Tunable Polarization-Entangled Near-Infrared Photons from Orthogonal GaAs Nanowires Enables Scalable Quantum Communication

Polarization-entangled photons represent a crucial resource for advancements in secure communication and precision sensing, yet their generation has traditionally relied on bulky crystals that hinder scalability and integration into modern devices. Elise Bailly-Rioufreyt, Zoya Polshchykova, and Grégoire Saerens, along with colleagues at ETH Zurich and IMEC, now demonstrate a pathway towards miniaturised, tunable sources of these entangled photons using gallium arsenide nanowires. The team successfully creates polarization entanglement using a pair of orthogonal nanowires, achieving control over the photon state at telecommunication wavelengths and reaching fidelities of up to 90%. This breakthrough paves the way for on-chip integration, potentially reducing fabrication costs and enabling new applications, particularly in satellite-based quantum communication systems.

GaAs Nanowires Generate Polarization Entangled Photons

Research into semiconductor nanowires, particularly gallium arsenide (GaAs), is advancing the development of entangled photons for quantum technologies like secure communication and quantum computing. These nanowires exhibit exceptionally strong second-harmonic generation, crucial for generating photon pairs through spontaneous parametric down-conversion. Researchers are meticulously engineering the crystal structure and geometry of these nanowires to generate polarized entangled photons, a key requirement for many quantum communication protocols. Controlling the growth and orientation of GaAs nanowires is paramount, with (111) oriented structures proving particularly promising for enhancing nonlinear optical properties.

Recent advances involve utilizing thin films of aluminum gallium arsenide (AlGaAs) to create flat sources of high-purity, orthogonally polarized entangled photons. Achieving efficient nonlinear conversion requires precise control of phase matching conditions, influenced by nanowire geometry and crystal orientation. Advanced microscopy techniques, including correlated X-ray and electron microscopy, are used to understand the crystal structure and nonlinear properties of individual nanowires. These entangled photons have significant implications for quantum communication, enabling secure key distribution and other advanced protocols, as well as enhancing the resolution and sensitivity of imaging techniques and improving the precision of measurements.

Tunable Photon Pairs from GaAs Nanowires

Scientists have pioneered a new quantum light source based on zinc blende gallium arsenide (GaAs) nanowires, engineered to generate tunable polarization states for quantum communication and sensing. This nanoscale device overcomes limitations of traditional bulk crystals by fabricating a structure from two perpendicularly arranged GaAs nanowires grown in the (111) direction and placed on a transparent silica substrate. This bottom-up fabrication approach leverages the intrinsically high second-order nonlinear susceptibility of GaAs, reaching 370pm/V, and ensures high crystalline quality with minimal defects. Precise control over nanowire diameter and length during growth enables fine-tuning of the generated photon pairs.

The study utilizes type-0 spontaneous parametric down-conversion within the nanowires, where the pump, signal, and idler photons share the same polarization. By carefully adjusting the polarization of the pump laser, scientists demonstrate the ability to generate both maximally entangled Bell states and separable states. Maximal entanglement is achieved when the pump polarization is approximately ±45° relative to the nanowire axes, while aligning the pump polarization with the nanowire axes produces separable states. This innovative nanosource operates at telecommunication wavelengths, a crucial advantage for long-distance, low-loss transmission and compatibility with existing optical fiber networks. The team characterized the effective nonlinear susceptibility tensor of individual nanowires, confirming their suitability for efficient photon pair generation, achieving coincidence rates up to 60GHz/Wm. This fully tunable source, capable of transitioning between entangled and separable states without post-selection, represents a significant advancement in quantum nanophotonics and paves the way for practical quantum communication and networking applications.

Tunable Entangled Photons from Gallium Arsenide Nanowires

Researchers have demonstrated a new nanoscale platform for generating tunable quantum states of light using zinc blende gallium arsenide (GaAs) nanowires. This breakthrough allows for precise control over the polarization of photon pairs at telecommunication wavelengths, essential for long-distance quantum communication and networking. The team successfully created a quantum nanosource capable of generating both entangled and separable states from two orthogonal nanowires, without requiring any post-selection of the emitted photons. Experiments reveal that by manipulating the pump polarization, the emitted photon pairs transition between entangled and separable states, reaching fidelities of 90%.

The nanosource operates at 1550nm, a key wavelength for compatibility with existing optical fiber networks and low-loss transmission. Detailed characterization of a single nanowire, using a focused 778nm laser, allowed precise determination of its long axis orientation by maximizing the second harmonic generation (SHG) intensity. By rotating the pump polarization and analyzing the resulting coincidence counts, scientists mapped the polarization response of the nanowires. Measurements confirm that the nanowires generate maximum photon-pair generation when the pump polarization is aligned with their long axis. Further experiments, varying the pump polarization among horizontal, vertical, diagonal, and antidiagonal orientations, enabled full control over the emitted photon polarization states. This achievement paves the way for miniaturized, integrated quantum light sources for secure communication and advanced sensing applications.

Tunable Entangled Photons from Gallium Arsenide Nanowires

Researchers have demonstrated a new platform for generating polarization-entangled photons using orthogonally oriented zinc blende gallium arsenide (GaAs) nanowires. They successfully generated photon pairs via spontaneous parametric down-conversion at a telecommunications wavelength, achieving high fidelity in controlling their quantum state. This nanoscale source represents a significant advance over traditional bulk crystals, offering potential for miniaturization, increased versatility, and easier integration into larger devices. The team not only created a tunable quantum source, capable of transitioning between separable and fully entangled states simply by adjusting the pump polarization, but also developed a robust method for characterizing the nanowires’ optical properties.

By fitting experimental data to theoretical models, they accurately determined the susceptibility tensor values of the nanowires, validating their approach and providing a deeper understanding of the generated quantum states. This achievement paves the way for advanced quantum functionalities, including quantum teleportation, and offers greater flexibility in quantum information processing. Future research directions include exploring more sophisticated architectures using assemblies of nanowires, potentially grown on photonic chips or placed within optical cavities.