Quantum Spatial Density as an Independent Probability in Shannon's Entropy?
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In the literature, one often finds a quantum expression for Shannon’s entropy of the form: - (W*W) ln(W*W) ((1)) where W*W is spatial density i.e. W(x)= the wavefunction. This implies W*(x)W(x) is an independent probability. Given that W(x)= Sum over p a(p) exp(ipx), and W*W= Sum over p1, p2 a(p1)a(p2) exp(ip1 x) exp(ip2 x), one may see that for p1/-p1 in the latter with a(p)=a(-p) leads to cos(p1x) terms. These are positive and negative in different x regions. In fact, in many cases, the overall spatial density exhibits peaks and valleys suggesting that W*(x)W(x) is correlated, i.e. not independent we argue. Furthermore, the form ((1)) uses only position when there is an expectation value for < p*p> an <p>, both functions of x, where p is momentum. Thus, the variance of p-ensemble average may change with x, yet position only is used in the computation of Shannon’s entropy, which we argue seems unusual. In a previous note (1), we suggest using a(1)exp(ip1 x) a(p2)exp(ip2 x) as the probability for Shannon’s entropy. This leads to a spatial form 2W x d/dx W which matches ((1)) for the ground state of the quantum oscillator case. For the ground state oscillator, W*W=C exp(-ax*x) i.e. a Gaussian. This suggests that for this case only, W*(x)W(x) represents an independent probability which may be used in Shannon’s entropy, we argue. We attempt to consider these issues in this note.
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