Dynamical Phases and Quantum Correlations in an Emitter-Waveguide System with Feedback

Abstract

We investigate the creation and control of emergent collective behavior and quantum correlations using feedback in an emitter-waveguide system using a minimal model. Employing homodyne detection of photons emitted from a laser-driven emitter ensemble into the modes of a waveguide allows to generate intricate dynamical phases. In particular, we show the emergence of a time-crystal phase, the transition to which is controlled by the feedback strength. Feedback enables furthermore the control of many-body quantum correlations, which become manifest in spin squeezing in the emitter ensemble. Developing a theory for the dynamics of fluctuation operators we discuss how the feedback strength controls the squeezing and investigate its temporal dynamics and dependence on system size. The largely analytical results allow to quantify spin squeezing and fluctuations in the limit of large number of emitters, revealing critical scaling of the squeezing close to the transition to the time-crystal. Our study corroborates the potential of integrated emitter-waveguide systemswhich feature highly controllable photon emission channels -for the exploration of collective quantum phenomena and the generation of resources, such as squeezed states, for quantum enhanced metrology.

Quantum fluctuations and correlations in open quantum Dicke models

“…For each parameter regime, we consider the dynamics of fluctuations emerging, in the thermodynamic limit, from an initial state which is stationary with respect to the mean-field observables and possesses Gaussian fluctuations. In this setting, the covariance matrix obeys the differential equation [28,44]…”

“…Finally, we analyze quantum correlations within each subsystem separately. These are measured by the squeezing parameter ξ = 2 min(Θ 1 , Θ 2 ) [44,[56][57][58] where Θ 1 , Θ 2 denote the eigenvalues of Γ s for spin squeezing and of Γ b for boson squeezing. The parameter ξ quantifies the minimum variance among all possible quadrature operators.…”

Composite picosecond control of atomic state through a nanofiber interface

“…In this scenario, a potentially paradigm-shifting technique is to precisely control the atomic dipoles with subwavelength spatial resolution. Similar to the case of free space control [10,11], the precise atomic dipolar spin control can be designed to modify the collective coupling strength, to reversible suppress collective emission into the guided mode on demand, and to access the subradiant manifold of collective dipoles [12,13] featuring many-body nonlinear quantum optics in the confined geometry [1,[14][15][16][17][18][19][20][21][22][23]. However, unlike controlling magnetic spins [24][25][26][27] or narrow optical transitions [28][29][30], optical control of strong transitions with qubit-level precision is itself an outstanding challenge.…”

Dipole-dipole Interactions Through a Lens

“…The ability to collect light from an emitter and guide it over long distances enables a variety of collective quantum optical phenomena, which has been a subject of significant interest in recent theoretical [12][13][14][15][16][17][18][19][20][21][22][23] and experimental works [24][25][26][27][28] in waveguide quantum electrodynamics (QED). Typically, these implementations rely on the evanescent light-matter coupling wherein the emitters are either placed nearby or embedded in a solid waveguide structure.…”