Introduction to Quantum Physics and Information Processing

Quantum Gates and Circuits 131

Exercise 7.13. Verify that the Bell states can be written as

|β

xy

i =

1

√

2

(|0yi + (−1)

x

|1¯yi) .

The reverse of the circuit 7.11 can be used to convert the Bell basis to the

computational one. Making a measurement after that can tell us which of the

Bell states we started with. This is called a Bell Measurement, depicted in

Figure 7.12.

•

H

x

|β

xy

i

y

FIGURE 7.12: Circuit for Bell measurement.

Example 7.2.3. Let us analyze the output of the circuit shown in Figure 7.13.

|ψi is a generic unknown qubit α|0i+β|1i. A Bell measurement is performed on

this qubit and one of an entangled pair prepared in the state |β

00

i (Equation

4.10).

|