Quantum optics with ultracold quantum gases: towards the full quantum regime of the light–matter interaction

Abstract

Although the study of ultracold quantum gases trapped by light is a prominent direction of modern research, the quantum properties of light were widely neglected in this field. Quantum optics with quantum gases closes this gap and addresses phenomena, where the quantum statistical nature of both light and ultracold matter play equally important roles. First, light can serve as a quantum nondemolition (QND) probe of the quantum dynamics of various ultracold particles from ultracold atomic and molecular gases to nanoparticles and nanomechanical systems. Second, due to dynamic light-matter entanglement, projective measurement-based preparation of the many-body states is possible, where the class of emerging atomic states can be designed via optical geometry. Light scattering constitutes such a quantum measurement with controllable measurement back-action. As in cavity-based spin squeezing, atom number squeezed and Schrödinger cat states can be prepared. Third, trapping atoms inside an optical cavity one creates optical potentials and forces, which are not prescribed but quantized and dynamical variables themselves. Ultimately, cavity QED with quantum gases requires a self-consistent solution for light and particles, which enriches the picture of quantum many-body states of atoms trapped in quantum potentials. This will allow quantum simulations of phenomena related to the physics of phonons, polarons, polaritons and other quantum quasiparticles.

Quantum-electrodynamical density-functional theory: Bridging quantum optics and electronic-structure theory

“…The self-consistent solutions of the Kohn-Sham equations (29) and (30) by construction obey Eqs. (27) and (28), as well as equations of motion similar to Eqs.…”

“…Already the validity of these effective Hamiltonians and their properties can be a matter of debate [24][25][26] and often further simplifications are adopted such as the JaynesCummings model in the rotating-wave approximation. The rapid progress in quantum-optical experiments, on the other hand, especially in the field of cavity QED [27][28][29][30] and circuit QED [31,32], allows us to study and control multiparticle systems ultrastrongly coupled to photons [33][34][35][36], where such a simple approximative treatment is no longer valid [37]. This new regime of light-matter interaction is widely unexplored for, e.g., molecular physics and material sciences [38].…”

Cavity-induced chiral states of fermionic quantum gases

“…Such measurements have been proposed [52][53][54][55][56][57][58] and conducted [59,60] in order to extract equal or many-time correlation functions of the atomic gas or the atomic quantum statistics.…”

Quantum backaction in spinor-condensate magnetometry

“…We also plan to include time dependence both of the magnetic field and of the optical measurement strength, e.g., stroboscopic measurements. In addition to understanding the potential sensitivity of condensate-based magnetic-field sensing, our formalism can also be applied to quantum-limited nondestructive imaging of magnetic textures in spinor condensates and the creation of novel many-body states via quantum nondemolition (QND) measurement [18].…”