A method of operating a quantum processing device (1, 2, 3) so as to implement one or more quantum gates, the quantum processing device (1, 2, 3) comprising a tunable coupler and at least two fixed frequency quantum circuits (11, 12, 13, 14, 1n) coupled to the tunable coupler, the method comprising: modulating a frequency of the tunable coupler so as to drive two first-order energy transitions, wherein the frequency of the tunable coupler is operated to be modulated by way of harmonic microwave signals applied to the tunable coupler so as to drive at least two selectively addressed first-order energy transitions in the quantum processing device (1, 2, 3); and in response to modulating the frequency of the tunable coupler so as to drive the two first-order energy transitions, causing a first excitation of one of the at least two fixed frequency quantum circuits (11, 12, 13, 14, 1n) such that the first excitation is at least partly transferred to at least another one of the at least two fixed frequency quantum circuits (11, 12, 13, 14, 1n), via the tunable coupler, so as to implement the one or more quantum gates; wherein the frequency of the tunable coupler is modulated at: a first frequency, so as to drive a first first-order energy transition and thereby transfer, at least partly, a first excitation of said one of the at least two fixed frequency quantum circuits (11, 12, 13, 14, 1n) to the tunable coupler; and at least one second frequency distinct from the first frequency, so as to drive at least one second first-order energy transition, respectively, and thereby further transfer, at least partly, the first excitation from the tunable coupler to said at least another one of the at least two fixed frequency quantum circuits (11, 12, 13, 14, 1n). modulating a frequency of the tunable coupler so as to drive two first-order energy transitions, wherein the frequency of the tunable coupler is operated to be modulated by way of harmonic microwave signals applied to the tunable coupler so as to drive at least two selectively addressed first-order energy transitions in the quantum processing device (1, 2, 3); and in response to modulating the frequency of the tunable coupler so as to drive the two first-order energy transitions, causing a first excitation of one of the at least two fixed frequency quantum circuits (11, 12, 13, 14, 1n) such that the first excitation is at least partly transferred to at least another one of the at least two fixed frequency quantum circuits (11, 12, 13, 14, 1n), via the tunable coupler, so as to implement the one or more quantum gates; wherein the frequency of the tunable coupler is modulated at: a first frequency, so as to drive a first first-order energy transition and thereby transfer, at least partly, a first excitation of said one of the at least two fixed frequency quantum circuits (11, 12, 13, 14, 1n) to the tunable coupler; and at least one second frequency distinct from the first frequency, so as to drive at least one second first-order energy transition, respectively, and thereby further transfer, at least partly, the first excitation from the tunable coupler to said at least another one of the at least two fixed frequency quantum circuits (11, 12, 13, 14, 1n). a first frequency, so as to drive a first first-order energy transition and thereby transfer, at least partly, a first excitation of said one of the at least two fixed frequency quantum circuits (11, 12, 13, 14, 1n) to the tunable coupler; and at least one second frequency distinct from the first frequency, so as to drive at least one second first-order energy transition, respectively, and thereby further transfer, at least partly, the first excitation from the tunable coupler to said at least another one of the at least two fixed frequency quantum circuits (11, 12, 13, 14, 1n).