11.2 What does it take to be a qubit?

In his 2000 paper ‘‘The Physical Implementation of Quantum Computation,’’ then-IBM Research Staff Member David P. DiVincenzo laid out five ‘‘requirements for the implementation of quantum computation.’’ [10]

In his words they are:

1. A scalable physical system with well characterized qubits
2. The ability to initialize the state of the qubits to a simple fiducial state, such as
3. Long relevant decoherence times, much longer than the gate operation time
4. A ‘‘universal’’ set of quantum gates
5. A qubit-specific measurement capability

Let’s discuss what each of these mean, following his lead.

Scalable physical system

In our physical system that we manufacture for quantum computing, we need to build a qubit that has two clearly delineated states, |0⟩ and |1⟩...