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Multiphoton cluster-state generation in the telecom C-band using an InAs/InP quantum dot

Petros Laccotripes, Junyang Huang, Ginny Shooter, Matthew S. Winnel, Andrea Barbiero, D. A. Ritchie, Andrew J. Shields, Tina Müller, R. M. Stevenson

Published Jan 1, 2026• 0 citations
Publisher

Abstract

Multiphoton entangled states are essential for memoryless quantum repeaters and measurement-based quantum computation. We demonstrate, for the first time, scalable multiphoton entanglement generation directly in the telecom C-band from a solid-state system, achieving two- and three-qubit fidelities of 59.5% and 52.7%.
DOI
10.1364/cleo_fs.2026.fth1b.1

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Multiphoton entangled states are a key resource for quantum networks and measurement-based quantum computation. Scalable protocols for generating such states using solid-state spin-photon interfaces have recently emerged, but practical implementations have so far relied on emitters operating at short wavelengths, incompatible with low-loss fibre transmission. Here, we take a key step towards the generation of telecom wavelength multi-qubit entangled states using an InAs/InP quantum dot. After establishing that all essential criteria for generating cluster states using a ground state spin as the entangler are satisfied, we implement a scalable protocol to entangle the resident spin with sequentially emitted photons directly in the telecom C-band. We demonstrate a two-qubit (spin-photon) entanglement fidelity of 59.5±8.7%59.5\pm 8.7\%59.5±8.7% and a lower bound of three-qubit (spin-photon-photon) entanglement fidelity of 52.7±11.4%52.7\pm 11.4\%52.7±11.4%. Our results close the performance gap between short-wavelength quantum dot systems and the existing telecom infrastructure, establishing a route towards practical large photonic cluster states for fibre-based quantum network applications.
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 %.
Quantum networks, relying on the distribution of quantum entanglement between remote locations, have the potential to transform quantum computation and secure long-distance quantum communication. However, a fundamental ingredient for fibre-based implementations of such networks, namely entanglement between a single spin and a photon directly emitted at telecom wavelengths, has been unattainable so far. Here, we use a negatively charged exciton in an InAs/InP quantum dot to implement an optically active spin qubit taking advantage of the lowest-loss transmission window, the telecom C-band. We investigate the coherent interactions of the spin-qubit system under resonant excitation, demonstrating high fidelity spin initialisation and coherent control using picosecond pulses. We further use these tools to measure the coherence of a single, undisturbed electron spin in our system. Finally, we demonstrate spin-photon entanglement in a solid-state system with entanglement fidelity F = 80.07 ± 2.9%, more than 10 standard deviations above the classical limit.
On-demand sources of entangled photons for the transmission of quantum information in the telecom C-band are required to realize fiber-based quantum networks. So far, non-deterministic sources of quantum states of light were used for long distance entanglement distribution in this lowest loss wavelength range. However, they are fundamentally limited in either efficiency or security due to their Poissonian emission statistics. Here, we show on-demand generation of entangled photon pairs in the telecom C-band by an InAs/GaAs semiconductor quantum dot. Using a robust phonon-assisted excitation scheme we measure a concurrence of 91.4 %91.4\,\%91.4% and a fidelity of 95.2 %95.2\,\%95.2% to Φ+Φ^+Φ+. On-demand generation of polarization entangled photons will enable secure quantum communication in fiber-based networks. Furthermore, applying this excitation scheme to several remote quantum dots tuned into resonance will enable first on-demand entanglement distribution over large distances for scalable real-life quantum applications.