Experimental superposition of time directions

Abstract

In the macroscopic world, time is intrinsically asymmetric, flowing in a specific direction, from past to future. However, the same is not necessarily true for quantum systems, as some quantum processes produce valid quantum evolutions under time reversal. Supposing that such processes can be probed in both time directions, we can also consider quantum processes probed in a coherent superposition of forwards and backwards time directions. This yields a broader class of quantum processes than the ones considered so far in the literature, including those with indefinite causal order. In this work, we demonstrate for the first time an operation belonging to this new class: the quantum time flip. Using a photonic realisation of this operation, we apply it to a game formulated as a discrimination task between two sets of operators. This game not only serves as a witness of an indefinite time direction, but also allows for a computational advantage over strategies using a fixed time direction, and even those with an indefinite causal order.

Improved manuscript, closer to published version. 15 pages, 5 figures

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Cited by in corpus (7)

• Experimental Aspects of Indefinite Causal Order in Quantum Mechanics
• Memory in quantum processes with indefinite time direction and causal order
• Indefinite Time Directed Quantum Metrology
• Expressibility, entangling power and quantum average causal effect for causally indefinite circuits
• Path superposition activating perfect quantum teleportation ability for separable states
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