"Exercise 6.6" u = (1,0) d = (0,1) uu = kronecker(u,u) ud = kronecker(u,d) du = kronecker(d,u) dd = kronecker(d,d) sigmaz = ((1,0),(0,-1)) sigmax = ((0,1),(1,0)) sigmay = ((0,-i),(i,0)) tauz = ((1,0),(0,-1)) taux = ((0,1),(1,0)) tauy = ((0,-i),(i,0)) I = ((1,0),(0,1)) sigmaz = kronecker(sigmaz,I) sigmax = kronecker(sigmax,I) sigmay = kronecker(sigmay,I) tauz = kronecker(I,tauz) taux = kronecker(I,taux) tauy = kronecker(I,tauy) S = (ud - du) / sqrt(2) -- singlet state "Verify expectation value" check(dot(conj(S),sigmax,tauy,S) == 0) "ok" Run