offset frequency, which ultimately changes the comb repetition frequency without shifting f CEO . An additional portion of the Mephisto light is picked off and modulated with an electro-optical modulator (EOM) for Pound-Drever-Hall locking of the enhancement cavity. The offset between the locked cavity resonance and the fundamental frequency comb can be tuned by adjusting the AOM offset frequency to mitigate intracavity plasma instabilities 56 , 57 . PZT, piezo-electric actuator.

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Zhang, C., Ooi, T., Higgins, J.S. et al. Frequency ratio of the 229m Th nuclear isomeric transition and the 87 Sr atomic clock. Nature 633 , 63–70 (2024). https://doi.org/10.1038/s41586-024-07839-6

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