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Paper 1

Superadditivity of Quantum Channel Coding Rate with Finite Blocklength Joint Measurements

Hye Won Chung, Saikat Guha, Lizhong Zheng

Year

2013

Journal

arXiv preprint

DOI

arXiv:1310.3793

arXiv

1310.3793

The maximum rate at which classical information can be reliably transmitted per use of a quantum channel strictly increases in general with $N$, the number of channel outputs that are detected jointly by the quantum joint-detection receiver (JDR). This phenomenon is known as superadditivity of the maximum achievable information rate over a quantum channel. We study this phenomenon for a pure-state classical-quantum (cq) channel and provide a lower bound on $C_N/N$, the maximum information rate when the JDR is restricted to making joint measurements over no more than $N$ quantum channel outputs, while allowing arbitrary classical error correction. We also show the appearance of a superadditivity phenomenon---of mathematical resemblance to the aforesaid problem---in the channel capacity of a classical discrete memoryless channel (DMC) when a concatenated coding scheme is employed, and the inner decoder is forced to make hard decisions on $N$-length inner codewords. Using this correspondence, we develop a unifying framework for the above two notions of superadditivity, and show that for our lower bound to $C_N/N$ to be equal to a given fraction of the asymptotic capacity $C$ of the respective channel, $N$ must be proportional to $V/C^2$, where $V$ is the respective channel dispersion quantity.

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Paper 2

Building a spin quantum bit register using semiconductor nanowires.

Baugh J, Fung JS, Mracek J, LaPierre RR.

Year

2010

Journal

Nanotechnology

DOI

10.1088/0957-4484/21/13/134018

arXiv

-

No abstract.

Open paper