Subnatural-linewidth biphotons from a Doppler-broadened hot atomic vapour cell

Area of Science:

• Quantum Optics
• Atomic Physics
• Quantum Information Science

Background:

• Biphotons are crucial for quantum optics and quantum networks.
• Narrowband single photons are needed for photon-atom interfaces.
• Current methods using laser-cooled atoms are complex and large.

Purpose of the Study:

• To develop a simpler, more scalable source of narrowband biphotons.
• To generate biphotons with bandwidths suitable for quantum network protocols.
• To explore spontaneous four-wave mixing in hot atomic vapor cells.

Main Methods:

• Utilized on-resonance spontaneous four-wave mixing in a hot 87Rb vapor cell.
• Employed a backward phase-matching scheme with spatially separated optical pumping.
• Operated the paraffin-coated 87Rb cell at 63°C.

Main Results:

• Generated subnatural-linewidth biphotons (<6 MHz) from a Doppler-broadened (530 MHz) atomic vapor.
• Achieved controllable biphoton bandwidths ranging from 1.9 to 3.2 MHz.
• Produced biphotons with coherence times between 47 and 94 ns.
• Successfully suppressed uncorrelated photons via optical pumping.

Conclusions:

• Demonstrated a compact and efficient method for generating narrowband biphotons.
• The hot atomic vapor cell approach offers a practical alternative to laser-cooled systems.
• This work advances the development of miniature narrowband biphoton sources for quantum technologies.