The asymmetric quantum Rabi model in the polaron picture

Abstract

The concept of the polaron in condensed matter physics has been extended to the Rabi model, where polarons resulting from the coupling between a two-level system and single-mode photons represent two oppositely displaced oscillators. Interestingly, tunneling between these two displaced oscillators can induce an anti-polaron, which has not been systematically explored in the literature, especially in the presence of an asymmetric term. In this paper, we present a systematic analysis of the competition between the polaron and anti-polaron under the interplay of the coupling strength and the asymmetric term. While intuitively the anti-polaron should be secondary owing to its higher potential energy, we find that, under certain conditions, the minor anti-polaron may gain a reversal in the weight over the major polaron. If the asymmetric amplitude ǫ is smaller than the harmonic frequency ω, such an overweighted anti-polaron can occur beyond a critical value of the coupling strength g; if ǫ is larger, the anti-polaron can even be always overweighted at any g. We propose that the explicit occurrence of the overweighted anti-polaron can be monitored by a displacement transition from negative to positive values. This displacement is an experimentally accessible observable, which can be measured by quantum optical methods, such as balanced Homodyne detection.

Frequency-renormalized multipolaron expansion for the quantum Rabi model

“…neling between two energy levels. This method can be applied to other more complicated quantum models like the spin-boson model [33,34], multi-qubit QRM [43,44], anisotropic QRM [45], and biased or asymmetric Rabi model [46] and so on. The further works are in progress.…”

Nonorthogonal-qubit-state expansion for the asymmetric quantum Rabi model

“…We notice that there is a correspondence between the NOQ Ansatz and the so-called polaron picture [41,43,50,[52][53][54]. This correspondence is not immediately obvious in the form of Eq.…”

Entanglement resonance in the asymmetric quantum Rabi model

“…Reflecting the non-locality nature of quantum physics, entanglement has been seen as a basic resource in quantum technology [52]. It also has been applied to study the level crossing in anisotropic QRM [39], spectral classification [53], and quantum phase transition in the QRM [54]. Here, by studying the entanglement of the eigenstates of the A-QRM in different coupling strengths and driving amplitudes, we find that the entanglement is sensitive to the energy-spectrum feature.…”