Quantum Networking and Quantum Computing with Atomic Tweezer Arrays in Cavities
Realizing fast high-fidelity quantum network channels is an important frontier in quantum information science with applications in distributed quantum computing and sensing, secure quantum communication, etc. The main limitations to current implementations of quantum networks are the low rates and fidelities of distributing entanglement between distant nodes. Our research will approach this challenge using the atomic tweezer array platform combined with micro-scale high-finesse optical cavities.
Neutral atom arrays have unique capabilities, placing them at the forefront of quantum processing platforms. Individual atoms trapped in optical tweezers have long coherence time (~ several seconds) and are projected to be able to scale to more than 10,000 physics qubits in the near future. More importantly, the ability to dynamically rearrange the atomic arrays and change the connectivity together with the ability to parallelize operations on physical and logical qubits, makes them one of the most promising platforms for realizing large-scale fault-tolerant quantum computing. Nevertheless, the number of physical qubits required for many important practical applications of quantum computing needs to scale beyond a million. Due to physical limitations of the objective field of view, the power-handling capabilities of optical elements and the complex control requirements, a single quantum processing unit (QPU) based on neutral atoms arrays seems unlikely to reach that number. Therefore, a promising path forward is to modularize and connect many QPUs. The main limitations to that approach are the noisy low-success rate quantum network channels and the difficulties associated with integrating Rydberg atoms with nearby surfaces, which host electric charges decohering the qubits.
Our approach is to use micro- and nano-scale high-finesse optical cavities together with coherent transport of atoms from a nearby Rydberg atom array. These cavities have a small footprint and have direct access to photons in optical fibers, making them highly scalable. The small photonic mode volume allows for strong atom-photon interactions and large cooperatives of more than 100. Coupling an array of ground state neutral atoms to such cavities allows for new capabilities, such as error-detected cavity-mediated many-body gates between all atoms coupled to the cavity, going beyond two-qubit gates. This platform is a starting point for several research directions:
When combined with a large field of view objective and coherent atom transport to and from a Rydberg atom array, this is a versatile platform and a promising candidate for a network-connected QPU module.
When combined with utilizing telecom transitions in atoms, this platform can be developed into the next-generation nodes and repeaters for long-distance quantum networks.
We are designing a setup with multiple atom array – cavity modules, which will serve as a testbed for various protocols for generating entanglement between distant Rydberg atom array modules.
Past Work
Cavity-Mediated Error-Corrected Gates in a Fiber Cavity
Strong atom-photon interactions in a high-finesse optical cavity can lead to new capabilities. Here we bring two atoms in optical tweezers to the photonic mode of a Fiber Fabry Perot optical cavity. We realize cavity-mediated entanglement with built-in error detection. More about this work here.
Rydberg Atom Arrays Coupled to Nanophotonic Cavities
Nanofabricated optical cavities offer a route towards strong atom-photon interactions in highly scalable structures. Such hybrid systems of individual atoms in optical tweezers and nano-cavities with an integrated optical fiber as an input-output interface can be used as quantum network nodes. Here we use a SiN slab (0.5×0.175×30 um) and couple to the evanescent mode by placing atoms ~260nm away from the surface. We have demonstrated single-atom cooperatively of C = 70 and cavity-mediated two-atom entanglement, which is preserved when transporting away from the cavity.
The next task is integrating such structures with Rydberg atom arrays for modular distributed quantum computing. The goal is to have a fully-functional Rydberg quantum processor some distance away from the cavity and then coherently transport ground state atoms to and from the cavity for atom-photon interactions. The main challenge is tackling stray electric fields from surface charges. Due to their small surface area, nanophotonic cavities are ideal candidates for such integration. The main question we explored here is what is the minimum distance from the cavity at which we can have coherent high-fidelity single and two-qubit operations. The requirement is that the Rydberg array and the cavity fit within the field of view of a single objective (~200um to 1mm). We demonstrated coherent operations as close as 100um, placing this hybrid system as a forefront candidate for a photonic interface for Rydberg atom arrays. More about this work here.
Quantum Simulation of the Spin-1/2 XXZ Model
The unprecedented level of control of ultracold atom systems offer a unique route to exploring experimentally paradigmatic models in Condensed Matter Physics. In Quantum Simulation, we use a known quantum system to simulate the clasically-intractable properties of another quantum system.
Here we realize the spin-1/2 XXZ model with tunable anisotropy and study spin transport properties at different anisotropy regimes. We find a whole range of behaviors spanning from sub-diffusive to ballistic transport. Our experimental system of ultracold Li 7 atoms is uniquely suited for these studies. The Feshbach resonances in the region of magnetic fields of 500-1100 Gauss offer a wide tunability of the atom-atom interactions and the small mass of lithium renders dynamics very fast. This allows us to study the decay of non-equilibrium spin distributions to long times and at different Hamiltonian parameters. More about this work here.