Curator's Take
This research tackles a critical challenge facing modular quantum computers, where connecting separate quantum processors or refrigerator units introduces significantly higher error rates than operations within each module. The proposed entanglement distillation protocols are remarkably efficient, achieving quadratic error suppression using just two qubits per module while minimizing the costly inter-module operations that often become the main performance bottleneck. This work provides a practical pathway for near-term quantum systems to overcome connectivity limitations by trading some computational overhead for dramatically improved entanglement quality between modules. The space-efficient approach could prove essential for scaling quantum computers beyond single-chip architectures, where maintaining high-fidelity connections across different physical units remains one of the biggest engineering hurdles.
— Mark Eatherly
Summary
Near-term and early fault-tolerant quantum computing architectures are expected to exhibit highly non-uniform error rates. In particular, local operations within a chip can be substantially more reliable than operations connecting different chips or dilution refrigerators. Such inter-module operations can therefore become a dominant bottleneck, even when quantum error correction is applied. Entanglement distillation provides a natural way to trade additional operations and qubits for higher-fidelity entanglement. Standard distillation protocols, however, are usually formulated in an LOCC resource model, in which several noisy Bell pairs are generated initially and all subsequent processing consists only of local operations and classical communication. Here, we consider a generalized model tailored to modular quantum computing hardware, in which the two modules have access to high-fidelity local operations and to repeated uses of the same noisy inter-module entangling operation during the protocol. We develop practical small-scale entanglement distillation protocols designed to minimize both space and time overhead. Remarkably, our main protocol requires only two qubits per module, yet achieves quadratic error suppression of inter-module errors, assuming local operations are much cleaner. Compared with existing small-scale protocols, our space-optimal protocol provides more space- and time-efficient quadratic error suppression and achieves the best performance in our simulations and experiments on noisy links of current superconducting quantum processors. These results suggest that inter-module-gate-assisted entanglement distillation can be a practical primitive for overcoming noisy links in modular quantum computing architectures.