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Work out the spin matrices for arbitrary spin , generalizing spin (Equations 4.145 and 4.147), spin 1 (Problem 4.31), and spin (Problem 4.52). Answer:

Sz=(s0000s-10000s-200000-s)Sx=2(0bs0000bs0bs-10000bs-10bs-20000bs-200000000b-s+10000b-s+10)Sy=2(0-ibs0000ibs0-ibs-10000-ibs-10-ibs-20000-ibs-200000000-ibs+10000-ibs+10)

where,bj(s+j)(s+1-j)

Short Answer

Expert verified

The spin matrices are, sy=2i0bs000-bs0-bs-100-bs-10-bs-200000-b-s-10000-b-s-10

Step by step solution

01

Definition of spin matrix

The spin related matrices are known as spin matrices. These are number of matrices. These matrices are complex that include involutory, unitary, and Hermitian.

02

Determination of spin matrices.

Write equation 4.135.

sz|sm=hm|sm

Write the matrix element of sz.

sznm=nszm=hmnm=hmnm

Write the matrix (diagonal matrix) with values of m ranging from s to -s along the diagonal.

Sz=(s0000s-10000s-200000-s)

Determine the value of s+nm.

s+nm=ns+m=h(s-m)(s+m+1)nm+1=hbnnm-1

Here,bm+1=(s-m)(s+m+1) .

Use the property of the function.

(s*)mw=bnnm+1

Write the matrix.

s+=0bs00000bs-100000bs-20b-s+100000

Write the value of s_nm.

role="math" localid="1658146052379" s_nm=ns_m=h(s+m)(s-m+1)nm-1=hbnnm-1

Write the value of s_ .

s_=h000.....0bs000...00bs-1.......00bs-2.......0000sx=12s++s-

Write the value ofrole="math" localid="1658143674691" sx.

sx=20bs000bs0bs-1000bs-10bs-200bs-200b-s+1000b-s+10b-s+10

Write the value ofsy .

sy=12i[s+-s-]sy=2i0bs000-bs0-bs-100-bs-10-bs-200000-b-s-10000-b-s-10

Thus, the spin matrices are2i0bs000-bs0-bs-100-bs-10-bs-200000-b-s-10000-b-s-10

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Most popular questions from this chapter

[Refer to Problem 4.59 for background.] In classical electrodynamics the potentials Aandare not uniquely determined; 47 the physical quantities are the fields, E and B.

(a) Show that the potentials

'-t,A'A+

(whereis an arbitrary real function of position and time). yield the same fields asand A. Equation 4.210 is called a gauge transformation, and the theory is said to be gauge invariant.

(b) In quantum mechanics the potentials play a more direct role, and it is of interest to know whether the theory remains gauge invariant. Show that

'eiq/

satisfies the Schr枚dinger equation (4.205) with the gauge-transformed potentials'andA', Since'differs fromonly by a phase factor, it represents the same physical state, 48and the theory is gauge invariant (see Section 10.2.3for further discussion).

Consider the observablesA=x2andB=Lz .

(a) Construct the uncertainty principle forAB

(b) EvaluateB in the hydrogen staten/m .

(c) What can you conclude about<xy>in this state?

Determine the commutator of S2withSZ(1)(whereSS(1)+S(2)) Generalize your result to show that

[S2,S1]=2Ih(S1S2)

Comment: Because Sz(1)does not commute with S2, we cannot hope to find states that are simultaneous eigenvectors of both. In order to form eigenstates ofS2weneed linear combinations of eigenstates ofSz(1). This is precisely what the Clebsch-Gordan coefficients (in Equation 4.185) do for us, On the other hand, it follows by obvious inference from Equation 4.187that the sumrole="math" localid="1655980965321" S(1)+S(2)does commute withdata-custom-editor="chemistry" S2, which is a special case of something we already knew (see Equation 4.103).

(a) Construct the spatial wave function ()for hydrogen in the state n=3,I=2,m=1.Express your answer as a function of r,,,anda(the Bohr radius) only鈥攏o other variables (p,z,etc.) or functions (p,v,etc.), or constants (A,c0,etc.), or derivatives, allowed (蟺 is okay, and e, and 2, etc.).

(b) Check that this wave function is properly normalized, by carrying out the appropriate integrals over, ,and.

(c) Find the expectation value of rsin this state. For what range of s (positive and negative) is the result finite?

The raising and lowering operators change the value of m by one unit:

Lflm=(Alm)flm+1, (4.120).

Where Almare constant. Question: What is Alm, if the Eigen functions are to be normalized? Hint: First show thatLis the Hermitian conjugate of L(Since LxandLyare observables, you may assume they are Hermitian鈥ut prove it if you like); then use Equation 4.112.

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