In September, physicists at the University of Aarhus in Denmark announced they had successfully entangled two clouds of a trillion cesium atoms. Previous experiments involved entangling no more than four beryllium ions. When physicists talk about entanglement, they mean there’s a correlation between two bodies, between, for example, two particles or the two aforementioned clouds.
These particles physicists work with are simple structures, with a small number of characteristics distinguishing one from another, the most important being the direction it spins. If a particle in one entangled body is spinning in an upward direction, a corresponding particle in the second body will spin down. What’s more, if the spin of a particle in one of the entangled bodies changes, perhaps because the particle collides with another, that change will cause a corresponding shift in the spin of a particle in the second body, all without any connections or wires or anything between the two bodies.
I appreciate your calling me back. Uh, yeah, so as I mentioned in my e-mail I’m doing this piece right now on…. [Pause.] Let me just bring up my notes. [Very long pause.] On quantum entanglement.
The Danish physicists injected about a trillion atoms of cesium gas into two cylindrical glass containers. When atoms in a cloud collide with anything, they often change the direction of their spins. To reduce the frequency of these collisions, the insides of the containers were coated with paraffin, and the entire experiment was shielded from stray magnetic fields. The physicists placed the containers, holding about one cubic inch of cesium, a few millimeters apart. Next, the physicists directed a pulse of light through both clouds, allowing them to measure the spins. I don’t know how that works. A second pulse, microseconds later, indicated that while some particles in both clouds had changed their spins, going from up to down, say, the overall correlation between the spins in both clouds remained the same. The clouds were entangled.
Dad: What are you working on?
Me: Oh, I’m trying to write this thing right now. It’s this short, 350-word non-fiction piece about quantum entanglement.
Me: Exactly, what. You already see my problem. It’s called quantum entanglement.
Dad: What’s that?
Me: Quantum entanglement is something that a handful of people understand, and those who understand it find it difficult to explain to people who don’t. Basically, right now you’re talking to a person who doesn’t understand it.
Dad: You shouldn’t quit.
Me: I’m not quitting, I’m just complaining.
Dad: I’m sure you’ll figure it out.
Roughly one one-thousandth of a second later, a long time by the standards of quantum physics, the experiment in Denmark was over. The cesium clouds were no longer entangled. Scientists are working to extend the duration of entanglement, entangle larger bodies, and place them farther apart. One day it may be possible for a message to be communicated between two entangled bodies, photon by photon.
Albert Einstein referred to these sorts of quantum experiments pejoratively as “spooky action at a distance.”
What a Friend Wrote When I Mentioned Quantum Entanglement in Passing.
You can’t mention something like “quantum entanglement” without engaging insatiable curiosity. Ever notice how the word “quantum” ratchets up everything? Take computing. A friend wrote an undergraduate thesis on “quantum computing” — doesn’t that sound exponentially cooler than just plain “computing”?
Me: You know what Einstein called this stuff? Einstein called this stuff “spooky action… spooky action, um….” He called this stuff “spooky action in the distance.”
Another Friend: Uh huh.
Me: That’s not the exact quote, but it’s something like that. It’s got the word “spooky” in it.
Another Friend: Uh huh.
Me: Everybody quotes it in these articles. Everybody compares it to Star Trek and then everybody has the spooky quote.
What I Wrote Back to the Friend Who Suggested the Word “Quantum” Ratchets Up Everything.
Now that you mention it, I’ve noticed that I seem to be getting a LOT more respect from people whenever I tell them I’m writing about quantum entanglement.
Science reporters seized on the discovery. But how to explain the spookiness to readers? They hunted for accurate analogies and, time and again, in Scientific American and publications from New York to Australia, described the experiment as an early precursor to teleportation. They made light-hearted comparisons to Star Trek and those transporters that beamed Kirk, Spock and company from the Enterprise down to the surface of planets and then beamed them back up again when things got too hairy.
Objects I Held in My Hands, Pointed at Inarticulately, or Moved around the Tops of Tables and Desks in Several Failed Attempts to Explain Quantum Entanglement.
Two pencils, salt shaker, pepper shaker, bottle of water, two pens, two identical-looking Styrofoam cups of water, fork, spoon, can of Coke, and lots of pennies.
Nobody in Denmark is beaming anybody anywhere, but the search for a good analogy is no trivial matter. From the trains that run side by side in explanations of Einstein’s theory of relativity to Schrödinger’s cat, analogies are vital to understanding even the basic concepts of physics.
Q: Do you employ analogies or metaphors to explain the concepts of quantum entanglement?
Dr. Eugene Polzik, leader of the Danish team of physicists: You have a bunch of coins, say a thousand, and I have a thousand. (In our experiment, it is a trillion “quantum coins,” that is spins.) The coins are quantum, meaning that before you look at them they do not have a definite position (head or tail). But if you look at your coins and count, say, 554 heads and the rest is tails, then you know that if or when I decide to look at my coins, I will also find the same number of heads and tails. This is like collective entanglement of our two atomic samples.
