EMT/QIS: GaAs hole spins as qubits: Eliminating hyperfine interaction-induced decoherence

EMT/QIS: GaAs空穴自旋作为量子比特：消除超精细相互作用诱导的退相干量子计算是一个新兴的科学和工程领域。它的总体目标是利用量子态的叠加来进行计算。量子计算机的基本组成部分是量子比特（qubit）。量子比特已经在各种各样的系统中得到了证明，从被捕获的离子，到半导体中的电子自旋，再到超导体。为了有用，一个量子位必须被正确地初始化、测量，并与其他量子位耦合。量子比特的质量由寿命（T1）和相干时间（T2）表征。从一个系统到另一个系统，这些时间尺度会变化几个数量级（例如，捕获离子与超导量子比特）。因此，习惯上引用一个质量因子Q，它是相干时间与典型栅极工作时间的比值。我们将在GaAs纳米级量子点中建立基于空穴自旋的量子比特。空穴自旋是有希望的候选者，因为空穴波函数具有类p轨道。因此，与宿主晶体核的超精细相互作用可以忽略不计，导致自旋相干时间接近300微秒的空穴自旋寿命。考虑到典型的门操作时间为~150 ps，如果实现，一个空穴自旋量子比特的质量因子可能接近200万，远远超过容错阈值。该项目的主要目标是精确测量并确定GaAs量子点中空穴自旋的量子相干时间的极限。

EMT/QIS: GaAs hole spins as qubits: Eliminating hyperfine interaction-induceddecoherenceQuantum Computing is an emerging area of science and engineering. Its broad goalis to harness the superposition of quantum states for computing purposes. The elementarybuilding block of a quantum computer is the quantum bit (qubit). Quantum bits have beendemonstrated in a wide variety of systems ranging from trapped ions, to electron spins insemiconductors, to superconductors. In order to be useful, a qubit must be properlyinitialized, measured, and coupled to other qubits. The quality of a qubit is characterizedby a lifetime (T1) and a coherence time (T2). These time scales vary by several orders ofmagnitude from one system to another (e.g. trapped ion versus superconducting qubits).It is therefore customary to quote a quality factor, Q, which is the ratio of the coherencetime to the typical gate operation time.We will build qubits based on hole spins in GaAs nanometer-size quantum dots.Hole spins are promising candidates since the hole wavefunctions have p-like orbitals. Asa result, hyperfine interactions with the host crystal nuclei are expected to be negligible,leading to spin coherence times approaching the hole spin lifetime of 300 microseconds.Taking into account the typical gate operation time of ~150 ps, a hole spin qubit, ifrealized, could have a quality factor of nearly 2 million, well beyond the threshold forfault tolerance. The primary goal of this project is to accurately measure, and determinewhat limits, the quantum coherence times of hole spins in GaAs quantum dots.