Production and trapping of cold circular Rydberg atoms

Cold circular Rydberg atoms are produced and magnetically trapped. The trap is characterized by direct spatial imaging of ion distributions, ion counting, and state-selective field ionization. At room temperature, we observe about 70% of the trapped atoms remaining after 6 ms. We measure a trap oscillation frequency increase of the circular Rydberg atom trap relative to the ground-state atom trap due to the larger magnetic moment of the circular Rydberg atoms. Simulations of the center-of-mass and internal-state evolution of circular states in our magnetic trap are performed and results are in good agreement with experimental observations.

Figure 1

Left: schematic of the experiment (to scale). Six gold-coated, copper electrodes enclose a magnetically trapped atom sample to control the electric fields at the excitation location. An MCP is used for ion detection. The location of the Z wire and the counterpropagating 480 and 780 nm beams for excitation to Rydberg states are also shown. Right: plot of the magnetic field strength in the $xy$ plane through the center of the trap. The linear gray scale ranges from $\left|B\right|=5.5$ G (white) to 9.5 G (black) in steps of 0.5 G. The hatched region indicates $\left|B\right|\ge 10$ G.

Figure 2

(a) Experimental Stark spectrum showing the intersection of $60P$ with the $n=57$ hydrogenic manifold. Plotted are average counts per excitation pulse [linear scale ranging from 0 (white) to $>3.5$ (black)] as a function of applied electric field and frequency offset of the 480 nm laser from an arbitrary reference frequency. Each data point is an average of 50 excitation pulses. The electric-field axis is scaled by a factor of 0.98 to match the calculation in (b). (b) Energy levels (solid lines) and excitation rates per atom calculated for our laser polarizations and intensities (overlay; linear gray scale from 0 to 150 s${}^{-1}$). In the excitation-rate calculation we assume Gaussian distributions for the excitation frequency and electric field, with FWHM of 5 MHz and 50 mV/cm, respectively. Minor deviations in frequency between (a) and (b) are attributed to long-term excitation-laser drifts.

Figure 3

(a) Experimental COM displacement in $\mathbf{y}$ vs $t_d$ (circles) in the MCP plane (left axis) with a fit to a sinusoid out to 4 ms (solid curve). The RMS spread of the data about the fit is 0.05 mm, indicated by the representative error bar. The simulated COM displacement in $\mathbf{y}$ vs $t_d$ in the object plane (right axis) is shown out to 10 ms (dashed curve). A linear offset is subtracted to match the experimental data, accounting for ion-imaging abberations. (b) Experimental COM displacement in $\mathbf{x}$ vs $t_d$. (c) Fraction of detected atoms remaining vs $t_d$. Based on the variance of the data points, we estimate an uncertainty shown by the representative error bar.

Figure 4

SSFI traces for an initial excitation into two different regions in Fig. 2: (a) into III, the $60P_{1/2}$ state and (b) into I, the first anticrossing at the $60P$-manifold intersection to generate the CS after the circularization procedure. In both (a) and (b) the thin and thick traces correspond to $t_d=0$ and 1 ms, respectively. Each trace is a sum of 20 000 experiments. The data are normalized such that for $t_d=0$ ms the curves integrate to the same value. The dashed curve in (a) shows the field-ionization ramp used in both experiments.