Coherent states and quantum nonperturbing measurements

Nikolaos K. Kollas, Dimitris Moustos, Miguel R. Muñoz

Employing a nonperturbative approach based on an instantaneous interaction between a two-level Unruh-DeWitt detector and a massive scalar field, we investigate the ability of the latter to generate or destroy coherence in the detector by deriving the cohering and decohering power of the induced quantum evolution channel. For a field in a coherent state a previously unobserved effect is reported in which the amount of coherence that the field generates displays a revival pattern with respect to the size of the detector. Extending previous results into the nonperturbative regime of an arbitrary coupling strength, it is demonstrated that in the case of a thermal field with a positive mass a detector initialized in a maximally coherent state experiences a smaller degree of decoherence after its interaction with the field, compared to the massless case. In both examples for a suitable choice of detector radius, field energy, and coupling strength it is possible to infer the mass of the field by either measuring the coherence present in the detector in the case of an interaction with a coherent field or the corresponding decoherence of a maximally coherent state in the case of a thermal field. In view of recent advances in the study of Proca metamaterials, these results suggest the possibility of utilizing the theory of massive electromagnetism for the construction of novel applications for use in quantum technologies.

Lajos Diósi

Petar Simidzija, Eduardo Martín-Martínez

We study (nonperturbatively) the interactions of delta-coupled detectors with coherent states of a scalar field. We show that the time-evolved density matrix spectra of (i) a single detector, (ii) two detectors, and (iii) the partial transpose of the latter, are all independent of which coherent state the field was in. Furthermore, we find that the eigenvalues in (iii) are non-negative, implying that a delta-coupled detector pair cannot harvest entanglement from the vacuum, or any other coherent field state.

Alex W. Chin, Brieuc Le Dé, Étienne Mangaud +2 more

Biomolecular light-harvesting antennas operate as nanoscale devices in a regime where the coherent interactions of individual light, matter, and vibrational quanta are nonperturbatively strong. The complex behavior arising from this could, if fully understood, be exploited for myriad energy applications. However, nonperturbative dynamics are computationally challenging to simulate, and experiments on biomaterials explore very limited regions of the nonperturbative parameter space. So-called quantum simulators of light-harvesting models could provide a solution to this problem, and here we employ the hierarchical equations-of-motion technique to investigate the recent superconducting experiments of Poto\ifmmode \check{c}\else \v{c}\fi{}nik et al. [A. Poto\ifmmode \check{c}\else \v{c}\fi{}nik et al., Nat. Commun. 9, 904 (2018)] used to explore excitonic energy capture. By explicitly including the role of optical driving fields, nonperturbative dephasing noise, and the full multiexcitation Hilbert space of a three-qubit quantum circuit, we predict the measurable impact of these factors on transfer efficiency. By analysis of the eigenspectrum of the network, we uncover a structure of energy levels that allows the network to exploit optical ``dark'' states and excited-state absorption for energy transfer. We also confirm that time-resolvable coherent oscillations could be experimentally observed, even under the strong, nonadditive action of the driving and optical fields.

M. T. DiMario, Elohim Becerra