Probing the ladder of dressed states and nonclassical light generation in quantum-dot-cavity QED

A single-optical mode confined inside an optical cavity behaves like a simple harmonic oscillator, where all the energy levels are equally spaced. When this cavity mode is strongly coupled to a two-level quantum emitter such as a quantum dot (QD), the energy structure of the coupled system becomes anharmonic. This anharmonic (Jaynes-Cummings) ladder has been recently probed in atomic [1] and superconducting [2] cavity quantum electrodynamics (cQED) systems. Nonclassical correlations between photons transmitted through the cavity can result from such anharmonicity, which in turn leads to fundamental phenomena of photon blockade and photon-induced tunneling. These effects have been recently demonstratedinatomicsystems[3],aswellasinthesolid-state platform [4]. Moreover, photon blockade and photon-induced tunnelingcanbeusedforapplicationsbeyondcQED,including the generation of single photons on demand [5] for quantum information processing, high precision sensing and metrology [6], as well as quantum simulation of complex many-body systems [7]. In this Rapid Communication, we explore the utility of the photon-induced tunneling and blockade for nonclassical light generation and probing of higher-order dressed states in the solid-state cQED system consisting of a single QD coupled to a photonic crystal cavity. First, we provide numerical simulation data showing that photon-induced tunneling can be used to preferentially generate specific multiphoton states. Following this, we present experimental data demonstrating the transition from a blockade to tunneling regimeinsuchasystemandshowthesignatureofhigher-order dressed states observed in the measured photon statistics. The probing of the ladder of dressed states by photon-correlation measurement has previously been performed experimentally only in an atomic cavity QED system [1], while in solid-state systems it has been studied theoretically [8] and signatures of higher-order dressed states were observed only using four wave mixing [9]. The dynamics of a coupled QD-cavity system, coherently driven by a laser field [Fig. 1(a)], is well described by the