1. A method for improving fidelity of a quantum operation on a quantum bit of interest, comprising: performing, using physical qubit assemblies and a corresponding control, a controlled quantum gate operation, controlled by the quantum bit of interest, on an ancillary quantum bit to produce an entangled state of the system formed by quantum bit of interest and the ancillary quantum bit, the entangled state comprising a superposition of a plurality of basis states; and measuring an energy state of the ancillary quantum bit to eliminate at least one basis state from the entangled state, wherein the controlled quantum gate operation is a Fredkin gate operation.