This really shows the marvel of HP being able to convert physics experiments to a useful product that can be calibrated with standard equipment and by people without a Nobel prize in their pockets. Your explanation is super clear. You were able to explain enough of the details so us noobs can understand what is going on.

I never thought that adjusting a clock could be so interesting!

Excellent discussion! I was happy to see the 5334B Frequency counter in the video as I was the Service Engineer for that product and designed the self test and service strategy for it.

My electrical engineering internship was in the Time and Frequency Division at NIST, Phase Noise Measurement group, '93-97, just down the hall from the NIST-7 cesium beam standard. 25 years later, after working in RF communication systems and test equipment, I recently started working at ColdQuanta on quantum computers based on laser cooled neutral Cesium atoms. Your explanation of Zeeman splitting, and demonstration of the tuning, really helped my understanding of clocks and MOTs. I know many of these concepts as absorbed facts I can regurgitate, without much intuition. It also gave some more insight into the march from parts in 1e14, to 5e-15 of NIST-7, to 1or2e-16 of NIST-F2. And, it's one thing to see an Allen Deviation chart of an atomic clock (or a wandering OCXO tone on a SPA), but watching atomic clock drift on an o-scope made it come alive. And fun fact, the gravitational redshift at Earth’s surface corresponds to a fractional frequency gradient of -9.8(2.3)×10-20/mm (at that particular lab in Boulder). With Strontium optical lattice clocks at the 1e-21 level, geopotential uncertainty is the dominate error term. It's fascinating to see all the metrology/sensing that atomic clocks play a huge role: magnetic fields, gravity, inertial navigation, Josephson voltage standards, atomic physics, astronomy, electric fields, mass..... arxiv.org/ftp/arxiv/papers/2109/2109.12238.pdf

18:00 Actually, that was very clear. Best ever. I found myself wishing you had chosen *not* to skip some of the details e.g. how the C-field disallows certain transitions. Very, very satisfying learning. Thanks.

When I studied engineering the quality of the lecturer absolutely steered my appreciation and interest in a particular subject, you have that gift, I dont know what you do professionally but if you dont lecture or teach its a waste.

I love those clocks! Great video, and I'm really interested to see your time dialation experiment.

Here I am learning about NMR spectroscopy in ochem 2, deciding to take a break with an exciting new CuriousMarc video, and getting most of the lecture theory explained back to me (plus a lot more.) No complaints though. Fascinating video. Thank you all for what you do and for taking the time to document it

The HP 5518A heterodyne laser Interferometer also uses Zeeman effect to split HeNe laser light into 2 opposite polarized beams, with a few MHz difference in frequency, so that the receiver can tell, if the measurement mirror is moving towards or away from receiver. Another instrument with lots of HP magic inside, can measure absolute distances in nm range or flatness of surface plate very accurately.

I, for one, get excited when the elevator music starts. Great stuff! I look forward to seeing how you use your clocks.

I opened this channel and looked at the picture. OMG this guy found a pair of HP Cesium clocks. When I was working with HP, I sold two of them. Both went to Lockheed. After delivery I never saw them again. In those days they were accurate to within one second in 200,000 years. Better accuracy now.

Here I am on the last steps of restoring and adjusting a french turn of the century mantel clock to + - 10 minutes PER DAY and super happy with that, and these guys adjusting to the billionth decimal a cesium clock.

The only thing better than this episode is the fact that I understood exactly what you were doing and explaining! I wish I had some of that test gear, and one of those beautiful clocks! Thank you Marc and Team for another amazing experience! I can't wait for the time dilation clock check!

What a fantastic explanation, you make a wonderful teacher Marc, Thank you.

That was an excellent and very good explanation of the C-field and why it is required. Thank you for another outstanding video. I've never understood why this channel sits under 150k subscribers, it's content and quality is outstanding every time.

