How many qubits do we need to be able to make the first quantum computer – cause i’ve heard that we’ve only managed

Question: How many qubits do we need to be able to make the first quantum computer - cause i've heard that we've only managed to isolate about 3 or 4 qubits and they're incredibly hard to store. Thanks :)
- Keywords:
  computer,
  computing,
  quantum,
  qubit
Asked by rulank to Suzanne on 19 Mar 2012.
- Suzanne McEndoo answered on 19 Mar 2012:
  
  If we had up to 100 qubits, that would already be awesome. This paper http://prl.aps.org/abstract/PRL/v83/i24/p5162_1 shows that 50 to 100 qubits would be able to solve some useful problems already.
  
  But you’re right, scalability is a huge challenge for quantum computers. We need to be able to get a large number of qubits, and we also need to be able to keep them safe for long enough times to be able to make the calculations. When you think about how many bits we use in a regular computer, it will take us decades to get anywhere near that.

Question: How many qubits do we need to be able to make the first quantum computer - cause i've heard that we've only managed to isolate about 3 or 4 qubits and they're incredibly hard to store. Thanks :)