# An Efficient Quantum Compiler that Reduces T Count

Earl Campbell ( University of Sheffield )

- 16:00 6th March 2018 ( Hilary Term 2018 )

Before executing a quantum algorithm, one must first decompose the algorithm into machine-level instructions compatible with the architecture of the quantum computer, a process known as quantum compiling. There are many different quantum circuit decompositions for the same algorithm but it is desirable to compile leaner circuits. A popular cost measure is the T count – the number of T gates in a circuit – since it closely approximates the full space-time cost for surface code architectures. For the single qubit case, optimal compiling is essentially a solved problem. However, multi-qubit compiling is a harder problem with optimal algorithms requiring classical runtime exponential in the number of qubits, n. Here, we present and compare several efficient quantum compilers for multi-qubit Clifford + T circuits.

*References:*Based on [arXiv:1712.01557v2] and some results from Section 4 of Phys. Rev. A 95 (022316), 2017