I wonder if a vector voltmeter such as the HP 8508A or 8405A might not be a better instrument for detecting minute phase drifts between clock signals. They offer phase resolution down to 0.1deg, which would be difficult to resolve with the oscilloscope. They might also be less susceptible to drift or jitter in the triggering point as compared to an oscilloscope.

Well, you just blew the old saying: A guy with one watch can tell you the time. A guy with two watches is never quite sure.. BRAVO !!

I’ll stay tuned (hope I don’t drift too much!) 👍

That's a very nice demonstration and explanation of the Zeeman effect and the magnetic alignment of the HP5061. I've never seen that before in such a detail. Anyhow, I suggest to do frequency comparisons (Cs vs Cs or vs GPS) by time-nuts methods. That is a phase comparison method by means of a high resolution T.I. counter, like your HP5334A. By using John Miles free TimeLab program, which might directly support your counter over GPIB, you can make comfortable stability (Allan Deviation) and uncertainty measurements down into the 10^-13 region, over many hours. That is required to overcome short / medium termed jitter especially of the GPS reference. Easy to accomplish, and maybe making a nice next video.

Waking up and finding 37 minutes of Marc discussing atomic clocks and Zeeman alignment is the best way to start the day.

I learned quite a lot. One of the most entertaining classes I ever attended.

I knew several of the words used in this video.

What a fantastic video, Marc and the guys on top form. I love the amount of work that went into explaining the somewhat complicated (understatement of the year) quantum physics - Marc, you're a hero.

Awesome explanation! I feel smarter for watching, and that often happens when I watch your vids

Every time a video is posted, I am amazed at what is presented. I would have bet money that 2 HP atomic clocks were not operable at this late date. Those tubes are not replaceable anymore.

Atomic physicist here - great explanation overall! Here's some additional information about selection rules: The 'selection rules' you mentioned are determined by the polarization of the light - the applied magnetic field matters, but only indirectly. If you (arbitrarily) choose any fixed direction in space, you can define your m_F levels to have fixed total angular momentum projection along that direction. If the polarization of the interrogation laser is aligned with this direction, then we call it 'pi-polarized' and it can only drive transitions that do not change m_F. Note that the definition of the m_F levels depends on your choice of quantization axis. The clock would still work perfectly in exactly zero B. At finite residual B, however, population will begin to be transferred between different m_F levels, unless the B-field is perfectly aligned along your preferred axis. The role of the C-field is to reduce the effect that stray fields have on the angle of the total B-field with respect to this axis. (Simple picture: moving the end of a meterstick by 1 cm changes its orientation much less than moving the end of a 30cm ruler by 1 cm.) An alternate view (equivalent in any nonzero B field) is to choose the direction of the B-field as your quantization axis. Then it's the impurity of the laser polarization projection (along the B-field axis) that causes the unwanted transitions to occur. This has the advantage of ensuring that the corresponding m_F levels are so-called 'energy eigenstates' of the full Hamiltonian, including the Zeeman interaction - but at the expense of more complex selection rules. But either way you do the computation, you get the same result - the component of the B field perpendicular to the light polarization must be zero, or you will get unwanted frequency components.

This video series really helps me appreciate 100 years of progress in the science of quantum physics. As a career EE it is also fascinating to learn how a thorough understanding of quantum physics led to the creation of a very precise frequency reference which could be manufactured in the 1960/1970’s era and (with calibration) still meet its specs many years later. I own a few vintage HP instruments myself but nothing in the “atomic clock” category. My collection includes a 412A DC VTVM and a 3456A 6.5 digit DVM which both function very well. I frequently use them. Neither required extensive restoration. I found my 412A many years ago in a junkyard/recycling center with its mains power cord and probe leads cut off. It was free for the taking. I picked it up mainly because it looked cool in a very retro way. I never expected it to be functional. But out of curiosity 2 years ago I decided to see if I could get it to work. I was rather surprised to find no faults or issues beyond needing to replace the missing cables and probes. All of its capacitors and vacuum tubes tested good. The optical chopper still worked. I love it’s 100 meg input resistance for DC voltage measurement. It also works very well for Ohms measurement. The 3456A was an eBay find which needed only the replacement of some electrolytic capacitors in its power supply. I also have an 8660C frequency generator which partially works but needs to have the bandpass filters in the 0-100 MHz plug-in rebuilt. Keep up the great videos please!

