Quantum switching

A.B.M Masum Billah Mim

Debarshi Das, Somshubhro Bandyopadhyay

Recent results have shown that quantum theory is compatible with novel causal structures where events happen without a definite causal order. In particular, the quantum switch describes a process in which two quantum channels act in a coherent superposition of their two possible orders. Furthermore, the quantum switch can perform communication tasks that are impossible within the framework of the standard quantum Shannon theory. The present paper considers the scenario of one-shot heralded qubit communication using a higher-order quantum switch constructed from two quantum switches. Specifically, we show that two quantum switches put in a superposition of their alternative causal orders can transmit a qubit, without any error, with a probability strictly higher than that achievable with each quantum switch. We discuss three examples that demonstrate this communication advantage. Notably, a higher-order quantum switch not only can outperform useful quantum switches but also becomes useful as a resource even if the quantum switches making it up are useless.

Debarshi Das, Somshubhro Bandyopadhyay

The quantum switch describes a quantum operation in which two or more quantum channels act on a quantum system with the order of application determined by the state of an order quantum system. And by suitably choosing the state of the order system, one can create a quantum superposition of the different orders of application, which can perform communication tasks impossible within the framework of the standard quantum Shannon theory. In this paper, we consider the scenario of one-shot heralded qubit communication and ask whether there are protocols using a given quantum switch or switches that could outperform the given ones. We answer this question in the affirmative. We define a higher-order quantum switch composed of two quantum switches, with their order of application controlled by another order quantum system. We then show that the quantum switches placed in a quantum superposition of their alternative orders can transmit a qubit, without any error, with a probability higher than that achievable with the quantum switches individually. We demonstrate this communication advantage over quantum switches that are useful as a resource and those that are useless. We also show that there are situations where there is no communication advantage over the individual quantum switches.

Subhashish Banerjee

Malin Premaratne, Govind Prasad Agrawal

Tao Lian, Min Nie

In order to solve the switching problem of quantum entanglement signalling, a signalling switching strategy was proposed first. And then the signalling switching process under the circumstance that quantum terminal was connected in the same switches and different switches was analysed respectively. We simulated the throughput rate of quantum signalling switches at last. The results show that throughput rate has a close relationship with swapping measurement success rate. The quantum signalling switches throughput rates (QTR) raise exponent-liked with the raising of measurement success rate. The QTR raises as the measurement time reduce on the condition of constant measurement success rate. The measurement time therefore should be less than lus to make sure that QTR of quantum signalling is more 30Mbps.