Ultrafast Photon-Photon Interaction in a Strongly Coupled Quantum Dot-Cavity System

Abstract

and † These authors contributed equallyWe study dynamics of the interaction between two weak light beams mediated by a strongly coupled quantum dot-photonic crystal cavity system. First, we perform all optical switching of a weak continuous-wave signal with a pulsed control beam, and then perform switching between two pulsed beams (40ps pulses) at the single photon level. Our results show that the quantum dot-nanocavity system creates strong, controllable interactions at the single photon level.Techniques to efficiently interact single photons with quantum emitters are fundamental to the field of quantum optics and quantum information and are at the core of a range of protocols, including two-qubit phase gates [1,2] and quantum non-demolition measurements [3]. In addition, single-photon-level optical nonlinearities may enable ultra-low power and high-speed all-optical gates and switches for classical optical information processing [4,5]. Recent experiments have shown that the necessary nonlinearity may be realized using atomic gases in the slow light regime [6] or solid-state systems consisting of a single quantum dot (QD) strongly coupled to a nano-cavity [7][8][9]. As a crucial next step in the solid state approach, we describe here the time-resolved dynamics of light interacting the QD-cavity system. We first study the the interaction of a weak continuous-wave signal and a pulsed control, and then the interaction of two short (40 ps) pulses.The experiment is performed using a QD dot strongly coupled to three-hole (L3) photonic crystal (PC) cavity [10], superposed with a grating to increase the emission directionality [11] (see Fig.1(a)). It was fabricated in a 160 nm thick membrane containing a central layer of self-assembled InAs QDs with a density of ∼ 50/µm 2 and an inhomogeneously distributed exciton emission between 925±15 nm.The eigen-frequencies ω ± of the QD-cavity system are:where ω r and ω d are the cavity and QD resonance frequencies, respectively; κ and γ are the cavity field decay rate and QD dipole decay rate; g denotes the coherent * Electronic address: englund@columbia.edu † Electronic address: arkam@stanford.edu interaction strength between the QD; and δ = ω d − ω r is the cavity-QD detuning. The parameters of the emittercavity system used in the experiment are g/2π = 25 GHz, κ/2π = 27 GHz, γ/2π = 0.1 GHz. Therefore, the expression under square root in Eq. 1 is positive for δ = 0, implying that the system is in the strong coupling regime of the cavity quantum electrodynamics (QED). We characterize the system in a confocal microscope setup in a He flow cryostat ( Fig.1(b)). The photoluminescence (PL) scans in Fig.1(c) show the anticrossing between the QD-like states and the cavity-like states as the temperature is raised from 36K to 42 K, giving the polariton energies given by Eq.1. The cavity reflectivity, obtained using a white light source in the cross-polarized configuration shown in Fig.1(b), shows the same mode splitting in Fig.1(d). These spectral measurements yield the system parameter...

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