Inas/inp Quantum Dots Generate C-band Entangled Photon Pairs Via Biexciton-Exciton Cascade with <10 eV Fine Structure Splitting

The creation of entangled photons, crucial for advances in quantum communication and computation, takes a step forward with research demonstrating efficient generation at the important C-band wavelength. Anna Musiał, Maja Wasiluk, and colleagues at Wrocław University of Science and Technology, alongside Katarzyna Roszak from the FZU, Institute of Physics of the Czech Academy of Sciences, and others, achieve this using a unique process involving cascading excitons within specially grown InAs/InP quantum dots. This method generates entangled photon pairs without the need for precise external tuning, a significant simplification for practical applications, and the team confirms the origin and properties of these entangled states through detailed measurements of emitted light. By meticulously analysing the characteristics of the entangled photons, the researchers not only demonstrate a viable path towards brighter and more robust quantum light sources, but also identify strategies for further enhancing performance through optimised excitation techniques.

Quantum Dots for Entangled Photon Sources

This research focuses on quantum dots and their potential in quantum technologies, specifically creating sources of single photons and entangled photon pairs, essential components for secure quantum communication, powerful quantum computing, and other emerging quantum applications. The team investigates the growth and characterization of semiconductor structures containing quantum dots, utilizing techniques like molecular beam epitaxy to precisely control their composition and size. Researchers employ a range of sophisticated techniques to understand and optimize the performance of these quantum dots, including photoluminescence spectroscopy to reveal optical properties, and confocal and time-resolved spectroscopy for detailed analysis of individual nanostructures. Polarization-resolved spectroscopy examines the polarization of emitted photons, while theoretical calculations model the quantum dot’s behaviour to guide experimental design. The team’s work explores improving the efficiency and purity of single-photon sources, generating highly efficient entangled photon pairs, and developing quantum memories for storing quantum information. They are also investigating quantum dots as building blocks for quantum repeaters, extending the range of quantum communication, and methods for creating quantum dots at precise locations.

Biexciton Cascade in InAs/InP Quantum Dots

This work demonstrates the generation of paired photons from InAs/InP quantum dots through a biexciton-exciton cascade, a process occurring naturally without requiring precise adjustments to the nanostructure’s properties, simplifying device design. Researchers grew these quantum dots using ripening-assisted molecular beam epitaxy, resulting in large nanostructures with a low density on the InP substrate. Detailed characterization of the quantum dots was performed using transmission electron microscopy, revealing their composition and structure. A distributed Bragg reflector was incorporated to enhance photon extraction, and cylindrical mesas were etched to isolate individual nanostructures for investigation. Scientists then used a microphotoluminescence setup with a low-temperature cryostat and a sophisticated spectrometer to study the emission characteristics of the quantum dots.

Telecom Entanglement via Quantum Dot Cascade

Scientists achieved the generation of polarization-entangled photon pairs at telecom C-band wavelengths using a biexciton-exciton cascade from InAs/InP quantum dots, significant because telecom wavelengths are ideal for long-distance communication through optical fibers. Crucially, this process occurs without requiring external tuning of the fine structure splitting, simplifying device fabrication and operation. Researchers identified excitonic complexes through magneto-microphotoluminescence and time-correlation measurements, confirming that the emitted photons originate from the same quantum dot. These experimental results are supported by detailed theoretical calculations, which reveal the structure of higher energy states and allow reconstruction of the quantum dot’s structural parameters.

Quantum state tomography was used to verify and quantify the entanglement, revealing a pathway to boost entanglement quality through a resonant, pulsed excitation scheme. The investigated structure consists of InAs/InP quantum dots grown using molecular beam epitaxy, resulting in a low density of large quantum dots. Microphotoluminescence experiments and magneto-optical measurements further characterize the emission properties, providing a detailed understanding of the entangled state.

Entangled Photons from Quantum Dot Cascade

This research demonstrates the generation of polarization-entangled photon pairs from a cascade of biexciton-exciton recombination within individual InAs/InP quantum dots. This process occurs naturally without the need for external tuning of the fine structure splitting, a significant advantage for practical applications. Detailed magneto-microphotoluminescence and time-correlation measurements were used to identify and characterize these excitonic complexes, confirming their origin from the same quantum dot. Researchers determined the biexciton binding energy and also identified evidence of a charged exciton within the same quantum dot. By reconstructing the two-photon density matrix, they analyzed the emitted quantum state, revealing a balance between phase accumulation and decoherence, and pointing towards a clear pathway for improving entanglement quality through the use of resonant, pulsed excitation and shortening radiative lifetimes.