I remember when I was a kid in 70s, I saw a TV science program which was about relativity, time and speed of light. They used two atomic clocks like those here. They put one in a NASA airplane and another one on the ground. After the airplane did a couple spins the atomic clocks showed some difference about a few nanoseconds. Then the funny guy placed his twin brother in an spaceship which traveled at the speed of light. After a couple minutes, he came back to Earth and he found his brother pretty old. They said the story wasn't a science fiction at all and it was very amazing for me. Perhaps the best science program I ever saw on TV in those years.

Fascinating. I wish you’d been a lecturer whilst I was at university. You’re a natural! Very clear, and your enthusiasm for the topic is infectious. This is a wonderful example of engineering as the application of science to a problem. Kudos to the HP engineers.

These videos are pretty awesome. Love the theoretical description next to the hands on demonstration.

I wish you had been my quantum mechanics teacher during my physics degree. You’re speaking directly to me when you express the theory intertwined with the experimentation and engineering utilization of the phenomenon. What an 18min!

Brilliant explanation as ever. Took me right back to Electronic Theory of Matter lectures 48 years ago.

I watched this video shortly after waking up and I still managed to follow your explanation of the hyperfine energy levels and Zeeman lines. Excellent job at communicating it clearly! You've now inspired me to dig into the literature on magnetic quantum numbers and selection rules, since that's a level of detail that I've only ever heard of in passing before. It's good to have a practical application to tie the knowledge back to.

me: forgets about daylight savings time and doesn't even notice for a day or two marc: my cesium clock is 0.0000000001Hz out of spec and we need to calibrate it.

I can't wait to see what experiments you're able to perform with two highly calibrated cesium clocks.

Great explanation. I was actually able to follow you, and I'm not the brightest bulb in the electromagnetic spectrum.

I think I understood more about this topic than the rest of my education in this one video. Very well done on the explanation and the restoration

@1:00 as Alec from Technology Connections would say, "through the magic of buying two of them!"

This video gave me a series of those headaches with pictures. You know, “an education!” That was awesome to see!

On the day of the transition from DST to normal time. What perfect timing! 😁

I don't understand anything you guys are talking about but love being subscribed watching your passion.

Very cool!!! Avoid brain twisting explanation you ask, NEVER! Thank you so much for sharing all this with us! I grew up around engineers, listening to your explanations give me a warm feeling of being home again. Fascinating stuff. By far my favorite episode on this channel. What could be more mysterious then time? Liquid gold!

I could listen to you lecture about this kind of stuff all day!

Marc, you guys should really get in touch with Tom Van Baak for your journey with cesium clocks and precision time keeping. His collection is probably second only to NIST itself.

I didn't understand a thing, and I still enjoyed it ;)

This atomic clock is a genuine condensate of Nobel prizes.

It's amazing how many 'explanations' for the clock are 'it measures hyperfine transitions of cesium.' And are as long if not longer than this video. It's like telling you how a car works: 'it makes gasoline explode.' Excellent work. You've done a great job especially on elements that are hard to grasp in text. I don't think people really appreciate the scale of these measurements. The leap from theory to a practical machine is almost unreal.

excellent video MARC and TEAM!

best physic video of my life u are great as hp designer of those clocks

Thank you , this was excellent theoretics and lab work.

Wow! This was just fantastic, I finally feel like I understand what the SI unit for 1 second actually means. A concrete example with HP cukcoo clocks and everything :D

Fascinating material and well explained. HP machine designers were in a class of their own. And most still operate as designed. I have several test machines from the 70’s and 80’s that still work as intended.

