该研究团队提出了在压缩驱动下克尔振荡器频谱中，多重同时双重简并的实验发现。这种压缩驱动由三波混频过程产生，结合克尔相互作用，在相位空间中以产生压缩的正弦驱动的一半频率旋转，产生有效的静态两阱势。值得一提的是，这些频谱简并可以根据实际需求灵活开启或关闭，甚至通过微调压缩驱动器的频率来增减简并的数量。
研究人员发现，当振荡器的频率与驱动器的次谐波之间的失谐Δ恰好是克尔系数K的偶数倍，即Δ/K=2m时，振荡器将表现出m+1个精确的、宇称保护的频谱简并，且这些简并对驱动器振幅的变化不敏感。
这些简并现象可以通过模拟实验中的双阱静态有效势经典禁区内的，隧穿路径中发生的非寻常破坏性干涉来解释。利用这种干涉效应，研究人员成功测量了非相干阱开关寿命的峰值增强，进而在振荡器的基态流形中构建了一个受保护的猫量子比特。这一研究成果揭示了驱动量子系统中简并与噪声保护之间的联系。
附：英文原文
Title: A driven Kerr oscillator with two-fold degeneracies for qubit protection
Author: Venkatraman, Jayameenakshi, Cortinas, Rodrigo G., Frattini, Nicholas E., Xiao, Xu, Devoret, Michel H.
Issue&Volume: 2024-6-5
Abstract: We present the experimental finding of multiple simultaneous two-fold degeneracies in the spectrum of a Kerr oscillator subjected to a squeezing drive. This squeezing drive resulting from a three-wave mixing process, in combination with the Kerr interaction, creates an effective static two-well potential in the phase space rotating at half the frequency of the sinusoidal drive generating the squeezing. Remarkably, these degeneracies can be turned on-and-off on demand, as well as their number by simply adjusting the frequency of the squeezing drive. We find that when the detuning Δ between the frequency of the oscillator and the second subharmonic of the drive equals an even multiple of the Kerr coefficient K, Δ/K=2m, the oscillator displays m+1 exact, parity-protected, spectral degeneracies, insensitive to the drive amplitude. These degeneracies can be explained by the unusual destructive interference of tunnel paths in the classically forbidden region of the double well static effective potential that models our experiment. Exploiting this interference, we measure a peaked enhancement of the incoherent well-switching lifetime, thus creating a protected cat qubit in the ground state manifold of our oscillator. Our results illustrate the relationship between degeneracies and noise protection in a driven quantum system.
DOI: 10.1073/pnas.2311241121
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2311241121