Demonstration of a small programmable quantum computer with atomic qubits

• Published in: Nature (London) Vol. 536; no. 7614; pp. 63 - 66
• Main Authors: Debnath, S., Linke, N. M., Figgatt, C., Landsman, K. A., Wright, K., Monroe, C.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 04.08.2016; Nature Publishing Group
• Subjects: 140/133; 639/624/1107/1110; 639/766/483/2802; 639/766/483/481; Algorithms; Analysis; Fourier transforms; Humanities and Social Sciences; Lasers; letter; multidisciplinary; Quantum computing; Quantum theory; Radio frequency; Science; Software; Supercomputers; United States
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature18648

A small programmable quantum computer is demonstrated that uses five trapped ions as qubits; the computer is reconfigurable and different algorithms can be compiled without changing the hardware. A quantum computer based on five atomic qubits The functional quantum computer is eagerly awaited in certain circles. For instance, for problems such as simulation of chemical reactions and factoring large numbers, a quantum computer would outperform any classical computer. Although algorithms have been run on small quantum computers, it has not so far been possible to design a programmable quantum computer that is easily reconfigurable and in which different algorithms can be compiled without changing the hardware. Here Shantanu Debnath and colleagues demonstrate such a small programmable quantum computer, using five trapped atomic ions as qubits. The architecture could in principle be scaled up to a larger number of qubits. Quantum computers can solve certain problems more efficiently than any possible conventional computer. Small quantum algorithms have been demonstrated on multiple quantum computing platforms, many specifically tailored in hardware to implement a particular algorithm or execute a limited number of computational paths 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 . Here we demonstrate a five-qubit trapped-ion quantum computer that can be programmed in software to implement arbitrary quantum algorithms by executing any sequence of universal quantum logic gates. We compile algorithms into a fully connected set of gate operations that are native to the hardware and have a mean fidelity of 98 per cent. Reconfiguring these gate sequences provides the flexibility to implement a variety of algorithms without altering the hardware. As examples, we implement the Deutsch–Jozsa 11 and Bernstein–Vazirani 12 algorithms with average success rates of 95 and 90 per cent, respectively. We also perform a coherent quantum Fourier transform 13 , 14 on five trapped-ion qubits for phase estimation and period finding with average fidelities of 62 and 84 per cent, respectively. This small quantum computer can be scaled to larger numbers of qubits within a single register, and can be further expanded by connecting several such modules through ion shuttling 15 or photonic quantum channels 16 .