Optimal Wire Cutting With Classical Communication

Abstract

Circuit knitting is the process of partitioning large quantum circuits into smaller subcircuits such that the result of the original circuits can be deduced by only running the subcircuits. Such techniques will be crucial for near-term and early fault-tolerant quantum computers, as the limited number of qubits is likely to be a major bottleneck for demonstrating quantum advantage. One typically distinguishes between gate cuts and wire cuts when partitioning a circuit. The cost for any circuit knitting approach scales exponentially in the number of cuts. One possibility to realize a cut is via the quasiprobability simulation technique. In fact, we argue that all existing rigorous circuit knitting techniques can be understood in this framework. Furthermore, we characterize the optimal overhead for wire cuts where the subcircuits can exchange classical information or not. We show that the optimal cost for cutting <italic>n</italic> wires without and with classical communication between the subcircuits scales as <inline-formula> <tex-math notation="LaTeX">$O(16^{n})$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$O(4^{n})$ </tex-math></inline-formula>, respectively.