# Multiqubit systems

We can now extend what we have learned so far for a single qubit to systems of multiple qubits. In this video David Elkouss (QuTech) introduces the topics of this module and of the following videos. You will learn that typically quantum mechanical phenomena emerge when going from one qubit to many.

## Prerequisite knowledge

So far you learned how to express a single qubit state in the braket notation and its representation on the Bloch sphere. In this video, David Elkouss (QuTech) will explain more in detail how these concepts extend to two and multiple qubit systems.

## Further thinking

If you take the tensor product of a 3x4 and a 1x2 matrix (n x m means n rows and m columns), what are the dimensions of the new matrix?

How many complex parameters are needed to describe the state of 4 qubits?

## Further reading

For a more detailed explanation on Multi-qubit systems see section 1.2.1 in M. A. Nielsen and I. L. Chuang, *Quantum computation and quantum information*, 10th anniversary ed. Cambridge ; New York: Cambridge University Press, 2010.