Microwave photons in superconducting circuits

We proposed [1] a scheme to detect single quanta (photons) of the electromagnetic field trapped in a superconducting resonator. The scheme relies on the use of a strong nonlinear (Kerr-type) interaction between this resonator and a second resonator used for readout. Both the storage and detection resonator contain a superconducting quantum interference device (SQUID); the nonlinear interaction is induced by the coupling of the persistent currents of the SQUIDs.

System proposed to perform photon detection. Each SQUID consists of a superconducting loop with two Josephson junctions (modeled by the “cross” element and representing the Cooper pair tunneling channel, together with the displacement current represented as a capacitor). Each SQUID is shunted by a capacitor to form a resonant circuit. The transmission line on the right is used to probe the detection resonator in a reflection measurement.

We estimate that states of up to ten photons can be detected with high fidelity. This will enable the observation of quantum jumps of the state of the resonator.

1. C. Deng, J. M. Gambetta, and A. Lupaşcu, Physical Review B (Rapid Communications) 82, 220505 (2010). Preprint arXiv:1008.3363.