Coherent control of Rydberg atoms near dielectric surfaces is a major challenge due to the large sensitivity of Rydberg states to electric fields. We demonstrate coherent single-atom operations and two-qubit entanglement as close as 100 μm from a nanophotonic device. Using the individual atom control enabled by optical tweezers to study the spatial and temporal properties of the electric field from the surface, we employ dynamical decoupling techniques to characterize and cancel the electric-field noise with submicrosecond temporal resolution. We further use entanglement-assisted sensing to accurately map magnitude and direction of electric-field gradients on a micrometer scale. Our observations open a path for integration of Rydberg arrays with micro- and nanoscale devices for applications in quantum networking and quantum information science.
Coherent control of Rydberg atoms near dielectric surfaces is a major challenge due to the large sensitivity of Rydberg states to electric fields. We demonstrate coherent single-atom operations and two-qubit entanglement as close as 100 μm from a nanophotonic device. Using the individual atom control enabled by optical tweezers to study the spatial and temporal properties of the electric field from the surface, we employ dynamical decoupling techniques to characterize and cancel the electric-field noise with submicrosecond temporal resolution. We further use entanglement-assisted sensing to accurately map magnitude and direction of electric-field gradients on a micrometer scale. Our observations open a path for integration of Rydberg arrays with micro- and nanoscale devices for applications in quantum networking and quantum information science.
Platforms consisting of neutral atoms individually trapped in arrays of optical tweezers have achieved important milestones in quantum simulation and quantum computation. With access to programmable Rydberg interactions, individual qubit control, long coherence times, and naturally identical qubit transitions, neutral atoms are a promising building-block for the use in future quantum machines. However, they face the same challenge as other quantum platforms in scaling the number of qubits needed to perform algorithms with a provable advantage over classical computers. An avenue toward scaling systems of neutral atoms may be to use a quantum network that connects individual systems to construct a distributed computing architecture. Key to this approach is for the atoms to have access to an efficient optical interface, where the quantum information can be mapped to a single photon and sent across a quantum network. This thesis explores using a nanophotonic crystal cavity to act as this interface. With our device, we have demonstrated high-cooperativity coupling of two atoms to the photonic mode, generated entanglement at the device using a projective measurement, and coherently transported an entangled pair of atoms away from the device. Furthermore, we have taken the first steps toward integrating this device with Rydberg-excited atoms. We have found that the nanoscale dielectric device creates a point-charge electric field that minimally perturbs ground-Rydberg qubit coherence at distances greater than 200 microns. Using the Rydberg blockade effect, we have created an entangled pair of atoms to perform entanglement-assisted sensing of the electric field to better understand its control. Overall, these experiments show how this nanophotonic device is a promising candidate to use as an optical interface for a Rydberg atom-based quantum computing node.
Realizing an efficient quantum optical interface for multi-qubit systems would enable their quantum network integration and the scaling-up of the qubit number via distributed quantum computing. This thesis presents the building blocks for integrating a quantum processor based on a Rydberg atom array with a nanophotonic cavity as an optical interface. In our approach, the integration would be achieved by coherently transporting tweezer-trapped atoms between the cavity near-field and free space. To that end, we first characterize the strong coupling between single photons and atoms enabled by the nanophotonic device. Two 87Rb atoms are trapped in optical tweezers and brought to the cavity near-field, while the cavity is probed in reflection. We observe Purcell enhancement and cavity-mediated interactions between the atoms, corresponding to a single atom cooperativity of C = 70 in the mode center. The qubits are encoded in atomic hyperfine ground states, which have good coherence properties even when the atoms are trapped in the cavity near-field. We create an atomic Bell state by pairing up the coherent manipulation of atomic qubits with a quantum nondemolition measurement, implemented via a single photon reflection from the cavity. Crucial to the integration, we show that single atom coherence and two-atom entanglement can be preserved as the atoms are moved away from the cavity. The nanophotonic dielectric surface can host charges which affect highly polarizable Rydberg states, and this influence is studied by measuring the n = 70 Rydberg state coherence at different distances from the cavity. Our measurements suggest that a Rydberg array may be placed ∼ 200 μm away from a nanophotonic device while retaining high quantum gate fidelities. Our methods can be applied to other atomic species and device geometries, paving the path to quantum networks of Rydberg array processors.
