Collective excitation and decay of waveguide-coupled atoms: from timed Dicke states to inverted ensembles

The collective absorption and emission of light by an ensemble of atoms is at the heart of many fundamental quantum optical effects and the basis for numerous applications. However, beyond weak excitation, both experiment and theory become increasingly challenging. Here, we explore the regimes from weak excitation to inversion with ensembles of up to one thousand atoms that are trapped and optically interfaced using the evanescent field surrounding an optical nanofiber. We realize strong inversion, with about 80% of the atoms being excited, and study their subsequent radiative decay into the guided modes. The data is very well described by a simple model that assumes a cascaded interaction of the guided light with the atoms. Our results contribute to the fundamental understanding of the collective interaction of light and matter and are relevant for applications ranging from quantum memories to sources of nonclassical light to optical frequency standards

Rapid flipping of parametric phase states

Since the invention of the solid-state transistor, the overwhelming majority of computers followed the von Neumann architecture that strictly separates logic operations and memory. Today, there is a revived interest in alternative computation models accompanied by the necessity to develop corresponding hardware architectures. The Ising machine, for example, is a variant of the celebrated Hopfield network based on the Ising model. It can be realized with artifcial spins such as the `parametron' that arises in driven nonlinear resonators. The parametron encodes binary information in the phase state of its oscillation. It enables, in principle, logic operations without energy transfer and the corresponding speed limitations. In this work, we experimentally demonstrate flipping of parametron phase states on a timescale of an oscillation period, much faster than the ringdown time \tau that is often (erroneously) deemed a fundamental limit for resonator operations. Our work establishes a new paradigm for resonator-based logic architectures.Comment: 6 pages, 3 figure

Feedback-cooling the fundamental torsional mechanical mode of a tapered optical fiber to 30 mK

Tapered optical fibers (TOFs) are used in many areas of physics and optical technologies ranging from coupling light into nanophotonic components to optical sensing and amplification to interfacing quantum emitters. Here, we study the fundamental torsional mechanical mode of the nanofiber-waist of a TOF using laser light. We find that this oscillator features a quality factor of up to $10^7$ and a $Qf$ product of 1 THz. We damp the thermal motion from room temperature to 28(7) mK by means of active feedback. Our results might enable new types of fiber-based sensors and lay the foundation for a novel hybrid quantum optomechanical platform

Linear feedback cooling of a levitated nanoparticle in free space

About a decade ago, optically levitated nanoparticles have been proposed for macroscopic tests of quantum mechanics. For such tests, the thermal motion of the particle’s center of mass is required to be close to its ground state of energy. Ever since these proposals, research groups around the world try to achieve ground-state cooling of optically levitated glass particles. In this dissertation, we cool the center-of-mass motion of a nanoparticle in an optical trap. Based on the position measurement of the particle, we apply a damping force in proportion to the particle’s speed, which leads to a cooling effect. We find that the cooling performance of our cold damping scheme is limited by the measurement imprecision. We analyze our detection principle theoretically and find an ideal detection scheme whose imprecision is at the fundamental noise level dictated by quantum mechanics. Such a Heisenberg-limited detection would, in principle, allow for ground-state feedback cooling. With these insights applied to our experiment, we cool the motion of our particle to an average of four quanta. Moreover, we resolve an asymmetry between the Stokes and anti-Stokes scattered light from the particle. This quantum effect allows us to calibrate the system to the ground state energy. Our work advances the research field of levitated optomechanics toward quantum control and therefore toward macroscopic tests of quantum mechanics

Optimal position detection of a dipolar scatterer in a focused field

ISSN:1094-1622ISSN:0556-2791ISSN:1050-294