Highly Stable High Fidelity Trapped Ion Systems
Abstract
We have recently demonstrated the first high-speed entangling logic gates for trapped-ion qubits [Schafer 2018]. We achieved a fidelity of 99.8% for a 1.6 us gate time, close to the highest reported two-qubit gate fidelities of 99.9% [Ballance 2014, Gaebler 2016], but more than an order of magnitude faster. At the fastest gate speed attempted (480 ns), however, the fidelity was poor (60%): most of the gate error arose from the breakdown of the Lamb-Dicke approximation and the fact that Ð without control of the optical phase of the laser field Ð this error source was not invertible and hence could not be suppressed. The fast gate mechanism we used does not work for Molmer-Sorensen (MS) gates, because of the presence of the carrier term in the MS Hamiltonian, which means that it cannot be applied directly to "atomic clock" qubits. Furthermore, off-resonant photon scattering sets a lower limit to the error of these Raman laser-driven gates at the 0.01% level in both the ion species (Ca+ and Be+) for which the highest fidelities have been achieved. In this proposal, we plan several major extensions to our previous demonstration of fast gates. First, we will investigate faster and/or lower-error implementations of our existing scheme which are enabled by control of the optical phase. Secondly, we will extend the optical phase control to gates driven on the quadrupole (optical qubit) transition, which will allow fast MS gates and also the elimination of the off-resonant photon scattering error that limits Raman gate errors. Finally, we will apply these fast quadrupole gates to a multi-ion chain to make the first demonstration of high-speed multi-ion control. We target at least one order of magnitude reduction in gate error for a sub-microsecond gate, compared with the present state-of-the-art.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 09, 2020
- Source ID
- W911NF2010038
Entities
People
- C. J. Ballance
Organizations
- Army Contracting Command
- National Security Agency
- University of Oxford