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arXiv:2607.21452

Directional telecom photons from a chirally coupled quantum dot

Kristina Bodiroga, Jacob Ewaniuk, Andrew N. Wakileh, Lucas Rantz, Ivanna M. Boras Vazquez, Dan Dalacu, Philip J. Poole, Robin L. Williams, Xiao-Liu Chu, Nir Rotenberg

quant-phSubmitted Jul 23, 2026• Announced Jul 24, 2026• 0 citations• Revised Jul 24, 2026 (v2)
v1 · Jul 23, 2026v2 · Jul 24, 2026
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Abstract

Chiral quantum light-matter interfaces, where the internal spin state of a quantum emitter determines the direction in which it emits, are essential building blocks of non-reciprocal quantum devices, deterministic quantum logical gates and entanglement generation protocols. Yet, a chiral quantum interface that operates at telecom wavelengths, and is compatible with telecommunication infrastructure and silicon photonics, does not yet exist. Here, we report on an integrated chiral quantum interface in the original telecom band (1260-1360 nm), created by interfacing InAs quantum dots with a waveguide-coupled InP microdisk. We tune 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, demonstrating the near-ideal chiral quantum coupling required for quantum information processing on integrated photonic devices.

Comments
7 pages, 4 figures

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Chiral quantum light-matter interfaces, where the internal spin state of a quantum emitter determines the direction in which it emits, are essential building blocks of non-reciprocal quantum devices, deterministic quantum logical gates and entanglement generation protocols. Yet, a chiral quantum interface that operates at telecom wavelengths, and is compatible with telecommunication infrastructure and silicon photonics, does not yet exist. Here, we report on an integrated chiral quantum interface in the original telecom band (1260-1360 nm), created by interfacing InAs quantum dots with a waveguide-coupled InP microdisk. We tune 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, demonstrating the near-ideal chiral quantum coupling required for quantum information processing on integrated photonic devices.
The ability to engineer chiral light-matter interactions is a valuable resource for realizing quantum networks and non-reciprocal quantum optics. Here, we demonstrate chiral coupling between light and a negatively charged exciton state, i.e., a four-level system, embedded in a standard photonic-crystal waveguide. By controlling the orientation and strength of an external magnetic field, we tune the polarization of the individual optical transition dipoles relative to the fixed elliptically polarized waveguide mode. In a two-sided waveguide, an optimized oblique magnetic field allows a selected transition to decay exclusively into a single propagation direction, enabling near-unity directional emission (0.99−0.02+0.010.99^{+0.01}_{-0.02}0.99−0.02+0.01​), despite the waveguide exhibiting imperfect polarization for chiral coupling. We further observe two tunable chiral branching ratios, the directional analogue of optical cyclicity, for two ΛΛΛ-systems, with one reaching 134−77+∞134_{-77}^{+\infty}134−77+∞​. The magnetic-field-dependent spectroscopy also allows reconstruction of the local guided-mode polarization at the emitter via the Stokes parameters relative to the emitter's dipole moments. Finally, we demonstrate that this local chirality enables coherent control of an electron spin via an optical Raman process mediated by waveguide driving. Building on the simultaneous realization of a large branching ratio, directionality and spin control achieved at the same oblique magnetic-field angle, we propose a protocol with high tolerance to photon loss for generating high-fidelity remote spin-spin entanglement. Our magnetic control opens a reconfigurable and generic route for enhancing on-chip chiral spin-photon coupling in standard nanophotonic interfaces without the need to carefully engineer the polarization of the waveguide.
Chiral quantum systems have received intensive attention in fundamental physics and applications in quantum information processing including optical isolation and photon unidirectional emission. Here, we design an on-chip emitter-resonator system with strong chiral light-matter interaction for a chiral single-photon interface. The system includes a microring resonator with a strong evanescent field and a near-unity optical chirality along both of the whole outside and inside walls, allowing a strong and chiral coupling of the whispering-gallery mode to a quantum emitter. By initializing a quantum dot in a specific spin ground state or shifting the transition energy with a polarization-selective optical Stark effect, we show a broadband optical isolation at the single-photon level over several gigahertz. Furthermore, a quantum emitter chirally coupling to the microring resonator can emit single photons unidirectionally. Our protocol paves the way to realize a multifunctional chiral single-photon interface for on-chip quantum information processing and quantum networks.
