A Fault-Tolerant Million Qubit-Scale Distributed Quantum Computer

A million qubit-scale quantum computer is essential to realize the quantum supremacy. Modern large-scale quantum computers integrate multiple quantum computers located in dilution refrigerators (DR) to overcome each DR's unscaling cooling budget. However, a large-scale multi-DR quantum computer introduces its unique challenges (i.e., slow and erroneous inter-DR entanglement, increased qubit scale), and they make the baseline error handling mechanism ineffective by increasing the number of gate operations and the inter-DR communication latency to decode and correct errors. Without resolving these challenges, it is impossible to realize a fault-tolerant large-scale multi-DR quantum computer.