Maris Ozols, Graeme Smith, John A. Smolin
Entanglement is a fundamental resource for quantum information processing. In its pure form, it allows quantum teleportation and sharing classical secrets. Realistic quantum states are noisy and their usefulness is only partially understood. Bound entangled states are central to this question---they have no distillable entanglement, yet sometimes still have a private classical key. We present a new and unexpected construction of bound entangled states with private key based on classical probability distributions. This construction gives a remarkable and long-sought classical analogue of bound entanglement. We also find states of smaller dimensions and higher key rates than previously known. Our construction has implications for classical cryptography: we show that existing protocols are insufficient for extracting private key from our distributions due to their "bound entangled" nature. We propose a simple extension of existing protocols that can extract key from them.
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http://arxiv.org/abs/1305.0848
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