A steady-state superradiant laser with less than one intracavity photon

Area of Science:

• Atomic, Molecular, and Optical Physics
• Quantum Optics
• Laser Physics

Background:

• Spectral purity of oscillators is critical for applications like gravity wave detection, timekeeping, and quantum computation.
• High spectral purity lasers are predicted to operate in the superradiant regime using narrow atomic transitions.
• The 'bad-cavity' or superradiant regime is characterized by a bare atomic linewidth much smaller than the cavity linewidth.

Purpose of the Study:

• To demonstrate a Raman superradiant laser source.
• To achieve high spectral purity by operating in the bad-cavity regime.
• To validate predictions for future superradiant lasers.

Main Methods:

• Constructed a Raman superradiant laser using rubidium-87 atomic dipoles.
• Operated the laser at a low intracavity photon number (less than 0.2 photons).
• Measured spectral purity and isolation of the collective atomic dipole from the environment using cavity frequency pulling.

Main Results:

• Demonstrated spontaneous synchronization of over one million atomic dipoles.
• Achieved isolation of the collective atomic dipole from the environment by over ten thousand times.
• The laser's frequency linewidth was narrower than single-particle decoherence and over ten thousand times below the quantum linewidth limit for good-cavity lasers.

Conclusions:

• The study successfully demonstrated a Raman superradiant laser operating in the bad-cavity regime.
• The results validate key predictions for superradiant lasers, showing significantly enhanced spectral purity.
• This work could lead to improved atomic clocks and new avenues for fundamental physics research.