Observation of Resonant Photon Blockade at Microwave Frequencies Using Correlation Function Measurements

Creating a train of single photons and monitoring its propagation and interaction is challenging in most physical systems, as photons generally interact very weakly with other systems. However, when confining microwave frequency photons in a transmission line resonator, effective photon-photon interactions can be mediated by qubits embedded in the resonator. Here, we observe the phenomenon of photon blockade through second-order correlation function measurements. The experiments clearly demonstrate antibunching in a continuously pumped source of single microwave photons measured by using microwave beam splitters, linear amplifiers, and quadrature amplitude detectors. We also investigate resonance fluorescence and Rayleigh scattering in Mollow-triplet-like spectra.

Figure 1

Rayleigh scattering and resonance fluorescence of lower Jaynes-Cummings doublet. (a) Energy level diagram of a resonantly coupled cavity QED system driven with amplitude ${\Omega }_R$ on the ground state $|g0⟩$ to lower doublet $|1-⟩$ transition. The Mollow-type transitions arising from the dressing of the dressed states by the drive are also indicated on the side. (b) Measured resonance fluorescence spectrum including Rayleigh-scattering peak (dots) at fixed drive amplitude of ${\Omega }_R/2\pi =7.9\mathrm{MHz}$ and the simulated spectrum (solid line). (c) Measured resonance fluorescence spectrum vs (indicated) drive amplitude ${\Omega }_R/2\pi$ (dots) and analytical spectrum (solid lines). The Rayleigh peak has been omitted in these plots. (d) Measured Mollow side peak frequencies ${\Omega }_{\mathrm{sp}}$ vs drive amplitude ${\Omega }_R$ (dots), linear dependence ${\Omega }_{\mathrm{sp}}={\Omega }_R$ (dashed black lines), and calculated frequencies ${\Omega }_{\mathrm{sp}}$ (solid red lines) are shown.

Figure 2

Correlation function measurements. (a) Second-order correlation function measurements $g^{(2)}(\tau )$ (dots) for indicated drive amplitudes ${\Omega }_R$ and master equation calculation with and without accounting for finite measurement bandwidth (gray and black lines, respectively). (b) $g^{(2)}(\tau )$ for a thermal field with mean photon number $⟨n_{\mathrm{th}}⟩\sim 1.4$ in the resonator. (c) $g^{(2)}(\tau )$ for a coherent drive with $⟨n_c⟩\sim 1$.