Have you seen the AT&T 4g network ad in which a friendly guy in a suit asks a group of young children, “What’s better, faster or slower?” The children sing out “Faster!” and give examples of things that are fast: “my mom’s car,” “a space ship,” “a cheetah.” None of them mentions light, which travels close to 200,000 miles per hour. Anything that moves that fast has to be unstoppable, right? Wrong. Superman could stop a speeding train, but it took a super woman to stop light.
Before I get to physicist Lene Hau’s story, let’s ask why anyone would want to stop light. While the process of slowing or stopping light is incredibly complex and precise, the reason for doing so is quite simple. Light can carry a lot of information very quickly. If you can pack light with gigantic collections of information and route it to super computers, you can process more data—solve more problems—more quickly than with the puny computers we use today.
While Physics for the 21st Century is designed to explore the frontiers of modern physics, unit 7, Manipulating Light, is also a testament to the profound contributions that women are making to science. Dr. Lene Hau, recipient of a MacArthur Fellowship “genius grant,” stopped light by ignoring skeptical colleagues, by using science and mathematics to tame the weird world of quantum mechanics, and by relentlessly pursuing her goal. She is one of two featured scientists in the unit 7 video. Also, see her talk about the process of slowing down light in this video from the Harvard YouTube channel.
Dr. Hau never stopped calculating:
“I remember I was taking off in the airplane from Boston to Copenhagen and following the speed of the airplane on the big screen there and thinking, oh, wow; now we are going faster than my light pulse in the lab. I was calculating if I had sent a light pulse from Boston at the time I left in the airplane I would arrive in Copenhagen an hour before my light pulse.”
And she reveled in the wonder of her accomplishment:
“. . . in the middle of the night and you were just sitting there and you’re just the first person in history being in this regime of nature seeing light go this slow. It was really amazing . . .”
To make her breakthroughs—first to slow light to “bicycle speed” and then to stop it altogether—Dr. Hau lived in a world of both absolutes and mystery. Her team put the fastest known thing into the coldest known thing. Light, at billionths of a degree above absolute zero, stops. Essentially, Dr. Hau and her team were manipulating light and atoms so that they share characteristics that they don’t appear to have in common in the non-quantum world. A mile-long pulse of light is compressed to .02 millimeters (less than half the width of a hair) and sent through a Bose-Einstein condensate, a super cold cloud of sodium atoms. When the light is slowed, the information carried by the light can be imprinted in the sodium matter.
Even though Dr. Hau was manipulating light in the minuscule, sub-atomic world, she never thought small or shied from taking risks:
“If you want to probe something, probe it as hard as you possibly can without it totally blowing apart.”
We are still some years away from seeing Dr. Hau’s amazing work being put to practical use in quantum computing and other still-unknown applications, but now is just the right time to applaud her and join her in imagining where she will take us from here. Use her story to inspire your students to pursue exciting work in the sciences.