IMSc Webinar

Quantum events: An indefinite causal structure

Tamal Guha

Indian Statistical Institute, Kolkata

The common notion of our daily life physics believes in a definite causal structure between two events. Special theory of relativity further allows the frame-dependent causal order of occurrence for two space-like separated events, which directs towards a subjective ignorance regarding their causal order. However, superposition, the fundamental non-classical ingredient of quantum theory, admits an inherent absence of causal order between two events beyond their subjective ignorance. Such quantum events have several strange as well as advantageous outcomes from the perspectives of computation, information processing and work extraction. We will show that placing two completely noisy transmission lines in an indefinite sequence, one is able to communicate perfectly. Further, we will demonstrate a similar scenario for a network of multiple receivers, each connected with the sender via noisy transmission lines and the identity of the true receiver is unknown to the sender before she communicates. Surprisingly, indefinite causal structure with almost zero quantum resource are able to perfectly accomplish such a task. Lastly, we will introduce a thermodynamic framework, where the indefinite causal order of occurrence of two thermal maps can enhance the potential of extracting work from a quantum system, even without any thermodynamic resource.

Ref:-
(1) New J. Phys. vol. 23, 033039 (2021)

(2) PRX Quantum vol. 2, 020350 (2021)

(3) Phys. Rev. A vol. 102, 032215 (2020)

Google Meet link of the talk: meet.google.com/uyg-jehp-oxo