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-offreedom 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.

No abstract

No abstract

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.

Using experiments and theory, we investigate the behavior of nonlinear acoustic modes in a physical system composed of an array of three coupled acoustic waveguides, two of which are externally driven with two different frequencies. Nonlinear modes with frequency given by linear combinations of the driving frequencies are realizations of so-called logical phi-bits. A phi-bit is a two-state degree of freedom of an acoustic wave, which can be in a coherent superposition of states with complex amplitude coefficients, i.e., a qubit analogue. We demonstrate experimentally that phi-bit modes are supported in the array of waveguides. Using perturbation theory, we show that phi-bits may result from the intrinsic nonlinearity of the material used to couple the waveguides. We have also isolated possible effects on phi-bit states associated with the systems’ electronics, transducers and ultrasonic coupling agents used to probe the array and that may introduce extrinsic nonlinearities. These extrinsic effects are shown to be easily separable from the intrinsic behavior. The intrinsic behavior includes sharp jumps in phi-bit phases occurring over very narrow ranges of driving frequency. These jumps may also exhibit hysteretic behavior dependent on the direction of driving frequency tuning. The intrinsic states of phi-bits and multiple nonlinearly correlated phi-bits may serve as foundation for robust and practical quantum-analogue information technologies.