A superconducting capacitively-driven tunable coupler system comprising: first (104, 202, 302, 402) and second (106, 204, 304, 404) quantum objects each having a ground end required to be connected to a DC path to a low-voltage rail and an open end required not to be connected to a DC path to the low-voltage rail; a coupler (102, 200, 206, 210, 214, 218, 224, 230, 234, 238, 300, 400) comprising: a first coupling capacitor (110, C 1) connected between the open end of the first quantum object and a first connecting node (112, V 1); a radio-frequency superconducting quantum interference device, RF SQUID, connected between the first connecting node and a second connecting node (V 2), the RF SQUID comprising a Josephson element (J 1, 226) connected between the first connecting node and the second connecting node; and at least one flux injection element (114, 208, 212, 216, 220, 222, 228, 232, 236, 240, 242, 406) configured to bias the Josephson element to variably weaken the strength of coupling between the first and second quantum objects by altering the inductance of the Josephson element in the RF SQUID to be switched between a low inductance state for coupling the first and second quantum objects to one another and thus to pass signals between the first and second quantum objects, and a high inductance state for decoupling the first and second quantum objects from one another and thus to block signals from passing between the first and second quantum objects, wherein the quantum objects are coupled together to pass signals between them in the absence of injected flux. first (104, 202, 302, 402) and second (106, 204, 304, 404) quantum objects each having a ground end required to be connected to a DC path to a low-voltage rail and an open end required not to be connected to a DC path to the low-voltage rail; a coupler (102, 200, 206, 210, 214, 218, 224, 230, 234, 238, 300, 400) comprising: a first coupling capacitor (110, C 1) connected between the open end of the first quantum object and a first connecting node (112, V 1); a radio-frequency superconducting quantum interference device, RF SQUID, connected between the first connecting node and a second connecting node (V 2), the RF SQUID comprising a Josephson element (J 1, 226) connected between the first connecting node and the second connecting node; and a first coupling capacitor (110, C 1) connected between the open end of the first quantum object and a first connecting node (112, V 1); a radio-frequency superconducting quantum interference device, RF SQUID, connected between the first connecting node and a second connecting node (V 2), the RF SQUID comprising a Josephson element (J 1, 226) connected between the first connecting node and the second connecting node; and at least one flux injection element (114, 208, 212, 216, 220, 222, 228, 232, 236, 240, 242, 406) configured to bias the Josephson element to variably weaken the strength of coupling between the first and second quantum objects by altering the inductance of the Josephson element in the RF SQUID to be switched between a low inductance state for coupling the first and second quantum objects to one another and thus to pass signals between the first and second quantum objects, and a high inductance state for decoupling the first and second quantum objects from one another and thus to block signals from passing between the first and second quantum objects, wherein the quantum objects are coupled together to pass signals between them in the absence of injected flux.