Consider the entangled state of two spin-1/2 particles: |Y)= (| +)₁|−)2 − |-)₁| +)₂) a) Show that this 2-spin state ) is properly normalized. b) Is this state (4) an eigenstate of S₁z (i.e. the operator associated with measuring the z- component of the spin of particle 1 only)? If so, what is the eigenvalue? If not, why not? c) Is state ) an eigenstate of the "total z-component of spin operator" S₁z + Szz? If so, what is the eigenvalue? If not, why not?

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The spin singlet state and the EPR experiment
Consider the entangled state of two spin-1/2 particles: |4) = (+)₁|-)2 − |−)₁| +)2)
Show that this 2-spin state ) is properly normalized.
b) Is this state ) an eigenstate of S₁z (i.e. the operator associated with measuring the z-
component of the spin of particle 1 only)? If so, what is the eigenvalue? If not, why not?
a)
c) Is state ) an eigenstate of the "total z-component of spin operator" S₁z + Szz? If so,
what is the eigenvalue? If not, why not?
d) Show that this entangled state ) is physically equivalent to the more general state:
(+)1n| -)2n − |-)₁n] +)2n), where ñî is a unit vector in an arbitrary direction. Hint: It may
be easier to start with the more general state and work your way backwards to the initial state.
This result shows why the two detectors in the EPR experiment record perfect anticorrelations in
their spin measurements, independent of the orientation of their detectors, when both detectors
are aligned along the same direction!
e) Given the state ), show that the probability of observer A to measure particle 1 with spin
up is 50% for any orientation of observer A's Stern-Gerlach apparatus. Hint: To find this
probability, sum over the joint probabilities for observer A to measure spin up for particle 1
along the chosen direction and observer B to measure any spin orientation for particle 2. To
simplify the calculation, choose observer B's Stern-Gerlach apparatus to be oriented along the z
direction. You'll have to add the probabilities for the cases where B measures spin up and spin
down.
Transcribed Image Text:2. The spin singlet state and the EPR experiment Consider the entangled state of two spin-1/2 particles: |4) = (+)₁|-)2 − |−)₁| +)2) Show that this 2-spin state ) is properly normalized. b) Is this state ) an eigenstate of S₁z (i.e. the operator associated with measuring the z- component of the spin of particle 1 only)? If so, what is the eigenvalue? If not, why not? a) c) Is state ) an eigenstate of the "total z-component of spin operator" S₁z + Szz? If so, what is the eigenvalue? If not, why not? d) Show that this entangled state ) is physically equivalent to the more general state: (+)1n| -)2n − |-)₁n] +)2n), where ñî is a unit vector in an arbitrary direction. Hint: It may be easier to start with the more general state and work your way backwards to the initial state. This result shows why the two detectors in the EPR experiment record perfect anticorrelations in their spin measurements, independent of the orientation of their detectors, when both detectors are aligned along the same direction! e) Given the state ), show that the probability of observer A to measure particle 1 with spin up is 50% for any orientation of observer A's Stern-Gerlach apparatus. Hint: To find this probability, sum over the joint probabilities for observer A to measure spin up for particle 1 along the chosen direction and observer B to measure any spin orientation for particle 2. To simplify the calculation, choose observer B's Stern-Gerlach apparatus to be oriented along the z direction. You'll have to add the probabilities for the cases where B measures spin up and spin down.
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