Collectively pumped superradiant laser with coherence scaling beyond the standard quantum limit

arXiv:2611.05976v1 Announce Type: new Abstract: For more than half a century, the standard quantum limit (SQL) was thought to limit the laser coherence $\mathfrak{C}$ -- the number of photons emitted from the laser into the beam in one coherence time -- to a scaling $\Theta(\mu^2)$, where $\mu$ is the mean number of optical-frequency excitations stored inside the laser. However, recently it has been shown [Baker et al., Nat. Phys. 17, 179 (2021)] that the Heisenberg limit -- an achievable ultimate limit set by quantum mechanics for the task of producing a beam with the standard properties of a laser beam -- is $\mathfrak{C}=\Theta(\mu^4)$, a quadratic enhancement. So far, proposals to demonstrate beyond-SQL scaling of $\mathfrak{C}$ have been limited to circuit QED, at microwave frequencies (i.e., a maser). Here, we introduce a class of generalized far-above-threshold (FAT) laser models, obtained by replacing the ordinary bosonic lowering operator $\hat{a}$ by a general lowering operator $\hat{L}$ in the superoperators appearing in the master equation that governs the FAT laser dynamics. We then show that an optical-frequency superradiant laser in the bad-cavity limit, with feedback-controlled collective pumping, realizes one such model, in which $\hat{L}$ is identified with the collective superradiant lowering operator $\hat{J}$. This model can surpass the SQL scaling, with the coherence exhibiting a scaling as large as $\mathfrak{C}= \Theta(\mu^{8/3})$ in the optimal parameter regime. Here, in the bad-cavity limit, $\mu\approx N/2$, where $N$ is the number of superradiant atoms.

Abstract:For more than half a century, the standard quantum limit (SQL) was thought to limit the laser coherence $\mathfrak{C}$ -- the number of photons emitted from the laser into the beam in one coherence time -- to a scaling $\Theta(\mu^2)$, where $\mu$ is the mean number of optical-frequency excitations stored inside the laser. However, recently it has been shown [Baker et al., Nat. Phys. 17, 179 (2021)] that the Heisenberg limit -- an achievable ultimate limit set by quantum mechanics for the task of producing a beam with the standard properties of a laser beam -- is $\mathfrak{C}=\Theta(\mu^4)$, a quadratic enhancement. So far, proposals to demonstrate beyond-SQL scaling of $\mathfrak{C}$ have been limited to circuit QED, at microwave frequencies (i.e., a maser). Here, we introduce a class of generalized far-above-threshold (FAT) laser models, obtained by replacing the ordinary bosonic lowering operator $\hat{a}$ by a general lowering operator $\hat{L}$ in the superoperators appearing in the master equation that governs the FAT laser dynamics. We then show that an optical-frequency superradiant laser in the bad-cavity limit, with feedback-controlled collective pumping, realizes one such model, in which $\hat{L}$ is identified with the collective superradiant lowering operator $\hat{J}$. This model can surpass the SQL scaling, with the coherence exhibiting a scaling as large as $\mathfrak{C}= \Theta(\mu^{8/3})$ in the optimal parameter regime. Here, in the bad-cavity limit, $\mu\approx N/2$, where $N$ is the number of superradiant atoms.

36 pages, 16 figures. Submitted to Physical Review X

Quantum Physics (quant-ph); Atomic Physics (physics.atom-ph); Optics (physics.optics)

arXiv:2611.05976 [quant-ph]

(or arXiv:2611.05976v1 [quant-ph] for this version)

https://doi.org/10.48550/arXiv.2611.05976 Focus to learn more arXiv-issued DOI via DataCite (pending registration)

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Collectively pumped superradiant laser with coherence scaling beyond the standard quantum limit

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