Environment-Assisted Speed-up of the Field Evolution in Cavity Quantum Electrodynamics

Abstract

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...

Controlling open quantum systems: tools, achievements, and limitations

“…In quantum dots, phonon-assisted decoherence was minimized [177,178]. Interestingly, presence of the environment may improve the quantum speed limit [179,180]. This has not yet been explored systematically but could be done, using quantum optimal control.…”

Solvable multistate model of Landau-Zener transitions in cavity QED

“…Traditional realizations of cavity QED in atomic physics [1] have recently been extended to numerous solid state applications, including superconductors [2], spins of defects and quantum dots [3] and fiber optics [4]. One of the most fundamental models in cavity QED is the Tavis-Cummings model [5] that describes coupling of N s two-level systems, which we will call spins for simplicity, to a single optical cavity mode and an external field.…”

“…The model (1) conserves the number of excitations, i.e. the Hamiltonian commutes with the operator of the number of bosons plus the number of spins up:…”

Relationship between quantum speed limit time and memory time in a photonic-band-gap environment

“…Interestingly, it is found that the non-Markovian evolution induced by the memory effect of environment can accelerate the quantum evolution13141516. A good example of this is the situation where an atom is coupled to a leaky single mode cavity13.…”