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arXiv:2502.07150 · Nature Communications

Computing efficiently in QLDPC codes

Alexander J. Malcolm, Andrew N. Glaudell, Patricio Fuentes, Daryus Chandra, Alexis Schotte, Colby DeLisle, Rafael Haenel, Amir Mohammad Ebrahimi, Joschka Roffe, Armanda O. Quintavalle, Stefanie J. Beale, N. R. Lee-Hone, Stephanie Simmons

Published May 20, 2026• 4 citations
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Abstract

Quantum error correction is essential for building utility-scale quantum computers that outperform classical machines, yet leading approaches incur substantial physical qubit overhead. Quantum low-density parity check (QLDPC) codes offer a promising alternative by significantly reducing the number of physical qubits required per logical qubit. However, existing work on QLDPC codes has focused primarily on quantum memories, with no efficient method known for implementing arbitrary logical Clifford operations at low circuit depth. Here, we introduce a new family of QLDPC codes that enables efficient implementation of the full Clifford group via transversal operations, allowing any m-qubit Clifford operation to be executed in at most O(m) syndrome extraction rounds. We run circuit-level simulations of depth-126 logical circuits to demonstrate the near-memory logical performance of these logical operations. In combination with known methods for implementing T gates, these results establish QLDPC codes as a viable route toward resource-efficient universal quantum computation. Quantum LDPC codes can shield quantum computers from decoherence with minimal overhead. In this work, the authors describe a new QLDPC family, SHYPS, as a path to practical fault tolerance with efficient Clifford circuit implementation on encoded states.

