# Physical Implementation

**Physical implementation** of quantum gates depends on the quantum computing platform. Different platforms (superconducting, trapped ion, photonic, etc.) realize gates differently.

## Superconducting Qubits

**Gates via microwave pulses**: drive qubits with resonant microwave fields.

- **Single-qubit gates**: RX, RY, RZ via microwave pulse duration and phase (~20–50 ns)
- **Two-qubit gates**: CNOT via flux pulse tuning (parametric interaction) (~20–100 ns)

Gate fidelity: 99.5–99.9% for single-qubit, 99–99.5% for CNOT (state-of-the-art).

## Trapped Ions

**Gates via laser pulses**: cool ions, then drive transitions with laser.

- **Single-qubit gates**: resonant pulses targeting transition frequencies (~microseconds)
- **Two-qubit gates**: Mølmer-Sørensen or other entangling laser interactions

Gate fidelity: 99.9%+ (best current platform), but slower gate times.

## Photonic Qubits

**Gates via optical components**: beam splitters, phase shifters, nonlinear media.

- **Single-qubit gates**: optical rotations and phase shifts (~nanoseconds)
- **Two-qubit gates**: nonlinear effects or probabilistic schemes (challenging)

Gate fidelity: ~95–99%, variable depending on architecture.

## NV-Centers and Spins

**Gates via resonance and coupling**:

- **Single-qubit**: microwave resonance (~microseconds)
- **Two-qubit**: magnetic dipole coupling or cavity-mediated

Fidelity: 99–99.9%, long coherence times (milliseconds).

## Gate Time vs. Fidelity

Fast gates accumulate errors quickly (off-resonance effects, spontaneous emission). Slow gates suffer decoherence. Optimal gate time balances these effects.

Typical gate times:
- Superconducting: 20–100 ns (fast, higher error rates)
- Trapped ion: 1–10 μs (slow, higher fidelity)
- Photonic: 1–100 ns (variable)