Title: Spectral investigation of the noise influencing multi-qubit states Show Chinese title

Title: 噪声对多量子比特态影响的光谱研究

Abstract: Characterizing and understanding noise affecting quantum states has immense benefits in spectroscopy as well as in realizing quantum devices. Transverse relaxation times under a set of dynamical decoupling (DD) sequences with varying interpulse delays were earlier used for obtaining the noise spectral densities of single-qubit coherences. In this work, using a pair of homonuclear spins and NMR techniques, we experimentally characterize noise in certain decoherence-free subspaces. We also explore the noise of similar states in a heteronuclear spin pair. Further, using a 10-qubit system, we investigate noise profiles of various multiqubit coherences and study the scaling of noise with respect to the coherence order. Finally, using the experimentally obtained noise spectrum of the 10-qubit NOON state, we predict the performance of a Uhrig DD sequence and verify it experimentally. Show Chinese abstract

Abstract: 表征和理解影响量子态的噪声在光谱学以及实现量子设备方面具有巨大好处。 先前使用一组动态解耦（DD）序列在不同脉冲间隔时间下的横向弛豫时间，用于获得单量子比特相干性的噪声谱密度。 在本工作中，我们使用一对同核自旋和核磁共振技术，对某些无退相干子空间中的噪声进行实验表征。 我们还研究了异核自旋对中类似状态的噪声。 此外，使用一个10量子比特系统，我们研究了各种多量子比特相干性的噪声轮廓，并研究了噪声与相干阶数的关系。 最后，利用实验获得的10量子比特NOON态的噪声谱，我们预测了Uhrig DD序列的性能，并通过实验进行了验证。