The computers we use every day are based on bits, which can be in one of two states (0 or 1). In contrast, quantum computers use qubits, which can also be in superpositions of states. These computers have the potential to solve some problems much faster than conventional computers. The majority of quantum computers so far have been “hardwired” to perform only a single type of calculation.
Shantanu Debnath, University of Maryland, College Park, USA, and colleagues have developed a quantum computer that can be programmed to run a variety of different algorithms. The team uses five 171Yb+ ions as qubits, arranged into a line with a spacing of about 5 μm. The ions are trapped in a so-called Paul trap, which uses changing electric fields to keep the ions in place. To “program” this quantum processor, the researchers change the state of the individual qubits using shaped laser pulses to build logic gates. Logic gates, the basic building blocks of computer chips, perform operations such as AND or OR.
Using this approach, the team has implemented and tested several quantum algorithms, such as the Deutsch-Jozsa and the Bernstein-Vazirani algorithm, which determine the properties of certain mathematical functions. The setup had average success rates for these algorithms of 95 % and 90 %, respectively. According to the researchers, the system could be expanded by increasing the number of qubits or combing multiple ion traps.
- Demonstration of a small programmable quantum computer with atomic qubits,
S. Debnath, N. M. Linke, C. Figgatt, K. A. Landsman, K. Wright, C. Monroe,
Nature 2016, 536, 63–66.