Demonstration of qubit readout with 99.99% fidelity and novel ion trap designs at Oxford

Jeff Sherman
Department of Physics, University of Oxford

We'll discuss an experimental technique to achieve very high fidelity qubit state readout in cold trapped ions with or without hyperfine structure, a necessary prerequisite for many scalable quantum computation schemes. Detailed in Myerson et al., PRL 100(20) 200502 (2008), we achieved 99.99(1)% measurement fidelity in 2 ms with a single Ca-40 ion, and 99.77(3)% fidelity with a Ca-43 ion. The technique can theoretically achieve greater than 99.95% fidelity in 10 us. The key idea is the division of a timed fluorescence measurement into small sub-bins and applying a maximum likelihood method to discern dark counts and cosmic ray PMT events from genuine bright single ion fluorescence following Poisson statistics. We will also summarize the several novel trap designs being built and tested in our group.