Quantum superposition of a single microwave photon in two different ’colour’ states

Quantum superposition of a single microwave photon in two different ’colour’ states: "

Quantum superposition of a single microwave photon in two different ’colour’ states


Nature Physics 7, 599 (2011).
doi:10.1038/nphys2035


Authors: Eva Zakka-Bajjani, François Nguyen, Minhyea Lee, Leila R. Vale, Raymond W. Simmonds & José Aumentado

Fully controlled coherent coupling of arbitrary harmonic oscillators is an important tool for processing quantum information. Coupling between quantum harmonic oscillators has previously been demonstrated in several physical systems using a two-level system as a mediating element. Direct interaction at the quantum level has only recently been realized by means of resonant coupling between trapped ions. Here we implement a tunable direct coupling between the microwave harmonics of a superconducting resonator by means of parametric frequency conversion. We accomplish this by coupling the mode currents of two harmonics through a superconducting quantum interference device (SQUID) and modulating its flux at the difference (∼7 GHz) of the harmonic frequencies. We deterministically prepare a single-photon Fock state and coherently manipulate it between multiple modes, effectively controlling it in a superposition of two different ’colours’. This parametric interaction can be described as a beamsplitter-like operation that couples different frequency modes. As such, it could be used to implement linear optical quantum computing protocols on-chip.