Single atom lases orderly light

Faye Flam

Luis S. Froufe‐Pérez, William Guerin, Rémi Carminati +1 more

We address the problem of achieving an optical random laser with a cloud of cold atoms, in which gain and scattering are provided by the same atoms. The lasing threshold can be defined using the on-resonance optical thickness b0 as a single critical parameter. We predict the threshold quantitatively, as well as power and frequency of the emitted light, using two different light transport models and the atomic polarizability of a strongly pumped two-level atom. We find a critical b0 on the order of 300, which is within reach of state-of-the-art cold-atom experiments. Interestingly, we find that random lasing can already occur in a regime of relatively low scattering.

Motoaki Bamba, Tetsuo Ogawa

In ultrastrong light-matter coupling regime, it is found theoretically that lasing accompanies odd-order harmonics of radiation field both inside and outside the cavity and even-order harmonics of atomic population. This qualitative difference from the normal laser is generally obtained independent of whether we choose the Coulomb gauge or the electric-dipole one, although quantitative behaviors strongly depend on the gauge choice due to the two-level and single-mode approximations used in our calculation. The lasing also shows a bistability for strong enough light-matter coupling and low enough cavity loss.

Antony Hewish

Andreas Osterwalder

Sheng-Wen Li, Moochan B. Kim, G. S. Agarwal +1 more

We study the statistics of the lasing output from a single atom quantum heat engine, which was originally proposed by Scovil and Schulz-DuBios (SSDB). In this heat engine model, a single three-level atom is strongly coupled with an optical cavity, and contacted with a hot and a cold heat bath together. We derive a fully quantum laser equation for this heat engine model, and obtain the photon number distribution for both below and above the lasing threshold. With the increase of the hot bath temperature, the population is inverted and lasing light comes out. However, we notice that if the hot bath temperature keeps increasing, the atomic decay rate is also enhanced, which weakens the lasing gain. As a result, another critical point appears at a very high temperature of the hot bath, after which the output light become thermal radiation again. To avoid this double-threshold behavior, we introduce a four-level heat engine model, where the atomic decay rate does not depend on the hot bath temperature. In this case, the lasing threshold is much easier to achieve, and the double-threshold behavior disappears.