Integrated photonic circuits provide a versatile toolbox of functionalities for advanced quantum optics applications. Here, we demonstrate an essential component of such a system in the form of a Purcell enhanced single-photon source based on a quantum dot coupled to a robust on-chip integrated resonator. For that, we develop GaAs monolithic ring cavities based on distributed Bragg reflector ridge waveguides.Under resonant excitation conditions, we observe an over twofold spontaneous emission rate enhancement using Purcell effect and gain a full coherent optical control of a QDtwo-level system via Rabi oscillations. Furthermore, we demonstrate an on-demand 1 single-photon generation with strongly suppressed multi-photon emission probability as low as 1% and two-photon interference with visibility up to 95%. This integrated single-photon source can be readily scaled up, promising a realistic pathway for scalable on-chip linear optical quantum simulation, quantum computation and quantum networks.
The photon spin is an important resource for quantum information processing as is the electron spin in spintronics. However, for subwavelength confined optical excitations, polarization as a global property of a mode cannot be defined. Here, we show that any polarization state of a plane-wave photon can reversibly be mapped to a pseudospin embodied by the two fundamental modes of a subwavelength plasmonic two-wire transmission line. We design a device in which this pseudospin evolves in a well-defined fashion throughout the device reminiscent of the evolution of photon polarization in a birefringent medium and the behavior of electron spins in the channel of a spin field-effect transistor. The significance of this pseudospin is enriched by the fact that it is subject to spin−orbit locking. Combined with optically active materials to exert external control over the pseudospin precession, our findings could enable spin-optical transistors, that is, the routing and processing of quantum information with light on a subwavelength scale.
Scalable quantum photonic technologies require the low-loss
integration
of many identical single-photon sources with photonic circuitry on
a chip. Relatively complex quantum photonic circuits have already
been demonstrated; however, sources used so far relied on parametric
down-conversion which has a probabilistic nature that intrinsically
limits its efficiency and scalability. Quantum emitter-based single-photon
sources are free of this limitation, but frequency matching of multiple
emitters within a single circuit remains challenging. In this work,
we demonstrate a key component in this regard in the form of a fully
monolithic GaAs circuit combining two frequency-matched quantum dot
single-photon sources interconnected with a low-loss on-chip beamsplitter
connected via single-mode ridge waveguides. This device enabled us
to perform a two-photon interference experiment on-chip with a visibility
reaching 66%. Our device could be further scaled up, providing a clear
path to increasing the complexity of quantum circuits toward fully
scalable integrated quantum technologies.
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