Other derivation of (4.68) which could be useful in quantum computing is as follows.
Let Hp the Hilbert space with orthonormal basis {|ωp>}. We define a unitary transformation
U:Hp→Hp
by the formula·
U=(−1)Fbe−βH
with
U|ωp>=(−1)pe−βEpb|ωp>
Let a quantum state given by
|Ψ>=∑p|ωp>.
Will all these ingredients we make the following computation.
Tr((−1)Fbe−βH)=Tr(U)=<Ψ|U|Ψ>=∑q∑p<ωq|U|ωp>,
Tr((−1)Fbe−βH)=Tr(U)=<Ψ|U|Ψ>=∑q∑p<ωq|(−1)pe−βEpb|ωp>,
Tr((−1)Fbe−βH)=Tr(U)=<Ψ|U|Ψ>=∑q∑p(−1)pe−βEp<ωq|b|ωp>,
Tr((−1)Fbe−βH)=Tr(U)=<Ψ|U|Ψ>=∑q∑p(−1)pe−βEp<ωp|b|ωp>δq,p,
Tr((−1)Fbe−βH)=Tr(U)=<Ψ|U|Ψ>=∑p(−1)pe−βEp<ωp|b|ωp>,
Tr((−1)Fbe−βH)=Tr(U)=<Ψ|U|Ψ>=∑p(−1)pχp(b)=χ(Mb).

Reference : Louis Kauffman, arXiv:1001.0354v3 [math.GT] 31 Jan 2010 Topological Quantum Information, Khovanov Homology and the Jones Polynomial (http://lanl.arxiv.org/pdf/1001.0354)