6 ms·

The innovation here appear to be the chamber. (caveat: I still need to read the paper). A few thoughts follow. They are going for a UHV***, probably <1e-10 mba

The innovation here appear to be the chamber. (caveat: I still need to read the paper). A few thoughts follow. They are going for a UHV***, probably <1e-10 mbar, but want to do it with a passive pumping design. In an ordinary chamber to get there you'd do a pump down, then bake it to remove the water. Then use an ion pump plus occasional firing of a titanium sublimation pump to remove the hydrogen that leaks in (ion pumps don't work so well for hydrogen at low pressures). They have some expensive chamber that doesn't suffer from these leaks. Still a lot of other work to do though. I see a table full of optics to make the MOT*. Also see a pair of anti-Helmholtz coils for the magnetic field. They could maybe replace those coils (which probably drive a few amps) with permanent magnets (assuming they don't need to switch the fields on and off which I imagine they don't because it can't imagine a pulsed design that wouldn't risk missing data) Passive getters work for a good long time with low leak rates. These you can just buy**. To be honest I'm not sure why you need such a fancy chamber. I'd guess a good NEG pump, a small chamber, and good seals would make you fine for a long time, but I'd need to do the math to be sure. *https://en.wikipedia.org/wiki/Magneto-optical_trap https://en.wikipedia.org/wiki/Magneto-optical_trap **https://www.saesgetters.com/products-functions/products/neg-pumps%26vacuum-solutions https://www.saesgetters.com/products-functions/products/neg-... ***https://en.wikipedia.org/wiki/Ultra-high_vacuum https://en.wikipedia.org/wiki/Ultra-high_vacuum

kragen 5y ago
Does passive pumping mean a chamber full of baked zeolite or something that's then chilled to adsorb all the gas? I guess I should read the paper too, but I don't have a copy.
- Fronzie 5y ago
  Or even without the chilling. CRT televisions had zeolite as vacuum pump as well. They kept vacuum for up to decades.
  - kragen 5y ago
    I think CRTs were mostly manufactured using conventional high-vacuum pumps with moving parts or liquids, not sorption pumps. They didn't normally include a pump in the cathode-ray tube itself; the pump stayed at the factory. And I think you're mistaken that the CRTs ever included any zeolite. Perhaps you're confusing zeolites with getters, which react irreversibly with any stray molecules that manage to get into the vacuum?
chana_masala 5y ago
HackerNews amazes me with how for nearly any topic there will be deep expertise in the thread. Thank you for sharing
- JohnJamesRambo 5y ago
  But then it also usually impresses me with how people think companies haven’t thought of and tried the things they thought of in reading the article and thinking about it for a few minutes.
  - jiggawatts 5y ago
    But sometimes they haven't thought of "it". These forums have an interesting kind of collective intelligence. People commenting here rarely (if ever) have full knowledge of the specifics of the particular instance of the topic at hand, but often have very deep knowledge of the associated theory. In my experience, if you take any 10 people and form a team or company to make some product, they won't have anywhere near the breath or depth of knowledge that people here could bring to bear. What they have is time and persistence, but I guarantee you that they're "flailing about" and wasting time on many wrong or suboptimal solutions. In most cases, someone here could set them on the right track within minutes. It's so strange to me that the Internet enables this, but we use this superpower for essentially nothing more than casual chit-chat. We show off our knowledge, where we happen to have a particularly impactful trick up our sleeve, win some meaningless points, and feel smug about ourselves for an afternoon. I do this all the time. It's fun. But what would happen if we did this properly? Like Uber? Made it into an app where startups, research teams, and software developer houses could use the collective knowledge and advice of hundreds of thousands of people instead of just the dozens on their staff? Just click here to get expert advice on your question, $55 guaranteed price? Would you click? Maybe it is time that we all plugged into the group consciousness and started contributing to the collective... /s
    - MauranKilom 5y ago
      To some extent, that's just StackOverflow (and the other StackExchange sites). Not quite as commercially focused as you imagine, but at least the code parts definitely are used like that. For more individualized problem solving, this just amounts to consultancies, no?
nuccy 5y ago
> Quantum sensors for PNT use atomic accelerometers or gyroscopes There is one fundamental problem with using any sensors for global positioning: a stationary frame of reference is indistinguishable from the one moving with a constant speed on a straight (actually geodesic [2]) line (inertial frame of reference, general principle of relativity [1]). So accelerometers and gyros indeed can give you accurate orientation and acceleration/deceleration data, but they will inevitably accumulate uncertainty for long eventless movements, so use of GPS will be needed to occasionally calibrate the true position. The obvious options is to augment this data with readings of wheels rotational, airspeed sensors, radars, etc, then such systems may last even longer without cross-calibration with GPS. 1. https://en.m.wikipedia.org/wiki/Principle_of_relativity https://en.m.wikipedia.org/wiki/Principle_of_relativity 2. https://en.m.wikipedia.org/wiki/Geodesics_in_general_relativity https://en.m.wikipedia.org/wiki/Geodesics_in_general_relativ...
- dtgriscom 5y ago
  > they will inevitably accumulate uncertainty for long eventless movements Actually, they constantly accumulate uncertainty; no change in motion required.
  - nuccy 5y ago
    True, but what you describe is related to the measurement and sampling accuracy. Until such sensors hit the Heisenberg uncertainty levels of precision on the readout/sensing, such uncertainties may be decreased further, there is no physical constrain on that (more sensors may help with that also). While it is in principle physically impossible to even identify the fact of movement linearly with constant speed without introducing external information (radar, GPS, wheels rotation, airspeed, magnetic and gravitational field change, Doppler shift in radio waves, etc). This is the relativity principle in action, which says that all the inertial frames of reference are equivalent.
horstbort 5y ago
Permanent magnets are typically a no-go, because these sensors employ matter-wave interferometry, i.e. interference between atoms. Those unfortunately do not only react to gravity, but also to magnet fields, so these need to be suppressed as far as possible, especially gradients. And yes, this will absolutely be a pulsed design. I think, the breakthrough here is that they maintain a decent vacuum even without NEGs, which you can of course buy off the shelf, but they still tend to be quite bulky. Also, they state a vacuum of about 10^{-7} torr. Far from UHV.
- avsteele 5y ago
  Great, thanks for the info

