Dynamical Decoupling, Error Mitigation and Noise Correlations in Multi-Qubit Systems

量子计算机是一种新型设备，可以利用量子叠加，量子纠缠和量子干涉的力量来显着减少具有挑战性的问题的计算时间。到目前为止，量子计算操作仅在具有少量量子比特（qubit）的系统中实现。困难在于量子比特对环境中的噪声非常敏感，这导致它们在有足够的时间进行任何计算之前就失去了量子特性。改进量子比特的一种方法是开发新的设计，使用新材料和更精细的制造技术。 一种补充方法是通过向量子比特施加一系列控制脉冲来主动抵消噪声的负面影响，这将它们从噪声环境中分离出来。该项目将开发和实现用于耦合量子比特系统的动态解耦技术，目标是进一步提高量子比特性能并降低多量子比特系统的错误率。任何现实的量子计算机都需要实现纠错算法，以便在出现残留错误时进行处理。有几种实现量子纠错的方案，但协议的共同点是它们对执行单量子位和多量子位门操作的允许错误率提出了严格的要求。尽管当代量子比特设计接近某些协议的阈值，但重要的是要认识到，大多数量子纠错协议假设单个量子比特的错误是不相关的，这对于大多数物理量子比特系统来说是过度简化的。该项目将专注于量化多量子比特系统中的相关噪声，这将是开发更有效的量子纠错协议的关键。此外，该团队还将开发新的量子位控制序列，通过减少靠近设备的准粒子数量来动态改善量子位弛豫和退相时间。

A quantum computer is a new type of device that could harness the power of quantum superposition, quantum entanglement, and quantum interference to dramatically reduce computation time for challenging problems. So far, quantum computational operations have only been realized in systems with a small number of quantum bits (qubits). The difficulty is that qubits are very sensitive to noise in their environment, which causes them to lose their quantum properties before there is enough time to perform any calculations. One way to improve the qubits is to develop new designs, using new materials and more refined fabrication techniques. A complimentary approach is to actively counteract the negative influence of the noise by applying a sequence of control pulses to the qubits, which decouples them from the noisy environment. This project will develop and implement such dynamical decoupling techniques for systems with coupled qubits, with the goal of further improving qubit performance and reducing error rates in multi-qubit systems.Any realistic quantum computer will need to implement error correction algorithms, so that residual errors can be handled as they occur. There exist several proposals for implementing quantum error correction, but common to protocols is that they put stringent requirements on the allowed error rate for performing single and multi-qubit gate operations. Even though contemporary qubit designs are close to threshold for certain protocols, it is important to realize that most quantum error correction protocols assume that the errors of individual qubits are uncorrelated, which is an oversimplification for most physical qubit systems. This project will focus on quantifying correlated noise in multi-qubit systems, which will be key for the development of more efficient quantum error correction protocols. In addition, this team will develop novel qubit control sequences for dynamically improving both qubit relaxation and dephasing times by reducing the number of quasiparticles close to the device.