Controlling coherent interaction between optical fields and quantum systems in scalable, integrated platforms is essential for quantum technologies. Miniaturised, warm alkali-vapour cells integrated with on-chip photonic devices represent an attractive system, in particular for delay or storage of a single-photon quantum state. Hollow-core fibres or planar waveguides are widely used to confine light over long distances enhancing light-matter interaction in atomic-vapour cells. However, they suffer from inefficient filling times, enhanced dephasing for atoms near the surfaces, and limited light-matter overlap. We report here on the observation of modified electromagnetically induced transparency for a non-diffractive beam of light in an on-chip, laterally-accessible hollow-core light cage. Atomic layer deposition of an alumina nanofilm onto the light-cage structure was utilised to precisely tune the high-transmission spectral region of the light-cage mode to the operation wavelength of the atomic transition, while additionally protecting the polymer against the corrosive alkali vapour. The experiments show strong, coherent light-matter coupling over lengths substantially exceeding the Rayleigh range. Additionally, the stable non-degrading performance and extreme versatility of the light cage provide an excellent basis for a manifold of quantum-storage and quantum-nonlinear applications, highlighting it as a compelling candidate for all-on-chip, integrable, low-cost, vapour-based photon delay.
Quantum memories can substantially increase the efficiency of long-distance communications by synchronizing entanglement swapping operations in quantum repeater nodes. To build a quantum memory, electromagnetically induced transparency (EIT) in atomic vapors can be exploited to coherently store light pulses even at room temperatures. As a quantum source of light, semiconductor quantum dots (QD) offer bright on-demand single photons with high purity.4 Interfacing QDs with atomic vapors has been shown by “slow light” but a quantum memory for QDs is yet to be demonstrated. In this work, we develop an EIT quantum memory hosted in warm cesium vapor. Storage of faint coherent light pulses on the single photon level shows high storage efficiency. A measured bandwidth in the order of 200 MHz makes the memory compatible with the Fourier-limited emission of QDs embedded in micropillar cavities. We show the first attempts to interface the emission from a QD-micropillar with our quantum memory by finetuning the emission wavelength of the emitters to one of the hyperfine transitions in Cs, where the EIT memory takes place. This work sets the base for a hybrid quantum memory based on atomic ensembles for an on-demand semiconductor single-photon source.
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