1. Institut für Experimentalphysik, Universität Innsbruck, Technikerstrae 25, A-6020 Innsbruck, Austria

Correspondence to: Rainer Blatt Correspondence and requests for materials should be addressed to R.B. (e-mail: Email: Rainer.Blatt@uibk.ac.at).

Abstract

Quantum computers have the potential to perform certain computational tasks more efficiently than their classical counterparts. The Cirac–Zoller proposal¹ for a scalable quantum computer is based on a string of trapped ions whose electronic states represent the quantum bits of information (or qubits). In this scheme, quantum logical gates involving any subset of ions are realized by coupling the ions through their collective quantized motion. The main experimental step towards realizing the scheme is to implement the controlled-NOT (CNOT) gate operation between two individual ions. The CNOT quantum logical gate corresponds to the XOR gate operation of classical logic that flips the state of a target bit conditioned on the state of a control bit. Here we implement a CNOT quantum gate according to the Cirac–Zoller proposal¹. In our experiment, two ⁴⁰Ca⁺ ions are held in a linear Paul trap and are individually addressed using focused laser beams²; the qubits³ are represented by superpositions of two long-lived electronic states. Our work relies on recently developed precise control of atomic phases⁴ and the application of composite pulse sequences adapted from nuclear magnetic resonance techniques^{5, 6}.

1. Institut für Experimentalphysik, Universität Innsbruck, Technikerstrae 25, A-6020 Innsbruck, Austria

Correspondence to: Rainer Blatt Correspondence and requests for materials should be addressed to R.B. (e-mail: Email: Rainer.Blatt@uibk.ac.at).