Output field-quadrature measurements and squeezing in ultrastrong cavity-QED

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 continuousvariable optical quantum-state tomography when optical resonators interact very strongly with other quantum systems. -+ ( )ˆ( ) x t x t , where + ( ) x t is the positive frequency component of the quadrature operator

Ultrastrongly dissipative quantum Rabi model

“…S(ω) is typically computed using the input-output formalism [30]. In this framework, output and input fields are related to the TLS state via a out = a out − i √ Γ TLS X − (t), where Γ TLS is the emission rate into the transmission line in wich the output signal is collected and X − is the negative frequency component of the qubit-TL coupling operators (σ x in our case) [31,32]. The emission spectrum is defined as…”

Enhanced optical squeezing from quasi-bound states in the continuum and Fano resonances without nonlinearity

“…According to equations (19a), (19b), (20) and the Boson commutation relation inside the PhC slab in equations (25a) and (25b), we can obtain the quantized input-output relation For convenience, we introduce operators…”

“…Thus, how to generate strongly squeezed states has become an important topic for decades. So far, there are considerable ways to obtain the squeezed states of light, including the optical parametric process [10][11][12][13][14], four-wave mixing [15][16][17], cavity-QED [18][19][20], soliton propagation [21,22] and so on. The commonality of these methods is that nonlinear optical processes have been employed.…”

Two-photon quantum Rabi model with superconducting circuits

“…Together with experimental advances, the theoretical interest in the USC regime has been steadily growing, concerning fundamental properties of ultrastrong light-matter interactions [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31], potential applications in quantum information [32][33][34][35][36][37] and effective implementations [38][39][40][41][42][43][44][45][46][47]. Such results have prompted a number of theoretical studies on generalizations of the QRM, including multiqubit [48] and multimode [49] cases, as well as anisotropic couplings [50,51] and two-photon interactions [52][53][54][55].…”