Quantum interference between two single photons of different microwave frequencies.

We have measured quantum interference between two single microwave photons trapped in the same superconducting resonator, whose frequencies are initially about 6 GHz apart. We accomplish this by use of a parametric frequency conversion process that mixes the mode currents of two cavity harmonics through a superconducting quantum interference device, and demonstrate that a two-photon entanglement operation can be performed with high fidelity.

Experimental determination of the statistics of photons emitted by a tunnel junction.

We report on an Hanbury Brown-Twiss experiment probing the statistics of microwave photons emitted by a tunnel junction in the shot-noise regime at low temperature. By measuring the cross correlation of the fluctuations of the occupation numbers of the photon modes of both detection branches, we show that while the statistics of electrons is Poissonian, the photons obey chaotic statistics. This is observed even for low photon occupation number when the voltage across the junction is close to hν/e.