Reviewed by Robert Egan – associate editor

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Photons initially travel through the waveguide without interacting (1) and are not frequency‑entangled. Upon reaching the quantum dot, the latter transitions to its excited state and re‑emits the two input photons (2). The photons are frequency‑entangled and travel away from the quantum dot (3). [Some elements of this image were generated using ChatGPT.] – Credit: Mohamed Meguebel, Telecom Paris, Institut Polytechnique de Paris

Researchers have designed a new device that can efficiently create multiple frequency‑entangled photons, a feat that cannot be achieved with today’s optical devices. The new approach could open a path to more powerful quantum communication and computing technologies.

“Entangling particles efficiently is a critical capability for unlocking the full power of quantum technologies—whether to accelerate computations, surpass fundamental limits in precision measurement, or guarantee unbreakable security using the laws of quantum physics,” said Nicolas Fabre (Telecom Paris, Institut Polytechnique de Paris).

“Photons are ideal because they can travel long distances through optical fibers or free space; however, there hasn’t been a way to efficiently generate frequency entanglement between more than two photons.”

Frequency entanglement ties photons’ colors (frequencies) together through quantum correlations, adding new spectral degrees of freedom for carrying information.

In the journal Optica Quantum, the researchers report numerical‑simulation results from their new device, which uses a quantum dot to entangle independent photons’ frequencies without needing to filter or select specific photon interactions afterward. The process can be repeated to entangle many photons and is compatible with on‑chip photonic platforms, providing a realistic path toward scalable, multi‑photon frequency entanglement.

“The entangled photons produced by this device could travel long distances and help guarantee communication that cannot be hacked—even with future quantum computers,” said Fabre. “Because the device works at telecom wavelengths, the entangled photons could be used to create long‑distance quantum networks with the fibers already in the ground.”

Sculpting spectrums

The work grew out of a broader effort in the quantum‑technology community to make better use of a photon’s time‑frequency degree of freedom—the color of the photon and the precise moment it arrives—for quantum information processing. To solve the challenge of generating frequency entanglement between multiple photons, the researchers developed a device concept called a shaping frequency entangling gate (FrEnGATE).

Normally, two photons pass through each other without interacting, but FrEnGATE contains a waveguide with a quantum dot that acts like an artificial atom. Under the right timing conditions, the quantum dot functions as a temporary mediator, causing the colors of the photons to become correlated and forming frequency‑entangled states known as qudits. These qudit states can carry more information per photon than the simple two‑level (qubit) states produced by most quantum systems.

“FrEnGATE ‘sculpts’ the joint spectrum of the two photons, turning simple input photons into a frequency‑entangled quantum state at the output,” said Fabre.

“A key theoretical insight that made this possible was to separate fast and slow dynamics so that all single‑photon transitions are suppressed while a much slower, but extremely useful, two‑photon interaction survives. This allows two independent photons to become frequency entangled.”

Modeling entanglement

To test the concept, the researchers created a detailed computer model of a realistic quantum dot in a waveguide. They derived the effective two‑photon interaction and simulated how various input photons evolve through the device. They also analyzed the output using standard tools to quantify the amount of frequency entanglement and tested how coupling strengths, linewidths and timing affect the gate’s performance.

The simulations showed that it should be feasible to fabricate a FrEnGATE thanks to recent advances in clean‑room fabrication technology that allow researchers to engineer the internal structure of quantum dots and embed them inside low‑loss waveguides to create strong light‑matter interactions with single guided photons in the 1550‑nm telecom band.

The researchers estimate that the probability of success to generate a frequency‑entangled photon state on each attempt is 15 %—a large improvement over the probability obtained with nonlinear crystals, which can create new entangled photons from scratch but cannot entangle pre‑existing ones.

According to the authors, improving this probability will be important for developing practical systems. Additionally, the quantum dot’s internal structure, coupling strength and fine‑structure splitting will need to be precisely engineered to create an experimental version of the FrEnGATE.

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More information

Mohamed Meguebel et al., “Generation of frequency entanglement with an effective quantum dot‑waveguide two‑photon quadratic interaction,” Optica Quantum (2025). DOI: 10.1364/opticaq.571592

Citation

Quantum‑dot device can generate multiple frequency‑entangled photons (2026, January 13). Retrieved 15 January 2026 from https://phys.org/news/2026-01-quantum-dot-device-generate-multiple.html

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