Trapped Ions and Quantum Information

We report large-scale fabrication of perfectly functional radio frequency (RF) surface ion traps on a 12-inch glass substrate with a standard CMOS-compatible backend process. Established 12-inch foundry backend process of electroplated Cu with Au finish are employed to fabricate the surface electrodes directly on the glass wafer substrate. We tested a trap by loading it with laser-cooled 88 Sr + ions. The trap shows a stable operation with RF amplitude in the range 100-230 V at 33 MHz frequency. The ion lifetime is on the order of 30 minutes for a pressure in the vacuum chamber of 5 x 10-11 mbar, which demonstrates an exciting potential for future implementation of quantum computing system with a standard foundry process on CMOS compatible and cost-effective platform.

We present a scheme for deterministic ion-photon qubit exchange, namely a SWAP gate, based on realistic cavity-QED systems with 171Yb+, 40Ca+ and 138Ba+ ions. The gate can also serve as a single-photon quantum memory, in which an outgoing photon heralds the successful arrival of the incoming photonic qubit. Although strong coupling, namely having the single-photon Rabi frequency be the fastest rate in the system, is often assumed essential, this gate (similarly to the Duan-Kimble C-phase gate) requires only Purcell enhancement, i.e. high single-atom cooperativity. Accordingly, it does not require small mode volume cavities, which are challenging to incorporate with ions due to the difficulty of trapping them close to dielectric surfaces. Instead, larger cavities, potentially more compatible with the trap apparatus, are sufficient, as long as their numerical aperture is high enough to maintain small mode area at the ion's position. We define the optimal parameters for the gate's operation and simulate the expected fidelities and efficiencies, demonstrating that efficient photon-ion qubit exchange, a valuable building block for scalable quantum computation, is practically attainable with current experimental capabilities.