Quantum Error Correction in Neutral Atom Quantum Computer

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This project seeks to develop a dual-species platform for quantum computing and simulation with neutral atoms, providing a route to implementing active quantum error correction essential for future scaling beyond 100 qubits. This hardware will simultaneously provide a versatile platform for analogue computing and simulation due to the ability to independently control inter- and intra-species interactions, providing a route to performing studies of complex many-body physics as well as increasing the diversity of real-world optimisation problems that can be tackled using neutral atom hardware.Quantum computation (QC) offers a revolutionary approach to information processing, providing a route to efficiently solve classically hard problems encountered across a diverse range of sectors, including financial services (e.g. portfolio optimisation), energy (e.g. network design and energy distribution), logistics (e.g. route planning), and IT (e.g. search, machine learning). Using hardware operating under the laws of quantum mechanics also creates a platform for studying physical systems, such as complex materials and molecules, with early demonstrations showing applications in materials science and quantum chemistry that could eventually be scaled up to accelerate drug design or optimised materials for aerospace and manufacturing.Whilst large-scale applications will require thousands of qubits, in the near-term small (100 qubit) quantum processors will reach a regime in which the quantum hardware is able to solve problems not accessible even on the largest available conventional supercomputers. However, scaling of quantum systems remains a major experimental challenge, with high-fidelity performance demonstrated for small, state-of-the-art ion and superconductor systems but with significant technical barriers to extending this performance beyond around 10-20 qubits. Over the last decade, neutral atoms have emerged as one of the most promising platforms for quantum information processing, with a major advantage over competing technologies arising from the ability to scale to large numbers of identical qubits as required for performing practical quantum computing. To date, several experiments have demonstrated trapping of qubit arrays with > 256 qubits. To couple neutral atom qubits, highly excited Rydberg states are used which have extremely large electric dipole moments giving rise to strong and controllable interactions. These can be exploited to perform high fidelity multi-qubit gates, with F>0.95 demonstrated for two qubits and intrinsic fidelities of F>0.995 for multi-qubit gates, or for performing quantum simulation of controllable spin models as required for studying materials or solving optimisation problems.Whilst there has been significant experimental progress, a number of challenges currently limit scaling to larger array sizes for hardware based on a single atomic species. The first arises from finite vacuum lifetime due to collisions with background atoms ejecting atoms from the trap. For room temperature operation, this is typically 10s for 1 atom but means only 10ms for a 1000 atom array. This can be solved by moving to operation at cryogenic temperatures down to 4 K where the cold surfaces cause significant increase in lifetime upwards of > 6000 seconds meaning recovery of times > 6s even for 1000 atoms. The next issue lies in the long readout time for neutral atom qubits, typically requiring 10-50 ms to readout qubit states. With a single species, the cross-talk and scattered light mean readout is destructive across the whole array, with no clear pathway to performing local measurements required for error correction to reach fault tolerant operation.