[Enlarge image]The transition from the disordered state of spontaneous emission (left) to the ordered state of superfluorescence (right) results in the emission of a coherent burst of light.
Light sources like LEDs usually send out photons in a haphazard way, scattering in all directions. Cutting-edge technologies, however, need the power of lasers, which generate light in a super-focused beam. Achieving this commonly requires expensive, complex setups involving mirrors and special chambers to carefully align and amplify the light.
The quantum phenomenon of superfluorescence, in which feedback is provided by the phase memory of the system, can eliminate the need for such complexities.1 Superfluorescence can be thought of as an emission from a large number of tiny emitters “dancing” in synchronization and releasing a powerful burst of light. This mirrorless lasing is a simple technique for creating powerful, focused light beams for applications in quantum devices. In work published this year,2 we observed superfluorescence from a semiconducting electron–hole plasma (EHP) without the need for ultralow temperatures or a complex setup—a development that we believe paves the way for such mirrorless laser technologies.
Superfluorescence from an EHP is extremely challenging in several respects. Motional fluctuation, carrier–carrier scattering and inhomogeneous broadening can all induce rapid decoherence. This necessitates very low temperatures, strong magnetic fields or complex microcavities, making the technique impractical.3 In our study, however, we demonstrated the superfluorescence from EHP up to a high temperature of 175 K, without applying any magnetic field or complex microcavities.
The key to our method2 lies in creating a cold EHP4 in a thin film of coupled metal halide perovskite quantum dots using near-band-gap excitation. The generated EHP initially is in a disordered state in which the quantum-dot emitters are uncorrelated. After a coherence buildup time, the emitters synchronize into a macroscopically ordered quantum state via the common field of spontaneously emitted photons. This phase transition from a disordered to an ordered state results in an abrupt, coherent burst of light pulses with high spatial and temporal coherence.
In our system, superfluorescence was exhibited by an ensemble of approximately 1,700 coupled emitters that decayed three orders of magnitude faster than the uncorrelated emitters. Interestingly, the emitted pulses also showed energy exchange with the system, as manifested by temporal Burnham–Chiao ringing. Spectacularly, superfluorescence took place up to a high temperature of 175 K. Above that temperature, thermal agitation hindered the formation of macroscopic coherence, and amplified spontaneous emission was observed as a residual effect.
We believe that this study isn’t just about “flashy physics,” but is important for the development of new chip-based laser technologies that can generate light in a super-focused beam. The work could, in our view, reshape the building of everything from super-precise medical tools to lightning-fast communication networks.
Researchers
Ajay K. Poonia and K.V. Adarsh, Indian Institute of Science Education and Research, Bhopal, India
References
1. M.G. Benedict (Ed.). Super-Radiance: Multiatomic Coherent Emission, 1st ed. (CRC Press, 2018).
2. A.K. Poonia et al. Phys. Rev. Lett. 132, 063803 (2024).
3. G. Timothy Noe II et al. Nat. Phys. 8, 219 (2012).
4. A.K. Poonia et al. Phys. Rev. Appl. 20, L021002 (2023).