# Summary: the qubit platforms compared

```{div} mo-lead
The four platforms of this part side by side.
```

| Platform | The qubit | Control | Readout |
|---|---|---|---|
| [Spin qubits](spin_qubits/spin_qubits.md) | The spin of a single electron trapped in a quantum dot in silicon | Microwave pulses and gate voltages | Spin-to-charge conversion, sensed by a nearby charge sensor |
| [Superconducting qubits](superconducting_qubits/superconducting_qubits.md) | Two energy levels of a superconducting circuit with a Josephson junction (the transmon) | Microwave pulses | Through a coupled microwave resonator |
| [NV centres](nv_center_qubits/nv_center_qubits.md) | The electron spin of a nitrogen-vacancy defect in diamond, with nearby nuclear spins as memory | Microwave pulses | Optically, by spin-dependent fluorescence |
| [Topological qubits](topological_qubits/topological_qubits.md) | Non-local states of Majorana modes in superconducting nanowires | Braiding the modes around one another | Measuring the parity of pairs of modes |

Spin and superconducting qubits are built with the tools of the semiconductor and microwave industries,
which makes them natural candidates for scaling up. NV centres keep their coherence over a wide range of
temperatures and link easily to photons, which suits quantum networks. Topological qubits promise
protection against errors from the physics itself, which is why they get the most space here; they are
also the least mature.