Behind a tiny door on the campus of Harvard University, hidden in a building at the far end of the Yard, a magician will reveal his tricks to you with no hesitation – enthusiasm, even. This magician has no magic wand, no black hat or cape. He coifs his ash blond hair with gel and wears Prada glasses, jeans and T-shirts. Although he moves his hands rapidly when he talks, he doesn’t intend to misdirect or confuse you.

Sean Garner has been called a magician by the scientific community because he and his colleagues achieved a revolutionary trick of quantum physics: they managed to manipulate light in a way it has never been done before. The Harvard scientists have almost stopped a pulse of light in one part of space and made it reappear two tenths of a millimeter away. They have changed light into matter, and matter into light again. This trick holds promise for the manipulation of light as a carrier of information, because it is easier to work with in its matter state.

Researchers cannot now readily control optical information during its journey, except to amplify the signal to avoid fading. The new work of Garner and his colleagues marks the first successful manipulation of coherent optical information.

To perform this trick, they employ a technique that was developed some years ago to store a light pulse as an ensemble of atoms. In 2000, two independent teams of researchers from Harvard University, one from the Department of Physics and the second from the Harvard-Smithsonian Center for Astrophysics, managed to slow a light pulse and trap it either in an ultra-cold group of atoms or in a vapor of atoms. But at that time, the trickiest part wasn’t performed. What Garner managed to do was to set the light information free and to revive the light pulse in another place.

Sean Garner is a post-doctoral associate in the Department of Physics of Harvard University. He grew up in Southern California, and graduated from the University of California in Santa Cruz in 1999 with a B.S in Physics and a B.A. in Math. He got his doctorate at Cornell University where he worked on magnetic fields with Professor John Marohn. He arrived in Professor Lene Vestergaard Hau’s Harvard laboratory in September of 2005. His work at Cornell was “very different from what I’m doing now!” Garner says, cracking a smile. At Cornell he wasn’t working in the same area or at the same scale. “I kept coming across results in atomic physics that really excited me, so I decided to switch after getting my PhD,” he explains. Today he works in the field he calls “ultra-cold atomic physics,” ultra-cold because they work at temperatures that flirt with absolute zero, minus 459.67 °F.

On the left-hand side at the entrance of Garner’s laboratory, the small chain of an emergency shower hangs from the ceiling. On the floor, a box filed with blue plastic shoe-protectors announces to a visitor she is entering an ultra-clean area. Before entering the lab, one needs to pass through two airlocks, and to step twice on a sticky square on the floor –the equivalent of a lint roller for footwear. “We want to make sure there is no dust inside the lab,” Garner explains, slipping a pair of the shoe protectors over his sneakers. The dust could spoil the material for the experiment, and lead to improper results. Inside the lab, the air blowing from a wind tunnel on the ceiling is deafening.

The equipment for the trick stands on two different tables, arranged in an L-shape, in the middle of the room. On one table is a tube that looks like a mini amusement park water slide. A forest of mirrors, each approximately four inches high, is spread over the second table. “I could not tell you exactly how many mirrors we use. Fifty maybe,” Garner says, shrugging off the question. He explains that atoms of sodium are thrown into the tube, slowed down and cooled to very low temperature. “Through this device, we create the Bose-Einstein Condensates (BEC) we need for the experiment,” he says, tracing the journey the atoms would take.

A Bose-Einstein Condensate is a state of matter where the atoms are taken to very low temperatures. About two million atoms form a cloud and acts almost as if it were only one atom. They’re all in the same quantum state. Imagine a school of fish moving all together, following exactly the same patterns, doing exactly the same movements.

Albert Einstein, building upon the work of Satyendra Nath Bose in 1925, first predicted this state of matter. Seventy years later, Eric Cornell and Carl Wieman at the University of Colorado produced the first such condensate. Cornell, Wieman and Wolfgang Ketterle at MIT received the Nobel Prize in Physics in 2001. Compared to more commonly encountered states of matter, the Bose-Einstein Condensates are extremely fragile. The slightest interaction with the outside world can be enough to warm them to a normal gas state, and have them lose their interesting properties. And those properties are very important for the experiment, because within these clouds, the atoms become phase-locked and lose individuality and independence.

“We keep the two BEC in the black box at the end of the tube,” Garner says. Once the atoms arrive at the end of the tube, they’re trapped in a magnetic field that will force them to stay still and hold in a precise direction. The magic trick occurs in that black box, about the size of two shoeboxes side by side. The BEC must be kept stable because if the clouds move, the scientists won’t see the light coming out of a tiny hole. “When the light comes out, we want to make sure it is not coming from anywhere else, so we made this small hole where it has to come out from, and some equipment measures the light coming out,” Garner says. The light pulse is so weak and so fast that it is quite hard to detect it by eye.

Garner switches off the room light to better see the laser, which give off a yellow-orange glow. “The atoms of sodium give them that cool color,” he says, showing the laser beams reflecting off the array of small mirrors. They used sodium atoms to create the laser beams for the experiment, to obtain the precise frequency of light that would not spoil the BEC. Even inside the black box, the clouds of atoms could spread and get lost if they were hit with too much energy.