Q: Do you use analogies or metaphors in discussing your work?
Brian Julsgaard, Ph.D. student working with Polzik: To colleagues, I don’t have to use metaphors and I seldom do. To people outside the field I usually use the pictures of tossing coins. E.g. two coins could be “entangled” so that if one shows head, we know the other is tail, and vice versa. Note: this resembles few particle experiments more than many particle experiments. You could use metaphors that resemble the actual physics of our experiment, but losing the simplicity of two coins is really not worth it if you only have a few minutes to explain.
Friend #3: What’s this piece about again?
Me: Quantum entanglement.
Friend #3: And what is that?
Me: Uh, are you sure you want to hear about this? I mean, are you really sure?
Friend #3: Well, I don’t want to hear about it for a half-hour or anything, but is there a two-minute explanation?
In September, physicists at the University of Aarhus in Denmark announced that they had successfully entangled two clouds of a trillion cesium atoms. In other words, the trillion particles in one cloud were correlated with the trillion particles in the second. Meaning if one cloud was imagined to be ten ordinary quarters, four showing “heads” and six “tails,” then the second cloud would feature four “tails” and six “heads.”
Story Based on an Analogy for Quantum Entanglement Suggested by Dr. Brian Greene, of Columbia University.
Pretend that you and a friend buy a pair of gloves. You place one glove inside one box and the other glove inside another box. You take one box and travel to one side of the universe. Your friend takes the other box and travels to the other side. You open your box, and find the left glove. You know immediately that your friend is going to open the box and find the right glove. You don’t need to call your friend on the telephone. Nor do you need to see inside the second box to confirm this fact. The gloves are, in a sense, entangled. One glove can tell you all you need to know about the other.
Verbatim Question Asked of Greene in an Interview.
I guess I was just looking for, um, I guess I’m not sure, I mean, a lot of the articles that I’m reading are talking about this in terms of transport, in terms of things being transported, or teleported, and it seems like it’s almost confusing. What is actually being teleported? I read about, you know, like a photon being created and then a copy of it being, or being destroyed and then created in the inter-, in the second object.
Another Verbatim Question.
And that, and that’s what something like a strange, a strange, seemingly crazy property like quantum entanglement is bearing out?
One Sadly Lopsided Conversation.
Greene: It’s much less surprising to say you do a measurement on some thing and it affects that some thing. It’s much more surprising to say you do a measurement on something way over there and it affects something way over here. That’s surprising. But if in some sense those two separated objects in space are really one. In other words, if space is not what we thought it was, if space is not the thing that necessarily ensures that two objects are distinct, then it’s less surprising, but then it challenges what we really mean by space.
Me: And, um, I guess one of the things this kind of points to is that in the case of these experiments we’re dealing or we’re talking about two objects — beryllium ions or clouds of cesium — that are artificially correlated, and would it be natural to assume that there are things that are just naturally correlated?
Greene: You know, sometimes people have taken this kind of result to mean that everything is connected to everything, and the universe has this wholeness.
Me: And is that too amorphous?
Greene: Right. My view on that is that those kind of ideas, while nice and fuzzy and touch the heart, really don’t reflect the science.
One Last Question, Exactly As Posed.
To your mind, is there, are there, I mean, is there any phenomenon that can’t be explained by quantum laws? Or do you believe that increasingly it will be quantum laws that — that will be accepted as descriptive and accurate?
Q: When a person asks you what you do, and this person is interested in a more detailed answer than “I’m a physicist” or “I work at the university,” what do you say?
Polzik: When my daughter was at high school, and I was asked by her classmates what it is to be a physicist, I used to say, "Imagine a toy store full of your favourite toys, and you can play with them all day. That is what we do all our lives.
A Not Altogether Successful Amplification of the Greene Analogy.
But the Danish physicists accomplished something much more complicated. Photons, for one thing, come in more varieties than left and right gloves. So imagine that the gloves you and your friend buy are special gloves. Each pair is comprised of one black glove and one white glove. One glove of every pair is leather and one is wool. And, of course, one glove of each pair is for a left hand and the other is for the right.
Now imagine once again that you and your friend travel to opposite sides of the universe. When you reach your destination, you stop, open your box and a trillion of these odd gloves fly out and swirl around you in a cloud. You reach up into the cloud and pick one glove. It’s white, made of wool, and it fits on your right hand. Because the clouds of gloves are entangled, because they’re connected in some spooky but nonetheless real way, you know for certain that on the other side of the universe, at the very moment you’re flexing your fingers in your glove, admiring the back and front of your hand, your friend has just slipped a black leather glove onto his left hand.
Q: When a person asks you what you do, what do you say?
Julsgaard: Also a good question! I have tried “I do quantum optics” or “I make entanglement.” In any case, I really have to use two coins to give the smallest idea of what I’m doing. Statements like “We shine laser light on atoms” really do not help! Saying that we try to understand the aspects of quantum mechanics, that this is basic research, is sometimes OK. It’s really hard to explain.