Positive Aspects of Noise Effect on Quantum Correlations

Mostafa Annabestani, Seyed Javad Akhtarshenas, Mohamad Reza Abolhassani

Abstract In this article we investigate the effects of shifting position decoherence, arising from the incoherent tunneling effect in the experimental realization of the quantum walk, on the one-dimensional discrete time quantum walk. We show that in the regime of this type of noise the quantum behavior of the walker does not vanish, in contrast to the coin decoherence for which the walker undergoes a quantum-to-classical transition even for weak noise. In particular, we show that the quadratic dependence of the variance on the time and also the coin–position entanglement, i.e. two important quantum aspects of the coherent quantum walk, are preserved in the presence of tunneling decoherence. Furthermore, we present an explicit expression for the probability distribution of the decoherent one-dimensional quantum walk in terms of the corresponding coherent probabilities, and show that this type of decoherence smooths the probability distribution.

Matthew Chen, Natalie Klco

One aspect of complexity for quantum many-body systems resides in their ability to exhibit entanglement, uniquely quantum correlations central to quantum computation. To quantitatively explore the diminishing effect that quantum noise has on entanglement resources, we focus on the negativity witness, an entanglement measure based on local time reversal transformations that provides a perfect witness in simple physical contexts. Beyond calculation of the negativity, we analyze the associated eigenvalue spectra of partially transposed density matrices for qudit-qudit bipartitions, finding that higher negativity rank provides greater(reduced) robustness to targeted(depolarizing) noise. In particular, we extend the maximum number of separable states that can be arbitrarily mixed into an entangled pure ensemble while retaining negativity to be exactly equal to the original negativity rank. Furthermore, we report how understanding the role of the negativity rank with respect to the completely depolarizing channel allows direct calculation of (1) certain noise boundaries for the Absolutely Positive Partial Transpose (APPT) subspace beyond which no unitary operator is capable of generating negativity and (2) the maximum qutrit-qutrit APPT purity. Beyond proving tight bounds and contributing to the ongoing search for APPT entanglement, these results expand our understanding of the nuanced relationship between computation with entanglement and practical environments for operating quantum devices.

Feng Liu, Fei Li, Yunxia Wei

Nicolas Brunner

Ferdi Altintas, Resul Eryiğit

Kai Wang, Yajie Li, Xiaokun Yang +2 more

The effect of quantum noise on different bit positions of ciphertext is different in Quantum Noise Stream Cipher. This feature makes the QNSC system vulnerable to different attacks, e.g. fast correlation attack. To balance the effect of quantum noise on different bit positions, this paper proposes a ciphertext mapping method based on Bitwise NOT Operation (BNO). The performance of BNO-based 16QAM/QNSC is investigated with different intensity noises and basis states. The simulation results demonstrate that bit error rate in different bit positions of ciphertext is close to 0.5 by using BNO-based 16QAM/QNSC. In addition, the proposed method has little influence on symbol error rate of Bob.