= Zero-point motion
<Zero-point motion> is the nonzero quantum fluctuation of position and momentum in a system's <ground state>. For a <quantum harmonic oscillator>, the <ground state> has <energy> $\hbar\omega/2$ and nonzero position and momentum variances even at zero <temperature>. It does not represent a thermal mixture and need not carry <entropy>. The large <zero-point motion> of light <helium> atoms helps explain why <helium> can remain a <liquid> at low <pressure> even as <temperature> approaches <absolute zero>.
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