Phase diagram of lasing under correlated pump from GPU-accelerated Truncated Wigner dynamics

Superradiant (SR) lasers are highly valued for their ultra-narrow linewidths and phase stability, but they face a fundamental trade-off: local pumping provides high coherence but requires drive intensities that scale linearly with the number of atoms (N), leading to significant recoil heating. Conversely, fully collective pumping avoids this scaling but limits the coherence of the emitted light. This paper investigates whether spatially correlated pumping—a middle ground between local and collective drives—can optimize this trade-off.

The authors model a chain of N two-level atoms coupled to a bad-cavity mode, where the incoherent pump rates between atoms follow a power-law decay defined by an exponent α. This exponent allows the researchers to interpolate continuously between collective pumping (α = 0) and local pumping (α → ∞). Because this setup breaks permutation symmetry, the authors employ the Truncated Wigner Approximation (TWA) accelerated by GPUs to simulate systems of up to 10^4 atoms, enabling a comprehensive scan of the steady-state phase diagram.

The study demonstrates that correlated pumping acts as a "spectroscopic dial" for laser performance. The researchers found that ultra-narrow emission persists for all values of α. Crucially, the drive strength required to achieve lasing is reduced by a factor of N^(1-α) for α < 1 and by log N as α approaches 1, which significantly suppresses recoil heating. While coherence improves as the pump becomes shorter-ranged, the authors show that fully coherent light (g^(2) → 1) is achievable even with non-local pumping (down to α ≈ 1). This confirms that local pumping is not a strict requirement for high-coherence superradiant emission.