Quantum Error Correction in a dual-species Rydberg array (QuERy)

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Quantum computing provides a new paradigm in which to use systems operating under the laws of quantum mechanics to solve complex problems such as in quantum chemistry for enhanced drug design or modelling of correlated media for designing new materials for aerospace and engineering which are currently beyond the capability of modern digital computers. Quantum hardware can also provide a dramatic speed-up of computationally expensive problems ranging from classical optimisation relevant to logistics (e.g. travelling salesman type problems) to factorisation. The major barriers to exploiting the advantages of quantum computing for these real world problems however are the technological challenges associated with building a system able to provide a sufficient number of high quality, low noise quantum-bits (qu-bits).Recent progress has seen the development of a number of different technologies to address this challenge, including superconducting qubits and trapped ions, however reconfigurable arrays of individually trapped atoms have emerged as a highly competitive approach able to scale to large numbers of identical qubits without loss of performance. These current systems with a few hundred qubits offer opportunities to explore early benefits of quantum computing, but suffer from noise and errors which place a limit on the performance and their ability to address useful problems.To overcome this limitation, it is necessary to perform error correction to fix the errors that otherwise corrupt the computer output. In digital hardware this is achieved by performing measurements on the information stored in logical registers. For a quantum computer this is much harder to implement, as the information is encoded in fragile superposition states which when measured directly results in a loss of information. One route to address this problem is to perform quantum error correction using a number of qubits to encode a single logical qubit by exploiting topologically protected states with specially chosen symmetry properties. To check for errors without erasing the quantum states, additional qubits (known as ancillas) are used to perform local measurements of the symmetries, after which errors can be corrected using standard gate protocols. Whilst a range of encoding schemes have been proposed for performing quantum error correction, this has so far only been implemented on few qubit systems of superconductors and ions and has yet to be demonstrated on the more scalable neutral atom platform due to challenges with cross talk when a only a single atomic species is used. In QuERy we will develop a new dual-species platform for neutral atom quantum computing to directly address major barriers to scaling up quantum hardware from 100s to millions of qubits, namely extending atom array trapping lifetimes through integration in a cryogenic environment to suppress errors due to atom loss, and demonstrating quantum error correction through the ability to perform cross-talk free, state-selective local measurements by using one species for encoding information and a second species to perform local ancilla measurements.This research will provide new modalities for neutral atom quantum computing, including enabling verification and benchmarking through randomised measurements, and develop algorithms able to exploit topological encodings to implement transverse gate operations. These results are crucial for the realisation of large-scale, fault-tolerant quantum computers as required to exploit the transformative benefits of quantum computing across both academia and industry, including applications such as material design, logistics and quantum chemistry for drug discovery.