Quantum optics with quantum gases: controlled state reduction by designed light scattering

TL;DR

This paper explores how controlled light scattering in cavity QED with ultracold gases can generate and manipulate quantum states like atom-number squeezing and Schrödinger cat states through measurement back-action.

Contribution

It introduces a method to engineer atomic many-body states via designed light scattering and photodetection, enabling controllable quantum state preparation.

Findings

Detection at Bragg angles creates atom-number squeezed states.

Detection at diffraction minima produces macroscopic superposition states.

Transmission measurements offer more robust superposition states.

Abstract

Cavity enhanced light scattering off an ultracold gas in an optical lattice constitutes a quantum measurement with a controllable form of the measurement back-action. Time-resolved counting of scattered photons alters the state of the atoms without particle loss implementing a quantum nondemolition (QND) measurement. The conditional dynamics is given by the interplay between photodetection events (quantum jumps) and no-count processes. The class of emerging atomic many-body states can be chosen via the optical geometry and light frequencies. Light detection along the angle of a diffraction maximum (Bragg angle) creates an atom-number squeezed state, while light detection at diffraction minima leads to the macroscopic superposition states (Schroedinger cat states) of different atom numbers in the cavity mode. A measurement of the cavity transmission intensity can lead to atom-number squeezed or macroscopic superposition states depending on its outcome. We analyze the robustness of the superposition with respect to missed counts and find that a transmission measurement yields more robust and controllable superposition states than the ones obtained by scattering at a diffraction minimum.