Bifluxon: FluxonParityProtected Superconducting Qubit
Abstract
We have developed and characterized a symmetryprotected superconducting qubit that offers simultaneous exponential suppression of energy decay from charge and flux noise, and dephasing from flux noise. The qubit consists of a Cooperpair box (CPB) shunted by a superinductor, thus 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 AharonovCasher interference. In this regime, the logicalstate wavefunctions reside in disjoint regions of phase space, thereby ensuring the protection against energy decay. By switching the protection on, we observed a tenfold increase of the decay time, reaching up to $100 \mu \mathrm{s}$. Though the qubit is sensitive to charge noise, the sensitivity is much reduced in comparison with the charge qubit, and the chargenoiseinduced dephasing time of the current device exceeds $1 \mu \mathrm{s}$. Implementation of the full dephasing protection can be achieved in the nextgeneration devices by combining several $\cos \phi / 2$ Josephson elements in a small array.
 Publication:

arXiv eprints
 Pub Date:
 October 2019
 arXiv:
 arXiv:1910.03769
 Bibcode:
 2019arXiv191003769K
 Keywords:

 Condensed Matter  Superconductivity;
 Quantum Physics
 EPrint:
 13 pages, 13 figures