Photoelectric detectors cover a wide frequency spectrum spanning from the far ultraviolet to the infrared light with high sensitivity, large quantum efficiency and low dark current.The equivalent photoelectric detection of microwave frequency photons has remained elusive due to inherent differences between microwave photon energy and the interband transition energies exploited in standard photoelectric detectors. Here we present the realization of a near-ideal microwave photon to electron converter at a frequency typical of circuit quantum electrodynamics. These unique properties are enabled by the use of a high kinetic inductance disordered superconductor, granular aluminium, to enhance the light-matter interaction. This experiment constitutes an important proof of concept regarding low energy microwave photon to electron conversion unveiling new possibilities such as the detection of single microwave photons using charge detection. It finds significance in quantum research openning doors to a wide array of applications, from quantum-enhanced sensing to exploring the fundamental properties of quantum states.
We demonstrate a new approach to dissipation engineering in microwave quantum optics. For a single mode, dissipation usually corresponds to quantum jumps, where photons are lost oneby one. Here, we are able to tune the minimal number of lost photons per jump to be two (or more) with a simple dc voltage. As a consequence, different quantum states experience different dissipation. Causality implies that the states must also experience different energy shifts. Our measurements of these Lamb shifts are in good agreement with the predictions of the Kramers-Kronig relations for single quantum states in a regime of highly non-linear bath coupling. This work opens new possibilities for quantum state manipulation in circuit QED, without relying on the Josephson effect.
Among the most exciting recent advances in the field of superconducting quantum circuits is the ability to coherently couple microwave photons in low-loss cavities to quantum electronicconductors (e.g.~semiconductor quantum dots or carbon nanotubes). These hybrid quantum systems hold great promise for quantum information processing applications; even more strikingly, they enable exploration of completely new physical regimes. Here we study theoretically the new physics emerging when a quantum electronic conductor is exposed to non-classical microwaves (e.g.~squeezed states, Fock states). We study this interplay in the experimentally-relevant situation where a superconducting microwave cavity is coupled to a conductor in the tunneling regime. We find the quantum conductor acts as a non-trivial probe of the microwave state; in particular, the emission and absorption of photons by the conductor is characterized by a non-positive definite quasi-probability distribution. This negativity has a direct influence on the conductance of the conductor.