Quantum computers are built of elementary operations called quantum gates that are similar to the logic gates in classical computers. Logic gates are devices that perform very basic data processing—instructions such as “and,” “or,” or “not.” To run on a quantum computer, an algorithm must be broken down, or decomposed, into a sequence of basic quantum gates. This process can be extremely difficult. The number of required quantum gates operations may be quite large, thus losing the advantage of quantum computing’s power. In this study, researchers developed a novel “hybrid” approach to quantum hardware design that replaces part of the quantum circuit with a physical evolution that relies on natural interactions within the system. Compared to conventional quantum gates, this approach significantly reduces the complexity of executing quantum algorithms.

Current intermediate scale quantum computers are not yet practical because of “noise.” This noise occurs because qubits—the most basic components of a quantum computer—can interact with the outside environment. This introduces errors. These errors occur quickly, limiting the amount of time a quantum computer can operate accurately. True error correction methods are far from being reliable. The hybrid hardware design may allow researchers to run quantum algorithms using current technologies for practical scientific applications.

Using the hybrid approach, researchers at Los Alamos National Laboratory proposed a specific realization of Grover’s algorithm. As one of the best-known quantum algorithms, Grover’s algorithm allows unstructured searches of large data sets that gobble up conventional computing resources.

The Grover algorithm involves a black-box operation, called the “oracle.” This operation generally requires execution of a large number of quantum gates. In this research, the team proposed to realize the oracle using just a single spin, naturally interacting with the rest of the computational qubits. No direct interactions between the computational qubits are ever needed. The entire oracle operation consists only of applying simple time-dependent external field pulses that rotate the single spin. Importantly, this approach is topologically protected, which means it is robust against imprecision of the control fields and other physical parameters, even without error correction.