Realisation of a programmable two-qubit quantum processor

TL;DR

This paper demonstrates a programmable two-qubit quantum processor using trapped ions, capable of implementing arbitrary unitary operations with high fidelity, advancing toward universal quantum computing.

Contribution

The authors realize a programmable two-qubit quantum processor that performs arbitrary unitary transformations, showcasing universal control in a trapped-ion system.

Findings

Achieved high-fidelity implementation of 160 random two-qubit operations

Demonstrated universal control equivalent to simulating any pairwise spin interaction

Validated the processor's capability through quantum state and process tomography

Abstract

The universal quantum computer is a device capable of simulating any physical system and represents a major goal for the field of quantum information science. Algorithms performed on such a device are predicted to offer significant gains for some important computational tasks. In the context of quantum information, "universal" refers to the ability to perform arbitrary unitary transformations in the system's computational space. The combination of arbitrary single-quantum-bit (qubit) gates with an entangling two-qubit gate is a gate set capable of achieving universal control of any number of qubits, provided that these gates can be performed repeatedly and between arbitrary pairs of qubits. Although gate sets have been demonstrated in several technologies, they have as yet been tailored toward specific tasks, forming a small subset of all unitary operators. Here we demonstrate a programmable quantum processor that realises arbitrary unitary transformations on two qubits, which are stored in trapped atomic ions. Using quantum state and process tomography, we characterise the fidelity of our implementation for 160 randomly chosen operations. This universal control is equivalent to simulating any pairwise interaction between spin-1/2 systems. A programmable multi-qubit register could form a core component of a large-scale quantum processor, and the methods used here are suitable for such a device.