Bifluxon: Fluxon-Parity-Protected Superconducting Qubit
Bifluxon: Fluxon-Parity-Protected Superconducting Qubit
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DOI：
10.1103/prxquantum.1.010307
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发表时间：
2020-09-03
期刊：
影响因子：
9.7
通讯作者：
Bell, Matthew
中科院分区：
文献类型：
--
作者：
Kalashnikov, Konstantin;Hsieh, Wen Ting;Bell, Matthew
我们开发和表征了一个对称保护的超导量子比特，它同时提供电荷和通量噪声的能量衰减的指数抑制，以及通量噪声的消相。量子比特由一个超导体分流的库珀对盒（CPB）组成，形成一个超导环路。假设CPB岛上的偏移电荷是奇数个电子，量子位电位对应于cos （phi/2）约瑟夫森元素的电位，通过Aharonov-Casher干涉保持环中通量子的宇称性。在这种状态下，逻辑态波函数驻留在希尔伯特空间的不相交区域，从而确保了对能量衰减的保护。通过打开保护开关，我们观察到衰减时间增加了10倍，达到100 μ s。尽管量子比特对电荷噪声敏感，但与电荷量子比特相比，灵敏度大大降低，并且当前器件的电荷噪声诱导的脱相时间超过1 μ s。在下一代器件中，通过将几个cos(phi/2) Josephson元件组合在一个小阵列中，可以实现完全脱相保护。
We develop and characterize a symmetry-protected superconducting qubit that offers simultaneous exponential suppression of energy decay from charge and flux noises, and dephasing from flux noise. The qubit consists of a Cooper-pair box (CPB) shunted by a superinductor, forming a superconducting loop. Provided the offset charge on the CPB island is an odd number of electrons, the qubit potential corresponds to that of a cos (phi/2) Josephson element, preserving the parity of fluxons in the loop via Aharonov-Casher interference. In this regime, the logical-state wavefunctions reside in disjoint regions of Hilbert space, thereby ensuring protection against energy decay. By switching the protection on, we observe a tenfold increase of the decay time, reaching up to 100 mu s. Though the qubit is sensitive to charge noise, the sensitivity is much reduced in comparison with the charge qubit, and the charge-noise-induced dephasing time of the current device exceeds 1 mu s. Implementation of full dephasing protection can be achieved in the next-generation devices by combining several cos(phi/2) Josephson elements in a small array.