Dür Wolfgang, Simon Christoph, Cirac J Ignacio
Sektion Physik, Ludwig-Maximilians-Universität München, Theresienstrasse 37, D-80333 München, Germany.
Phys Rev Lett. 2002 Nov 18;89(21):210402. doi: 10.1103/PhysRevLett.89.210402. Epub 2002 Oct 31.
Several experiments and experimental proposals for the production of macroscopic superpositions naturally lead to states of the general form /phi(1)>( multiply sign in circle N)+/phi 2 >( multiply sign in circle N), where the number of subsystems N is very large, but the states of the individual subsystems have large overlap, /<phi 1/phi 2 >/ 2=1-epsilon 2. We propose two different methods for assigning an effective particle number to such states, using ideal Greenberger-Horne-Zeilinger states of the form /0>( multiply sign in circle n)+/1>( multiply sign in circle n) as a standard of comparison. The two methods are based on decoherence and on a distillation protocol, respectively. Both lead to an effective size n of the order of N epsilon 2.
几个用于产生宏观叠加态的实验及实验方案自然地导致了一般形式为|φ₁⟩(⊗ᴺ)+|φ₂⟩(⊗ᴺ)的态，其中子系统的数量N非常大，但各个子系统的态有很大的重叠，|⟨φ₁|φ₂⟩|² = 1 - ε²。我们提出了两种不同的方法，以形式为|0⟩(⊗ⁿ)+|1⟩(⊗ⁿ)的理想格林伯格 - 霍恩 - 蔡林格态作为比较标准，来为这类态赋予一个有效粒子数。这两种方法分别基于退相干和一种提纯协议。两者都得出有效大小n为Nε²量级。
