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International Conference on Transparent Optical Networks

An all-fibred, telecom technology compatible, room temperature, single-photon source

Nathan Lecaron, Max Meunier, Grégory Sauder, Romain Dalidet, Yoann Pelet, Sébastien Tanzilli, Jesús Zúñiga-Pérez, Olivier Alibart

Published Jul 6, 2025• 0 citations
Publisher

Abstract

Single-photon sources are essential building blocks for for all aspects of quantum information technologies and more specifically for quantum communications. However, their widespread adoption is hindered by impractical constraints, such as cryogenic operation and emission wavelengths outside telecom windows. Leveraging telecom technology and point defects in GaN crystals, we present the first fully fibre-integrated single photon source operating at room temperature in the telecom O-band, meeting telecom photonics standards. We characterise an emitter producing single photons at 1292 nm, with a spectral broadening of 13 nm and a brightness of 25 kcps per mW of pump power and a purity of g(2)(0) = (5.9±0.5)×10−2at room temperature, demonstrating strong potential for integration into transportable quantum cryptography devices.

DOI
10.1109/icton67126.2025.11125129

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Single-photon sources are essential building blocks for for all aspects of quantum information technologies and more specifically for quantum communications. However, their widespread adoption is hindered by impractical constraints, such as cryogenic operation and emission wavelengths outside telecom windows. Leveraging telecom technology and point defects in GaN crystals, we present the first fully fibre-integrated single photon source operating at room temperature in the telecom O-band, meeting telecom photonics standards. We characterise an emitter producing single photons at 1292 nm, with a spectral broadening of 13 nm and a brightness of 25 kcps per mW of pump power and a purity of g(2)(0) = (5.9±0.5)×10−2at room temperature, demonstrating strong potential for integration into transportable quantum cryptography devices.
Single photon sources are essential building blocks for fundamental quantum optics, and quantum information networks. Their widespread use is currently hindered by impractical features, such as the need for operation at cryogenic temperatures and emission wavelengths lying outside telecom windows. Taking advantage of telecom technology and point defects in GaN crystals, we present, for the first time, the development of a fully-fibered source of single photons operating at room temperature, emitting photons in the telecom O-band and fulfilling the standards of telecom photonics. We characterise an emitter producting single photons at the wavelength of 1292 nm, a spectral broadening compatible with CWDM channels of 13 nm, and a brightness of 25 kcps per mW of pump power. The source shows a signal-to-noise ratio of 16.5 and a purity g(2)(0) = (5.9 ± 0.5) × 10−2 at room temperature, showing high potential for being integrated transportable quantum cryptography devices.
On-demand, single-photon emitters (SPEs) play a key role across a broad range of quantum technologies. In quantum networks and quantum key distribution protocols, where photons are used as flying qubits, telecom wavelength operation is preferred because of the reduced fiber loss. However, despite the tremendous efforts to develop various triggered SPE platforms, a robust source of triggered SPEs operating at room temperature and the telecom wavelength is still missing. We report a triggered, optically stable, room temperature solid-state SPE operating at telecom wavelengths. The emitters exhibit high photon purity (~5% multiphoton events) and a record-high brightness of ~1.5 MHz. The emission is attributed to localized defects in a gallium nitride (GaN) crystal. The high-performance SPEs embedded in a technologically mature semiconductor are promising for on-chip quantum simulators and practical quantum communication technologies.
Single photons and entangled photon pairs are a key resource of many quantum secure communication and quantum computation protocols, and non-Poissonian sources emitting in the low-loss wavelength region around 1,550 nm are essential for the development of fibre-based quantum network infrastructure. However, reaching this wavelength window has been challenging for semiconductor-based quantum light sources. Here we show that quantum dot devices based on indium phosphide are capable of electrically injected single photon emission in this wavelength region. Using the biexciton cascade mechanism, they also produce entangled photons with a fidelity of 87 ± 4%, sufficient for the application of one-way error correction protocols. The material system further allows for entangled photon generation up to an operating temperature of 93 K. Our quantum photon source can be directly integrated with existing long distance quantum communication and cryptography systems, and provides a promising material platform for developing future quantum network hardware.
Quantum communication networks are formed of secure links, where information can be transmitted with security guaranteed by the quantum nature of light. An essential building block of such a network is a source of single photons and entangled photon pairs, compatible with the low-loss fibre telecom window around 1550 nm. Previous work based on semiconductor quantum dots (QDs), colour centres in diamond and single atoms has been limited by emission wavelengths unsuitable for long distance applications. Efforts have been made to use standard gallium arsenide based QDs by extending their operating wavelength range, however, electrically driven quantum light emission from quantum dots in this telecommunication window has not yet been demonstrated. In this work, indium phosphide based QD devices have been developed to address this problem. The industry favoured growth method, metalorganic vapour phase epitaxy (MOVPE), has been used to create droplet QDs with low fine structure splitting (FSS). This growth scheme allows us to produce the first optoelectronic devices for single and entangled photon emission in the 1550 nm telecom window. We show single-photon emission with multi-photon events suppressed to 0.11±0.02. Furthermore, we obtain entangled light from the biexciton cascade with a maximum fidelity of 0.87± 0.04 which is sufficient for error correction protocols. We also show extended device operating temperature up to 93 K, allowing operation with liquid nitrogen or simple closed-cycle coolers. Our device can be directly integrated with existing long distance quantum communication, cryptography and quantum relay systems providing a new platform for developing quantum networks.
Single-photon sources (SPSs) are directly applicable in quantum key distribution (QKD) because they allow the implementation of the canonical BB84 protocol. To date, QKD implementations using SPSs are not widespread because of the need for cryogenic operation, or frequency conversion to a wavelength efficiently transmitted over telecommunication fibers. We report an observation of polarization-encoded QKD using a room-temperature telecom SPS based on a GaN defect. A field test over 3.5 km of deployed fiber with 4.0-dB loss yielded a quantum bit error rate (QBER) of 5.0% and a secure key rate of 585.9 bps. Further testing in a 32.5-km fiber spool (attenuation of 11.2 dB), which exhibited substantially lower polarization mode dispersion, yielded a QBER of 3.2% and a secure key rate of 50.4 bps. These results illustrate the potential of the GaN defects for supporting polarization-encoded quantum communication.
Single photons are the key ingredient for many photonic quantum technologies including quantum key distribution and measurement-based quantum computing. However, it remains difficult to create devices with the appropriate specifications for use in non-laboratory environments. The optical microcavity platform provides an attractive route towards a room temperature single photon source device. Our ultra-small focused ion beam (FIB) milled open-access cavities offer enhancement of the spontaneous emission rate, tunability of the emission spectrum and increased light collection. The embedment of solid-state emitters within these cavities enables us to create a robust room temperature single photon source device, with the potential for high efficiencies and single photon purities. Defects such as the nitrogen-vacancy (NV) centre in diamond have been shown to be stable room-temperature sources of single photons. There are new single emitters emerging in two-dimensional materials such as hexagonal boron nitride (hBN). Here we present developments in room-temperature coupling of single defects to open-access microcavities of a planar-hemispherical geometry with mode volumes down to λ3. We report enhancements in the spectral density of photons into a single cavity mode, combined with improved single photon purities. It will be shown that the NV-cavity system provides a ~3% single photon emission efficiency with purities of up to 94%. The hBN-cavity system provides count rates >1Mcts/s into a single cavity mode with purities up to 96%. With these high single photon purities, such devices would be robust against photon number splitting attacks making them attractive for applications in quantum cryptography.