Subtleties of witnessing quantum coherence in nonisolated systems

Abstract

Identifying non-classicality unambiguously and inexpensively is a long-standing open challenge in physics. The No-Signalling-In-Time protocol was developed as an experimental test for macroscopic realism, and serves as a witness of quantum coherence in isolated quantum systems by comparing the quantum state to its completely dephased counterpart. We show that it provides a lower bound on a certain resource-theoretic coherence monotone. We go on to generalise the protocol to the case where the system of interest is coupled to an environment. Depending on the manner of the generalisation, the resulting witness either reports on system coherence alone, or on a disjunction of system coherence with either (i) the existence of non-classical system-environment correlations or (ii) non-negligible dynamics in the environment. These are distinct failure modes of the Born approximation in non-isolated systems.

Experimental test of non-macrorealistic cat states in the cloud

“…Then we run another experiment where one deterministically prepares the system in the state i, and measures p t2;t1 ðjjiÞ. This scenario, which we call 'prepare-and-measure', replaces the non-invasive measurement assumption with an ideal-state preparation and a more explicit non-Markovian evolution assumption (see refs 53,63 ).…”

“…(14) alone is equivalent to the test employed in ref. 63 . One just needs to sum up the outcomes j in Eq.…”

Towards a spectroscopic protocol for unambiguous detection of quantum coherence in excitonic energy transport

“…We briefly revisit the idea behind this witness before presenting an experimental scheme for obtaining it. For a more detailed discussion of W b (t; T ) we refer to our previous work [33]. The quantum state of a system coupled to a bath subject to a joint unitary evolution propagates between two times t P and t P as (see Fig.…”

“…where τ = t P − t P , can therefore serve as a witness to the quantum coherence of the state at time t Γ provided Γ is non-invasive in that it excises the off-diagonal elements in ρ SB (t Γ ) instantaneously without affecting the subsequent dynamics in any way [24,33].…”

“…The same is true when the system under consideration is not isolated from its environment -as is the case for electronic excitations of chromophores in EET in relation to its vibrational modes, provided the Born approximation is satisfied at the time of this interruption. If not, as is likely in practice, subtleties arise [33].…”