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.