We measure the quantum speed of the state evolution of the field in a weakly-driven optical cavity QED system. To this end, the mode of the electromagnetic field is considered as a quantum system of interest with a preferential coupling to a tunable environment: the atoms. By controlling the environment, i.e., changing the number of atoms coupled to the optical cavity mode, an environment assisted speed-up is realized: the quantum speed of the state re-population in the optical cavity increases with the coupling strength between the optical cavity mode and this non-Markovian environment (the number of atoms). PACS numbers: 42.50.Pq, 42.50.Lc,32.50.+d Identifying time-optimized processes is a ubiquitous goal in virtually all areas of quantum physics, such as quantum communication [1], quantum computation [2], quantum thermodynamics [3], quantum control and feedback [4], and quantum metrology [5]. To this end, the notion of a quantum speed limit (QSL) has proven to be useful and important. The QSL determines the theoretical upper bound on the speed of evolution of a quantum system. It can be understood as a generalization of the Heisenberg uncertainty relation for energy and time. It has been derived for isolated, uncontrolled systems [6-8], time-dependent Hamiltonians [9-13], and more recently for more general open system dynamics [14][15][16][17][18][19][20][21]. Although fundamental in nature, practical consequences or even experimental applications of the QSL are still lacking. Nevertheless, achieving the maximal quantum speed is of high practical relevance, especially in the development of quantum information processing devices.On the theoretical side, a recent study [14] hinted at the possibility of observing speed-ups of the quantum evolution if an open quantum system is subject to environmental changes. Ref. [14] analyzes the dynamics of the damped Jaynes-Cummings model, which describes many cavity QED systems. These systems in both the intermediate and strong coupling regime can exhibit environmentassisted evolution [22] -such as non-exponential decay.This letter reports an experimental realization of the theoretically proposed environment assisted speed-up [14]. To this end, we look at the system in an unusual way -as just consisting of the cavity field. This allows us to treat the atomic number that generates the atomic polarization (the off diagonal elements of the atomic master equation) as a tunable environment with a range of coupling constants. We demonstrate that increasing the interaction of the optical cavity field with the environment by tuning the number of atoms, modifies the time dependent non-classical intensity correlation function, enhancing -speeds-up-the rate of evolution of the cavity field in a range with no clear oscillations present.Our cavity QED system operates in the intermediate coupling regime, where the cavity-atom parameters are of the same order: (g, κ, γ) /2π = (3.2, 4.5, 6.0) MHz. Here g denotes the electric dipole interaction strength of an atom maximally coupled to th...
Abstract. We implement a simple feedback mechanism on a two-mode cavity QED system to preserve the Zeeman coherence of a ground state superposition that generates quantum beats on the second-order correlation function. Our investigation includes theoretical and experimental studies that show how to prevent a shift away from the Larmor frequency and associated decoherence caused by Rayleigh scattering. The protocol consists of turning off the drive of the system after the detection of a first photon and letting it evolve in the dark. Turning the drive back on after a pre-set time reveals a phase accumulated only from Larmor precession, with the amplitude of the quantum beat more than a factor of two larger than with continuous drive.
We measure the modification of the transmission spectra of cold 87 Rb atoms in the proximity of an optical nanofiber (ONF). Van der Waals interactions between the atoms an the ONF surface decrease the resonance frequency of atoms closer to the surface. An asymmetric spectra of the atoms holds information of their spatial distribution around the ONF. We use a far-detuned laser beam coupled to the ONF to thermally excite atoms at the ONF surface. We study the change of transmission spectrum of these atoms as a function of heating laser power. A semi-classical phenomenological model for the thermal excitation of atoms in the atom-surface van der Waals bound states is in good agreement with the measurements. This result suggests that van der Waals potentials could be used to trap and probe atoms at few nanometers from a dielectric surfaces, a key tool for hybrid photonic-atomic quantum systems.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.