Telecom Photons Controlled by Quantum Dot Chirality at 1260nm

Researchers at Queen’s University, Nanyang Technological University and the National Research Council of Canada have achieved directional control of photons at the 1260nm wavelength, a crucial band for long-distance fiber optic communication.

The team fabricated an integrated platform consisting of indium phosphide microdisks alongside indium arsenide quantum dots with a density of 108 cm-2, demonstrating near-ideal chiral quantum coupling required for quantum information processing. They tuned the quantum dot transitions through the photonic cavity using a strong magnetic field, observing a peak cavity enhancement of 3.3 and an emission directionality of 0.985, meaning the spin of the quantum dot dictates the direction the photon is emitted. These “chiral quantum light–matter interfaces” are essential building blocks for advanced quantum devices, including deterministic quantum logical gates and entanglement generation protocols.

Chiral Quantum Optics Enables Quantum Devices A peak cavity enhancement of 3.3 has been demonstrated, signaling a significant step towards practical quantum photonic circuits. This achievement focuses on manipulating light and harnessing the intrinsic spin of a quantum dot to dictate a photon’s path, opening avenues for advanced, non-reciprocal quantum devices.

The team fabricated an integrated platform consisting of indium phosphide microdisks alongside indium arsenide quantum dots within an InP membrane, carefully engineered to support whispering-gallery-mode resonances. These microdisks, with radii ranging from 2.5 to 4.5 µm, exhibit quality factors of 8.8 x 104, 1.2 x 105, and 1.5 x 105 (with 95% confidence intervals) for the first, second, and third-order radial modes respectively. The researchers targeted the third-order resonance, noting its larger spatial distribution assists in finding well-coupled quantum dots. The core of this advance lies in the creation of what the authors term. By applying a strong magnetic field, the team tuned the quantum dot transitions through the photonic cavity, observing a more than three-fold reduction in emitter lifetime when on resonance, while Zeeman-splitting of the transition energies makes the directional nature of the emitted photons clearly visible in the output spectra. The resulting emission directionality reached 0.985, demonstrating the near-ideal chiral quantum coupling required for quantum information processing on integrated photonic devices. This high-quality integrated chiral quantum element is now able to provide critical functionalities in future quantum information technologies, offering a pathway towards complex silicon photonic circuits and potentially revolutionizing data transmission and security. This work details the creation of “chiral quantum light–matter interfaces” by coupling indium arsenide (InAs) quantum dots with indium phosphide (InP) microdisk resonators. The fabrication process begins with growing the InAs quantum dots using chemical beam epitaxy, resulting in dots exhibiting excellent optical properties across the telecom bands at cryogenic temperatures. These dots, with a density of 108 cm-2, are within an InP membrane alongside microdisks ranging from 2.5 to 4.5 µm in radius, designed to support well-spaced resonances. Their work centers on creating “chiral quantum light–matter interfaces”, structures where the quantum spin of an emitter dictates the direction a photon travels, and achieving this functionality within the established telecom band represents a significant advance.

The team’s approach utilizes indium arsenide quantum dots within an InP membrane alongside indium phosphide microdisks, designed to enhance and direct photon emission. These microdisks, ranging from 2.5 to 4.5 µm in radius, are engineered to support well-spaced resonances, crucial for manipulating light at specific wavelengths. The results demonstrate a peak cavity enhancement of 3.3 and an emission directionality of 0.985, indicating near-ideal chiral quantum coupling. These findings suggest a pathway towards building complex silicon photonic circuits with integrated functionalities for quantum information technologies. Whispering-Gallery-Mode Resonances in Photonic Circuits The ability to manipulate single photons with precision is rapidly becoming central to advances in secure communication and quantum computing. This isn’t merely light manipulation; it’s a pathway toward integrating quantum functionalities directly into current infrastructure.

The team employed chemical beam epitaxy to grow indium arsenide quantum dots, achieving a density of 108 cm-2, within an InP membrane alongside the microdisks. These quantum dots serve as the light emitters, and their placement within the microdisk is carefully considered; simulations reveal ideal locations where the field amplitude remains significant and within the boundary of the disk. Crucially, the team demonstrated control over the quantum dot’s emission direction by applying an external magnetic field. This tuning allows for manipulation of the quantum dot’s energy levels, effectively shifting it into or out of resonance with the photonic cavity. Measurements reveal a peak cavity enhancement of 3.3, indicating a substantial amplification of the light-matter interaction. An emission directionality of 0.985 was observed, signifying near-ideal chiral quantum coupling. This compatibility is essential for building functional quantum devices and networks, offering a solid-state approach to quantum photonics that could ultimately unlock new possibilities in data transmission and quantum computation. Conventional understanding of light emission assumes photons radiate outwards in all directions. However, researchers are increasingly capable of dictating the path of single photons, leveraging the quantum properties of light-emitting materials. This isn’t simply about bending light; it’s about engineering a chiral quantum interface operating within the vital “telecom” band, the wavelengths used for long-distance fiber optic communication.

The team fabricated an integrated platform consisting of indium phosphide microdisks alongside indium arsenide quantum dots within an InP membrane, a configuration designed to enhance light-matter interaction. Finite-element simulations guided the placement of quantum dots within the microdisk, identifying regions where both significant field amplitude and appropriate chirality existed, and within the boundary of the disk.

The team tuned the quantum dot transitions through the photonic cavity using a strong magnetic field. The observed emission directionality reached 0.985, signifying near-ideal chiral quantum coupling. This level of control is confirmed by Zeeman-splitting of the transition energies, a phenomenon directly linked to the magnetic field’s influence on the quantum dot’s spin and, consequently, the photon’s trajectory. Directionality Simulated via Radial Position Analysis Researchers meticulously modeled the optimal placement of quantum dots within the indium phosphide microdisk to maximize directional photon emission, a crucial step toward realizing practical chiral quantum interfaces. Finite-element simulations, detailed in the team’s work, revealed that a quantum dot’s position relative to both the cavity’s field amplitude and polarization dictated the emitted photon’s direction. These calculations pinpointed specific radial locations within the boundary of the disk where chiral coupling could be near-ideal. The simulations weren’t merely theoretical exercises; they directly informed the fabrication process and subsequent experimental validation.

The team focused on the third-order radial mode of the microdisk, chosen for its larger spatial distribution which aided in locating suitable quantum dot positions. Analysis of the field maximum for this mode, visualized in cross-section, confirmed the presence of linearly polarized regions alongside areas of circular polarization, essential for achieving chiral coupling. The calculated directionality, presented as a function of radial position, demonstrated a clear correlation between location and emission preference, predicting a strong directional effect for QDs positioned within the identified zones. This precise control over photon directionality is enabled by the application of an external magnetic field, which tunes the quantum dot’s energy levels. Measurements reveal a peak cavity enhancement of 3.3, indicating a substantial amplification of the light-matter interaction. Source: https://arxiv.org/abs/2607.21452 Stay currentSee today’s quantum computing news on Quantum Zeitgeist for the latest breakthroughs in qubits, hardware, algorithms, and industry deals. Tags: