Visualization of Coherent Destruction of Tunneling in an Optical Double Well System

Abstract

We report on a direct visualization of coherent destruction of tunneling (CDT) of light waves in a double well system which provides an optical analog of quantum CDT as originally proposed by Grossmann, Dittrich, Jung, and Hänggi [Phys. Rev. Lett. 67, 516 (1991)]. The driven double well, realized by two periodically-curved waveguides in an Er:Yb-doped glass, is designed so that spatial light propagation exactly mimics the coherent space-time dynamics of matter waves in a driven double-well potential governed by the Schrödinger equation. The fluorescence of Er ions is exploited to image the spatial evolution of light in the two wells, clearly demonstrating suppression of light tunneling for special ratios between frequency and amplitude of the driving field.PACS numbers: 42.50. Hz, 03.65.Xp, 42.82.Et Control of quantum tunneling by external driving fields is a subject of major relevance in different areas of physics [1,2]. The driven double-well potential has provided since more than one decade a paradigmatic model to investigate tunneling control in such diverse physical systems as cold atoms in optical traps, superconducting quantum interference devices, multi-quantum dots and spin systems. Depending on the strength and frequency of the driving field, suppression [3,4] or enhancement [5] of tunneling can be achieved. Tunneling enhancement is usually observed for high field strengths and driving frequencies close to the classical oscillation frequency at the bottom of each well. Since the enhancement generally involves a transition through an intermediate state which is chaotic for strong enough driving amplitudes, it is often referred to as "chaos-assisted tunneling" [1,6]. Observations of chaos-assisted tunneling have been reported in atom optics experiments [7] and in electromagnetic analogs of quantum mechanical tunneling [8,9]. In particular, tunneling enhancement has been observed in two coupled optical waveguides [9]. In the opposite limit, Grossmann, Hänggi and coworkers [3] found that, for certain parameter ratios between amplitude and frequency of the driving, tunneling can be brought to a standstill. They termed this effect "coherent destruction of tunneling" (CDT) and, since then, it has been of continuing interest. Driven tunneling is related to the problem of periodic nonadiabatic level crossing and Landau-Zener (LZ) transitions [1,10]. In particular, in the strong modulation limit CDT may be viewed as a destructive interference effect [10]. In spite of the great amount of theoretical work devoted to CDT, to date most of experimental evidences of CDT are rather indirect. In condensed-matter systems, dephasing and many-particle effects make tunneling control more involved [11]. In Ref.[12] coherent control of Rabi oscillations in Josephson-junction circuits irradiated by microwaves has been reported, however the condition for CDT was not reached. Quantum interference effects and evidences of CDT in qubit systems have been recently reported in [13,14], whereas suppression of quantum diffusion, als...

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