Atomic Self-Trapping Induced by Single-Atom Lasing

We study atomic center of mass motion and field dynamics of a single-atom laser consisting of a single incoherently pumped free atom moving in an optical high-$Q$ resonator. For sufficient pumping, the system starts lasing whenever the atom is close to a field antinode. If the field mode eigenfrequency is larger than the atomic transition frequency, the generated laser light attracts the atom to the field antinode and cools its motion. Using quantum Monte Carlo wave function simulations, we investigate this coupled atom-field dynamics including photon recoil and cavity decay. In the regime of strong coupling, the generated field shows strong nonclassical features such as photon antibunching, and the atom is spatially confined and cooled to sub-Doppler temperatures.

Figure 1

Average photon number $\overline{n}$ (solid line), scaled uncertainty ${\Delta }_n/\overline{n}$ (dashed), and upper state population (dash-dotted) as a function of $g/\kappa$ for the atom kept at fixed position. The parameters are $(\gamma ,\delta ,\Delta )=(5,37.5,250)\kappa$. The little insets show the emitted light spectrum for $g=(5,25,45)\kappa$.

Figure 2

Average photon number $\overline{n}$ and Mandel $Q$ parameter for the lasing startup phase including atomic motion. The parameters are $(\gamma ,\delta ,g)=(5,40,50)\kappa$ where the cavity field is detuned from the atomic transition by $\Delta =250\kappa$.

Figure 3

Mean square velocity in units of the Doppler temperature $T_D$ for $\Delta =250\kappa$. The other parameters are $(\gamma ,\delta ,g)=(5,40,50)\kappa$; $T_D$ is indicated by the dashed line. For negative detuning the atom gets heated up; see inset where $\Delta =-250\kappa$.

Figure 4

Position distribution of an atom trapped at an antinode for the parameters of Fig. 3 (solid line) and for a increased pumping rate $\delta =60\kappa$ (dashed).

Figure 5

(a) Photon number expectation value for a single trajectory of a trapped atom within ten cavity relaxation times for $(\gamma ,\delta ,g)=(10,60,50)\kappa$. The dashed line indicates the mean photon number. (b) Corresponding single-trajectory $q$ factor.

Figure 6

Mean photon number and Mandel parameter vs pumping strength $\delta /\kappa$.