Compiler Management of Communication and Parallelism for Quantum Computation

Abstract

Quantum computing (QC) offers huge promise to accelerate a range of computationally intensive benchmarks. Quantum computing is limited, however, by the challenges of decoherence: i.e., a quantum state can only be maintained for short windows of time before it decoheres. While quantum error correction codes can protect against decoherence, fast execution time is the best defense against decoherence, so efficient architectures and effective scheduling algorithms are necessary. This paper proposes the Multi-SIMD QC architecture and then proposes and evaluates effective schedulers to map benchmark descriptions onto Multi-SIMD architectures. The Multi-SIMD model consists of a small number of SIMD regions, each of which may support operations on up to thousands of qubits per cycle.Efficient Multi-SIMD operation requires efficient scheduling. This work develops schedulers to reduce communication requirements of qubits between operating regions, while also improving parallelism.We find that communication to global memory is a dominant cost in QC. We also note that many quantum benchmarks have long serial operation paths (although each operation may be data parallel). To exploit this characteristic, we introduce LongestPath-First Scheduling (LPFS) which pins operations to SIMD regions to keep data in-place and reduce communication to memory.Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from permissions@acm.org. ASPLOS '15, March 14-18, 2015, Istanbul, Turkey. Copyright c 2015 ACM 978-1-4503-2835-7/15/03. . . $15.00. http://dx.doi.org/10.1145 The use of small, local scratchpad memories also further reduces communication. Our results show a 3% to 308% improvement for LPFS over conventional scheduling algorithms, and an additional 3% to 64% improvement using scratchpad memories. Our work is the most comprehensive software-to-quantum toolflow published to date, with efficient and practical scheduling techniques that reduce communication and increase parallelism for full-scale quantum code executing up to a trillion quantum gate operations.

Application-Motivated, Holistic Benchmarking of a Full Quantum Computing Stack

“…15 These passes are composed to form compilation strategies which should output executable quantum circuits. Quantum compiling is an active area of research [65][66][67][68][69][70][71], and there are many pieces of software available for quantum compiling. As noted above, in this work we use two: t|ket and the compiler available in Qiskit.…”

OpenFermion: the electronic structure package for quantum computers

“…Moreover, to maximize usefulness within the field, every effort has been made to design OpenFermion as a modular library which is agnostic with respect to quantum programming language frameworks. Through its plugin system, OpenFermion is able to interface with, and benefit from, any of the frameworks being developed for both more abstract quantum software and hardware specific compilation [70][71][72][73][74][75][76][77][78][79]91].…”

Constant depth fault-tolerant Clifford circuits for multi-qubit large block codes

“…Another candidate is the optimization type algorithms like quantum approximate optimization algorithm (QAOA) [42], which needs to rapidly apply Hadamards. On the other hand, to generate large mount ancilla states, single instruction multiple data (SIMD) style architecture [43,44] that apply the same quantum gates on multiple qubits in the same region simultaneously, maybe particularly useful.…”