Chirolli Luca, Moore Joel E
Department of Physics, University of California, Berkeley, California 94720, USA.
Istituto Nanoscienze-CNR, I-56127 Pisa, Italy.
Phys Rev Lett. 2021 May 7;126(18):187701. doi: 10.1103/PhysRevLett.126.187701.
In superconducting circuits interrupted by Josephson junctions, the dependence of the energy spectrum on offset charges on different islands is 2e periodic through the Aharonov-Casher effect and resembles a crystal band structure that reflects the symmetries of the Josephson potential. We show that higher-harmonic Josephson elements described by a cos(2φ) energy-phase relation provide an increased freedom to tailor the shape of the Josephson potential and design spectra featuring multiplets of flat bands and Dirac points in the charge Brillouin zone. Flat bands provide noise-insensitive energy levels, and consequently, engineering band pairs with flat spectral gaps can help improve the coherence of the system. We discuss a modified version of a flux qubit that achieves, in principle, no decoherence from charge noise and introduce a flux qutrit that shows a spin-1 Dirac spectrum and is simultaneously quite robust to both charge and flux noise.
在由约瑟夫森结中断的超导电路中，通过阿哈罗诺夫 - 卡什效应，能谱对不同岛状物上的偏移电荷的依赖性呈2e周期性，并且类似于反映约瑟夫森势对称性的晶体能带结构。我们表明，由cos(2φ)能量 - 相位关系描述的高次谐波约瑟夫森元件为定制约瑟夫森势的形状以及设计在电荷布里渊区具有平带和狄拉克点多重态的能谱提供了更大的自由度。平带提供对噪声不敏感的能级，因此，设计具有平谱隙的能带对有助于提高系统的相干性。我们讨论了一种原则上能实现无电荷噪声退相干的磁通量子比特的改进版本，并引入了一种磁通三量子比特，它显示出自旋 - 1狄拉克能谱，并且对电荷和磁通噪声都相当稳健。
