Abstract
We study the squeezing of output quadratures of an electro-magnetic field escaping from a resonator coupled to a general quantum system with arbitrary interaction strengths. The generalized theoretical analysis of output squeezing proposed here is valid for all the interaction regimes of cavity-quantum electrodynamics: from the weak to the strong, ultrastrong, and deep coupling regimes. For coupling rates comparable or larger then the cavity resonance frequency, the standard input–output theory for optical cavities fails to calculate the variance of output field-quadratures and predicts a non-negligible amount of output squeezing, even if the system is in its ground state. Here we show that, for arbitrary interaction strength and for general cavity-embedded quantum systems, no squeezing can be found in the output-field quadratures if the system is in its ground state. We also apply the proposed theoretical approach to study the output squeezing produced by: (i) an artificial two-level atom embedded in a coherently-excited cavity; and (ii) a cascade-type three-level system interacting with a cavity field mode. In the latter case the output squeezing arises from the virtual photons of the atom-cavity dressed states. This work extends the possibility of predicting and analyzing the results of continuous-variable optical quantum-state tomography when optical resonators interact very strongly with other quantum systems.
Highlights
A new regime of cavity quantum electrodynamics (QED) has been experimentally reached in different solid state systems and spectral ranges [1,2,3,4,5,6,7,8]
The splitting can be attributed to the resonant coupling of the states |e, 0 and |g, 2, the ultrastrong coupling (USC) regime implies that the resulting dressed states | ̃2 and | ̃3 contain small contributions from other bare states, as |g, 1 and |e, 1
This splitting cannot be found in the rotating wave approximation, where the coherent coupling between states with a different number of excitations is not allowed, nor does it occur with the standard Rabi Hamiltonian (θ = 0)
Summary
A new regime of cavity quantum electrodynamics (QED) has been experimentally reached in different solid state systems and spectral ranges [1,2,3,4,5,6,7,8]. This result stems from the finite number of photons which are present in the ground state due to the counter-rotating terms in the interaction Hamiltonian [19] It has been shown [13, 20] that the photon rate emitted by a resonator and detectable by a photo-absorber is no longer proportional to a†(t)a(t) (as predicted by the standard input-output theory), where aand a† are the photon destruction and creation operators of the cavity mode, but to x−(t)x+(t) , where x+(t) is the positive frequency component of the quadrature operator x(t) = a(t) + a†(t) and x−(t) = (x+(t))†. We demonstrate that for arbitrary cavity-embedded quantum systems, independently on the coupling rate, no squeezing can be found in the output field quadratures if the system is in its ground state
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
