Nature Podcast：空间实验室

又到了每周一次的 Nature Podcast 时间了！欢迎收听本周由Shamini Bundell  和 Nick Howe 带来的一周科学故事，本期播客片段里讨论了国际空间站上的量子实验室。欢迎前往iTunes或你喜欢的其他播客平台下载完整版，随时随地收听一周科研新鲜事。

音频文本：

Interviewer: Geoff Marsh

Have you pressed record on the voice memos?

Interviewee: Rob Thompson

Okay, now, yeah.

Interviewer: Geoff Marsh

By the looks of this video call, you’re not at NASA. You’re in your basement.

Interviewee: Rob Thompson

Yeah, we’ve been operating the Cold Atom Lab remotely from our homes since the middle of March. So, it’s a little bit strange with everything going on in the world to sit down in front of a computer and be talking to an instrument that’s on the International Space Station, kind of zipping around over our heads at 17,000 miles an hour and so on. It took a little getting used to. My name’s Rob Thompson. I’m a scientist working on a project called the Cold Atom Lab that’s on board the International Space Station. It is a multi-user facility to study ultra-cold matter at temperatures very close to absolute zero. It traps atoms with magnetic fields on something called an atom chip and uses techniques of evaporative cooling to cool those atoms down to very cold temperatures so that they form a Bose condensate.

Interviewer: Geoff Marsh

Why are physicists so keen to create these little clouds of this kind of unique quantum state of matter?

Interviewee: Rob Thompson

One of the things that sort of fascinates me about them is that we can think of it as kind of a magnifying glass for the quantum world.

Interviewer: Geoff Marsh

No one is helping with the instrumentation up there on the Space Station, are they?

Interviewee: Rob Thompson

Yeah, we operate it completely remotely from the ground, so there’s no day-to-day operations. The astronauts don’t help us. One of the things that we’re fairly proud about this mission is that it really does demonstrate that you can do, I think, some very sophisticated science that previously could only be done in a laboratory setting on Earth. We do rely on the astronauts for the initial installation, but the system is also designed to be repairable and upgradable, and so we just recently have had an upgrade where the astronauts kind of replaced the heart of the instrument, which is the science module that contains the vacuum system and atom chip and those kinds of things.

Interviewer: Geoff Marsh

As you’ve said, nowadays, these Bose-Einstein condensates are created quite routinely in hundreds of labs around the world. Why go to all the effort to perform these experiments in microgravity on the Space Station?

Interviewee: Rob Thompson

So, one thing is we just get to look at the atoms for a longer amount of time if they’re just kind of floating, and that means that, for certain very sensitive measurements, you get a much more powerful enhancement. In fact, if you’re trying to measure accelerations or, alternatively, gravity using an atom interferometer, you get a really big improvement in the sensitivity. So, we ultimately think that a lot of these types of quantum sensors, they belong in space. There’s lots of things out in space that we might want to measure, things like tests of general relativity. People have proposed searches for candidates for dark energy and dark matter. People have proposed using these as a tool to search for gravitational waves as well. Beyond that, there’s actually just a lot more basic science that can be done with ultra-cold atoms. One of our principal investigators is doing an experiment where he is trying to make what we call quantum bubbles – spherical-shaped condensates – and they’re just impossible to make on the ground where gravity would pull the atoms down to the bottom of whatever trap that you put them in. In the absence of gravity, they can spread around and form this sort of bubble. One of the things that we will be trying to do in the near future is look at mixtures of different types of cold atoms – rubidium and potassium – at the same time. If you try to do those types of experiments on Earth, you do have to worry about the fact that the rubidium is heavier so it tends to pull down to the bottom of the trap compared to potassium, so you don’t get these perfectly overlapping mixtures and clouds.

Interviewer: Geoff Marsh

And the Cold Atom Lab also allows you to achieve colder atoms.

Interviewee: Rob Thompson

Yeah, one of the sort of standard ways that we get these gases colder once we’ve produced a Bose condensate is simply to relax the trap and make it weaker and weaker. As it gets weaker, the atomic cloud expands and as we do that, the atoms get cooler and cooler and cooler. You can do that on Earth, but eventually, the tug of gravity will make the atoms kind of spill out of your trap, so there’s kind of a limit to how weak you can make a trap on Earth. In space, you don’t have that limitation. There’s no fundamental limit to how cold we could get them. 

Interviewer: Geoff Marsh

Presumably, just the restrictions of having to be an instrument that was transported up to space and operate unmanned in space poses lots of its own limitations?

Interviewee: Rob Thompson

Yeah, that’s absolutely true, and just in terms of how big a condensate you can make, it’s nice that for the magnetic field, things sort of scale pretty nicely. The trap strengths actually get a little bit stronger. But that’s not true for the laser cooling and for laser cooling you want the biggest beams you can have to collect the most atoms in the fastest way, and so there is a trade-off there between size and weight and how many atoms you can collect.

Interviewer: Geoff Marsh

Is it a bit like a synchrotron or a big telescope where like lots of different research groups can book in some time?

Interviewee: Rob Thompson

Yeah, and this is actually very interesting because this is, of course, the particle physicists and the astronomers have been working on this paradigm for decades, right? But it’s not the way atomic physicists work, that we’re used to building our own instruments and turn knobs as we see fit.

Interviewer: Geoff Marsh

I wonder what that will do to the science output? In some ways, you might think that having a diversity of minds using such a sophisticated instrument could bear more fruit.

Interviewee: Rob Thompson

Well, yes, I think so because we do weekly meetings with the PIs and they talk about their results and they share back and forth. It’s going to be an interesting new paradigm.

Host: Shamini Bundell

That was Rob Thompson from the Jet Propulsion Laboratory at NASA in the US. 

《自然》论文：Observation of Bose–Einstein condensates in an Earth-orbiting research lab

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