A program transformation and architecture support for quantum uncomputation

Quantum computing's power comes from new algorithms that exploit quantum mechanical phenomena for computation. Quantum algorithms are different from their classical counterparts in that quantum algorithms rely on algorithmic structures that are simply not present in classical computing. Just as classical program trans- formations and architectures have been designed for common classi- cal algorithm structures, quantum program transformations and quantum architectures should be designed with quantum algorithms in mind. Because quantum algorithms come with these new algorith- mic structures, resultant quantum program transformations and architectures may look very different from their classical counter- parts. This paper focuses on uncomputation, a critical and prevalent structure in quantum algorithms, and considers how program trans- formations, and architecture support should be designed to accom- modate uncomputation. In this paper, we show a simple quantum program transformation that exposes independence between uncom- putation and later computation. We then propose a multicore archi- tecture tailored to this exposed parallelism and propose a scheduling policy that efficiently maps such parallelism to the multicore archi- tecture. Our policy achieves parallelism between uncomputation and later computation while reducing cumulative communication dis- tance. Our scheduling and architecture allows significant speedup of quantum programs (between 1.8x and 2.8x speedup in Shor's factor- ing algorithm), while reducing cumulative communication distance 26%. Categories and Subject Descriptors: C.m ( Computer Systems Organization ): Miscellaneous, D.1.3 ( Programming Techniques ): Concurrent Programming - Parallel Programming.