Finite elements computational modeling of coupled elastic waveguides

The theoretical study of one-dimensional-infinite systems of elastically coupled parallel waveguides has established the existence of band structures with pseudo-spin characteristics. Those systems, which are named f-bits, have been shown to exhibit a spinor character associated with directional degrees of freedom, which makes them potential quantum mechanical analogs. The realization of such systems is challenged by the three-dimensional and finite nature of physical elastic waveguides. We address this problem, and with it the design of f-bits in general, by developing finite elements models based on COMSOL Multiphysics (R). We model systems of one or more coupled finite length Al rods. The analysis of their dispersion relations, transmission spectra, and amplitudes establishes their phi-bit character. For three coupled finite length Al rods, the elastic field is associated with wavefunctions, tensor products of a spinor part related to the directional degrees of freedom, and an orbital angular momentum part representing the phase of the coupled waveguides. We demonstrate the possibility of creating non-separable states between these degrees of freedom. (c) 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Experimental demonstration of elastic analogues of nonseparable qutrits

The creation of multilevel quantum states, qudits, has revolutionized concepts for quantum computing. Classical systems that capture behavior analogous to quantum systems have been demonstrated. In this spirit, we consider a three-level classical analogue of the qudit composed of coupled acoustic waveguides. Here, we demonstrate both the experimental realization of a three-level classical analogue of the qudit and the creation and tuning of nonseparable superpositions of two of these analogues, which are classically "entangled." Measurements of velocities and transmission inform our assignment of these nonseparable states.12 month embargo; published online: 20 April 2020This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Directional Elastic Pseudospin and Nonseparability of Directional and Spatial Degrees of Freedom in Parallel Arrays of Coupled Waveguides

We experimentally and numerically investigated elastic waves in parallel arrays of elastically coupled one-dimensional acoustic waveguides composed of aluminum rods coupled along their length with epoxy. The elastic waves in each waveguide take the form of superpositions of states in the space of direction of propagation. The direction of propagation degrees of freedom is analogous to the polarization of a quantum spin; hence, these elastic waves behave as pseudospins. The amplitude in the different rods of a coupled array of waveguides (i.e., the spatial mode of the waveguide array) refer to the spatial degrees of freedom. The elastic waves in a parallel array of coupled waveguides are subsequently represented as tensor products of the elastic pseudospin and spatial degrees of freedom. We demonstrate the existence of elastic waves that are nonseparable linear combinations of tensor products states of pseudospin/ spatial degrees of freedom. These elastic waves are analogous to the so-called Bell states of quantum mechanics. The amplitude coefficients of the nonseparable linear combination of states are complex due to the Lorentzian character of the elastic resonances associated with these waves. By tuning through the amplitudes, we are able to navigate both experimentally and numerically a portion of the Bell state Hilbert space.W. M. Keck FoundationOpen access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

The sound of Bell states

Nonseparable states, analogous to “entangled” states, have generated great scientific interest since the very beginning of quantum mechanics. To date, however, the concept of “classical nonseparability” has only been applied to nonseparable states of different degrees-of-freedom in laser beams. Here, we experimentally demonstrate the preparation and tunability of acoustic nonseparable states, i.e. Bell states, supported by coupled elastic waveguides. A Bell state is constructed as a superposition of elastic waves, each a tensor product of a spinor part and an orbital angular momentum (OAM) part, which cannot be factored as a single tensor product. We also find that the amplitude coefficients of the nonseparable superposition of states must be complex. By tuning these complex amplitudes, we are able to experimentally navigate a sizeable portion of the Bell state’s Hilbert space. The current experimental findings open the door to the extension of classical nonseparability to the emerging field of phononics.W.M. Keck FoundationOpen access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Experimental demonstration of coherent superpositions in an ultrasonic pseudospin

We experimentally demonstrate the existence and control of coherent superpositions of elastic states in the direction of propagation of an ultrasonic pseudospin i.e., a phi-bit. The experimental realization of this mechanical pseudospin consists of an elastic aluminum rod serving as a waveguide sandwiched between two heavy steel plates. The Hertzian contact between the rod and the plates leads to restoring forces which couple the directions of propagation (forward and backward). This coupling generates the coherence of the superposition of elastic states. We also demonstrate. phi-bit gate operations on the coherent superposition analogous to those used in quantum computing. In the case of a. phi-bit, the coherent superposition of states in the direction of propagation are immune to wave function collapse upon measurement as they result from classical waves.W.M. Keck FoundationOpen access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Temperature-controlled spatiotemporally modulated phononic crystal for achieving nonreciprocal acoustic wave propagation

International audienceWe computationally investigate a method for spatiotemporally modulating a material's elastic properties, leveraging thermal dependence of elastic moduli, with the goal of inducing nonreciprocal propagation of acoustic waves. Acoustic wave propagation in an aluminum thin film subjected to spatiotemporal boundary heating from one side and constant cooling from the other side was simulated via the finite element method. Material property modulation patterns induced by the asymmetric boundary heating are found to be non-homogenous with depth. Despite these inhomogeneities, it will be shown that such thermoelasticity can still be used to achieve nonreciprocal acoustic wave propagation

Direct Synthesis of van der Waals Solids

The stacking of two-dimensional layered materials, such as semiconducting transition metal dichalcogenides (TMDs), insulating hexagonal boron nitride (hBN), and semimetallic graphene, has been theorized to produce tunable electronic and optoelectronic properties. Here we demonstrate the direct growth of MoS₂, WSe₂, and hBN on epitaxial graphene to form large-area van der Waals heterostructures. We reveal that the properties of the underlying graphene dictate properties of the heterostructures, where strain, wrinkling, and defects on the surface of graphene act as nucleation centers for lateral growth of the overlayer. Additionally, we show that the direct synthesis of TMDs on epitaxial graphene exhibits atomically sharp interfaces. Finally, we demonstrate that direct growth of MoS₂ on epitaxial graphene can lead to a 10³ improvement in photoresponse compared to MoS₂ alone