Realization of a cavity-coupled Rydberg array

TL;DR

The work addresses the challenge of coupling scalable neutral-atom arrays to both optical cavities and Rydberg excitations to enable distributed quantum processing. The authors realize a cavity-coupled Rydberg array by integrating a 49-site optical tweezer array with a near-concentric high-finesse cavity and a two-photon Rydberg excitation scheme, achieving strong atom–photon coupling evidenced by dispersive cavity shifts and collective Rydberg interactions. They demonstrate a near-unity cooperativity after accounting for mode-profile effects, observe blockade-enabled collective Rabi oscillations with Ω_N = Ω√N for ensembles inside the blockade radius, and show robust Rydberg control with electric-field shielding that minimizes perturbations from the cavity environment. This platform opens routes to quantum network nodes, cavity-assisted non-destructive readout, photonic-state engineering, and hybrid quantum simulators, with planned improvements aimed at further boosting cooperativity and gate fidelity.

Abstract

Scalable quantum computers and quantum networks require the combination of quantum processing nodes with efficient light-matter interfaces to distribute quantum information in local or long-distance quantum networks. Neutral-atom arrays have both been coupled to Rydberg states to enable high-fidelity quantum gates in universal processing architectures, and to optical cavities to realize interfaces to photons. However, combining these two capabilities and coupling atom arrays to highly excited Rydberg states in the mode of an optical cavity has been an outstanding challenge. Here we present a novel cavity-coupled Rydberg array that achieves this long-standing goal. We prepare, detect, and control individual atoms in a scalable optical tweezer array, couple them strongly to the optical mode of a high-finesse optical cavity and excite them in a controlled way to Rydberg states. We show that strong coupling to an optical cavity - demonstrated via the dispersive shift of the resonance of the cavity in presence of the atoms - and strong Rydberg interactions - demonstrated via the collective enhancement of Rydberg coupling in the atomic array - can be achieved in our setup at the same spatial location. Our presented experimental platform opens the path to several new directions, including the realization of quantum network nodes, quantum simulation of long-range interacting, open quantum systems and photonic-state engineering leveraging high-fidelity Rydberg control.

Figures (4)

• Figure 1: Experimental setup and array generation.a Close-up of the optical cavity including the electric-field shielding platform, and atomic array. The counter-propagating dark red (blue) beams along the $x$-axis represent the 1015nm (420nm) components of the Rydberg excitation. The light red arrow represents the polarizer beam pumping to the state $\ket{F=2, m_F=-2}$. The orange arrow represents the Raman beam. The light red shading between the mirrors denotes the cavity mode (not to scale). b Array of Rydberg-blockaded ensembles of $2\times2$ tweezers inside the cavity mode volume (red, not to scale), stochastically loaded with $^{87}\mathrm{Rb}$ atoms. The magnetic quantization field is aligned with the $x$-axis. The Rydberg blockade disk is indicated in blue. The single-atom coupling to cavity mode $g$, the cavity decay rate $\kappa$, and the free-space atomic decay rate $\Gamma$ are indicated. c Level diagram for two atoms, including the Raman, Rydberg, and cavity-coupling transitions. $\ket{g^\prime} = \ket{5\mathrm{S}_{1/2}, F=2, m_F = -2}, \ket{g} = \ket{5\mathrm{S}_{1/2}, F=1, m_F = -1}, \ket{e} = \ket{5\mathrm{P}_{3/2}, F=3}, \ket{i} = \ket{6\mathrm{P}_{3/2}, F=3}, \ket{r} = \ket{53\mathrm{S}_{1/2}}$. For a distance $R<R_b$, the Rydberg interaction energy shift $V$ leads to Rydberg blockade. d Loading individual atoms in the optical traps, we perform high-fidelity ($99.988(3)\%$) and high-survival ($99.88(2)\%$) imaging with bimodal count histograms. Measurement of the loss dynamics of tweezer-trapped atoms yields a lifetime of 322(3)s. e Starting from atoms optically pumped to the state $\ket{F=2, m_F = -2}$ using circularly polarized light, we demonstrate high-fidelity manipulations of the internal states of $^{87}\mathrm{Rb}$ via a Raman beam detuned from the D1 line.
• Figure 2: Cavity geometry and atom-cavity interaction.a Relevant levels to probe the cavity spectrum. The probe beam, resonant with the cavity, is detuned from the $D_2$-cycling transition by $\Delta_{ca}$ and the probe is varied around that point by $\Delta_{pc}$. b Scanning the cavity resonance in the absence of atoms with the probe, we obtain a spectrum of the cavity modes. Instead of the expected single Lorentzian peak, we find a family of several lines split by approximately 3MHz, which we attribute to mode hybridization as described in the main text. c Dispersive shift of the cavity resonance measured in the presence of atoms in the cavity (orange) compared with the empty cavity resonance (grey). The solid lines are the results of fitting a sum of Lorentzian peaks to the cavity transmission signal, taking into account the two dominant neighboring peaks (see right inset for a zoom out). The dashed line represents a single Lorentzian peak extracted from the fitted sum and used for estimating the cavity cooperativity. Orange (grey) ticks indicate the position of the cavity resonance with (without) atoms. The left inset shows the spatial structure of the mode as measured via the pushing effect on a $7\times7$ tweezer array at $\Delta_{ca} = \Delta_{pc}=0$.
• Figure 3: Electric field shielding.a Rydberg excitation scheme. We couple the Rydberg state $53\mathrm{S}_{1/2}$ starting from the ground state $5\mathrm{S}_{1/2}$ via the intermediate state $6\mathrm{P}_{3/2}$ with an intermediate-state detuning of $\Delta = 2\pi\times 2GHz$ via lasers at 420nm and 1015nm. b Measuring the Rydberg resonance as a function of the applied voltage to the piezos, we find only a weak shift that agrees well with our ab-initio modeling of the cavity assembly including the electric field shield (solid line). The inset shows the resonance scan at each piezo voltage from which we extract the shift. c Comparison of the electric field at the position of the atoms in a configuration where the mirrors sit on exposed piezos (light green) with our configuration where they are buried in a titanium platform (dark green). Top: Case where only one piezo is driven to 100V. Bottom: Symmetric case where both piezos are driven. The weak dependence observed in b is hence a direct consequence of our shielding of the piezo. We find that a suppression of the electric field by more than one order of magnitude is achieved, which corresponds to close to three orders of magnitude suppression of the resonance shifts (right axis).
• Figure 4: Collective Rydberg coupling.a Preparing a tweezer array with groups of four tweezers within a Rydberg blockade radius $R_b=4.8µm$, indicated by the radius of the circle in the inset in b, we measure the probability of finding maximally one excitation in the system after suddenly turning on the Rydberg coupling light (blue points). When postselecting on the initially prepared number of atoms, $N$, we find that the Rabi frequency increases with atom number, as extracted from a cosinusoidal fit of the form $A(1-e^{-(t-t_0)/\tilde{\tau}}\cos(\tilde{\Omega}(t-t_0) + \phi))$. b We find quantitative agreement with the expected dependence of the extracted Rabi frequency (blue points) with a prediction based on scaling the extracted Rabi frequency $\Omega$ for $N=1$ with the square-root of the number of atoms within a blockade radius, $\Omega_N = \Omega\sqrt{N}$ (solid line). The left panel in the inset shows the Rabi oscillations in the presence of a full-amplitude piezo scan (cyan datapoints), together with a fit (solid line). The right panel shows the extracted "quality factor" $\Omega_N\tau$ without (with) scanning the piezos in blue (cyan). We find no difference between the two cases within errorbar.