Summary
Fanout operations in quantum computers help copy information from one qubit to many others, but doing this safely across different parts of a network is tricky and can need a lot of communication. The authors propose a smarter way to perform these operations using special codes that protect quantum information and allow certain actions to be done simultaneously across different parts. They focus on a specific type of code called the Bivariate Bicycle code to show how this works. This method reduces the need for complex communication and extra resources, making distributed quantum computing more practical. They also explore how this approach can help build other distributed quantum operations efficiently.
Quantum computingQuantum error correctionLogical qubitFanout operationFault toleranceDistributed computingControlled-NOT gateTransversal operationBivariate Bicycle codeEntanglement
Abstract
We study a resource-efficient approach for implementing logical fanout operations in fault-tolerant distributed quantum computing using transversal operations on quantum error-correcting code blocks. Logical fanout, comprising multiple controlled-NOT operations from a common control qubit to target qubits located at remote nodes, is an important primitive for distributed quantum computation but can require substantial non-local communication when implemented directly between encoded blocks. We exploit the structure of encoded blocks and the availability of transversal logical operations to construct distributed fanout circuits that reduce the required non-local operations while preserving the logical action of the fanout operation. The construction is developed for encoded quantum information and illustrated using Bivariate Bicycle (BB)-code blocks. We analyze the resulting physical gate, entanglement, circuit-depth, and ancilla requirements. The approach provides a systematic method for implementing large logical fanout operations across distributed error-corrected quantum processors. Also, we study a distributed implementation of the global gate GCZ involving logical qubits (encoded using BB-code blocks), exploiting the concurrency in transversal distributed fanouts.