Ultrabright Narrow-Linewidth Source of Biphotons Generated from a Heated Vapor Cell

Ite Yu^1,2*

¹Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
²Center for Quantum Science and Technology, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:Ite Yu, email:yu@phys.nthu.edu.tw

Optical qubits are made of single photons. Due to photons’ excellent fidelity, we can expect that optical qubits or single photons will play a more important role in future quantum communication. As single photons are generated one by one, they appear randomly and it is difficult to utilize qubits in random timing. Therefore, the practical operation method is to generate a pair of single photons, i.e., biphoton. The first photon of a pair heralds the coming of the second photon of the same pair, which is the heralded single photon for a subsequent quantum operation.

We employed a hot atomic vapor to generate biphotons. For the first time, the all-copropagation scheme was utilized in our system, resulting in an excellent phase match. The phase-match scheme enables us to make the linewidth of the single-photon wave packets as narrow as 290 kHz [1]. This is the world record for the narrowest linewidth of single-mode single photons generated from room-temperature or hot media, which can only be surpassed by that of our cold-atom single photon source with a linewidth of 50 kHz [2]. Using the hot atomic vapor, we increased the spectral brightness of biphotons to about 380,000 pairs/s/MHz [3]. This spectral brightness is the best result to date among all kinds of media such as hot or cold atomic vapors, solid crystals, and integrated photonic chips. A biphoton source of a higher generation rate can produce information carriers faster for a higher bandwidth of information transmission. A quantum operation utilizing biphotons of a narrower linewidth can achieve a better efficiency. Hence, the generation rate per linewidth, i.e., spectral brightness, is an important figure of merit of a biphoton source, and strongly influences the success rate of quantum information transmission.

The hot-atom source of biphotons developed by us has the following advantages: (1) The frequency is very stable and has an adjustable range larger than 0.5 GHz. (2) The linewidth is highly controllable and can be narrower than 300 kHz or broader than 3 MHz, being compatible with quantum devices with different characteristics. (3) The ultrahigh spectral brightness is close to the ultimate limit, being a milestone and representing a high success rate in quantum communication. This source can become a key component in the future quantum network. This work was supported by Grants Nos. 111-2639-M-007-001-ASP, 112-2119-M-007-007, and 112-2112-M-007-020-MY3 of National Science and Technology Council, Taiwan.

References
[1] C.-Y. Hsu, Y.-S. Wang, J.-M. Chen, F.-C. Huang, Y.-T. Ke, E. K. Huang, W. Hung, K.-L. Chao, S.-S. Hsiao, Y.-H. Chen, C.-S. Chuu, Y.-C. Chen, Y.-F. Chen, I. A. Yu, “Generation of sub-MHz and spectrally-bright biphotons from hot atomic vapors with a phase mismatch-free scheme,” Opt. Express 29, 4632 (2021).
[2] Y.-S. Wang, K.-B. Li, C.-F. Chang, T.-W. Lin, J.-Q. Li, S.-S. Hsiao, J.-M. Chen, Y.-H. Lai, Y.-C. Chen, Y.-F. Chen, C.-S. Chuu, and I. A. Yu, “Temporally ultralong biphotons with a linewidth of 50 kHz,” APL Photonics 7, 126102 (2022).
[3] J.-M. Chen, C.-Y. Hsu, W.-K. Huang, S.-S. Hsiao, F.-C. Huang, Y.-H. Chen, C.-S. Chuu, Y.-C. Chen, Y.-F. Chen, and I. A. Yu, “Room-temperature biphoton source with a spectral brightness near the ultimate limit,” Phys. Rev. Res. 4, 023132 (2022).

Keywords: biphoton, heralded single photon, optical qubit, spectral brightness, linewidth