Showing papers by "Stéphane Guérin published in 2019"

Robust stimulated Raman exact passage using shaped pulses

Abstract: We developed single-shot shaped pulses for ultrahigh (UH)-fidelity population transfer on a three-level quantum system in $\mathrm{\ensuremath{\Lambda}}$ configuration. To ensure high fidelity, we use the Lewis-Riesenfeld (L-R) method to derive a family of solutions leading to an exact transfer, where the solutions follow a single dynamical mode of the L-R invariant. Among this family, we identify a tracking solution with a single parameter to control simultaneously the fidelity of the transfer, the population of the excited state, and robustness. We define a measure of the robustness of an UH-fidelity transfer as the minimum percentile deviation on the pulse areas at which the infidelity rises above ${10}^{\ensuremath{-}4}$. The robustness of our shaped pulses is found to be superior to that of Gaussian and adiabatically optimized pulses for moderate pulse areas.

Non-hermitian Hamiltonian description for quantum plasmonics: from dissipative dressed atom picture to Fano states

Abstract: We derive effective Hamiltonians for a single dipolar emitter coupled to a metal nanoparticle (MNP) with particular attention devoted to the role of losses. For small particles sizes, absorption dominates and a non-hermitian effective Hamiltonian describes the dynamics of the hybrid emitter-MNP nanosource. We discuss the coupled system dynamics in the weak and strong coupling regimes offering a simple understanding of the energy exchange, including radiative and non-radiative processes. We define the plasmon Purcell factors for each mode. For large particle sizes, radiative leakages can significantly perturbate the coupling process. We propose an effective Fano Hamiltonian including plasmon leakages and discuss the link with the quasi-normal mode description. We also propose Lindblad equations for each situation and introduce a collective dissipator for describing the Fano behavior.

Canonical quantization for quantum plasmonics with finite nanostructures

Abstract: The quantization of plasmons has been analyzed mostly under the assumption of an infinite-size bulk medium interacting with the electromagnetic field. We reformulate it for finite-size media, such as metallic or dielectric nanostructures, highlighting sharp differences. By diagonalizing the Hamiltonian by means of a Lippmann-Schwinger equation, we show the contribution of two sets of bosonic operators, one stemming from medium fluctuations and one from the electromagnetic field. The results apply to general models including dissipative and dispersive responses.

Cooperative emission in quantum plasmonic superradiance

Abstract: Plasmonic superradiance originates from the plasmon mediated strong correlation that builds up between dipolar emitters coupled to a metal nanoparticle. This leads to a fast burst of emission so that plasmonic superradiance constitutes ultrafast and extremely bright optical nanosources of strong interest for integrated quantum nano-optics platforms. We elucidate the superradiance effect by establishing the dynamics of the system, including all features like the orientation of the dipoles, their distance to the particle and the number of active plasmon modes. We determine an optimal configuration for Purcell enhanced superradiance. We also show superradiance blockade at small distances. PACS numbers: Introduction. In a seminal work, Dicke discovered that a set of N e atoms radiate collectively when they occupy a subwavelength volume. Their emission is much faster (τ Ne = τ 1 /N e) and stronger (I Ne = N 2 e I 1) than for independent atoms. This so-called superradiance originates from spontaneous phase-locking of the atomic dipoles through a same mode and is very similar to the building of cooperative emission in a laser amplifier [1]. Superradiant emission produces original states of light with applications such as narrow linewidth lasers [2] or quantum memories [3, 4]. Single collective excitation of atoms in a nanofiber has been demonstrated [5] and superradiant-like behaviour was suggested in a plasmon-ics junction [6] or a nanocrystal [7], pushing further integration capabilities of quantum technologies. Putso-vits and Shahbazyan identifyed plasmon enhanced collective emission for dipoles coupled to a metal nanopar-ticle (MNP) [8], considering a classical approach which however cannot describe the Dicke cascade at the origin of the cooperative emission. In this communication, taking benefit from recent advances on quantum plasmonics and open quantum systems [9-17], we derive a quantum approach for plasmonic superradiance and discuss the dy

Invariant-based optimal composite stimulated Raman exact passage

Abstract: Shortcuts to adiabaticity have been put forward for accelerating slow adiabatic passages in various quantum systems with tremendous applications for performing quantum information processing tasks. In this paper, we propose a hybrid protocol to achieve stimulated Raman exact passage (STIREP) by combining invariant-based inverse engineering, optimal control, and composite pulse approaches. We first derive the general solution and the corresponding pulse shapes by invariant-based inverse engineering. Counterintuitive and optimal (intuitive) pulse sequences are formulated in this context and incorporated into composite sequences. Such composite STIREP not only features robustness against the fluctuation of laser intensity, but also reduces the operation time and energy cost.

A generalized vibronic-coupling Hamiltonian for molecules without symmetry: Application to the photoisomerization of benzopyran

Abstract: We present a model for the lowest two potential energy surfaces (PESs) that describe the photoinduced ring-opening reaction of benzopyran taken as a model compound to study the photochromic ring-opening reaction of indolinobenzospiropyran and its evolution toward its open-chain analog. The PESs are expressed in terms of three effective rectilinear coordinates. One corresponds to the direction between the equilibrium geometry in the electronic ground state, referred to as the Franck-Condon geometry, and the minimum of conical intersection (CI), while the other two span the two-dimensional branching space at the CI. The model correctly reproduces the topography of the PESs. The ab initio calculations are performed with the extended multiconfiguration quasidegenerate perturbation theory at second order method. We demonstrate that accounting for electron dynamic correlation drastically changes the global energy landscape since some zwitterionic states become strongly stabilized. Quantum dynamics calculations using this PES model produce an absorption spectrum that matches the experimental one to a good accuracy.

Critical review of quantum plasmonic models for finite-size media

Abstract: We provide a critical analysis of some of the commonly used theoretical models to describe quantum plasmons. We summarize the standard approach based on a Fano diagonalization and we show explicit discrepancies in the obtained results by taking the limit of vanishing coupling between the electromagnetic field and the material medium. We then discuss the derivation of spontaneous emission in a plasmonic environment, which usually relies on a Green tensor and is based on an incomplete identity. The effect of the missing terms is calculated in a one-dimensional model.