kragen 5y ago

Does passive pumping mean a chamber full of baked zeolite or something that's then chilled to adsorb all the gas? I guess I should read the paper too, but I don't have a copy.

Fronzie 5y ago
Or even without the chilling. CRT televisions had zeolite as vacuum pump as well. They kept vacuum for up to decades.
- kragen 5y ago
  I think CRTs were mostly manufactured using conventional high-vacuum pumps with moving parts or liquids, not sorption pumps. They didn't normally include a pump in the cathode-ray tube itself; the pump stayed at the factory. And I think you're mistaken that the CRTs ever included any zeolite. Perhaps you're confusing zeolites with getters, which react irreversibly with any stray molecules that manage to get into the vacuum?

chana_masala 5y ago

HackerNews amazes me with how for nearly any topic there will be deep expertise in the thread. Thank you for sharing

JohnJamesRambo 5y ago
But then it also usually impresses me with how people think companies haven’t thought of and tried the things they thought of in reading the article and thinking about it for a few minutes.
- jiggawatts 5y ago
  But sometimes they haven't thought of "it". These forums have an interesting kind of collective intelligence. People commenting here rarely (if ever) have full knowledge of the specifics of the particular instance of the topic at hand, but often have very deep knowledge of the associated theory. In my experience, if you take any 10 people and form a team or company to make some product, they won't have anywhere near the breath or depth of knowledge that people here could bring to bear. What they have is time and persistence, but I guarantee you that they're "flailing about" and wasting time on many wrong or suboptimal solutions. In most cases, someone here could set them on the right track within minutes. It's so strange to me that the Internet enables this, but we use this superpower for essentially nothing more than casual chit-chat. We show off our knowledge, where we happen to have a particularly impactful trick up our sleeve, win some meaningless points, and feel smug about ourselves for an afternoon. I do this all the time. It's fun. But what would happen if we did this properly? Like Uber? Made it into an app where startups, research teams, and software developer houses could use the collective knowledge and advice of hundreds of thousands of people instead of just the dozens on their staff? Just click here to get expert advice on your question, $55 guaranteed price? Would you click? Maybe it is time that we all plugged into the group consciousness and started contributing to the collective... /s
  - MauranKilom 5y ago
    To some extent, that's just StackOverflow (and the other StackExchange sites). Not quite as commercially focused as you imagine, but at least the code parts definitely are used like that. For more individualized problem solving, this just amounts to consultancies, no?

nuccy 5y ago

> Quantum sensors for PNT use atomic accelerometers or gyroscopes There is one fundamental problem with using any sensors for global positioning: a stationary frame of reference is indistinguishable from the one moving with a constant speed on a straight (actually geodesic [2]) line (inertial frame of reference, general principle of relativity [1]). So accelerometers and gyros indeed can give you accurate orientation and acceleration/deceleration data, but they will inevitably accumulate uncertainty for long eventless movements, so use of GPS will be needed to occasionally calibrate the true position. The obvious options is to augment this data with readings of wheels rotational, airspeed sensors, radars, etc, then such systems may last even longer without cross-calibration with GPS. 1. https://en.m.wikipedia.org/wiki/Principle_of_relativity https://en.m.wikipedia.org/wiki/Principle_of_relativity 2. https://en.m.wikipedia.org/wiki/Geodesics_in_general_relativity https://en.m.wikipedia.org/wiki/Geodesics_in_general_relativ...

dtgriscom 5y ago
> they will inevitably accumulate uncertainty for long eventless movements Actually, they constantly accumulate uncertainty; no change in motion required.
- nuccy 5y ago
  True, but what you describe is related to the measurement and sampling accuracy. Until such sensors hit the Heisenberg uncertainty levels of precision on the readout/sensing, such uncertainties may be decreased further, there is no physical constrain on that (more sensors may help with that also). While it is in principle physically impossible to even identify the fact of movement linearly with constant speed without introducing external information (radar, GPS, wheels rotation, airspeed, magnetic and gravitational field change, Doppler shift in radio waves, etc). This is the relativity principle in action, which says that all the inertial frames of reference are equivalent.

horstbort 5y ago

Permanent magnets are typically a no-go, because these sensors employ matter-wave interferometry, i.e. interference between atoms. Those unfortunately do not only react to gravity, but also to magnet fields, so these need to be suppressed as far as possible, especially gradients. And yes, this will absolutely be a pulsed design. I think, the breakthrough here is that they maintain a decent vacuum even without NEGs, which you can of course buy off the shelf, but they still tend to be quite bulky. Also, they state a vacuum of about 10^{-7} torr. Far from UHV.

avsteele 5y ago
Great, thanks for the info