Opening the gate to robust quantum computing

Scientists have overcome a major hurdle facing quantum computing: how to protect quantum information from degradation by the environment while simultaneously performing computation in a solid-state quantum system. The research was reported in the April 5 issue of Nature.

A group led by U.S. Department of Energy’s Ames Laboratory physicist Viatsheslav Dobrovitski and including scientists at Delft University of Technology; the University of California, Santa Barbara; and University of Southern California, made this big step forward on the path to using the motions of single electrons and nuclei for quantum information processing. The discovery opens the door to robust quantum computation with solid-state devices and using quantum technologies for magnetic measurements with single-atom precision at nanoscale.

Quantum information processing relies on the combined motion of microscopic elements, such as electrons, nuclei, photons, ions, or tiny oscillating joists. In classical information processing, information is stored and processed in bits, and the data included in each bit is limited to two values (0 or 1), which can be thought of as a light switch being either up or down. But, in a quantum bit, called a qubit, data can be represented by how these qubits orient and move in relationship with each other, introducing the possibility for data expression in many tilts and movements.

This power of quantum information processing also poses a major challenge: even a minor “bump” off course causes qubits to lose data. And qubits tend to interact quite sensitively with their environment, where multiple forces bump them off track.

But, because the key to quantum information processing is in the relationship between qubits, the solution is not as easy as isolating a single qubit from its environment.

“The big step forward here is that we were able to decouple individual qubits from the environment, so they retain their information, while preserving the coupling between the qubits themselves” said Dobrovitski.

Solid-state hybrid systems are useful for quantum information processing because they are made up of different types of qubits that each perform different functions, much like different parts of a car combine to move it down the road. In the case of Dobrovitski’s work, the hybrid system includes magnetic moments of an electron and a nucleus.

“This type of hybrid system may be particularly good for quantum information processing because electrons move fast, can be manipulated easily, but they also lose quantum information quickly. Nuclei move very slow, are difficult to manipulate, but they also retain information well,” said Dobrovitski. “You can see an analogy between this hybrid quantum system and the parts of a classical computer: the processor works fast but doesn’t keep information long, while the memory works slowly but stores information for a long time.”

Usually, when you decouple qubits from their environment to protect their quantum data, you decouple them from everything, even from each other.