A team of Austrian Researchers has recently published a paper in the Optica Publishing group that has proven a universal time-rewinding protocol for two-level quantum systems in the study. Unlike earlier proposed protocols, their work has shown an arbitrarily high success rate. It is considered asymptotically optimal regarding the time necessary to conduct the rewinding, indicating whether quantum mechanics principles permit such operations.
Researchers from the University of Vienna, Faculty of Physics & Research Network Quantum & Aspects of Space-Time, P. Schiansky, T. Strömberg, and V. Saggio, together with the team from Institute for Quantum Optics and Quantum Information, D. Trillo, B. Dive, M. Navascués, and P. Walther led this experiment, and have discovered this new phenomenon.
Given control over the system in issue, the unitary structure of time development makes it essentially reversible in quantum physics. Surprisingly, multiple recent demonstrations of protocols for reverting unknown unitaries in settings where even the interactions with the target system are unknown have occurred. Because of their probabilistic nature, these protocols raise the question of whether time-reversal could be conducted deterministically.
This conceptual simplicity, which directly translates into a straightforward laboratory implementation based on the recently invented quantum switch, enables us to overcome the restrictions of prior ideas. In its most basic form, the quantum switch transforms two unitaries into a controlled superposition of the two gates being applied in different orders.
Their research demonstrated a protocol using a photonic platform, reverting the discrete time evolution of a polarization state with an average state fidelity of more than 95%.
In this study, the researchers presented a revolutionary universal time-reversal protocol whose success probability can be arbitrarily high, making it deterministic. The protocol is built around the non-commutativity of quantum operators, a fundamental principle in quantum mechanics.
The Universal time-reversal protocol
According to the paper, while trials using cold atom interferometers revealed the fundamental building elements for the protocol, big particle implementations would still be complex. In contrast, the photonic implementation in the study provides a very simple and robust solution that uses a mature technical platform, specifically for constructing the commutator of temporal evolutions via a quantum switch.
The results demonstrated that the approach is not limited to photonic quantum systems because the concepts used make no assumptions about the physical system to which the protocol is applied.
Given recent advancements in integrated quantum photonics, the researchers predicted that fully monolithic designs capable of better fidelity operations would enable demonstrations of active error correction in the near future. Further research could involve non-optical implementations of the protocol and extensions to higher dimensions, as stated.
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