In one of the previous blog posts, David DiVincenzo reviewed his criteria. Here we will follow this theme and look how these criteria translate onto a physical system. Currently, there are a few qubit implementations that look quite promising. The most prominent examples are superconducting qubits, ion traps and spin qubits. We will focus on the latter one, since that’s the one I’m working on. All the platforms mentioned above fulfill the so called DiVincenzo criteria. These criteria, defined in 2000 by David DiVincenzo, need to be fulfilled for any physical implementation of a quantum computer:
- A scalable physical system with well characterized qubits.
- The ability to initialize the states of the qubits to a simple state, such as |000⟩.
- Long relevant coherence times, much longer than the gate operation time.
- A “universal” set of quantum gates.
- A qubit-specific measurement capability.
In this article we will go through all these criteria and show why spin qubits fulfill these criteria, but before doing that, let’s first introduce spin qubits.
Spin qubits are qubits where the information is stored in the spin momentum of an electron. A spin of a single electron in a magnetic field can either be in the spin down (low energy) or in the spin up (high energy) state. Comparing to a classical bit, the spin down state will be the analogue to a zero and spin up to a one.