Quantum Information Applications Without Computers

You don’t even need a quantum computer for many powerful applications of quantum information. Many useful things can be done with the underlying technology. NIST researchers are developing the technology and exploring applications on multiple fronts.

Coming full circle, atomic clocks potentially could be used as quantum sensors. Borrowing techniques from quantum information science, a new design known as a quantum logic clock uses a pair of ions: one serves as the “clock” and the other controls and measures the first ion so that lasers can tune themselves as accurately as possible to get a good time signal.

These quantum logic clocks are part of a new generation of ultraprecise timekeeping devices. The new devices are so precise that they can do more than tell time; they can act as sensors of gravity and other properties.

According to Einstein’s general theory of relativity, time ticks more slowly in a large gravitational potential such as the vicinity of a black hole. This is the second form of time dilation predicted by Einstein. At sea level, where Earth’s gravity is stronger, an atomic clock will tick slightly more slowly than it would on the top of Mount Everest. The NIST ion group has measured the slower ticking of an atomic clock when it was just 33 centimeters (1 foot) lower than another atomic clock used as a reference. But these clocks can do more than confirm Einstein.

If there is an oil deposit underground, that means there is a stronger gravitational field on the ground than there would be if there were a hollow cavern underneath it. An atomic clock above the oil deposit would tick more slowly and help prospectors detect the oil. The atomic clocks being used today are not precise enough to detect such slowdowns. But next-generation clocks being developed promise to help researchers someday detect hidden oil and mineral deposits.

Techniques borrowed from atomic clocks and quantum information also promise to help researchers better control individual molecules. Researchers are also exploiting techniques from the quantum world to make new kinds of magnetic switches, which may lead to novel electronic devices.

Meanwhile, NIST researchers Liz Donley, John Kitching and colleagues have made an “atom gyroscope,” a rotation sensor, by harnessing wave-particle duality.

We usually think of atoms as tiny balls—in other words, particles. But under the right circumstances, atoms can act as waves. An atom’s wavelength—the distance between successive peaks and valleys—is too small to be noticeable, but if you make the atoms colder, their wavelength is big enough to be detectable in present-day experiments.

In Donley’s experiment, a gas of about 8 million very cold rubidium atoms is released in a chamber. As the atoms fall, their waves can separate and recombine to create interference patterns. If the chamber is rotated by even a tiny amount, this can affect their interference patterns. So, the researchers made a gyroscope that was far more sensitive to rotations than traditional designs. Atom gyroscopes could potentially be deployed on satellites, airplanes and ships and help them navigate even when GPS signals are jammed or otherwise unavailable. True to the collaborative nature of the field, atom interferometers for metrology were originally pioneered and developed by Stanford’s Mark Kasevich and Steven Chu, who shared the 1997 Nobel Prize in physics with NIST’s Bill Phillips.

NIST also has dabbled in quantum teleportation. In “Star Trek” teleportation, Scotty beams Captain Kirk and his crew (usually including at least one ill-fated, red-shirted officer) onto a planet. In this fictional transportation, matter gets beamed from spaceship to planet. In quantum teleportation, quantum information gets instantly transferred from one qubit to another.

NIST established earlier distance records for quantum teleportation by transmitting information between photons separated by 100 kilometers. Quantum teleportation is expected to be useful for quantum computing and other forms of quantum information transfer.

A major new initiative at NIST is the Randomness Beacon Project. NIST researchers are tapping the quantum world to create truly random numbers. Industry relies on random-number generators to create, for example, passwords that are hard to predict. But fundamentally, these random-number generators are based on software or devices that rely on classical physics, and so they will be predictable to some extent.

The quantum world, however, is a bastion of randomness. When an atom is in a superposition of two states, such as a higher and lower energy, it’s completely random as to whether it will collapse into one of the two states. NIST researchers are using photons to generate random numbers. The photons are in a superposition of states, which can be represented as 0 or 1. The researchers then measure them, and the result is either 0 or 1. The value is completely random and then can be used as a digit for a random-number generator. And, if quantum entanglement is used in the process, then it ensures that no sender, transmitter or eavesdropper could have known the outcome before the random bit was generated.

This randomness has been verified by “spooky action” tests, including a worldwide demonstration known as the Big Bell Test in which members of the public were invited to provide input for the experiment.

When discussing the ultimate limits of quantum computing, Boisvert likes to bring up the comedic science-fiction franchise known as “The Hitchhiker’s Guide to the Galaxy.” In the series, author Douglas Adams described a computer named Deep Thought that seeks to answer the question of “Life, The Universe, and Everything.” Deep Thought’s answer (spoiler alert) was 42. Deep Thought then tries to build a more powerful computer to find out the exact question that the first computer was answering. That computer is the Earth.

“That begs the question of how powerful is this latter computer, or, in other words, what is the computational power of the universe?” Boisvert says. “Does a quantum computer have that power?”

To the Hitchhiker characters’ disappointment, they later found out that the ultimate question was, “What do you get when you multiply six by nine?”

Researchers expect real-life quantum computers to come up with more useful results, though that doesn’t mean their ideas are any less lofty than Deep Thought’s explorations. Quantum information researcher Stephen Jordan has explored the computational potential of black holes and the ability of quantum computers to simulate high-energy physics phenomena to gain a better understanding of them. Researchers see simulations as one of the earliest applications of quantum information.

You don’t even need quantum computers to create a so-called “analog” quantum simulator. Simply entangling lots of particles and seeing how they behave according to the rules of quantum mechanics enables researchers to simulate quantum processes.

“Neutral atoms are particularly well-suited for quantum simulation because you can trap and cool a large number of them in lattice-like structures,” says Trey Porto, a NIST fellow at JQI.

Just as a wave pool in a theme park can mimic waves in an ocean, gaseous atoms in an analog quantum simulator can interact with one another in ways that mimic, for example, electrons orbiting atoms in magnetic materials. Particles in a quantum simulator can behave like electrons in a high-temperature superconductor and provide valuable insights into them. Room-temperature versions of superconductors, if they could be developed, offer a potential revolution in transmitting electric power, as they would allow electricity to travel without resistance at ordinary temperatures.

A collaboration involving NIST and JILA recently demonstrated an analog quantum simulator, made by entangling hundreds of ions. A pair of independent teams, including one led by JQI’s Chris Monroe, recently created analog quantum simulators controlling more than 50 qubits to obtain insights into magnetism at the atomic scale.

A more complicated “digital” quantum simulator would contain the components of a quantum computer with its logic gates and algorithms. Its digital operation would enable it to mathematically model the interactions between particles such as atoms and molecules precisely according to the rules of quantum mechanics. This is the harder type of simulator to build because it requires all of the complex features of quantum computers—including a robust error-correction system.

Researchers anticipate that digital quantum simulators could precisely model chemical reactions such as those that are important for drug development, energy production and agricultural processes. Because chemical reactions at the atomic and molecular level obey the rules of quantum mechanics, computers that obey the same rules can simulate them much more efficiently than ordinary computers. They could potentially help scientists design new drugs, better electric batteries and more efficient food production techniques.

Some of the ideas for quantum simulations are even more ambitious. Since the universe operates according to the laws of physics, including quantum physics, why not use quantum simulators to simulate the universe itself? Jordan and other NIST researchers are imagining running simulations of the standard model of particle physics, which describes three of the four fundamental forces in the universe. Physics beyond the standard model may provide insights into the fourth force, gravity, as well as possible new particles and forces.