Efficient generation of entanglement between a stationary matter-qubit and a propagating photonic-qubit is a scientific and technological challenge of utmost importance for the realisation of fully-fledged quantum networks. Solid-state quantum emitters in the telecom C-band are a promising platform due to the minimal absorption of photons at these wavelengths and deterministic generation of high purity single photon flying qubits. Here, we use an InAs/InP quantum dot to implement an optically active spin-qubit and demonstrate high fidelity spin initialisation and coherent spin control of the resident electron. Lastly, for the first time we demonstrate high-fidelity spin-photon entanglement in a solid-state system with direct emission into the telecom C-band and obtain a lower bound on the entanglement fidelity of 80.07 %.
Solid-state quantum light sources offer a scalable pathway for interfacing stationary spin qubits with flying photonic qubits, forming the backbone of future quantum networks. Telecom-band spin-photonic qubits, operating in the 1260-1675 nm wavelength range, are particularly well-suited for long-distance quantum communication due to minimal loss in standard optical fibers. Achieving scalability, however, hinges on fulfilling several stringent criteria: coherent spin-state control, deterministic and indistinguishable single-photon emission, and integration with nanophotonic structures that enhance radiative properties, such as lifetime, coherence, and photon indistinguishability. This study explores the state-of-the-art spin-photonic qubits across solid-state platforms, including diamond color centers, silicon carbide defect centers, quantum dots, and two-dimensional materials. Special attention is given to silicon-based emitters, particularly G, T, C- and Ci-centers, which promise monolithic integration with complementary metal-oxide-semiconductor (CMOS) technology and telecom-band operation. We classify these systems based on spin-photon interface availability, CMOS process compatibility, and emitter scalability. We also discuss recent advances in cavity quantum electrodynamics (cQED), including Purcell enhancement and quality factor engineering in integrated photonic (circuits) environments. The work highlights emerging demonstrations of quantum networking over metropolitan scales and outlines the trajectory toward chip-scale quantum photonic integrated circuits (QPICs). It combines deterministic emitter creation, coherent spin manipulation, and quantum information processing. These developments pave the way for global quantum networks, enabling secure communication, distributed quantum computing, and quantum-enhanced sensing.
Highly efficient single photon sources are important building blocks for optical quantum information processing. For practical use and long-distance quantum communication, single photons should have fiber-compatible telecom wavelengths. In addition, most quantum communication applications require high degree of indistinguishability of single photons, such that they exhibit interference on a beam splitter. However, deterministic generation of indistinguishable single photons with high brightness remains a challenging problem in particular at telecom wavelengths. We demonstrate a telecom wavelength source of indistinguishable single photons using an InAs/InP quantum dot in a nanophotonic cavity. To obtain the efficient single quantum dot emission, we employ the higher order mode in L3 photonic crystal cavity that shows a nearly Gaussian transverse mode profile and results in out-coupling efficiency exceeding 46 {\\%} and unusual bright single quantum dot emission exceeding 1.5 million counts per second at a detector. We also observe Purcell enhanced spontaneous emission rate as large as 4 and high linear polarization ratio of 0.96 for the coupled dots. Using this source, we generate high purity single photons at 1.3 ??m wavelength and demonstrate the indistinguishable nature of the emission using a two-photon interference measurement.
Photonic cluster states are a key resource for photonic quantum information processing. So far, deterministic generation of these states has been limited to the near-infrared wavelength range. To achieve quantum advantage in communication while maintaining compatibility with silicon photonics, operation in the telecom wavelength range is required. In this work, we demonstrate deterministic cluster state generation directly in the telecom C-band. This is achieved through repetitive excitation of a hole spin confined in an indium-arsenide quantum dot subjected to an external magnetic field. We characterize the quantum process that generates the cluster state by measuring its process map, obtaining a fidelity of F=0.71±0.01\mathrm{F} = 0.71 \pm 0.01F=0.71±0.01 to the ideal case. As part of this characterization, we observe spin--photon polarization entanglement with a negativity of N=0.27±0.02\mathrm{N} = 0.27 \pm 0.02N=0.27±0.02. The emitted photons exhibit indistinguishability of at least 83%, demonstrating the potential for future fusion gates necessary for photonic cluster state generation beyond linear connectivity.