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Quantum computing can solve problems that are too complicated for standard machines, but understanding when and how this “quantum advantage” will be realised has remained a significant question
Now, researchers from Kyoto University have found a link between this advantage and the principles of quantum cryptography. The findings suggest that the same conditions that make quantum communication secure may also define when quantum computing begins to outperform classical systems.
As the demand for secure data transmission methods increases, traditional technologies are reaching their limits. Based on classical physics, current systems are increasingly vulnerable.
Quantum communication, however, may be the key to overcoming these challenges. By using quantum properties of light, specifically single photons, researchers are aiming to build next-generation communication systems that are not only faster but also more secure.
The role of single photons in quantum communication
Single photons are the building blocks of quantum communication. Unlike conventional signals that use many photons or electrons at once, single-photon transmission ensures high security and minimal signal loss. However, generating single photons efficiently and reliably continues to be a technological challenge.
To address this challenge, the Kyoto research team turned to a new class of materials known as two-dimensional semiconductors. These materials are just a few atoms thick and have impressive electrical and optical properties, making them ideal for future quantum devices.
A material with promise
The researchers focused on tungsten diselenide (WSe₂), a two-dimensional semiconductor that has recently gained attention for its unique properties. By introducing a controlled defect into a single atomic layer of WSe₂, they hypothesised that they could create a localised trap for excitons. These pairs of electrons and electron holes would emit only one photon at a time.
To test their theory, they carefully prepared a sample of monolayer WSe₂ and applied heat to induce a small number of structural defects. This deliberate disruption created asymmetry in the crystal, which over time led to the appearance of two distinct luminescence peaks, corresponding to “bright” and “dark” excitons.
The experiment was conducted at extremely low temperatures, around -265°C, to reduce thermal noise and allow precise measurements. The team applied an external magnetic field to manipulate the photon emission further. It was discovered that even a relatively weak magnetic field significantly increased the emission intensity, confirming their ability to control the process externally.
The emitted light showed signs of “photon antibunching,” which is a key indicator that the photons were being emitted one at a time. This behaviour confirms that the system can function as a single-photon source.
The future of quantum devices
This discovery is an essential step in building compact, efficient, and secure quantum information systems. By showing that two-dimensional semiconductors like WSe₂ can emit single photons under controlled conditions, the Kyoto researchers have opened the door to practical quantum communication technologies.
AloJapan.com