How Do You Catch An Atom And Pin It Down? Mikkel Andersen, a physicist at New Zealand's University of Otago, isolated a single atom of rubidium and then used a special astronomical camera to snap its picture. Andersen describes the process of turning lasers into optical tweezers and what catching atoms means for quantum computing.
NPR logo

How Do You Catch An Atom And Pin It Down?

  • Download
  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript
How Do You Catch An Atom And Pin It Down?

How Do You Catch An Atom And Pin It Down?

  • Download
  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript


This is SCIENCE FRIDAY from NPR. I'm Ira Flatow.

Catching an atom is not easy. Let me tell you, they're fast, they like to travel in packs, but a new study in the journal Nature Physics has instructions for an atom trap.

Here's what you'll need. You need two lasers, a vacuous, light-free space and some Rubidium-85. Oh, and if you want to take a photo, a photo memory so you can show it to everybody, you'll need a special camera for taking picture of deep space. Of course.

How do you do it? How do you put it all together? Well, here to tell us is the guy who did it, and if you're on Twitter, you can sign up @scifri to talk about it, and if you'd like to call, our number is 1-800-989-8255.

Let me introduce him. Mikkel Andersen is a lecturer in the Department of Physics at the University of Otago in New Zealand. Thanks for getting up so early to join us this hour.

Dr. MIKKEL ANDERSEN (Lecturer, Department of Physics, University of Otago): Yes, hello, good morning.

FLATOW: Good morning to you. Joining me now, also with me is Flora Lichtman, our digital media editor, who has a special interest in this topic. Welcome, Flora.


FLATOW: Is it the laser beams, Flora, that interest you the most?

LICHTMAN: I can't tell if it's the laser beams which I really like or if it's the atoms. I mean, I think of them as so tiny and fast. Dr. Andersen, how do you, how do you get them to slow down so that you can trap them?

Dr. ANDERSEN: Yes, so first we use laser cooling to slow them down, and this is actually invented by the current U.S. secretary of energy Steven Chu. So and we use laser light, and the thing is that when you expose an atom to laser light, it absorbs the light, and the light carries momentum, and the atom recoils off this momentum.

So if you put an atom inside a laser beam, it feels a force, a push by the light. That's actually the same force that causes comets to have tails.

The tail of a comet are dust particles thats blown off the comet by radiation pressure from the sun. So it's usually we don't feel this force, or we don't know about it. When we walk out into the sunshine, we don't feel pressure from the light. But because atoms are so tiny, it's actually a very, very strong force.

LICHTMAN: So is it that the lasers are actually pushing the atoms in the opposite direction that they want to go?

Dr. ANDERSEN: Yes, yes.

LICHTMAN: I mean because I think when people think of lasers, they think of heat, not cooling.

Dr. ANDERSEN: Yes, so usually, we know that lasers can cut big steel plates and so forth by generating a lot of heat. But you have this force that can push the atom, and because the atom has very they only interact with very, very specific colors, and you can then you can make it such that you can push the atom only the opposite its direction of motion all the time.

LICHTMAN: Okay, so you push it in the opposite direction, and then it must slow down long enough so that you can...

FLATOW: And why do you want to capture an atom to begin with?

Dr. ANDERSEN: Well, we want to there's a number of different reasons. So first, of course, we want to make things like what we call quantum technologies, that builds we want to take advantage of the physics that govern small, tiny systems like, such as atoms.

But also, I learned in elementary school that it's impossible to see an atom in a microscope. So this was a personal motivation for it.

LICHTMAN: So this is the part that also really captured my imagination How do you actually take a picture of something so tiny? And is that the big challenge in capturing the photo?

Dr. ANDERSEN: Yeah, it is a big challenge. Because it's so small, the light we can scatter off it is very, very low. So we have to cancel all other light sources to see this very, very dim light from the atoms. So that's a big challenge.

LICHTMAN: So no flash, I guess.

(Soundbite of laughter)

Dr. ANDERSEN: No, not at all. Well, laser flash that makes the atom glow while we - that this light that we use to image with, in the microscope.

FLATOW: And how long do you hold it for? I mean, do you just sit there and look at it, or do you do something with it and let it go? How long does it sit there?

Dr. ANDERSEN: So we typically, in our experiments, we can hold it for around three seconds.

FLATOW: That's an eternity in your time.


LICHTMAN: And is the camera you're using, I mean, if you're working with this really low amount of light, do you need a special camera for that?

Dr. ANDERSEN: Yeah, that's a very special camera. It's made for telescopes who look at far-away galaxies. So it's very low-light sensitive. And that's how we can see even the very little light that the atom emits.

A lot of our images of atoms have only, what do we say, around 100 photons in the image. So this is almost no light, basically.

LICHTMAN: Wow, that's tiny. So why did you choose this particular element to try to isolate?

Dr. ANDERSEN: So this was this we chose to a large extent due to costs. Though we are grateful that the New Zeeland Foundation for Research Science and Technology supports us, we don't have an infinite amount of money. And this element is actually close to the color of the light that you need to manipulate this element. It's close to the wavelength that is used in CD players.

LICHTMAN: What do you mean, in the lasers in CD players?

Dr. ANDERSEN: Yes, yes, the lasers of CD players have, they have a wavelength very close to the wavelength we need to manipulate this kind of atom.

FLATOW: So it's pretty cheap. Anybody can get a laser, a CD-player laser, right?

Dr. ANDERSEN: Yes, yes. So this is very, very low-cost to buy, and actually, the objective lens in the microscope, the very powerful lens we use to image the atoms, is also from a CD player.


Dr. ANDERSEN: So this cuts down the cost quite enormously.

FLATOW: And there are a lot of people who want to isolate atoms, and the idea is to, you know, think about hooking the atoms together to make devices, maybe a quantum computer. Is this something that interests you, too?

Dr. ANDERSEN: Yes, yes, most certainly. And this is where we see that our work can progress science is that we now have so what we have developed, there are other groups in the world who have isolated individual atoms before but only with it happened kind of at random, only with a probability of 50 percent of success was the record before us.

But what we have developed now is a method that can do it much better.

FLATOW: All right. Well, thank you for coming. I'm going to rip my CD player apart now.

(Soundbite of laughter)

FLATOW: I'm not going to be able to do this one at home, am I, Dr. Andersen?

Dr. ANDERSEN: No, no. It still takes quite a lot of other equipment, as well.

FLATOW: All right, yeah, we'll get a bigger budget. Thank you for joining us. Mikkel Andersen is a lecturer in the Department of Physics University of Otago in New Zealand, and Flora Lichtman, thank you for taking time, too.

LICHTMAN: Thanks Lichtman.

FLATOW: Bring us this very fascinating talk about isolating a single atom and capturing it between a couple of laser beams.

Copyright © 2010 NPR. All rights reserved. Visit our website terms of use and permissions pages at for further information.

NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.