Exploiting the composite character of Rydberg atoms for cold-atom trapping

By investigating the quantum properties of magnetically trapped $n{S}_{1/2}$ Rydberg atoms, it is demonstrated that the composite nature of Rydberg atoms significantly alters their trapping properties opposed to pointlike particles with the same magnetic moment. We show how the specific signatures of the Rydberg trapping potential can be probed by means of ground-state atoms that are off-resonantly coupled to the Rydberg state via a two photon laser transition. In addition, it is demonstrated how this approach provides an alternative possibility of generating traps for ground-state atoms. Simulated time-of-flight pictures mirroring the experimental situation are provided.

Figure 1

(Color online) (a) Contour plot of the $40S_{1/2},m_j=1/2$ Rydberg surface for $B=1\text{G}$ and $G=10{\text{Tm}}^{-1}$. The loss of the azimuthal symmetry introduced by the composite nature of the Rydberg atom as given by Eq. (4) is evident. The depth of the minimum along the diagonals corresponds to $\sim 18\hslash \omega$, $\omega =2\pi \times 1.3\text{kHz}$ being the trap frequency of the harmonic confinement at the origin. (b) Idealized level scheme for an off-resonant two photon coupling of the ground and Rydberg state of ${}^{87}\text{R}\text{b}$. In a IP trap, additional atomic levels and polarizations contribute away from the trap center; see text.

Figure 2

(Color online) (a) Contour plot of the dressed ground-state surface $E_{-}$ for $n=40$, $B=10\text{G}$, and $G=5{\text{Tm}}^{-1}$. (c) Section along $X=Y$ of the same energy surface. The deviation from the harmonic confinement of nondressed ground-state atoms (dashed line) due to the composite nature of the Rydberg atom is evident. The energy scale is given in terms of the trap frequency $\omega =2\pi \times 200\text{Hz}$. (b) and (d) The same as on the left panel but for $B=1\text{G}$, $G=5{\text{Tm}}^{-1}$. In this high gradient regime the Rabi frequency and therefore the light shift $V_s$ exhibit a strong spatial dependence resulting in the maximum at the trap center; for the dashed line the contribution $E_{\kappa }^{\left(2\right)}\left(\mathbf{R}\right)$ of the composite character is omitted. Without dressing, a ground-state atom would experience a trap frequency of $\omega =2\pi \times 638\text{Hz}$. For values of the Rabi frequencies and detunings see text.

Figure 3

Temporal evolution of the probability density of a dressed ground-state atom in position (upper row) and momentum (lower row) space, respectively. The momentum distribution simulates TOF expansion measurements. Being initially in the lowest nondressed c.m. eigenstate with a trap frequency of $\omega =2\pi \times 638\text{Hz}$, the atom subsequently evolves in the potential given in Fig. 2b. The time scale of 5 ms corresponds to the first oscillation of the c.m. wave packet. The loss of the azimuthal symmetry due to the composite character of Rydberg atoms is evident once the wave function has probed the outer parts of the potential surface $\left(t>2.75\text{ms}\right)$.