We employed an atomic vapor cell, a practical component, to develop the source of biphoton quantum light. For the first time, we utilized the all-copropagation scheme and developed a high isolation technique. The source＇s linewidth and spectral brightness are the world records to date. It has a stable frequency with a wide adjustable range, a highly tunable linewidth compatible with various quantum devices, and ultrahigh brightness, leading to a key apparatus in the future quantum communication.

For the first time, we utilized the all-copropagation scheme and developed a 130-dB high isolation technique. Our biphoton quantum source has a linewidth down to 290 kHz, the narrowest one of all single-mode sources made of room-temperature or hot media. The spectral brightness of our source is 3.8*10^5 pairs/s/MHz, a world record to date among all kinds of media (hot/cold atoms, crystals, photonic chips, etc.), and is close to the ultimate limit, an important milestone in quantum communication.

Our biphoton quantum source is based on a commercially-available atomic vapor cell. It also includes 2 low-power lasers and a few optical components. The narrow-linewidth source has a world-record spectral brightness. The source＇s entity is a movable apparatus. It can run uninterrupted 24 hours a day in the environment like a telecom hub nowadays. The superior performances of our source will become the reliable machine in network hubs and play an influential role in quantum communication.