TheperiodiceffectivepotentialofasuperconductingquantuminterferencedevicecontaininganunderdampedJosephsonjunctioninthefirstbranchandadouble-barrierjunctioninthesecondisstudied.Aneffectivenon-sinusoidalexpressionforthecurrent–phaserelationwithanadditionalhalfharmonictermisusedforthedouble-