Observation of Rydberg Blockade Induced by a Single Ion

We study the long-range interaction of a single ion with a highly excited ultracold Rydberg atom and report on the direct observation of an ion-induced Rydberg excitation blockade mediated over tens of micrometer distances. Our hybrid ion-atom system is directly produced from an ultracold atomic ensemble via near-threshold photoionization of a single Rydberg excitation, employing a two-photon scheme that is specifically suited for generating a very low-energy ion. The ion’s motion is precisely controlled by small electric fields, which allows us to analyze the blockade mechanism for a range of principal quantum numbers. Finally, we explore the capability of the ion as a high-sensitivity, single-atom-based electric field sensor. The observed ion-Rydberg-atom interaction is of current interest for entanglement generation or studies of ultracold chemistry in hybrid ion-atom systems.

Figure 1

Concept for observing ion-induced Rydberg blockade. (a, top) Single Rydberg atom excitation is probed in the presence of an ion at distance $R$, determined by the ion’s trajectory in an external electric field $E$ after time of flight $t_{\mathrm{tof}}$. Focused lasers provide spatial control of ion and Rydberg atom production. (a, bottom) Pair-interaction potential $V(R)$ between ion and Rydberg atom for $n=71$ (dotted line) and $n=100$ (solid line) as a function of $R$. The shaded red curve indicates the Rydberg excitation bandwidth $\mathrm{\Gamma }$. (b) Rydberg excitation and photoionization scheme. (c) Mean number of detected Rydberg atoms $N_{\mathrm{R}}$ as a function of the ion’s time of flight $t_{\mathrm{tof}}$ in the external stray electric field. Error bars indicate one standard deviation obtained from averaging over 19 realizations. (d) Experimental sequence consisting of first Rydberg excitation (RE I), ion production via photoionization (PI), second Rydberg excitation (RE II), two-step electric field pulse (EF) for selective ion and Rydberg atom detection, and temporarily separated detection events on the MCP.

Figure 2

Ion-induced Rydberg blockade for different principal quantum numbers. Mean number of detected Rydberg atoms $N_{\mathrm{R}}$, normalized to the value obtained in the absence of the ion, as a function of the applied electric field $E_x$ for $n=51$ (diamonds), $n=71$ (squares), $n=90$ (triangles), and $n=100$ (circles). The ion’s time of flight in the presence of $E_x$ is set to $t_{\mathrm{tof}}=7\mu \mathrm{s}$ for all data sets. Solid lines are error-function fits to the data to extract the blockade radius (see text for details). Error bars indicate one standard deviation obtained from averaging over typically 20 realizations.

Figure 3

Blockade radius for different principal quantum numbers. Symbols show the measured blockade radius $R_{\mathrm{b}}$ extracted from the data in Fig. 2 as a function of $n$. Error bars include the effects of residual stray fields and finite pulse length for photoionization and Rydberg excitation. The solid line shows the prediction according to Eq. (2). The dash-dotted line is the result of an extended theoretical description taking into account the effect of the applied electric field $E_x$ during the measurement. The inset shows the bare (solid line) and the modified (dash-dotted line) $V(R)$ in the presence of the field $E^{\star }$ for $n=100$. Dotted lines indicate the shift of $R_{\mathrm{b}}$ for the experimental value of $\mathrm{\Gamma }=1.09(1)\mathrm{MHz}$.

Figure 4

A single ion as an electric field probe. (top row) Mean number of detected Rydberg atoms $N_{\mathrm{R}}$ as a function of applied electric field $E_i$ in all spatial directions $i=\{x,y,z\}$ for $n=100$. Here, the ion’s time of flight $t_{\mathrm{tof}}=34\mu \mathrm{s}$. Solid lines are Gaussian fits to the data to extract the center of the ion-induced blockade feature, which is identified with zero field strength for the respective spatial component. Error bars show one standard deviation obtained from averaging over typically four realizations. (bottom row) Temporal drift $\mathrm{\Delta }{E}_i$ of the three electric field components. Symbols denote the change of the fitted centers obtained from scans as shown in the top row. Error bars indicate the $1\sigma$ confidence bound for the fit result.