I knew a lot of this from studying physics, but I still watched all of it because I found the explanation from an instrument/technician’s perspective to be an interesting change from the atom’s-perspective way I was taught it. All the same components of course, just a different reference frame.

Should you ever wonder again whether to include 18 minutes of theory, by all means, do include it. This was one of your best episodes ever.

Fascinating stuff! ^^) That is mind-blowing, having such equipment at hand in your basement!

Excellent experiment.

I hope the 'maybe' at the end was not a threat ;-). Thank you Professor Marc for this wonderful Monday morning lecture. Although all of the quantum stuff goes way above my hat I could grasp the overal gist of your explanation. I also never could have surmised two of my fellow countrymen (whose names I once found in a Dutch science museum) would be mentioned in your famous lecture. Wonderful video and looking forward to your 'dual Cesium clock experiment' :o)

Patience:) Good alignment and calibration!

It would be super cool to see you repeat the Hafele and Keating time dilation experiment. Also expensive I would imagine! You need a pretty long flight to get results in the nanoseconds. It would be fascinating to try to predict the results of the experiment beforehand and see how it plays out in reality.

Please make a detailed no hold back video about this. This is just so captivating.

I wonder if Segal's Law ( "a man with a watch knows the time. A man with two does not" ) still applies when both the timepieces are Atomic?

If Dr. Barney M. Oliver were still around, he would love to see your workshop. So would I, if I still lived in the Bay Area! Barney would be able to tell you exactly what to do to calibrate the clock, and why -- even if he had nothing to do with the clock product. He had the kind of curious mind that never let anything go by without understanding it, in a way, similar to you, Marc! Barney Oliver was a fascinating man, and a kind mentor to this young engineer, once upon a time, many years ago.

It's CuriousMarc lecturing on physical chemistry and quantum physics, and it's so cool! You laid out the spectral lines better than any professor at my university when I studied chemistry. Makes me wish I watched this video in 2007 or so. Zeeman's lab gear and experiments (and that stained glass too)? Definitely great and brilliant in its simplicity! Coming up with it was the hard part, doing actual experiments is straightforward, with no multi-million-yankee-bucks worth of equipment. Makes me wonder if there's still some science to be done that doesn't require very advanced and expensive technology. That HP scope is nice, but fades in comparison with Usagi's HP 150A :) So, any video on NMR, EPR or (unrelated, but close) mass spectrometry? That would be great. I was taught the theory of operation and how to interpret the spectra (and determine the structures), but never worked on a NMR or mass spectrometer myself. Nice watch too.

Amazing Sir! Thank You!

This video gave me enough confidence to finally try adjusting the kitchen scale clock back to "normal" aka winter time

Absolutely amazing video as always Marc! You are so lucky to have access to not one but two of those clocks! I managed to get hold of an old rubidium reference module from an aircraft but haven't done anything with it to make it into a useful reference yet. Even when I do it'll be way less accurate than those big boys hehe

As I'm watching this I realise that the c field is like the heater in a oven crystal clock, kinda, The magnetic shielding is like the insulation on a oven crystal clock as well, Block out/insulate as much as possible, and then provide your own standard/reference above what still leaks in (out in the case of oven clocks but still, I think this analogy is almost perfect)

Nice, I got it, well bits of it but more than when I started !...cheers.

I can't wait for the seemingly inevitable episode about the Ramsey effect!

I certainly didn't skip ahead ! I find it fascinating ! Getting some sort of glimpse of what is the fine structure (difference of energy levels dependin on spin) and the hyperfine structure (when applied inside a magnetic field) - and how this applies to define a constant for time (or rather the measurement of time within a reference frame) - and then how it this all applies to the real world.. and so how it really works and how it is calibrated and how it can be done.. (I didn"t understand 10% of it, but it's fascinating nonetheless)

Fantastic, awesome episode guys. I vote for more tests. 😊

Very interesting, thanks for the nice video. I have a couple of Symmetricom Rb oscillators I play with every now and then. To compare them I built a 10X frequency multiplier do the scope pattern at 100Mhz instead of 10Mhz, of course the noise increases but the error difference is much more pronounced. In the late 60's our USAF lab had a rack mounted instrument called a frequency error expander (could have been from HP) that did the same thing. Not sure how it worked pll, mixers, comb generator etc.

