The breakthrough brings researchers a step closer to compact quantum technologies, in which light sources, circuits and potentially detectors can be integrated into a single device. Today, these components often rely on different materials that are difficult and costly to combine.
In a study published in Nature Communications, Pietro Metuh and co-workers demonstrate a promising alternative: a bright, high-quality single-photon source integrated directly with a light-guiding circuit made from atomically thin materials. The work was led by Associate Professor Battulga Munkhbat.
The device delivers around one million single photons per second into the circuit, offering a potential route towards smaller and more scalable quantum technologies. “This is an important milestone for our ERC project, TuneTMD, where we are working towards quantum photonic circuits built from atomically thin material,” says Munkhbat.
Two ultrathin materials, two essential jobs
Photons are the smallest individual packets of light. Unlike ordinary light, which typically contains vast numbers of photons, quantum technologies can use individual photons to carry information or perform operations that rely on the laws of quantum physics.
But producing single photons is only half the challenge. Researchers must also be able to guide them reliably through a chip to where they are needed.
To achieve both, the team combined two atomically thin materials, each with a different role.
The first, tungsten diselenide, produces the photons. When placed over a tiny nanostructure, the material develops microscopic wrinkles that trap energy in extremely small regions. This allows the trapped energy to be released as individual photons.
The second material, tungsten disulfide, acts as a network of optical pathways. Shaped into narrow channels known as waveguides, it guides light across the chip while minimising losses along the way.
The researchers stacked the photon source directly above one of these channels, with an ultrathin insulating layer in between. This arrangement allows the photons to pass from the source into the waveguide and travel along the chip.
In other words, the researchers have brought two essential functions of a quantum photonic circuit together in a device made from materials only a few atoms thick.
A million photons per second
For quantum technologies, it’s not enough to produce light. A useful source must produce individual photons without accidentally emitting several at once, which can disrupt quantum operations.
The researchers tested how reliably their device produced single photons. Their measurements showed near-perfect single-photon purity, meaning that unwanted emissions containing multiple photons were almost entirely suppressed.
At the same time, the source delivered around one million single photons per second into the waveguide, making it unusually bright for this type of integrated quantum emitter.
Two design choices helped achieve this result.
- First, the waveguide was designed to support several modes of light, giving the ultrathin emitter more opportunities to transfer its photons into the circuit.
- Second, the researchers used a way of exciting the emitter that increases the desired light emission while suppressing background light, making the source roughly ten times brighter than it would be with the less effective excitation approach.
The researchers also demonstrated that the chip could be used to test the quantum properties of the emitted light. By collecting photons from both ends of the waveguide and comparing their arrival patterns, they could verify the single-photon behaviour without relying on the external optical equipment normally used for such measurements.
One material platform, many possibilities
Getting light from an atomically thin source into a chip circuit has been a longstanding challenge. Because the source is so thin, it interacts only weakly with light travelling through conventional waveguides.
The researchers addressed this by carefully designing a waveguide that gives the photons more ways to enter the circuit. The approach could also help researchers integrate atomically thin light sources with established photonic technologies, including silicon and silicon nitride platforms.
The longer-term goal is to bring more of the components needed for quantum technologies onto the same chip: sources that generate individual photons, circuits that manipulate them, and detectors that register them. Related atomically thin materials are already being investigated for single-photon detection.
Combining these functions could reduce the need to assemble devices from materials that are difficult to manufacture together. And because atomically thin crystals can be transferred onto other materials, they could potentially be incorporated into existing chip technologies.
The possibilities range from quantum communication, which uses quantum physics to protect information, to photonic quantum computing and more precise sensing technologies.
There’s still an important step ahead. For many quantum applications, photons must not only be produced one at a time; they must also be indistinguishable from one another, so that they behave identically in quantum operations.
The new study establishes a promising foundation: a bright, high-quality source of single photons, integrated with a circuit that guides them, using materials just a few atoms thick.
