Nathaniel Tornow

We present the Quantum Gate Virtualization Machine (QVM), an end-to-end generic system for scalable execution of large quantum circuits with high fidelity on noisy and small quantum processors (QPUs) by leveraging gate virtualization. QVM exposes a virtual circuit intermediate representation (IR) that extends the notion of quantum circuits to incorporate gate virtualization. Based on the virtual circuit as our IR, we propose the QVM compiler—an extensible compiler infrastructure to transpile a virtual circuit through a series of modular optimization passes to produce a set of optimized circuit fragments. Lastly, these transpiled circuit fragments are executed on QPUs using our QVM runtime—a scalable and parallel infrastructure to virtualize and execute circuit fragments on a set of QPUs. We evaluate QVM on IBM’s 7- and 27-qubit QPUs. Our evaluation shows that our approach allows for the execution of circuits with up to double the number of qubits compared to the qubit-count of a QPU, while improving fidelity by 4.7× on average compared to larger QPUs and that we can effectively reduce circuit depths to only 40% of the original circuit depths.

Stateful serverless applications need to persist their state and data. The existing approach is to store the data in general purpose storage systems. However, these approaches are not designed to meet the demands of serverless applications in terms of consistency, fault tolerance and performance. We present FlexLog, a storage system, specifically a distributed shared log, distinctively designed to meet the requirements of stateful serverless computing while mitigating the relevant system bottlenecks. FlexLog's data layer leverages the state-of-the-art persistent memory (PM) to offer low latency I/O and improve performance. To match the performance, FlexLog's ordering layer employs a scalable design, namely a tree-structure set of sequencer nodes. Importantly, this design provides serverless applications with the flexibility to implement different consistency guarantees and to seamlessly support multi-tenancy configurations. We implement FlexLog from the ground up on a real hardware testbed and we also prove the correctness of our protocols. In particular, we evaluate FlexLog on a cluster of 6 machines with 800 GB Intel Optane DC PM over a 10 Gbps interconnect. Our evaluation shows that FlexLog scales to millions of operations per second while maintaining minimal latency. Our comparison with the state-of-the-art shared log for serverless, Boki, shows that we achieve 10x better throughput in the storage layer and 2x-4x lower latency in the ordering layer, while also providing flexibility to support different consistency properties and multi-tenancy.