# Schrödinger's cat and the difficulty of macroscopic superposition state

The Schrödinger's cat was regarded as peculiar since we seldom encounter a superposition state in macroscopic scale: $$| \mathrm{dead \,\,cat} \rangle + | \mathrm{alive \,\, cat}\rangle$$

We more often describe an unknown cat as $$| \mathrm{dead \,\,cat} \rangle \langle \mathrm{dead \,\,cat} |+ | \mathrm{alive \,\, cat}\rangle \langle \mathrm{alive \,\, cat}|$$

without superposition.

I often heard that it is difficult to prepare and maintain a large-scale superposition state. Similar difficulty also occurs in quantum computing.

My question is, actually what is the reason for the difficulty to prepare and maintain a large-scale superposition state? If it is decoherence, why decoherence happens? Is that because of entropy?

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I don't know the answer but I just wanted to point out that $k\ln N$ and $k \ln 2N$ differ by $k \ln 2$ regardless of the value of $N$. The difference between the entropies is constant (though does become relatively smaller as $N$ increases). – JeffDror Mar 2 '14 at 17:05
Thanks a lot.... – user26143 Mar 2 '14 at 17:17