Abstract
Cavity-QED systems have recently reached a regime where the light-matter interaction strength amounts to a non-negligible fraction of the resonance frequencies of the bare subsystems. In this regime, it is known that the usual normal-order correlation functions for the cavity-photon operators fail to describe both the rate and the statistics of emitted photons. Following Glauber’s original approach, we derive a simple and general quantum theory of photodetection, valid for arbitrary light-matter interaction strengths. Our derivation uses Fermi’s golden rule, together with an expansion of system operators in the eigenbasis of the interacting light-matter system, to arrive at the correct photodetection probabilities. We consider both narrow- and wide-band photodetectors. Our description is also valid for point-like detectors placed inside the optical cavity. As an application, we propose a gedanken experiment confirming the virtual nature of the bare excitations that enrich the ground state of the quantum Rabi model.
Highlights
The problem of the theoretical description of the photon-detection process was addressed by Glauber in ref.[1]
In cavity quantum electrodynamics[2,3], where atoms interact with discrete electromagnetic field modes confined in a cavity, it is often the photons leaking out from the cavity that are detected in experiments
The master equation cannot be directly applied to derive the output field that is to be detected. This gap between the quantum system and the external detector is typically bridged by input-output theory[6,7], which can be used to determine the effect of the intra-cavity dynamics on the quantum statistics of the output field in a very clear and simple way
Summary
We consider a generic quantum system with light-matter coupling. This quantum system is weakly coupled to a photo-absorber, which is modelled as a quantum system with a collection of modes at zero temperature, described by the Hamiltonian (we set = 1 throughout this article unless otherwise specified). (3), the results from Sec. II imply that the probability to absorb a photon from the quantum circuit in the initial state |Ei〉 is proportional to the mean value of the operator x−x+, where, in this case, x+ = ∑ ∑ ∑ Φ(ZmPF) 〈Ej|(am + am† )|Ek〉|Ek〉〈Ej|. We observe that, in the presence of time-dependent Hamiltonians (e.g., an abrupt switch-off of the interaction)[34,35,88], or spontaneous decay effects[40], virtual photons can be converted (not directly detected) into real ones These considerations apply to artificial atoms coupled to resonators, and, in general, to any (natural or artificial) two-level system coupled to any bosonic mode. In QFT virtual particles can appear in any process described by a Feynman diagram where at some intermediate point energy conservation is violated
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
