Towards optimal single-photon sources from polarized microcavities (1907.06818v1)

Abstract: An optimal single-photon source should deterministically deliver one and only one photon at a time, with no trade-off between the source's efficiency and the photon indistinguishability. However, all reported solid-state sources of indistinguishable single photons had to rely on polarization filtering which reduced the efficiency by 50%, which fundamentally limited the scaling of photonic quantum technologies. Here, we overcome this final long-standing challenge by coherently driving quantum dots deterministically coupled to polarization-selective Purcell microcavities--two examples are narrowband, elliptical micropillars and broadband, elliptical Bragg gratings. A polarization-orthogonal excitation-collection scheme is designed to minimize the polarization-filtering loss under resonant excitation. We demonstrate a polarized single-photon efficiency of 0.60+/-0.02 (0.56+/-0.02), a single-photon purity of 0.975+/-0.005 (0.991+/-0.003), and an indistinguishability of 0.975+/-0.006 (0.951+/-0.005) for the micropillar (Bragg grating) device. Our work provides promising solutions for truly optimal single-photon sources combining near-unity indistinguishability and near-unity system efficiency simultaneously.

• The paper introduces a method using quantum dots in birefringent Purcell microcavities to control polarization symmetry and reduce efficiency losses.
• It reports single-photon efficiency values of 0.60 in micropillars and 0.56 in Bragg gratings, with photon purity of 0.991 and indistinguishability of 0.973.
• The work provides a scalable approach for quantum technologies, enhancing applications in quantum computing and telecommunications through improved photon sources.

Examination of Polarized Single-Photon Sources from Microcavities

The paper advances the design and performance of single-photon sources by addressing the efficiency and distinguishability deficiencies present in existing solid-state photon emission systems. Traditional approaches, depending on non-deterministic polarization filtering techniques, persistently suffer from performance bottlenecks due to efficiency losses around 50%. This research introduces a significant improvement through the integration of quantum dots within polarization-selective Purcell microcavities, specifically utilizing narrowband elliptical micropillars and broadband elliptical Bragg gratings.

Key Contributions

At the heart of this work is the development of a technologically feasible method to control the polarization symmetry of quantum dot emission efficiently. The approach involves coupling a single quantum dot to a geometrically birefringent cavity within the Purcell regime to enhance the polarized emission while minimizing background loss through strategic cavity mode excitation.

Strong Numerical Results

A pivotal outcome of this paper is the reported single-photon efficiency of 0.60(2) when embedded in micropillars, and 0.56(2) in Bragg gratings. The photon purity, as characterized by second-order correlation function measurements, reaches 0.991(3) and indistinguishability of 0.973(5), achieving near-unity values essential for scalable quantum telecommunications. These efficiencies surpass those thresholds required for photon-loss-tolerant quantum computing models, such as boson sampling, which demands at least a 50% efficiency considering photon loss.

Implications for Quantum Technologies

The advancements in single-photon source efficiency and indistinguishability have profound implications for quantum information systems. These systems could facilitate more robust implementations of quantum computing and communication, potentially impacting the reliability and scalability of future optical networks. This investigation provides a realistic framework with potential adaptability across various photonic structures, including micropillars, photonic crystals, and nanowire arrays, suggesting broad applicability.

Future Directions

The paper leaves open avenues for optimization of fabrication techniques and coupling strategies, which could further improve the quantum efficiency of photonic sources. Moreover, combining elements of narrowband and broadband structures could yield hybrid systems that capitalize on the confinement and phonon suppression. The future focus will likely include enhancing quantum dot stability through surface passivation and electric field modulation to augment device performance further.

Overall, this work marks a significant step toward practical, efficient single-photon sources, suggesting new directions in the design and implementation of photonic quantum information technology involved in future operational protocols.