Quantum Entanglement I

[SsDd]

The lecture video is embedded below.

Additionally, slides used in the lecture are embedded below, or can also be downloaded directly from here.

Questions after the lecture? Please feel free to post them in the same thread.

Click to play embedded YouTube video.

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[gtwace]

Just to confirm the weirdness, it means that when Alice measures X axis and Bob measures Z axis, they both measures a 50-50 spin, however, whenever Alice and Bob measures the same axis e.g. both measure X axis or both measure Z axis, one of them will get an Up spin while the other gets a Down spin ?

[maplebayou1]

Just to be clear - When each person makes a measurement, they get only a single value for spin (up or down). If Alice measures the spins of particles on the X axis, she gets up or down for each particle, and about a 50/50 ratio if she measures many. Similarly, if Bob measures spin on the Z axis, he gets up or down for each particle, and about 50/50 for many. If they measure the same axis, X for example, they still get only one spin value for each particle, and about a 50/50 ratio for many. But comparing notes afterward, they will find that their measurements for each particle show opposite spin values.

It should be noted that the 50/50 ratio is approximate - it is a merely a statistical ratio, it is not required that the spin values balance. The entanglement effect merely requires that a given pair of particles have opposite spin values, not that a collection of such particles be exactly half and half.