Trap-integrated qubit control and readout elements for scaling trapped ion quantum computers*

The integration of qubit control and readout elements into microfabricated surface-electrode ion traps offers potential advantages for scaling to larger trapped-ion systems. I will describe two efforts in this direction from our group. The first is the implementation of trap-integrated superconducting photon detectors to detect qubit-state-dependent ion fluorescence for qubit readout. The newest generation of integrated detectors are electrically shielded from trapping rf, enabling operation in a fully functional trap at temperatures up to 6 K, and should be suitable for high-fidelity readout of trapped Ca⁺ ions. The second effort is the implementation of high-fidelity single-qubit and two-qubit gates driven by magnetic fields and magnetic field gradients generated from trap-integrated current-carrying electrodes. This technique should enable a single set of applied control currents to carry out high-fidelity qubit manipulations simultaneously, in an individually-addressable manner, across many different trap zones in a scaled-up multi-zone ion trap processor. We envision these two efforts combining to enable a mixed-species “gradient quantum logic isolated qubit” architecture for fully-integrated trapped ion quantum computers. We pair an entirely laser-free “data” species (here ²⁵Mg⁺), which encodes quantum information in hyperfine states, with a co-trapped auxiliary “helper” species (here ⁴⁰Ca⁺) that provides sympathetic cooling and quantum-logic-based state preparation/readout of the data ions. Only low-power resonant lasers are required for the helper species, making the architecture compatible with trap-integrated waveguides for laser light delivery across many trap zones. Helper ion readout is accomplished with trap-integrated photon detectors. All operations on the data ions, and some on the helper ions, are driven using magnetic fields and magnetic field gradients generated by currents in the trap electrodes rather than laser beams. This architecture eliminates memory errors/readout crosstalk from stray data qubit laser light and offers the potential for extremely low data qubit SPAM errors.