Near Transform-Limited Quantum Dot Linewidths in a Broadband Photonic Crystal Waveguide

Abstract

Planar nanophotonic structures enable broadband, near-unity coupling of emission from quantum dots embedded within, thereby realizing ideal single-photon sources. The efficiency and coherence of the single-photon source is limited by charge noise, which results in the broadening of the emission spectrum. We report suppression of the noise by fabricating photonic crystal waveguides in a gallium arsenide membrane containing quantum dots embedded in a p-i-n diode. Local electrical contacts in the vicinity of the waveguides minimize the leakage current and allow fast electrical control (≈4 MHz bandwidth) of the quantum dot resonances. Resonant linewidth measurements of 51 quantum dots coupled to the photonic crystal waveguides exhibit near transform-limited emission over a 6 nm wide range of emission wavelengths. Importantly, the local electrical contacts allow independent tuning of multiple quantum dots on the same chip, which together with the transform-limited emission are key components in realizing multiemitter-based quantum information processing.

Scalable integrated single-photon source

“…1 ) leads to a number of salient features: The embedded QDs can be electrically tuned, the charge state of the QD is stabilized so that emission only on the desired transition takes place, and spectral diffusion due to residual charge noise in the structures can be strongly suppressed. As a consequence, near–transform-limited optical linewidths can be achieved in the photonic nanostructures ( 19 , 30 , 31 ), which is essential for generating a scalable resource of indistinguishable photons as well as for more advanced applications of the system for photonic quantum gates and entanglement generation ( 21 ). Low-noise operation is demonstrated by exciting the QD with a tunable laser and collecting the resonance fluorescence.…”

“…We implement electrical control of QDs coupled to photonic crystal waveguides through precise nanofabrication of low-noise electrical contacts that suppresses these detrimental effects. Our approach of combining high-quality semiconductor heterostructure growth together with advanced device design and nanofabrication is shown to robustly recover the transform-limited emission line shape ( 30 ), which is a key indicator for the generation of highly coherent single photons. In our improved source, we demonstrate coherence extending to at least 115 photons, as is proven by measuring the mutual degree of indistinguishability between photons emitted with a time delay approaching a microsecond.…”

Wafer-Scale Epitaxial Low Density InAs/GaAs Quantum Dot for Single Photon Emitter in Three-Inch Substrate

“…Site-controlled growth, which addresses spatial randomness, has suffered from defects in previously processed surfaces which diminish the quantum efficiency and coherence of emitted photons [ 13 ]. For the S–K growth, In(Ga)As/GaAs QD-based devices have shown great performance as quantum emitters with close to unity quantum efficiency [ 14 , 15 ] and near transform-limited emission [ 16 ]. However, reliable wafer-scale growth techniques have proved elusive.…”

Experimental Reconstruction of the Few-Photon Nonlinear Scattering Matrix from a Single Quantum Dot in a Nanophotonic Waveguide

“…These devices can exhibit near-unity light-matter coupling efficiency (β ≥ 0.98 [23]) and nonlinear interaction sensitive at the level of single photons [14,16]. Moreover, near-transform-limited emission lines have been demonstrated with QDs [24] and recently also in photonic-crystal waveguides [25]. The combination of unity coupling efficiency and low dephasing enables the deterministic scattering of few photons by a QD operating as a two-level emitter (TLE).…”

“…2(a)], corresponding to a transform-limited linewidth of 1.22 GHz, meaning that additional broadenings due to phonons and slow spectral diffusion are less important. A full study of the statistics of QD linewidths in photonic-crystal waveguides is published elsewhere [25].…”