A Japanese research team has discovered important properties of non-Fokker states (iNFS) in quantum technologies, revealing their stability through multilinear optics, paving the way for advances in optical quantum computing and sensing. Quantum objects, such as electrons and photons, behave differently from other objects, enabling quantum technology. This is the key to unlocking the mystery of quantum entanglement, in which multiple photons exist in multiple modes, or frequencies.

Achieving and verifying photon correlation beyond the limit of linear optics using photonic quantum circuits Source: Kyoto University/Shigeki Takeuchi

In the pursuit of photonic quantum technology, previous research has confirmed the usefulness of Fokker states (photon number states). These multiphoton, multimodal states are achieved by cleverly combining multiple single-photon inputs through so-called linear optics techniques. However, some important and valuable quantum states require more than this photon-by-photon approach.

Now, a research team from Kyoto University and Hiroshima University has theoretically and experimentally confirmed the unique advantage of non-Fokker states, or iNFS, that complex quantum states require more than a single photon source and linear optical elements.

"We successfully confirmed the existence of iNFS using multi-photon optical quantum circuits." Co-author Geobae Park added: "Our research will bring breakthroughs to applications such as optical quantum computers and optical quantum sensing."

Photons are a promising carrier because they can be transported over long distances while maintaining their quantum state at constant room temperature. Harnessing many photons in multiple modes will enable long-distance optical quantum encryption, optical quantum sensing, and optical quantum computing.

Co-author Ryo Okamoto explained: "We painstakingly generated a complex iNFS using Fourier transform photon quantum circuits to represent two photons in three different paths, which is the biggest challenge in realizing the conditional coherence phenomenon."

Comparison with quantum entanglement

Additionally, the study compared another phenomenon to the widely used quantum entanglement, which appears and disappears simply by passing through a linear optical element. Quantum entanglement refers to quantum states with two or more related states in a superposition between two independent systems.

Holger F Hofmann of Hiroshima University noted: "Surprisingly, this study shows that the properties of iNFS do not change when passing through a network of many linear optical elements, marking a leap forward in light quantum technology."

Takeuchi's team believes that iNFS exhibits conditional coherence, a somewhat mysterious phenomenon in which even the detection of one photon means that the remaining photons are present in a superposition of multiple paths.

Takeuchi Shigeki announced: "Our next phase goal is to realize larger-scale multi-photon, multi-modal and optical quantum circuit chips. This research marks a potential leap in understanding and exploiting quantum phenomena."

Compiled from /ScitechDaily