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arXiv:1804.11108 · APL Photonics

Invited Article: Time-bin entangled photon pairs from Bragg-reflection waveguides

H. Chen, S. Auchter, M. Prilmüller, A. Schlager, T. Kauten, K. Laiho, B. Pressl, H. Suchomel, Martin Kamp, Sven Höfling, C. Schneider, Gregor Weihs

Published Aug 1, 2018• 25 citations
arXivHTMLPDF

Abstract

Semiconductor Bragg-reflection waveguides are well-established sources of correlated photon pairs as well as promising candidates for building up integrated quantum optics devices. Here, we use such a source with optimized non-linearity for preparing time-bin entangled photons in the telecommunication wavelength range. By taking advantage of pulsed state preparation and efficient free-running single-photon detection, we drive our source at low pump powers, which results in a strong photon-pair correlation. The tomographic reconstruction of the state’s density matrix reveals that our source exhibits a high degree of entanglement. We extract a concurrence of 88.9(1.8)% and a fidelity of 94.2(9)% with respect to a Bell state.

DOI
10.1063/1.5038186

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Semiconductor Bragg-reflection waveguides are well-established sources of correlated photon pairs as well as promising candidates for building up integrated quantum optics devices. Here, we use such a source with optimized non-linearity for preparing time-bin entangled photons in the telecommunication wavelength range. By taking advantage of pulsed state preparation and efficient free-running single-photon detection, we drive our source at low pump powers, which results in a strong photon-pair correlation. The tomographic reconstruction of the state’s density matrix reveals that our source exhibits a high degree of entanglement. We extract a concurrence of 88.9(1.8)% and a fidelity of 94.2(9)% with respect to a Bell state.
We demonstrate efficient photon pair generation for quantum communication using an all-semiconductor approach. In an AlGaAs Bragg-reflection waveguide we employ spontaneous parametric down-conversion to produce photon pairs at telecommunication wavelengths. The various phase-matching solutions present in our device can be used to create timebin or polarization entanglement. This approach can to lead to a fully integrated photon pair source with the pump laser, active and passive optical devices all on a single semiconductor chip.
The quick development of quantum technologies and quantum communication demands a continuous search for more efficient and with higher performance quantum sources and devices. In particular, quantum dots are firmly established sources of single photon emitters and entangled photon pairs, with entanglement of photons emitted by a single quantum dot probed in polarization[1], time-bin[2] and hyperentanglement[3]. Although spontaneous parametric down conversion sources (SPDC) are widely used as entangled photon sources with the highest values of entanglement[4], are being reached by quantum dot devices[5]. With similar quality as SPDC sources, QDs however stand out as sources with sub-Poissonian statistics, essential for safe quantum communication. Still, most of the quantum dots devices exhibit low extraction efficiencies. Attempts to maximize the extraction efficiency involve sophisticated engineered photonic systems[6,7]. Furthermore, the accurate alignment of the quantum dot-cavity system is crucial for an effective quantum dotcavity coupling and hence an emission enhancement into free space[8]. All of this implies the need of intricated nanofabrication processes. Here we present a simple, scalable photonic device that grants efficient creation of entangled photon pairs from InAs quantum dots. The device, spontaneously formed during the growth process, is based on pairs of bottom/top distributed bragg reflectors (DBRs). A propagating deformation in the DBRs, leads to the formation of self-aligned dimples on top of the QDs, resulting in a self-aligned quantum-dot cavity system[9]. Therefore, costly and complex deterministic nanofabrication techniques are not required. In this work, the device performance was characterized, showing experimental collection efficiencies of 0.17, with theoretically pair extraction efficiencies above 0.45. Furthermore, a Purcell enhancement up to 1.7 was obtained. Finally, the device potential to generate time-bin entangled photons was investigated performing state tomography measurements. The subsequent reconstruction of the density matrix yields a concurrence of 0.70(10) and a fidelity of 0.84(5).
We demonstrate experimentally that spontaneous parametric down-conversion in an AlxGa(1-x)As semiconductor Bragg reflection waveguide can make for paired photons highly entangled in the polarization degree of freedom at the telecommunication wavelength of 1550 nm. The pairs of photons show visibility higher than 90% in several polarization bases and violate a Clauser-Horne-Shimony-Holt Bell-like inequality by more than 3 standard deviations. This represents a significant step toward the realization of efficient and versatile self pumped sources of entangled photon pairs on-chip.
We explore the potential of versatile and efficient entangled photon pair generation by spontaneous parametric downconversion in Bragg reflection waveguides. By employing a quantum treatment of modes in channel waveguides, and by accounting for group velocity dispersion in the modes, the quantum state of the generated biphotons is realistically calculated. The pair production rate is predicted to reach 4×108 pairs/s/nm/mW of pump light in a 2 mm-long structure, on par with or exceeding the performance of previously reported designs. This is attributable to an enhanced nonlinear interaction through tight mode confinement in the waveguide. Strategies for device performance optimization and phase matching wavelength tunability are outlined and numerically demonstrated. The proposed design platform is versatile and allows photon pair generation with controllable flux, bandwidth, Schmidt number, and degree of polarization entanglement. The possibility of monolithic integration with a diode laser pump offers a way to design an electrically pumped entangled photon source.
Hybrid photonic devices represent a promising solution to the effective on-chip integration of all the components required for the generation, manipulation and detection of non-classical states of light encoding quantum information. We present an AlGaAs source of highly entangled photon pairs envisioned for the hybridization with silicon-on-insulator integrated platforms, in order to take benefit from the strong second order nonlinearity and the compliance with electrical pumping of the III-V platform and the maturity and CMOS compatibility of silicon photonic circuitry, enabling a wide variety of quantum information applications.