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Paper 1

Demonstrating real-time and low-latency quantum error correction with superconducting qubits

Laura Caune, Luka Skoric, Nick S. Blunt, Archibald Ruban, Jimmy McDaniel, Joseph A. Valery, Andrew D. Patterson, Alexander V. Gramolin, Joonas Majaniemi, Kenton M. Barnes, Tomasz Bialas, Okan Buğdaycı, Ophelia Crawford, György P. Gehér, Hari Krovi, Elisha Matekole, Canberk Topal, Stefano Poletto, Michael Bryant, Kalan Snyder, Neil I. Gillespie, Glenn Jones, Kauser Johar, Earl T. Campbell, Alexander D. Hill

Year

2024

Journal

arXiv preprint

DOI

arXiv:2410.05202

arXiv

2410.05202

Quantum error correction (QEC) will be essential to achieve the accuracy needed for quantum computers to realise their full potential. The field has seen promising progress with demonstrations of early QEC and real-time decoded experiments. As quantum computers advance towards demonstrating a universal fault-tolerant logical gate set, implementing scalable and low-latency real-time decoding will be crucial to prevent the backlog problem, avoiding an exponential slowdown and maintaining a fast logical clock rate. Here, we demonstrate low-latency feedback with a scalable FPGA decoder integrated into the control system of a superconducting quantum processor. We perform an 8-qubit stability experiment with up to $25$ decoding rounds and a mean decoding time per round below $1$ $μs$, showing that we avoid the backlog problem even on superconducting hardware with the strictest speed requirements. We observe logical error suppression as the number of decoding rounds is increased. We also implement and time a fast-feedback experiment demonstrating a decoding response time of $9.6$ $μs$ for a total of $9$ measurement rounds. The decoder throughput and latency developed in this work, combined with continued device improvements, unlock the next generation of experiments that go beyond purely keeping logical qubits alive and into demonstrating building blocks of fault-tolerant computation, such as lattice surgery and magic state teleportation.

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Paper 2

Entanglement-assisted Quantum Error Correcting Code Saturating The Classical Singleton Bound

Soham Ghosh, Evagoras Stylianou, Holger Boche

Year

2024

Journal

arXiv preprint

DOI

arXiv:2410.04130

arXiv

2410.04130

We introduce a construction for entanglement-assisted quantum error-correcting codes (EAQECCs) that saturates the classical Singleton bound with less shared entanglement than any known method for code rates below $ \frac{k}{n} = \frac{1}{3} $. For higher rates, our EAQECC also meets the Singleton bound, although with increased entanglement requirements. Additionally, we demonstrate that any classical $[n,k,d]_q$ code can be transformed into an EAQECC with parameters $[[n,k,d;2k]]_q$ using $2k$ pre-shared maximally entangled pairs. The complexity of our encoding protocol for $k$-qudits with $q$ levels is $\mathcal{O}(k \log_{\frac{q}{q-1}}(k))$, excluding the complexity of encoding and decoding the classical MDS code. While this complexity remains linear in $k$ for systems of reasonable size, it increases significantly for larger-levelled systems, highlighting the need for further research into complexity reduction.

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