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arXiv quant-ph/0203105quant-phcs.ITmath-phmath.ITmath.MPmath.OA
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混合量子存储器的容量

The capacity of hybrid quantum memory

Greg Kuperberg

摘要:

一般稳定的量子存储单元是由一个经典数位和一个分配给每个经典态的量子数位组成的混合体。记忆的形状是这些qudits的大小的向量,它们可能不同。我们确定当一个量子存储器A的N个副本嵌入另一个量子存储器B的N(1+o(1))个副本时。这种关系捕捉了这样一个概念,即在批量限制的所有目的中,B至少与A一样有用。我们证明了嵌入存在的充要条件是对所有p >= 1,A的形状的p-范数不超过B的形状的p-范数。A的形状的p范数的对数可以解释为A上所有混合态ρ上S(ρ)+ H(ρ)/p(量子熵加上折扣经典熵)的最大值。我们还建立了一个无噪声编码定理,证明这些熵。无噪声编码定理和批量嵌入定理一起说,要么A以完美的保真度盲目地批量编码到B中,要么A承认一个状态,该状态不会以高保真度明显地批量编码到B中。总之,混合量子存储器的效用取决于其同时处理经典熵和量子熵的能力,这不是一个有限的数字列表,而是经典-量子熵平面上的凸区域。

英文摘要:

The general stable quantum memory unit is a hybrid consisting of a classical digit with a quantum digit (qudit) assigned to each classical state. The shape of the memory is the vector of sizes of these qudits, which may differ. We determine when N copies of a quantum memory A embed in N(1+o(1)) copies of another quantum memory B. This relationship captures the notion that B is as at least as useful as A for all purposes in the bulk limit. We show that the embeddings exist if and only if for all p >= 1, the p-norm of the shape of A does not exceed the p-norm of the shape of B. The log of the p-norm of the shape of A can be interpreted as the maximum of S(ρ) + H(ρ)/p (quantum entropy plus discounted classical entropy) taken over all mixed states ρon A. We also establish a noiseless coding theorem that justifies these entropies. The noiseless coding theorem and the bulk embedding theorem together say that either A blindly bulk-encodes into B with perfect fidelity, or A admits a state that does not visibly bulk-encode into B with high fidelity. In conclusion, the utility of a hybrid quantum memory is determined by its simultaneous capacity for classical and quantum entropy, which is not a finite list of numbers, but rather a convex region in the classical-quantum entropy plane.

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