
Quantum ComputingQuantum Computing 321
Information from qubits can be extracted only through measurements.
A qubit has infi nitely different states, however, we can extract the same
amount of information from a qubit than from a boolean bit. If we make a
measurement on the qubit described by (15.5.2) to see if it is or , the
result will be 0 or 1 with probability or , and the state immediately after
the measurement will be or . This is because, with the measurement,
the sate vector collapses to the corresponding eigenvalue observed.
15.5.1 The Bloch sphere
The Bloch sphere shown in Fig. 15.7 is a 3D geometric representation of
the state ...