DOI
10.1038/s41467-026-73061-9

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Quantum error correction is essential for building utility-scale quantum computers that outperform classical machines, yet leading approaches incur substantial physical qubit overhead. Quantum low-density parity check (QLDPC) codes offer a promising alternative by significantly reducing the number of physical qubits required per logical qubit. However, existing work on QLDPC codes has focused primarily on quantum memories, with no efficient method known for implementing arbitrary logical Clifford operations at low circuit depth. Here, we introduce a new family of QLDPC codes that enables efficient implementation of the full Clifford group via transversal operations, allowing any m-qubit Clifford operation to be executed in at most O(m) syndrome extraction rounds. We run circuit-level simulations of depth-126 logical circuits to demonstrate the near-memory logical performance of these logical operations. In combination with known methods for implementing T gates, these results establish QLDPC codes as a viable route toward resource-efficient universal quantum computation. Quantum LDPC codes can shield quantum computers from decoherence with minimal overhead. In this work, the authors describe a new QLDPC family, SHYPS, as a path to practical fault tolerance with efficient Clifford circuit implementation on encoded states.
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Quantum low-density parity-check (qLDPC) codes can achieve high encoding rates and good code distance scaling, providing a promising route to low-overhead fault-tolerant quantum computing. However, the long-range connectivity required to implement such codes makes their physical realization challenging. Here, we propose a hardware-efficient scheme to perform fault-tolerant quantum computation with high-rate qLDPC codes on reconfigurable atom arrays, directly compatible with recently demonstrated experimental capabilities. Our approach utilizes the product structure inherent in many qLDPC codes to implement the non-local syndrome extraction circuit via atom rearrangement, resulting in effectively constant overhead in practically relevant regimes. We prove the fault tolerance of these protocols, perform circuit-level simulations of memory and logical operations with these codes, and find that our qLDPC-based architecture starts to outperform the surface code with as few as several hundred physical qubits at a realistic physical error rate of 10−310^{-3}10−3. We further find that less than 3000 physical qubits are sufficient to obtain over an order of magnitude qubit savings compared to the surface code, and quantum algorithms involving thousands of logical qubits can be performed using less than 10510^5105 physical qubits. Our work paves the way for explorations of low-overhead quantum computing with qLDPC codes at a practical scale, based on current experimental technologies.
Quantum low-density parity-check (qLDPC) codes can substantially reduce the qubit overhead of fault-tolerant quantum computation, but any useful architecture based on such codes also requires an efficient mechanism to implement non-Clifford gates in a fault-tolerant manner. We introduce a space-time-efficient magic state factory for high-rate qLDPC codes by combining the transversal non-Clifford gates of recently developed tricycle codes with single-shot four-dimensional balanced product quadcycle codes. The key ingredient is an efficient "escape" mechanism that teleports postselected logical magic states from tricycle codes to larger distance quadcycle codes. Under a standard circuit-level noise model at physical error rate 10−310^{-3}10−3, our factories produce CCZ\mathrm{CCZ}CCZ states at logical error rates as low as 10−910^{-9}10−9 with 10-40 times lower space-time cost than state-of-the-art magic state generation methods. The resulting states are directly encoded in high-rate blocks suitable for computation. We identify the quadcycle codes by an AI-assisted search and show that they can serve as excellent memories capable of single-shot error correction. Finally, we present a concrete implementation of the entire factory with highly efficient atom transport on reconfigurable neutral-atom quantum computers. Together, these results provide an end-to-end, practical protocol for producing and utilizing high-fidelity magic states within a high-rate qLDPC architecture, with the lowest space-time cost to date.
For quantum low-density parity check (qLDPC) codes, the ability to manipulate individual logical units of information, i.e. the use of addressable gates, enables maximal utility of their efficient encoding. We introduce explicit low-depth unitary circuits that realize fully addressable and fault-tolerant two-qubit Clifford gates for a subset of two-dimensional translationally invariant qLDPC codes. Our transversal unitaries are created by applying a geometrically structured sparsification procedure to round-robin circuits. We verify the general applicability of our protocol by proposing and numerically simulating a range of addressable CZs between toric, cyclic hypergraph-product, color, gross, and directional codes, demonstrating fault-tolerant memory-like logical error rate scaling.
Quantum low-density parity-check (qLDPC) codes are promising candidates for fault-tolerant quantum computation due to their high encoding rates and distances. However, implementing logical operations using qLDPC codes presents significant challenges. Previous research has demonstrated that self-dual qLDPC codes facilitate the implementation of transversal Clifford gates. Here we introduce a method for constructing self-dual qLDPC codes by stacking non-self-dual qLDPC codes. Leveraging this methodology, we develop double-chain bicycle codes, double-layer bivariate bicycle (BB) codes, double-layer twisted BB codes, and double-layer reflection codes, many of which exhibit favorable code parameters. Additionally, we conduct numerical calculations to assess the performance of these codes as quantum memory under the circuit-level noise model, revealing that the logical failure rate can be significantly reduced with high pseudo-thresholds.
High-rate quantum LDPC (qLDPC) codes reduce memory overhead by densely packing many logical qubits into a single block of physical qubits. Here we extend this concept to high-rate computation by constructing \emph{batched} fault-tolerant operations that apply the same logical gate across many code blocks in parallel. By leveraging shared physical resources to execute many logical operations in parallel, these operations realize high rates in space-time and significantly reduce computational costs. For \emph{arbitrary} CSS qLDPC codes, we build batched gadgets with \emph{constant space-time overhead} (assuming fast classical computation) for (i) single-shot error correction, state preparation, and code surgeries (ii) code switching, and (iii) addressable Clifford gates. Using these batched gadgets we also construct parallel non-Clifford gates with low space-time cost. We outline principles for designing parallel quantum algorithms optimized for a batched architecture, and show in particular how lattice Hamiltonian dynamical simulations can be compiled efficiently. We also propose a near-term implementation using new self-dual Bivariate-Bicycle codes with high encoding rates (∼1/10\sim 1/10∼1/10), transversal Clifford gates, and global TTT gates via parallel magic state cultivation, enabling Hamiltonian simulations with a lower space-time cost than analogous surface-code protocols and low-rate qLDPC protocols. These results open new paths toward scalable quantum computation via co-design of parallel quantum algorithms and high-rate fault-tolerant protocols.