# Measuring Entanglement

Measurement causes the collapse of the wave function.
We will study what happens when we measure a single qubit or two entangled qubits.

When we talked about measuring a single qubit, we described three ways to measure it. They correspond to the X, Y and Z axes on the Bloch sphere we saw back in the article on qubits. To measure a qubit, you pick an axis through the middle of the sphere, and as you do the measurement you’ll find the qubit either on the near end or far end of that axis. For the Z axis, that’s the north pole and the south pole. For the X axis, it’s the left and right points.

For a single qubit, it’s simple enough, if different from classical systems. What happens when we measure two entangled qubits? We will see the correlation between the two qubits happens even when our two qubits are physically separated by an arbitrary distance – the phenomenon known as “spooky action at a distance”.

## 3-D Printing

If you would like to print your own copy of the 3-D model of the Bloch sphere shown in this video, you can use either of these two files:

• STL file Most 3-D printing software will take this file for printing. You will probably want to adjust the scale to suit your printer. For your printer settings, we recommend printing this with a raft and support. You will need a small file to remove the supports once printed.
• OpenSCAD file If you would like to modify the shape and are willing to do a little programming, this was created in a language called OpenSCAD.

# 量子もつれを測定する

## 3Dプリント

このビデオで使ったブロッホ球の3Dモデルを印刷したい方は、次の2つのファイルのいずれかをご利用ください。

• STLファイル ほとんどの3Dプリントのソフトウェアで利用できるファイルです。 お使いのプリンタに合わせてスケールを調整してください。お使いのプリンタの設定では 、ラフト(床)とサポート(支え)を一緒に印刷することをお勧めします。 印刷後は、サポートを削除するために小さなファイルが必要になります。