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Register a new userExperimental observation of Aharonov-Bohm caging using orbital angular momentum modes in optical waveguides
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C. Jorg
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The discovery of artificial gauge fields, controlling the dynamics of uncharged particles that otherwise elude the influence of standard electric or magnetic fields, has revolutionized the field of quantum simulation. Hence, developing new techniques to induce those fields is essential to boost quantum simulation in photonic structures. Here, we experimentally demonstrate in a photonic lattice the generation of an artificial gauge field by modifying the input state, overcoming the need to modify the geometry along the evolution or imposing the presence of external fields. In particular, we show that an effective magnetic flux naturally appears when light beams carrying orbital angular momentum are injected into waveguide lattices with certain configurations. To demonstrate the existence of that flux, we measure the resulting Aharonov-Bohm caging effect. Therefore, we prove the possibility of switching on and off artificial gauge fields by changing the topological charge of the input state, paving the way to access different topological regimes in one single structure, which represents an important step forward for optical quantum simulation.
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In this work we demonstrate the existence of orbital angular momentum (OAM) bright and dark supermodes in a three-evanescently coupled cylindrical waveguides system. Bright and dark supermodes are characterized by their coupling and decoupling from one of the waveguides, respectively. In addition, we demonstrate that complex couplings between modes of different waveguides appear naturally due to the characteristic spiral phase-front of OAM modes in two-dimensional configurations where the waveguides are arranged forming a triangle. Finally, by adding dissipation to the waveguide uncoupled to the dark supermode, we are able to filter it out, allowing for the design of OAM mode clonners and inverters.
We reveal for the first time a direct relationship between the diffraction of optical beams and their carrying orbital angular momentum (OAM). We experimentally demonstrate a novel phenomenon that the anisotropic diffraction can be induced by the OAM, predicted by us [Opt. Express, textbf{26}, 8084 (2018)], via the propagations of the elliptic beams with the OAM in linearly and both-linearly-and-nonlinearly isotropic media, respectively. In the former case, when its carrying OAM equals the so-called critical OAM, the spiraling elliptic Gaussian beam (fundamental eigenmode) is observed in the free space, where only the eigenmode with cylindrical-symmetry is supposed to exist for the beam without the OAM. In the latter case, the spiraling elliptic soliton, predicted by Desyatnikov et al. [Phys. Rev. Lett, textbf{104}, 053902 (2010)], is observed to stably propagate in a cylindrical lead glass. The power-controllable rotation of such an elliptic beam is also experimentally demonstrated.
This is a brief review on the theoretical interpretation of the Aharonov-Bohm effect, which also contains our new insight into the problem. A particular emphasis is put on the unique role of electron orbital angular momentum, especially viewed from the novel concept of the physical component of the gauge field, which has been extensively discussed in the context of the nucleon spin decomposition problem as well as the photon angular momentum decomposition problem. Practically, we concentrate on the frequently discussed idealized setting of the Aharonov-Bohm effect, i.e. the interference phenomenon of the electron beam passing around the infinitely-long solenoid. One of the most puzzling observations in this Aharonov-Bohm solenoid effect is that the pure-gauge potential outside the solenoid appears to carry non-zero orbital angular momentum. Through the process of tracing its dynamical origin, we try to answer several fundamental questions of the Aharonov-Bohm effect, which includes the question about the reality of the electromagnetic potential, the gauge-invariance issue, and the non-locality interpretation, etc.
The linear diamond chain with fine-tuned effective magnetic flux has a completely flat energy spectrum and compactly-localized eigenmodes, forming an Aharonov-Bohm cage. We study numerically how this localization is affected by different types of disorder (static and time-evolving) relevant to recent realizations of Aharonov-Bohm cages in periodically-modulated optical waveguide arrays. We demonstrate robustness of localization under static and periodically-evolving disorder, while in contrast non-quenched (time-dependent) disorder leads to wavepacket spreading and delocalization.
Geometric phases appear ubiquitously in many and diverse areas of physical sciences, ranging from classical and molecular dynamics to quantum mechanics and solid-state physics. In the realm of optics, similar phenomena are known to emerge in the form of a Pancharatnam-Berry phase whenever the polarization state traces a closed contour on the Poincare sphere. While this class of geometric phases has been extensively investigated in both free-space and guided wave systems, the observation of similar effects in photon-tunneling arrangements has so far remained largely unexplored. Here, for the first time, we experimentally demonstrate that the tunneling or coupling process in a twisted multi-core fiber system can display a chiral geometric phase accumulation-analogous to that of the Aharonov-Bohm effect resulting from the presence of a nonzero magnetic flux. In our experiments, the tunneling geometric phase is manifested through the interference of the corresponding supermodes. In this system, and for specific values of the twist rate, the tunneling between opposite cores ceases, thus signifying an Aharonov-Bohm suppression of tunneling. Our work provides the first observation of this intriguing effect in an optical setting.
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