A coupler, comprising: a first capacitor including a first capacitor end portion and a first capacitor other-end portion; a first inductor including a first inductor end portion electrically connected with the first capacitor end portion, and a first inductor other-end portion; a second capacitor including a second capacitor end portion and a second capacitor other-end portion; a second inductor including a second inductor end portion electrically connected with the second capacitor end portion, and a second inductor other-end portion electrically connected with the first capacitor other-end portion, the first inductor other-end portion, and the second capacitor other-end portion; a first Josephson junction including a first Josephson junction end portion electrically connected with the first capacitor end portion, and a first Josephson junction other-end portion electrically connected with the second capacitor end portion, a space being surrounded with the first inductor, the second inductor, and the first Josephson junction; a third capacitor including a third capacitor end portion electrically connectable with a first nonlinear resonator, and a third capacitor other-end portion (13e, 13f) electrically connected with the first capacitor end portion; and a fourth capacitor including a fourth capacitor end portion electrically connectable with a second nonlinear resonator and a fourth capacitor other-end portion electrically connected with the second capacitor end portion, the coupler is made to resonate in a plurality of modes, at least two of resonant frequencies in the modes being higher than a resonant frequency of the first nonlinear resonator, being higher than a resonant frequency of the second nonlinear resonator, and being lower than a sum of the resonant frequency of the first nonlinear resonator and the resonant frequency of the second nonlinear resonator. a first capacitor including a first capacitor end portion and a first capacitor other-end portion; a first inductor including a first inductor end portion electrically connected with the first capacitor end portion, and a first inductor other-end portion; a first inductor end portion electrically connected with the first capacitor end portion, and a first inductor other-end portion; a second capacitor including a second capacitor end portion and a second capacitor other-end portion; a second inductor including a second inductor end portion electrically connected with the second capacitor end portion, and a second inductor other-end portion electrically connected with the first capacitor other-end portion, the first inductor other-end portion, and the second capacitor other-end portion; a second inductor end portion electrically connected with the second capacitor end portion, and a second inductor other-end portion electrically connected with the first capacitor other-end portion, the first inductor other-end portion, and the second capacitor other-end portion; a first Josephson junction including a first Josephson junction end portion electrically connected with the first capacitor end portion, and a first Josephson junction other-end portion electrically connected with the second capacitor end portion, a space being surrounded with the first inductor, the second inductor, and the first Josephson junction; a first Josephson junction end portion electrically connected with the first capacitor end portion, and a first Josephson junction other-end portion electrically connected with the second capacitor end portion, a space being surrounded with the first inductor, the second inductor, and the first Josephson junction; a third capacitor including a third capacitor end portion electrically connectable with a first nonlinear resonator, and a third capacitor other-end portion (13e, 13f) electrically connected with the first capacitor end portion; and a third capacitor end portion electrically connectable with a first nonlinear resonator, and a third capacitor other-end portion (13e, 13f) electrically connected with the first capacitor end portion; and a fourth capacitor including a fourth capacitor end portion electrically connectable with a second nonlinear resonator and a fourth capacitor other-end portion electrically connected with the second capacitor end portion, a fourth capacitor end portion electrically connectable with a second nonlinear resonator and a fourth capacitor other-end portion electrically connected with the second capacitor end portion, the coupler is made to resonate in a plurality of modes, at least two of resonant frequencies in the modes being higher than a resonant frequency of the first nonlinear resonator, being higher than a resonant frequency of the second nonlinear resonator, and being lower than a sum of the resonant frequency of the first nonlinear resonator and the resonant frequency of the second nonlinear resonator.