I'm trying to track down the best (lowest) vacuum pressure ever achieved. I'm talking about absolute pressures, not relative, so I wouldn't call the environment in a submarine the winner even though it achieves a very large magnitude negative pressure differential relative to the high ambient pressures deep in the ocean. I've heard some talk about CERN having the best vacuum. They certainly have the largest, but I don't know about best. I'm sure they would, if they could keep the whole thing cryogenic, but my understanding is that the experimental hall portions of the beam line are kept at room temperature, and pumped with ion pumps for noble gases and getter coatings for everything else. In this piece, they talk about reaching 10-10 torr in the beamline. I've heard other people claim that the Wake vacuum measurement performed by dragging a shield from a space station is the record, but this is certainly not so. They are only claiming 10-11 torr or so: http://www.sciencedirect.com/science/article/pii/S0042207X01003839. Their original expectation was 10-14, but this was not reached, possibly just due to bakeout issues. I've done better myself with an ion pumped vacuum chamber, as is common in AMO physics. I know of several labs that use ion pumps in combination with Titanium sublimation pumps, which deposit Titanium films on the walls to adsorb molecules, to reach pressures below 10-12 torr. My suspicion however is that experiments which maintain a completely cryogenic environment should do even better than this, because at those temperatures any metallic chamber wall behaves as a getter or cryopump without the need for titanium sublimated coatings, not to mention that whatever gas isn't adsorbed is traveling at lower speeds and thus exerting a lower pressure force. I believe I've heard people toss around numbers like 10-16 torr in conference talks, but I haven't found any direct claims. Can anyone substantiate this hypothesis or point me to an experiment operating in these extreme vacuum regimes? Does anyone know of a lab directly claiming to have the world's lowest vacuum pressure? I know that there aren't gauges at these pressures, but any trapping experiment would have a good guess at their pressure from the lifetime of the species of interest. Thanks!