Garner had used the equipment for previous experiments. He explains that they first started with only one Bose-Einstein Condensate. They would send a laser beam into it and store the light inside the BEC. “Sometimes when you work on something else and you ask yourself ‘what if I changed that part?’ and then a new idea pops up.” The scientists first did the experiment with one BEC that they split. But then, they realized their trick would have more impact if the light reappeared in a totally separate BEC. “So we had to restart the experiment with two truly independent BEC that didn’t know anything about each other.” That set the bar much higher, and once they decided to do the experiment it took them six months or so to become quantum magicians. Garner says those were months of very hard work where sometimes they had to spend long nights in the laboratory. “This experiment has such a huge setting that it can take hours before it’s even working. So once you get it going, you wanna do all you can before going home.” At the end, when they pretty much knew it was going to work, the team stayed up until 5 a.m. to see it through.

After all that preparation, the actual magic trick only lasts two to three milliseconds. Three milliseconds sounds short in human terms; it is briefer than the winking of an eye. But for quantum coherent dynamics it is actually a very long time. So what actually happens during those milliseconds?

To understand the trick, you need to set aside what you know about classical physics and throw your imagination to the atomic scale. Even though atoms are described as spheres, they don’t act like apples or oranges. At such a low temperature, the atoms’ motions are virtually halted and they begin to behave more like waves than particles.

A first laser beam is fired. When it enters the first Bose-Einstein Condensate, the light slows down from 186,000 miles per second to the speed of a human runner so that one pulse can fit comfortably in the cloud of atoms. A second, “control” laser, coming from the opposite direction, writes the shape of the pulse into the atom waves. “It leaves a sort of imprint that has caught the optical information,” Garner explains. When the control beam is turned off, the light pulse disappears, but what’s called the “matter copy” remains in the BEC.

At the same time, the light has given enough energy for the “matter copy” of atom waves to move out of the first BEC, cross free space and reach the second BEC suspended in the magnetic trapping field less than a millimeter away. But Garner explains that the particle state doesn’t move; it stays in the cloud.

Quantum theory, disturbingly, reveals a profoundly counter-intuitive reality in which, for instance, a particle can exist in a “superposition” of states where it can do two or more things at once.

In 1935, Erwin Schrödinger came up with his famous thought experiment to highlight a consequence of this. He imagined a cat shut in a box together with a vial of poison. The decay of a radioactive atom could prompt a hammer to smash the vial and kill the cat. Crucially, if the atom was in a superposition in which it simultaneously did and did not decay, the cat would be both dead and alive at the same time. The only way to know would be to open the box. This thought experiment catapulted quantum weirdness out of the microscopic realm and into the everyday world, where researchers had no choice but to deal with it.

So, the laser has given enough energy to the matter imprint to continue its travel at approximately 700 feet an hour through the cloud, exiting the first BEC, continuing on through free space, and ultimately entering the second BEC.

The control laser is then rekindled and the laser pulse is revived and exits the second BEC at its original speed of 186,000 miles per second. By turning the control beam on the second cloud, the added atoms are encouraged to spread their message throughout the whole cloud. All the atoms come into step with each other again, giving this second cloud a memory of the original laser pulse. They re-radiate this pulse with about one-fiftieth as much of the original light energy.

In the quantum world, particles of the same kind are indistinguishable. “The lock-step nature of atoms in the BEC makes it possible for the information in the initial light pulse to be replicated exactly within the second cloud where the atoms collaborate to revive the light pulse,” Garner explains.

If they had turned on the control laser before the messenger had reached the second Bose-Einstein Condensate, the light would have spread incoherently in all directions. To make sure the matter wave had reached the second BEC, Garner and his colleagues were able to photograph it traveling through free space. “So we knew exactly when to turn the control beam back on,” Garner says.

When the light pulse is in a matter state between the two BEC, Garner explains. “We can grab it with a laser beam, put it on the shelf, so to speak, and later let it back on its way and revive it in the second BEC.” During this “shelved” period, the matter wave can be manipulated by physicists and will preserve any changes when it is revived again as a laser. These manipulations can potentially be used in the processing and encoding of optical information. Data could be sent through optical fibers much like what many Internet service providers use to facilitate Internet communication, and be manipulated in the process by using the sodium clouds. “Matter is much easier to manipulate than light,” explains Alexander Sergienko, professor at the Boston University Departments of Physics and Electrical and Computer Engineering.

“While the matter is traveling between the two BEC we can trap it, for minutes, and reshape it, change it, in whatever way we want.” This novel form of quantum control could also have applications in quantum cryptography. What is hard in quantum communication is to maintain the quantum state. Light is a very good means of communication because it goes very fast and can be sent very far without being attenuated. “One thing that is nice about slowing the light, is that it offers a way to manipulate the light,” Sergienko says.

While this experiment opens the possibilities of a whole new way to manipulate light, it is only a first step because “nobody will put this enormous apparatus in a computer,” Garner says. But the work of Garner’s team opens new avenues of experimentation, and may eventually give scientists a new degree of control over fiber-optic communication and quantum processing.