ABSTRACT

Non-Technical Abstract
Quantum computers, which utilize quantum mechanics, will be able to solve problems that are not tractable on today's types of computers. An example relevant to national security is the factorization of large numbers into component prime numbers. This computationally hard task underlies modern encryption protocols used for secure communication. An example relevant to materials discovery is quantum simulation. Because interactions between atoms within a material are quantum mechanical, an efficient materials simulator must also have quantum mechanical features. A critical resource for quantum computers is quantum entanglement. In this project, we will design, implement, and test integrated quantum circuits in diamond with the aim to significantly increase quantum entanglement generation rates. Specifically, we aim to increase this rate by integrating three specialized layers: a quantum layer based on light-emitting defects in diamond, a photonic layer which routes photons on the surface of the diamond chip, and a detector layer which detects the single photons. These on-chip integrated photonic circuits would then be the processor chip for a future quantum computer or a node of a quantum network. Faster entanglement rates will impact our ability to scale up the number of quantum bits used for calculations. As an integrable part of this research, graduate students and undergraduate students will be trained in nanofabrication, integrated photonics, and quantum technologies, skill areas currently in high demand in industry and government labs.

Technical Abstract
Quantum entanglement, a fundamental resource for quantum information processing, can theoretically be efficiently heralded via photon measurement. Heralded schemes have some striking characteristics. First, qubits do not need to be moved. Second, qubits do not need to interact with each other. This latter condition limits the number of decoherence channels that may be present, boosting the prospects for scalability. Finally, photon-mediated heralded entanglement is uniquely suited to (and perhaps can only be realized by) on-chip integrated photonics. This proposal seeks to realize an on-chip integrated photonics entanglement generator. The integrated photonics entanglement generator is based on a layered device of different materials for integrated functionality: (1) quantum defects in diamond, (2) a gallium phosphide photonics layer, and (3) waveguide-integrated NbN superconducting single detectors. The main goal of integration is to increase the entanglement generation rate to enable scaling to large (>2) qubit networks. Estimates that neglect the photon purity in the integrated device indicate kHz rates are possible, five orders of magnitude greater than free space implementations. However, we emphasize that at the current state of integrated quantum photonics, it will be a major achievement to simply outperform free space implementations in a scalable platform. Device and system-level evaluation will be performed to give a roadmap toward efficient systems. The demonstration of efficient generation of measurement-based entanglement is expected to propel integrated photonics into viability as a universal quantum computation platform.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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