Integer Fluxonium Qubit
Raymond Mencia, Wei-Ju Lin, Hyunheung Cho, Maxim Vavilov, Vladimir Manucharyan
Abstract
We describe a superconducting qubit derived from operating a properly designed fluxonium circuit in a zero magnetic field. The qubit has a frequency of about 4 GHz and an energy relaxation quality factor <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <a:mi>Q</a:mi> <a:mo>≈</a:mo> <a:mn>0.7</a:mn> <a:mo>×</a:mo> <a:msup> <a:mn>10</a:mn> <a:mn>7</a:mn> </a:msup> </a:math> , even though the dielectric loss quality factor of the circuit components is in the low- <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <d:msup> <d:mn>10</d:mn> <d:mn>5</d:mn> </d:msup> </d:math> range. The Ramsey coherence time exceeds <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <g:mn>100</g:mn> <g:mspace width="0.2em"/> <g:mtext fontfamily="times">μ</g:mtext> <g:mrow> <g:mi mathvariant="normal">s</g:mi> </g:mrow> </g:math> , and the average fidelity of Clifford gates is benchmarked to <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <m:mrow> <m:mi mathvariant="script">F</m:mi> </m:mrow> <m:mo>></m:mo> <m:mn>0.999</m:mn> </m:math> . These figures are expected to improve with optimized fabrication and measurement procedures. Our work establishes a ready-to-use “partially protected” superconducting qubit functioning in the frequency range of conventional transmons. Published by the American Physical Society 2024