When Marc starts the elevator music, time to grab the popcorn and pay attention! IMHO, the best part of the videos. Now to see what @MarcoReps has cooked up.

Wow, my grandfather co-invented the color spectrophotometer in the 1920s at MIT - I had no idea it was used to tell time too!

That was very well explained, I was actually able to follow it !

Thanks!

Also just wow so cool and nice explanations

Fantastically clear explanation of both the underlying physics and the calibration process. I feel like I actually understand how cesium clocks work now!It’s beautiful the way you can use very pedestrian lab equipment to calibrate an instrument to deliver time accuracy on the order of 10^-13. What an absolutely brilliant device! Next up: Cesium fountain clock? 😉 BTW: What’s the lifetime of the cesium tube? Does the cesium somehow recirculate, or does it eventually get used up and the tube needs to be replaced?

Remember to redo the procedure every time something changes in or around the lab. Like a truck parking in the driveway. 🙂

whow superduper hammer thank you so much for your reserch and giving us this knowledge about the fundamentals of discovering the secrets of atoms

All I can tell from this video. Is that Hollywood really nailed the characterisation of a 21st century scientist.

Fantastic. I was thinking about an experiment which would be possible in the basement without too much expense. How about verifying the speed of light in different mediums?

This video proves the peak of humanity was July 20th, 1969 and we’ve been in a social and technological decline ever since.

Now you have 2 clocks you are uncertain again. You now need to get another 3, so you have a cluster of 5, so that you can use the average to get the error from the outliers, and use that average to both get the right time, and also verify all 5 are operating correctly.

When comparing the beam current after C-field adjustment hasn't the "beam I-meter" pot been adjusted to keep the maximum on scale when adjusting the amplitude of the audio oscillator, so couldn't that explain the beam current reduction post-adjustment? Not having a 5061 to hand I seem to remember that one just adjusts this so the beam current reads 20 in operation.

Ow wow, the original notes from professor Zeeman. Zeeman means Sailor by the way :) I'm Dutch, I can read those notes!

Love the video. I'm curious do you have to "calibrate" the clock every time you power them up ?

Great video! And now I know how to really pronounce "Lissajous."

Just the kind of video I need at 7am after I’ve just woken up

I'd love it if you went back to some more teletype stuff - I could understand that!

Wow, one CuriousMarc episode about caesium clock calibration, and now I feel like I understand enough about quantum physics to make sense of quantum computing cubits. If that Zeeman calibration would also apply to cubit sensors, I cannot help but wonder why only three axis are used for quantum compute, wouldn't four axis of spin be measurable? An axis for each surface of a tetrahedron?

BTW, is there access to the 9.1GHz from the caesium tube directly? Should be easier to see sub-ns differences there, with like a 2 channel sampling scope.

Watched the first part. Fascinating. Thank you. If I understand correct, one singe period of electromagnetic radiation in caesium-133 proceeds 9192.63177 picoseconds? My imagination tells me that this device inherently measures the difference in the course of processes depending on gravity, magnetic fields, electrical fields, force, motion, temperature etc. Anyway I’m starting to watch the second part.

I hope the next episode involves rocket science.

Talk about leaving us hanging! 😄

@curiousmarc kudos to you reading those Quantum Physics textbooks. It is truly big Science/Physics you are dealing with here. And if it was easy, everyone would be doing it.

Finally, really exited about this

Didn’t understand a thing, but it was awesome😂

omg - what an HP quality device those clocks were! best I can do here is ntp, stratum 3... or some fancy contraption with an ublox neo module and gps time... ^_^

“A-ha! I thought it was one of the prime numbers of the Zeeman series. I haven’t changed!” - Flash Gordon