Quantum harmonic oscillators show up everywhere in physics, from electromagnetic fields to the vibrations of molecules. Their excitations come as bosons, things like photons or phonons, and the simplest interactions (the ones that just create or destroy single bosons) give you coherent states, the “plain vanilla” quantum states. Push further into higher-order nonlinear interactions, though, and things get more interesting: second-order interactions unlock squeezing, while going even higher opens the door to non-Gaussian states, the kind useful for continuous-variable quantum computation. The catch? These stronger interactions tend to be either too weak to use or demand very specialized hardware.
That’s where a hybrid setup comes in. Researchers coupled an oscillator to a spin through a linear interaction, an approach that sidesteps some of those hardware headaches. Working with a single trapped ion, the team combined two spin-dependent linear bosonic interactions to build up nonlinear bosonic interactions as high as fourth order. The focus was on generalized squeezing, and here’s the part that stands out: they didn’t just get regular squeezing, they demonstrated and characterized trisqueezing and quadsqueezing too, going on to reconstruct the Wigner function of these states.
It’s a small system, one ion, but the layered nonlinearity packed into it is what makes this notable. Second-order squeezing was already known territory; getting to third and fourth order in the same hybrid oscillator-spin platform is what pushes this into new ground, according to the findings published in Nature Physics.
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