# How many classical registers are there on (IBM) quantum computers?

I have a circuit where I only use 3 qubits but need to utilize hundreds of classical registers. My questions are: what is the maximum number of classical bits on the current IBM Qs? What is the quantum computer with the highest number of classical bits right now that is available for researchers and the public?

Edit: I'm doing sort of like a Quantum Zeno effect on qubit: I want to keep track of whether a qubit will turn to $$|1\rangle$$ after a certain amount of gates. It's possibly much better if there's a measurement gate that will read the qubit and fix the classical register as $$|1\rangle$$ forever once it caught the qubit at $$|1\rangle$$ state, sort of like this. Is there such a method?

$$\begin{array}{|c|c|} \hline \text{Qubit Classical bit} & \text{Classical bit} \\ \hline \begin{array}{cc}0 & & & & 0\end{array} & \begin{array}{cc}0 \end{array} \\ \hline \begin{array}{cc}1 & & & & 0\end{array} & \begin{array}{cc}1 \end{array} \\ \hline \begin{array}{cc}0 & & & & 1\end{array} & \begin{array}{cc}1 \end{array} \\ \hline \begin{array}{cc}1 & & & & 1\end{array} & \begin{array}{cc}1 \end{array} \\ \hline \end{array}$$

Here's one of the circuits that I ran. Because I don't have that kind of measurement, I use Python to counts the time when $$q[1]$$ turn to $$|1\rangle$$:

Thank you!

• What do you need the large amount of classical registers for? I think your question may get answered more directly if we know what it is you want to do. – Matthew Stypulkoski Sep 25 '19 at 13:58
• I'm doing sort of like a Quantum Zeno effect on qubit: I want to keep track of whether a qubit will turn to |1> after a certain amount of gates. It's possibly much better if there's a measurement gate that will read the qubit and fix the classical register as |1> forever once it caught the qubit at |1> state. Is there such a method? – Kim Dong Sep 25 '19 at 16:40

As far as I am aware you can have as many ClassicalRegisters as you need, assuming they fit in the memory of the classical device controlling the Quantum Computer. I would suggest trying to reuse them if possible if you are concerned about this!