NIST had a major head start in quantum information in the 1990s. NIST researchers already had qubits—but under a different name.
“They’re called atomic clocks,” says Williams.
“Those subjects sound quite a bit different, but in fact, the experiments are very much the same,” says Wineland.
Chris Monroe, a fellow at the Joint Quantum Institute (NIST/Maryland), recalls how his research on atomic clocks with Nobel laureate Dave Wineland in the 1990s led to some of the very first work on quantum computers.
“The field of quantum information sort of fell in our laps,” recalls Monroe, who worked with Wineland as an early-career staff scientist in the mid-1990s. “We were playing around with atoms in a certain way that would make them better for atomic clocks.”
The NIST ion lab, where Wineland worked until December 2017, has been a fertile ground for atomic clock research since the 1970s.
“He was already there when the field broke open,” says Boisvert. “By looking at his experiments from a different perspective, it became quantum information.”
At NIST and the JILA labs, state-of-the-art atomic clock setups have inspired quantum information innovations from the beginning.
Atomic clocks tell time with amazing precision. The NIST-F2, the most accurate U.S. atomic clock used for timekeeping, keeps time to an accuracy of less than a millionth of a billionth of a second. That may seem like overkill, but GPS satellites contain atomic clocks and depend on such precision to send time-stamped signals that help us pinpoint our locations anywhere on Earth to within about a meter.
The NIST-F2 clock is an atomic clock that serves as one of the primary time and frequency standards for the United States.
The clocks work by tuning the frequency of microwaves or other forms of electromagnetic radiation to the exact value needed to make electrons in ions jump from one energy level to another. Electrons in cesium, currently the atomic clock standard, respond to a microwave frequency of 9,192,631,770 hertz, or cycles of radiation per second. So, by tuning microwaves to cesium, you can effectively split the second into 9,192,631,770 parts, as each cycle of radiation corresponds to 1/9,192,631,770 of a second.
Usually, the atoms or ions in a clock are flying around as part of a gas, and their motion reduces the accuracy to which the microwaves can be tuned to the atoms. Thanks (or no thanks) to Albert Einstein’s special theory of relativity, an effect known as “time dilation” causes time to slow down ever so slightly for the moving atoms in relation to the laboratory, and it also causes slight shifts in the microwave frequencies that they absorb from the lab equipment.
In the 1990s, at the NIST laboratories in Boulder, Colorado, Wineland and his colleagues were studying how to make even more accurate atomic clocks. They were steeped in the physics of ions when they heard through the grapevine about mathematician Peter Shor’s discovery. Until then, physicists who were aware of quantum information were few and far between.
In the late spring of 1994, when discussions of Shor’s result were circulating via e-mail, NIST physicist Charles Clark organized the NIST Workshop on Quantum Computing and Communication, which took place in Gaithersburg that August.
“It was the first major workshop in this field,” recalls Clark, “and it brought together physicists, mathematicians, computer scientists—people from industry, academia, national labs and the intelligence community.”
One of the co-organizers of that workshop was Artur Ekert, then a physicist at the University of Oxford. Ekert was making the rounds in the community to spread the word about these exciting new ideas.
“I had heard a fascinating talk by Artur Ekert at MIT on cryptology and quantum mechanics,” recalls Daniel Kleppner, an atomic physicist at MIT, and supervisor of the Ph.D. thesis of NIST Nobel Laureate Bill Phillips.
"I was given a completely different congregation to preach to, but I felt I was preaching to the converted. I was amazed how enthusiastic the atomic physicists were about the subject of quantum computation," said Artur Ekert, now a professor at the University of Oxford, the National University of Singapore and the director of the Centre for Quantum Technologies in Singapore.
Kleppner recommended that Ekert be invited to speak at the International Conference of Atomic Physics to be held in Boulder in July 1994.
We gave him a totally different community to present his ideas, and they picked up on it,” Kleppner says.
With his presentations at the seminal 1994 meetings in Gaithersburg and Boulder, "I have only recently realized the importance of NIST in my research career," said Ekert, a key figure in the development of quantum information. Several years earlier in 1991, Ekert had introduced the theory of entanglement-based quantum key distribution, an essential component of quantum cryptography, which became realized in actual devices later in the decade.
Inspired by Ekert’s talk, theoretical physicists Ignacio Cirac and Peter Zoller of the University of Innsbruck in Austria (who had each spent time in appointments at JILA a few years earlier) imagined making quantum computers a reality in the laboratory. They envisioned using trapped ions in, it turned out, exactly the kind of experimental system the NIST group had developed.
"After Artur's talk, we became obsessed with the problem of how to build a quantum computer," says Cirac, currently at the Max Planck Institute of Quantum Optics in Garching, Germany. “We were studying quantum phenomena with a single ion qubit, so we had figure out how to manipulate many of those qubits.”
“It was a very imaginative idea,” Kleppner says.
In the proposed scheme, researchers would trap a group of individual ions in a line, like birds on a wire. Lasers would manipulate the ions’ energy states so that they each represented 0s and 1s or superpositions of the two. Each ion would communicate with another by rocking back and forth. The rocking would enable each ion to exchange information with its neighbors. In this way, researchers would be able to carry out computations with the qubits.
When Wineland and colleagues saw this paper, they immediately saw parallels between controlling atoms in an atomic clock and performing a quantum computation.
He recalls thinking, “Hey, this is great! We can do this.”
“The kind of technology we use—the lasers and the experiment control—is very much the same,” he says.
So, he and group member Chris Monroe used lasers to control the ions’ energy states in a way that affected their motion. And in December 1995, they announced the first component of a quantum computer.
“Our claim to fame is the first logic gate based on individual quantum bits,” says Wineland.