Qubit ZooDescription
The Mølmer-Sørensen (MS) gate is the standard high-fidelity entangling gate in trapped-ion systems, implemented by bichromatic driving near red/blue motional sidebands to produce an effective spin-spin interaction.
Figure
Hamiltonian
In interaction picture, the gate implements approximately:
where and is set by drive detuning and Lamb-Dicke coupling. Evolution for calibrated time gives maximally entangling XX/YY interactions.
Motivation
The Mølmer-Sørensen gate became dominant because it is experimentally robust: unlike early sideband gates, it can operate without strict ground-state cooling and is less sensitive to certain motional-state preparation errors. It maps naturally onto global-beam plus local-addressing hardware used in modern ion-trap systems.
Key Findings
- Enables high-fidelity entanglement in long-lived hyperfine and optical-ion qubits.
- Naturally implements XX/YY interactions useful for digital and analog simulation.
- Compatible with pulse-shaping and amplitude/frequency modulation for error suppression.
- Scales to multi-ion entangling operations in programmable ion chains.
Key Metrics
| Metric | Value | Notes | Fidelity reference |
|---|---|---|---|
| 2Q gate fidelity | 99.5–99.9% | state of the art trapped-ion gates | Ballance et al. 2016 |
| Gate time | 10–200 μs | detuning/fidelity tradeoff | — |
| Cooling requirement | no ground-state requirement (robust variants) | major practical advantage | — |