Extracting Success from IBM’s 20-Qubit Machines Using Error-Aware Compilation

Abstract

NISQ (Noisy, Intermediate-Scale Quantum) computing requires error mitigation to achieve meaningful computation. Our compilation tool development focuses on the fact that the error rates of individual qubits are not equal, with a goal of maximizing the success probability of real-world subroutines such as an adder circuit. We begin by establishing a metric for choosing among possible paths and circuit alternatives for executing gates between variables placed far apart within the processor, and test our approach on two IBM 20-qubit systems named Tokyo and Poughkeepsie. We find that a single-number metric describing the fidelity of individual gates is a useful but imperfect guide. Our compiler uses this subsystem and maps complete circuits onto the machine using a beam search-based heuristic that will scale as processor and program sizes grow. To evaluate the whole compilation process, we compiled and executed adder circuits, then calculated the Kullback–Leibler divergence (KL-divergence, a measure of the distance between two probability distributions). For a circuit within the capabilities of the hardware, our compilation increases estimated success probability and reduces KL-divergence relative to an error-oblivious placement.

Scheduling of Operations in Quantum Compiler

“…Although this certainly contributes to obtaining computational results with higher fidelity, there should be more direct approaches that attempt to maximize the output fidelity by considering gate-dependent errors. In fact, such approaches have recently proposed in qubit routing [29]- [31]. Utilizing techniques like this for QOS is also left for future work.…”

Timing and Resource-Aware Mapping of Quantum Circuits to Superconducting Processors

“…Routing refers to the task of finding a series of movement operations that enables the execution of two-qubit gates on a given processor topology with low communication overhead. To do so, multiple routing paths are evaluated and one is selected based on various optimization criteria such as the number of added movement operations, increase of circuit depth, or decrease of circuit reliability [6], [17]- [23], [25], [41], [42]. Afterwards, the corresponding movement operations are inserted.…”

“…Although all these metrics affect the success probability of a quantum circuit, an analysis on which ones are more critical to be minimized is required. Recent works [20], [22], [23], [41], [42], [45] suggest to choose the routing path based on the fidelity of the two-qubit gates along the path as they are used to implement the movements (noise-aware mapper). However, the reliability of a path is calculated by simply multiplying the fidelity of each gate without considering error propagation and decoherence, which makes this metric incomplete and not 0278-0070 (c) 2021 IEEE.…”

“…Content may change prior to final publication. Citation information: DOI 10.1109/TCAD.2021.3057583, IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems very accurate and it thus sometimes fails in predicting the most reliable route [23]. A more accurate metric that can well represent success probability and also can be easily used by the mapping procedure needs to be developed.…”

A lightweight approach to detect malicious/unexpected changes in the error rates of NISQ computers

“…The goal of the quantum compilation/mapping is to minimize quantum circuit errors. The estimated success probability of the quantum circuit [22] is defined as:…”