10094199The QUantum Advantage-Ready Trapped-Ion Exploration Testbed: QUARTETClosedSmall Business Research InitiativeInnovate UKQuantum computing has the potential to transform industries from finance to pharmaceuticals by allowing us to solve problems which are intractable using classical supercomputers. While no quantum computer today can outperform classical supercomputers on real-world applications, a milestone known as Practical Quantum Advantage (PQA), there is significant interest in using them to learn about Quantum Computing ahead of PQA. This makes it critically important to have access to hardware testbeds: stable and well-characterised development platforms which can be used to study quantum computing and learn about hardware performance and bottlenecks. Currently available quantum computers are not well-suited to this application for two reasons: they are **closed boxes** based on **non-scalable technologies. The QUantum Advantage-Ready Trapped-Ion Exploration Testbed ("QUARTET")** addresses both of these limitations to provide a well-characterised, deployable prototype universal quantum computer offering state-of-the-art performance level that is both open-box and scalable to PQA through low-cost field upgrades of the quantum processing unit (QPU) only. QUARTE is a complete trapped-ion quantum computing testbed. It provides ultra-low error rates (two qubit gates with \>99.9% fidelity, single-qubit gates with \>99.99%), full (any-any connectivity) and universal computation. It includes all hardware and software required to operate it. It is an open-box, with a software interface that supports both running quantum circuits using the industry-standard OpenQASM format, as well as a pulse-level control API for in-depth studying of hardware performance and bottlenecks. A key feature of the testbed is its support of field-replaceable Quantum Processing Units (QPUs), using a robust interface with industry-standard electrical and optical connectors. The QUARTET testbed already supports all optical and electrical connectors needed to fully operate QPUs with 256 useful qubits capable of reaching PQA. Low cost field upgrades ensure that the testbed has a long lifetime, with continuous upgrades all the way to practical quantum advantage. The testbed builds on 3 generations of quantum testbeds that have already been produced at OI, providing proven performance and reliability with world-leading error rates. Working closely on QUARTET with its lead customer, the National Quantum Computing Centre ("NQCC"), Oxford Ionics will deliver and demonstrate a commercial prototype quantum computing testbed, to be deployed at the NQCC. Based on our discussions regarding the needs of the NQCC, it was emphasised that there is a need for a scalable quantum testbed that can be characterised, experimented with, and benchmarked in real-world applications. We believe QUARTET is perfectly in line with these end-user needs.