arXiv subjects

Martin Fasser

Publications and source records attributed to Martin Fasser.

3 recordsLinked to original sources

arXiv2026

Continuous Narrow-Linewidth Superradiance in Waveguide QED

Superradiant lasers promise continuous, narrow-linewidth coherent emission at the bare atomic transition frequency, enabling frequency references of exceptional precision. Recent experiments have advanced the field, but achieving truly continuous operation remains technically challenging. Here we propose an alternative route to an active optical frequency reference with fewer emitters using all-to-all dipole-dipole interactions mediated by a nanophotonic waveguide. We show that selectively pumping only a sub-ensemble of emitters, rather than the full ensemble, substantially improves emission characteristics. The collective interactions with unpumped emitters provide narrowband frequency selection and establish an effective feedback mechanism analogous to the role of a macroscopic cavity. We find directional superradiant emission with strongly phase-synchronized emitter correlations and a narrow output spectrum close to the bare emitter resonance. Our results demonstrate a strong metrological gain from selective partial pumping of quantum emitters with the second-order intensity correlation $g^{(2)}(0)\simeq 1$, indicating reduced equal-time intensity fluctuations, and open a route to waveguide-based optical frequency references using small clock-atom ensembles for chip-scale precision metrology.

quant-ph↗

arXiv2024

Subradiance and Superradiant Long Range Excitation Transport among Quantum Emitter Ensembles in a Waveguide

In contrast to free space, in waveguides the dispersive and dissipative dipole-dipole interactions among quantum emitters exhibit a periodic behavior over remarkably long distances. We propose a novel setup exploiting this long-range periodicity in order to create highly excited subradiant states and facilitate fast controlled collective energy transport amongst far-apart ensembles coupled to a waveguide. For sufficiently large ensembles collective superradiant emission into the fiber modes dominates over its free space counterpart. We show that for a large number of emitters a fast transverse coherent pulse can create almost perfect subradiant states with up to $50\%$ excitation. On the other hand, for a coherent excitation of one sub-ensemble above an overall excitation fraction of $50\%$ we find a nearly lossless and fast energy transfer to the ground state sub-ensemble. This transport can be enhanced or suppressed by controlling the positions of the ensembles relative to each other, while it can also be realized with a random position distribution. In the optimally enhanced case this fast transfer appears as superradiant emission with subsequent superabsorption, yet, without a superradiant decay after the absorption. The highly excited subradiant states as well as the superradiant excitation transfer appear as suitable building blocks in applications like active atomic clocks, quantum batteries, quantum information protocols and quantum metrology procedures such as fiber-based Ramsey schemes.

quant-ph↗

arXiv2023

Threshold studies for a hot beam superradiant laser including an atomic guiding potential

Recent theoretical predictions hint at an implementation of a superradiant laser based on narrow optical clock transitions by using a filtered thermal beam at high density. Corresponding numerical studies give encouraging results but the required very high densities are sensitive to beam collimation errors and inhomogeneous shifts. Here we present extensive numerical studies of threshold conditions and the predicted output power of such a superradiant laser involving realistic particle numbers and velocities along the cavity axis. Detailed studies target the threshold scaling as a function of temperature as well as the influence of eliminating the hottest part of the atomic distribution via velocity filtering and the benefits of additional atomic beam guiding. Using a cumulant expansion approach allows us to quantify the significance of atom-atom and atom-field correlations in such configurations. We predict necessary conditions to achieve a certain threshold photon number depending on the atomic temperature and density. In particular, we show that the temperature threshold can be significantly increased by using more atoms. Interestingly, a velocity filter removing very fast atoms has only almost negligible influence despite their phase perturbing properties. On the positive side an additional conservative optical guiding towards cavity mode antinodes leads to significantly lower threshold and higher average photon number. Interestingly we see that higher order atom-field and direct atom-atom quantum correlations play only a minor role in the laser dynamics, which is a bit surprising in the superradiant regime.

physics.atom-ph↗