Observation of Rydberg Blockade Due to the Charge-Dipole Interaction between an Atom and a Polar Molecule

We demonstrate Rydberg blockade due to the charge-dipole interaction between a single Rb atom and a single RbCs molecule confined in optical tweezers. The molecule is formed by magnetoassociation of a $\mathrm{Rb}+\mathrm{Cs}$ atom pair and subsequently transferred to the rovibrational ground state with an efficiency of 91(1)%. Species-specific tweezers are used to control the separation between the atom and molecule. The charge-dipole interaction causes blockade of the transition to the Rb(52s) Rydberg state, when the atom-molecule separation is set to 310(40) nm. The observed excitation dynamics are in good agreement with simulations using calculated interaction potentials. Our results open up the prospect of a hybrid platform where quantum information is transferred between individually trapped molecules using Rydberg atoms.

Figure 1

(a) Pair state energy shift as a function of the separation $R_{\mathrm{am}}$ between a Rb atom in state $|r⟩=|52\mathrm{s}⟩$ and a RbCs molecule in state $|G⟩=|{\mathrm{X}}^1{\mathrm{\Sigma }}^{+},v=0,N=0⟩$. The shaded region (shown inset) highlights the region relevant to the blockade measurements; the dashed line shows our best estimate of $R_{\mathrm{am}}$ and the range reflects the associated uncertainty. (b) A surface plot of the radial electron density of the Rydberg electron for $R_{\mathrm{am}}=230\mathrm{nm}$. (c) Schematic of the experiment showing the atom and molecule trapped in species-specific optical tweezers separated along the $y$ axis.

Figure 2

Formation of ground state RbCs molecules in optical tweezers. (a) Electronic potential curves for RbCs showing the pump and Stokes transitions that couple states $|F⟩$, $|E⟩$, and $|G⟩$. (b) Formation of weakly bound molecules by magnetoassociation of atom pairs using a Feshbach resonance at 197 G. The top panel shows the magnetic field ramps used to form molecules and then navigate the near-threshold bound states shown in the middle panel. STIRAP is performed at 181.6 G when the molecule occupies the state $|F⟩$ (indicated point). The lower panel shows the pump-induced loss of weakly bound molecules. The atom-pair survival probability $P_{11}$ is measured after reversing the field ramp to dissociate any remaining molecules. (c) Atom-pair survival probability for a round trip $|F⟩\to |G⟩\to |F⟩$ as a function of the one-photon detuning ${\mathrm{\Delta }}_{1\mathrm{p}}$ of either the pump (from the transition $|F⟩\to |E⟩$) or the Stokes (from the transition $|E⟩\to |G⟩$) when the other laser is on resonance. (d) Repeated STIRAP transfers between states $|F⟩$ and $|G⟩$ with a one-way efficiency of 91(1)%. The dashed lines show the experimental contrast; the shaded regions are the uncertainties. The inset shows the pulse profiles for a round-trip transfer.

Figure 3

Collisions between ground state RbCs molecules and Rb atoms held in separate species-specific optical tweezers. Particle survival probabilities are plotted as a function of the tweezer separation, $R_t$. For the molecule we report the atom-pair survival probability, post-selected on cases where a weakly bound molecule was formed [55]. Upper panel: experimental runs where either a single Rb atom (blue squares) or a single RbCs molecule (red circles) is present. Lower panel: runs where both the atom and the molecule are present. The dashed lines (and shaded regions) correspond to the mean values (and errors) from the one-body cases. The purple dotted line at $R_t=420\mathrm{nm}$ shows the tweezer separation for the measurement in Fig. 4. Insets: The potential energy of the atom (blue) and molecule (red) resulting from their own tweezer (dashed lines) and both tweezers (solid lines) for $R_t=2000$ (left) and $R_t=420\mathrm{nm}$ (right).

Figure 4

(a) Survival probability of the Rb atom as a function of the Rydberg pulse duration for $R_{\mathrm{am}}=310(40)\mathrm{nm}$. Atoms excited to $|r⟩$ are ejected from the trap and lost. Events are postselected on the detection of a molecule in $|G⟩$ (purple squares) or unsuccessful formation of a molecule (green circles). The solid lines show the results of simulations using the Lindblad master equation [55] using our estimated atom-molecule separation. (b) Rb atom survival probability as a function of the two-photon detuning, $\mathrm{\Delta }$, using a $1\mathrm{\mu }\mathrm{s}$ pulse for $R_{\mathrm{am}}=700(40)$ (upper panel) and $R_{\mathrm{am}}=310(40)\mathrm{nm}$ (lower panel). The detuning is defined relative to the transition center in the absence of a molecule. Symbols are as in (a) and solid lines show the results of simulations using the estimated atom-molecule separations.