A Gate-Level Approach To Compiling For Quantum Computers

Programming language constructs generally operate on data words, and so does most compiler analysis and transformation. However, individual word-level operations often harbor pointless, yet resource and power hungry, lower-level operations. By transforming complete programs into gate-level operations on individual bits, and optimizing operations at that level, it is possible to dramatically reduce the total amount of work needed to execute the program's algorithm. This gate-level representation can be in terms of any complete set of logic gate types; earlier work targeted conventional multiplexor gates, but the work reported here centers on targeting CSWAP (FredKin) gates without fanout - a form that can be implemented on a quantum computer. This paper will overview the approach, describe the current state of the prototype compiler, and suggest some ways in which compiler automatic parallelization technology might be extended to allow ordinary programs to take advantage of the unique properties of quantum computers.