scholarly journals Indefinite causal order enables perfect quantum communication with zero capacity channels

2021 ◽  
Vol 23 (3) ◽  
pp. 033039 ◽  
Author(s):  
Giulio Chiribella ◽  
Manik Banik ◽  
Some Sankar Bhattacharya ◽  
Tamal Guha ◽  
Mir Alimuddin ◽  
...  
2020 ◽  
Vol 20 (15&16) ◽  
pp. 1261-1280
Author(s):  
Francisco Delgado ◽  
Carlos Cardoso-Isidoro

Indefinite causal order has introduced disruptive procedures to improve the fidelity of quantum communication by introducing the superposition of { orders} on a set of quantum channels. It has been applied to several well characterized quantum channels as depolarizing, dephasing and teleportation. This work analyses the behavior of a parametric quantum channel for single qubits expressed in the form of Pauli channels. Combinatorics lets to obtain affordable formulas for the analysis of the output state of the channel when it goes through a certain imperfect quantum communication channel when it is deployed as a redundant application of it under indefinite causal order. In addition, the process exploits post-measurement on the associated control to select certain components of transmission. Then, the fidelity of such outputs is analysed to characterize the generic channel in terms of its parameters. As a result, we get notable enhancement in the transmission of information for well characterized channels due to the combined process: indefinite causal order plus post-measurement.


Science ◽  
2008 ◽  
Vol 321 (5897) ◽  
pp. 1812-1815 ◽  
Author(s):  
G. Smith ◽  
J. Yard

Author(s):  
Seid Koudia ◽  
Abdelhakim Gharbi

Quantum non-Gaussian states are considered a useful resource for many tasks in quantum information processing, from quantum metrology and quantum sensing to quantum communication and quantum key distribution. Another useful tool that is gaining attention is the newly constructed quantum switch. Its applications in many tasks in quantum information have been proved to outperform many existing schemes in quantum communication and quantum thermometry. In this contribution, we demonstrate this to be very useful for engineering highly non-Gaussian states from Gaussian operations whose order is controlled by degrees of freedom of a control qubit. The nonconvexity of the set of Gaussian states and the set of Gaussian operations guarantees the emergence of non-Gaussianity after post-selection on the control qubit deterministically, in contrast to existing protocols in the literature. The nonclassicality of the resulting states is discussed accordingly.


Symmetry ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 1904
Author(s):  
Carlos Cardoso-Isidoro ◽  
Francisco Delgado

Quantum teleportation has had notorious advances in the last decade, being successfully deployed in the experimental domain. In other terrains, the understanding of indefinite causal order has demonstrated a valuable enhancement in quantum communication to correct channel imperfections. In this work, we address the symmetries underlying imperfect teleportation when it is assisted by indefinite causal order to correct the use of noisy entangled resources. In the strategy being presented, indefinite causal order introduces a control state to address the causal ordering. Then, by using post-selection, it fulfills the teleportation enhancement to recover the teleported state by constructive interference. By analysing primarily sequential teleportation under definite causal order, we perform a comparison basis for notable outcomes derived from indefinite causal order. After, the analysis is conducted by increasing the number of teleportation processes, thus suggesting additional alternatives to exploit the most valuable outcomes in the process by adding weak measurement as a complementary strategy. Finally, we discuss the current affordability for an experimental implementation.


Quantum ◽  
2017 ◽  
Vol 1 ◽  
pp. 10 ◽  
Author(s):  
Mateus Araújo ◽  
Adrien Feix ◽  
Miguel Navascués ◽  
Časlav Brukner

To study which are the most general causal structures which are compatible with local quantum mechanics, Oreshkov et al. introduced the notion of a process: a resource shared between some parties that allows for quantum communication between them without a predetermined causal order. These processes can be used to perform several tasks that are impossible in standard quantum mechanics: they allow for the violation of causal inequalities, and provide an advantage for computational and communication complexity. Nonetheless, no process that can be used to violate a causal inequality is known to be physically implementable. There is therefore considerable interest in determining which processes are physical and which are just mathematical artefacts of the framework. Here we make the first step in this direction, by proposing a purification postulate: processes are physical only if they are purifiable. We derive necessary conditions for a process to be purifiable, and show that several known processes do not satisfy them.


2012 ◽  
Author(s):  
Dirk Englund ◽  
Karl Berggren ◽  
Jeffrey Shapiro ◽  
Chee W. Wong ◽  
Franco Wong ◽  
...  

2011 ◽  
Author(s):  
Dirk Englund ◽  
Karl Berggren ◽  
Seth Lloyd ◽  
Jeffrey Shapiro ◽  
Chee W. Wong ◽  
...  

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