Integrating Rydberg-state control of atom-atom interactions with cavity control of atom-light interactions enables the combination of local entangling operations with photon-mediated long-range coupling, measurement, and communication. Such integration is challenging because electric fields generated by charges on cavity optics and by cavity-stabilizing actuators may disturb Rydberg-state coherence. Here, we couple a Rydberg tweezer array to a high-cooperativity optical cavity, suppressing the electric fields produced by cavity length actuation so that the residual field variation of about 3mV/cm rms does not limit Rydberg coherence. We demonstrate two capabilities that neither system provides alone. First, we use Purcell-enhanced fluorescence to read out atoms directly in the ground-Rydberg basis within 7.5μs, well within the Rydberg-state lifetime, with ground- and Rydberg-state detection infidelities of 3% and 5%, respectively, and with low atom loss. Second, we use Rydberg-Rydberg interactions to control collective light-atom scattering into the cavity mode. Specifically, we drive blockaded Rabi oscillations between a state with two ground-state atoms, which scatter collectively with a superradiant or subradiant rate controlled by the atomic positions, and an entangled state with a single Rydberg excitation, which scatters like a single atom. These capabilities open routes toward networked Rydberg processors, mid-circuit measurements in analog quantum simulators, and many-body quantum optics with entangled emitters coupled collectively to light.
Rydberg atoms as versatile tools for quantum applications are extremely sensitive to electric fields. When utilizing these atoms, it becomes imperative to comprehensively characterize and mitigate ambient electric field noise. Using single Rydberg atoms in optical tweezer arrays, we reveal that the dominant ambient electric field noise originates from electrons bound to the vacuum cell surface. These electrons are found to be generated by the 297-nm light used for single-photon Rydberg excitation. Once the electrons are effectively desorbed from the surface through exposure to ultraviolet or red light, the coherence of the ground-Rydberg transition is enhanced significantly. Furthermore, we demonstrate collective oscillations of four atoms in the full Rydberg blockade regime. Our investigations will advance the control and reliability of Rydberg-atom-based systems for various quantum technologies.
Microwave (MW) field sensing is foundational to modern technology, yet its evolution, reliant on classical antennas, is constrained by fundamental physical limits on field, temporal, and spatial resolutions. Here, we demonstrate an MW electrometry that simultaneously surpasses these constraints by using individual Rydberg atoms in an optical tweezer array as coherent sensors. This approach achieves a field sensitivity within 13% of the standard quantum limit, a response time that exceeds the Chu limit by more than 11 orders of magnitude, and in-situ near-field mapping with λ/3000 spatial resolution. This work establishes Rydberg-atom arrays as a powerful platform that unites quantum-limited sensitivity, nanosecond-scale response time, and sub-micrometer resolution, opening new avenues in quantum metrology and precision electromagnetic field imaging.
Generating entanglement between two Rydberg atoms is at the core of neutral-atom quantum computers. Current two-qubit gates operate in the Rydberg-blockade regime, in which the full strength of the van der Waals interaction between the two Rydberg atoms is not directly exploited, to avoid sensitivity to the position noise of the tweezer-trapped atoms, at the cost of a longer time spent in the Rydberg state. Here, we propose a set of techniques based on coherent control of the atomic motion obtained by combining optical tweezers and a two-dimensional optical lattice, and a sequence of multiple on/off pulses. The protocols keep the two-qubit gate error contribution from position noise below 10−4, heat the atom by less than~Δn=0.01, while being robust to alignment errors of the potential up to 50~nm and thermal excitation up to nˉ=3. This toolbox opens the path for new two-qubit Rydberg gates directly, or partially, driven by the interaction, in which the atoms spend only ∼10~ns in the Rydberg state, minimizing the increasingly dominant error source originating from its finite lifetime.