Quantum Computing with Trapped Electrons

Project Overview

This feasibility study explored a new, promising hardware platform for quantum computing: electrons held in a radio frequency (RF) Paul trap. In this system, qubits are encoded in the electrons' spins and entanglement is generated through collective motion driven by microwave signals. Motivated by recent experimental progress trapping electrons in a room temperature prototype system by our collaborators, the Häffner group at University of California (UC) at Berkeley, we analytically and numerically studied the performance of quantum gates for trapped electrons in a generic system, as well as in a concrete experimental proposal that balances buildability and expected equipment performance against full system performance and uses numerical modeling to identify motional heating and magnetic field gradient inhomogeneity as the leading performance bottlenecks. This study bears out the promise of the trapped electron system, predicting that even this initial system will achieve two-qubit gate fidelities on par with best trapped ion systems. A variant of the proposed system will be built at UC Berkeley.

This feasibility study will result in two papers, currently in draft form. The first paper "Feasibility study of quantum computing using trapped electrons" directly addresses the project objectives: modeling the obtainable error rates for trapped electron gates in a near-term realizable experimental platform. It additionally describes many of the tradeoffs that go into that system design, which was optimized for gate fidelity as well as design criteria including realizability, state preparation and readout, and thermal loading in the cryostat. The second paper "Sources of Infidelity for One- and Two-Qubit Gates in Laser-Free Trapped Ions and Electrons" derives analytic expressions for the infidelity introduced by motion in the low-error limit. In this limit, different error terms are additive. The derived analytic expressions are compared with numeric simulations to validate their accuracy and applicability.

Mission Impact

Quantum computing is a growing area of disruptive computing. While quantum computers themselves are not yet able to provide insight into practical problems, quantum computation is expected to develop into a widely applicable tool for high performance computing problems with diverse application space including many areas of the NNSA mission. Research into new, disruptive platforms for quantum computing such as the trapped electron system enables us to push the field forward to develop the science and technology tools and capabilities that will enable us to meet future national security challenges.

This feasibility study also built and strengthened connections between new Lawrence Livermore National Laboratory (LLNL) staff and the ion trapping groups at UC Berkeley and UC Riverside, as well as continuing the research connection with a former LLNL scientist now at the University of Texas at San Antonio. The project afforded an opportunity to virtually meet several undergraduate and graduate students at UC Berkeley and UC Riverside and introduce them to the quantum program at LLNL. With initial results from this LDRD feasibility study, our team (LLNL, UC Berkeley and UC Riverside) responded to the Next New and Emerging Qubit Science and Technology (next NEQST) call from the Army Research Office and the Laboratory for Physical Sciences. While that proposal was not funded, a separate proposal to the Air Force Office of Scientific Research was awarded to UC Berkeley and UC Riverside and will enable the experimental realization of the plans we put together this year.

Publications, Presentations, and Patents

Beck, K.M. 2021. "Computing with Trapped Ions in the NISQ Era." Conference on Lasers and Electro-Optics (CLEO). May 14, 2021. LLNL-PRES-822391.