# Optimizing Quantum Programs against Decoherence: Delaying Qubits into Quantum Superposition

## TL;DR

This paper introduces QLifeReducer, a compiler tool that delays qubits into superposition to reduce decoherence effects, improving quantum program accuracy on real hardware and simulators.

## Contribution

It proposes a novel method to minimize qubit lifetime by delaying qubits into superposition, addressing decoherence in NISQ-era quantum computing.

## Key findings

- Reduces quantum program error rate by 11% on IBM Q 5 Tenerife.
- Decreases longest and average qubit lifetime by over 20% in most workloads.
- Demonstrates effectiveness on real hardware and self-developed simulator.

## Abstract

Quantum computing technology has reached a second renaissance in the last decade. However, in the NISQ era pointed out by John Preskill in 2018, quantum noise and decoherence, which affect the accuracy and execution effect of quantum programs, cannot be ignored and corrected by the near future NISQ computers. In order to let users more easily write quantum programs, the compiler and runtime system should consider underlying quantum hardware features such as decoherence. To address the challenges posed by decoherence, in this paper, we propose and prototype QLifeReducer to minimize the qubit lifetime in the input OpenQASM program by delaying qubits into quantum superposition. QLifeReducer includes three core modules, i.e.,the parser, parallelism analyzer and transformer. It introduces the layered bundle format to express the quantum program, where a set of parallelizable quantum operations is packaged into a bundle. We evaluate quantum programs before and after transformed by QLifeReducer on both real IBM Q 5 Tenerife and the self-developed simulator. The experimental results show that QLifeReducer reduces the error rate of a quantum program when executed on IBMQ 5 Tenerife by 11%; and can reduce the longest qubit lifetime as well as average qubit lifetime by more than 20% on most quantum workloads.