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arXiv:1611.06859 · Applied Physics Letters

Two-photon interference from remote deterministic quantum dot microlenses

Alexander Thoma, Peter Schnauber, J. Böhm, Manuel Gschrey, J.-H. Schulze, A. Strittmatter, Sven Rodt, Tobias Heindel, Stephan Reitzenstein

Published Jan 2, 2017• 35 citations
arXivHTMLPDF

Abstract

We report on two-photon interference (TPI) experiments using remote deterministic single-photon sources. Employing 3D in-situ electron-beam lithography, we fabricate quantum-light sources at specific target wavelengths by integrating pre-selected semiconductor quantum dots within monolithic microlenses. The individual single-photon sources show TPI visibilities of 49% and 22%, respectively, under pulsed p-shell excitation at 80 MHz. For the mutual TPI of the remote sources, we observe an uncorrected visibility of 29%, in quantitative agreement with the pure dephasing of the individual sources. Due to its efficient photon extraction within a broad spectral range (>20 nm), our microlens-based approach is predestinated for future entanglement swapping experiments utilizing entangled photon pairs emitted by distant biexciton-exciton radiative cascades.

DOI
10.1063/1.4973504

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We report on two-photon interference (TPI) experiments using remote deterministic single-photon sources. Employing 3D in-situ electron-beam lithography, we fabricate quantum-light sources at specific target wavelengths by integrating pre-selected semiconductor quantum dots within monolithic microlenses. The individual single-photon sources show TPI visibilities of 49% and 22%, respectively, under pulsed p-shell excitation at 80 MHz. For the mutual TPI of the remote sources, we observe an uncorrected visibility of 29%, in quantitative agreement with the pure dephasing of the individual sources. Due to its efficient photon extraction within a broad spectral range (>20 nm), our microlens-based approach is predestinated for future entanglement swapping experiments utilizing entangled photon pairs emitted by distant biexciton-exciton radiative cascades.
A key requirement for implementing photonic quantum information networks is the mutual two-photon interference between photons emitted by spatially separated quantum light sources. In order to up-scale such networks, the deterministic fabrication of efficient sources of single and indistinguishable photons is of crucial importance. So far, few experiments reported on two-photon interference (TPI) from spatially separated QD-based single photon sources, which is required for entanglement swapping, and deterministic sources have been applied only recently [1]. However, narrowband enhancement of photon extraction in high-Q microcavities hinders their application for advanced quantum communication schemes based on polarization entangled photon pairs from the biexciton-exciton radiative cascade.
Generating identical photons from remote emitter-based bright single-photon sources is an important step for scaling up optical quantum technologies. Here, we study the Hong-Ou-Mandel interference of photons emitted from remote sources based on semiconductor quantum dots (QDs). We make use of a deterministic fabrication technique to position the QDs in a spectrally resonant micropillar cavity and fine-tune their operation wavelength electrically. In doing so, we can match four pairs of sources between five distinct sources, study them under various excitation schemes, and measure their degree of indistinguishability. We demonstrate remote indistinguishabiltity between 44 ± 1% and 69 ± 1% depending on the pair of sources and excitation conditions, record values for QDs in cavities. The relative contribution of pure dephasing and spectral diffusion is then analyzed, revealing that the remaining distinguishability is mostly due to low-frequency noise.
We demonstrate an ultra-compact source of on-demand, maximally entangled photon pairs using single GaAs quantum dots embedded in monolithic microlenses coupled to a lensed single-mode fiber. A 3D-printed micro-objective with a numerical aperture of 0.6 enables efficient fiber coupling and near-diffraction-limited performance with 604(16) nm resolution directly in the cryogenic environment at 3.8 K. The system achieves high single-photon emission rates [392(20) kHz] and purities [99.2(5)%] using two-photon resonant excitation. Leveraging the exciton–biexciton cascade, it produces near-maximally entangled photon pairs with peak entanglement negativities of 2n = 0.96 ± 0.02. The presented quantum light source combines state-of-the-art performance and long-term stability with a dramatically reduced system footprint, making it well-suited for seamless industrial integration.
In this paper, we study the influence of quasiresonant and nonresonant excitation on the interference properties of single photons emitted from quantum dots (QDs). The quasiresonant excitation scheme leads to an increase of interference visibility of photons emitted from the same QD to 69% compared to 12% for nonresonant excitation. Furthermore, we demonstrate quantum interference of photons emitted from separate QDs which are simultaneously excited into their ppp shell. We can readily extract a two-photon interference visibility as high as (39 \ifmmode\pm\else\textpm\fi{} 2)% for nonpostselected coincidences exceeding the predicted value based on coherence and radiative decay times of the quantum dot emission ($\ensuremath{\sim}$25%). We account for this observation by treating the emission of both quantum dots as inhomogeneously broadened ensembles of Fourier-limited photons and observe good congruence between experiment and model.
Scalable quantum photonic technologies require deterministic sources of entangled photons that are compatible with established semiconductor manufacturing platforms. While self-assembled III-V semiconductor quantum dots are among the most promising sources of on-demand entanglement generation, their integration with silicon-based architectures remains a central challenge. Here, we demonstrate energy-time entanglement from a single InGaAs/GaAs quantum dot monolithically grown on a silicon substrate. Under resonant two-photon excitation, we achieve coherent control of the biexciton-exciton cascade, evidenced by the formation of dressed-states and Rabi oscillations. Using a four-channel Franson interferometer, we observe phase-dependent two-photon interference with visibilities up to (64.0 ± 7.0)% for a 80 ps integration window (and (49.4 ± 1.9)% for a 1600 ps window), approaching the threshold for Bell inequality violation at short timescales. Despite these constraints, the observation of Franson interference establishes monolithic III-V-on-silicon quantum dots as viable sources of energy-time entangled photons. These results represent a crucial step toward fully integrated, silicon-substrate-compatible quantum photonic circuits for large-scale quantum communication and information processing.
Quantum dots in cavities have been shown to be very bright sources of indistinguishable single photons. Yet the quantum interference between two such bright quantum dot sources, a critical step for photon-based quantum computation, still needs to be investigated. Here, we report on such a measurement, taking advantage of a deterministic fabrication of the devices. We show that cavity quantum electrodynamics can efficiently improve the quantum interference between remote quantum dot sources: Poorly indistinguishable photons can still interfere with good contrast with high quality photons emitted by a source in the strong Purcell regime. Our measurements and calculations show that cavity quantum electrodynamics is a powerful tool for interconnecting several quantum dot devices.