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Research
Acoustic Pseudospin and Topological Metamaterials Laboratory
The Acoustic Pseudospin and Topological Metamaterials (APTM) Laboratory studies and illustrates a general connection between acoustic and quantum-mechanical waves for time-independent systems, due to a formal equivalence between the wave equation for sound in the acoustic limit and the Schrödinger equation. Interestingly, the mathematical framework underpinning a quantum system can be found, or engineered, in systems behaving according to classical physics. Motivated by this insight, the APTM lab focuses on analyzing classical acoustic systems with the aim of identifying advantages similar to those presented by true quantum systems.
Project 1: Acoustic Analogous to “Entangled” States of Quantum Bits (and Trits)
In this project, we focus on the nonseparability of superpositions of acoustic pseudospin states, which is analogous to quantum entanglement: the most fascinating property of quantum mechanics and the core/essential ingredient for applications of quantum information processing. Using specially designed acoustic waveguides, in a prototype setting, superpositions of amplitudes of acoustic waves that are analogous to Bell states can be prepared and tuned (over their corresponding Hilbert space). Acoustic analogues of Bell states can be realized such that they scale superlinearly (exponentially) with the number of available degrees of freedom. Acoustic Bell states can operate at room temperature unlike today’s true quantum information processing devices.
Using arrays of coupled acoustic waveguides, we have been able to experimentally demonstrate the concept of “classical entanglement” of superpositions of acoustic waves. These acoustic Bell states were realized between different degrees of freedom of the same physical manifestation, in particular, as the tensor products of orbital angular momentum (OAM) and pseudospin degrees of freedom. Noncontact Laser Doppler vibrometry have been used to measure the classically entangled Bell state: a feat impossible in true quantum systems due to quantum phenomenon of wave function collapse. COMSOL computational model of the three-dimensional-finite acoustic system further confirms the feasibility of the physical realization of acoustic Bell states and provide further insights of the design parameters.
Contributions: Our experimental realization and computational validation of nonseparable acoustic superpositions of states offer a transformative new solution to reach some of the goals of quantum information science using materials-based acoustic quantum analogues.
Project 2: Topological Characteristics in Classical Wave Metamaterials
Metamaterials are artificially structured materials, which takes into account the geometric arrangement of crystals rather than, for example, their chemical characteristics. Recently, the study of classical wave metamaterials has been rejuvenated by incorporating symmetry breaking elements that lead to nontrivial topology, which were also the topic of 2016 Nobel Prize in physics. By finely tuning the geometrical and material parameters of acoustic lattices/crystals, it is possible to engineer and introduce such topological characteristics that give rise to exciting new functional capabilities and applications. In this project, we work on the extension of the quantum topological states to phononic systems, benefiting from their large scale in both time and space, which makes the control of fabrication and the measurement process much easier and more robust. In particular, one class of topological acoustic system exploits amplitudes with a geometric phase or, more specifically, with a Berry phase, arising from symmetry breaking and leading to non-conventional topologies (see animations). The importance of finding the topological structures through Berry phases is that according to the bulk edge correspondence principle, at an interface between topologically different crystals, a localized state forms. Topological interface states have prospects for realization of disorder-robust one-way transport of information.
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