New breakthroughs in quantum computing

Researchers at UC Santa Barbara are breaking new ground in demonstrating the effectiveness of using the quantum properties of matter to build new “quantum processors” for the next generation of computers.

Quantum computers use atoms to represent arithmetical bits that are called “qubits,” but in order to show that quantum processors can be built, the qubits must be able to be embedded into a computing system.

An article appearing in Nature Physics, written by UCSB researchers in the Department of Physics, explains the new results.

Erik Lucero, the main author of the paper, is now a research scientist at the IBM T.J. Watson Research Center in Yorktown Heights, N.Y. Lucero explains that quantum computers will be able to handle very complex calculations in the field of biology and medicine that cannot be handled with current technology.

“We can envision being able to solve really complex problems that before all we could do was give a best guess at on a classical computer,” Lucero said.

“This is a very simple demonstration and we are still years away from a quantum computer.”

Lucero explains that the upcoming era of quantum computing will bring with it new levels of secure communication, due to the unique properties of matter at the quantum level.

“With the quantum computer there’s actually a higher level of encryption called ‘quantum encryption,’” Lucero said. “What’s great about it is we will know if someone has been eavesdropping on our communication because the system will have changed.”

Data encoded at the quantum level will be changed in some way, depending on whether the data has been observed by a third party.

The power of quantum processors will be exponentially greater than current computers because certain advanced forms of arithmetical computation can be mirrored by quantum operations.

The researchers demonstrated the possibility of four qubits interacting in a special process called “multipartite entanglement.”

“A single qubit is not enough to build the basic logic gates for a quantum computer,” said Matteo Mariantoni, who is a postdoctoral researcher in the UCSB physics department. “You also need connectivity on your quantum machine. This connectivity is given by ‘entanglement,’ where two qubits are talking to each other. Once you are able to control one and two qubits with very high accuracy, you then make the quantum machine bigger and bigger.”

The interactions of the qubits in a quantum processor function similar to the way electrons flow through transistors in a conventional computer. However, instead of using silicon-based transistors, the new networks of logic gates at the quantum level exhibit a simultaneity of function that cannot be achieved at the macro level.

Current computers, or “classical computers,” are reaching the physical limits of how small they can be constructed.

“We’re getting to the limit where we can’t make [classical processors] any smaller,” said Daniel Sank, a graduate student in physics at UCSB. “The size of the wires [in current computers] is 45 nanometers. We’re running up against all these limits and at some point people realized that if we used a different kind of physical interaction, namely [the type in] quantum mechanics, you can do computations in a different way, and in some cases this winds up being enormously fast.”

Lucero predicts that quantum computers will be able to be used for research in ways that classical computers fall short, such as in computations dealing with protein foldings and the efficient simulation of biological systems needed to design new drugs.

BRIAN RILEY can be reached at