Thursday, 8 May 2008

mp.mathematical physics - The Quantum Operations On The Bipartite Systems

Given two distinct and noninteracting quantum mechanical
systems mathfrakS1 and mathfrakS2 with state spaces
mathcalH1 and mathcalH2, respectively, the state space
of the combined system mathcalS1+mathcalS2 is the
tensor product Hilbert space
mathcalH=mathcalH1otimesmathcalH2. Density operators
WinmathcalD(mathcalH), and effects
FinmathcalE(mathcalH). Similarly, there are corresponding
symbols WiinmathcalD(mathcalHi),FiinmathcalE(mathcalHi) for subsystems
mathfrakSi(i=1,2), respectively.



Given any quantum operation, Phi:mathcalD(mathcalH)rightarrowmathcalD(mathcalH), of
the composite system mathcalS1+mathcalS2.



Problem: (1) Do there exist whether or not two quantum
operation phi1 and phi2, of the subsystems mathfrakS1
and mathfrakS2, respectively, such that the following
diagram is commutative:



begindiagramnodemathcalD(mathcalH1)arrow[4]e,tphi1node[4]mathcalD(mathcalH1) node nodemathcalD(mathcalH1otimesmathcalH2)arrow[2]n,lTr2arrow[4]e,tPhiarrow[2]s,lTr1node[4]mathcalD(mathcalH1otimesmathcalH2)arrow[2]s,rTr1arrow[2]n,rTr2 node nodemathcalD(mathcalH2)arrow[4]e,bphi2node[4]mathcalD(mathcalH2)enddiagram


i.e.
begin{eqnarray} Tr_2(Phi(W))&=&frac{tr(Phi(W))}{tr(phi_1(Tr_2(W)))}phi_1(Tr_2(W)),\ Tr_1(Phi(W))&=&frac{tr(Phi(W))}{tr(phi_2(Tr_1(W)))}phi_2(Tr_1(W)), end{eqnarray}

where phii:mathcalD(mathcalHi)rightarrowmathcalD(mathcalHi)(i=1,2) and Tri:mathcalD(mathcalH)rightarrowmathcalD(mathcalHi) is a partial trace with respect to the subsystem mathfrakSi(i=1,2).



(2) If quantum operation phi1 and phi2 exist, give the
relationship among the quantum operations Phi,phi1 and
phi2.

No comments:

Post a Comment