Soft quantum vibrations of PT-symmetric nonlinear ion chain

TL;DR

This paper investigates the quantum dynamics of a PT-symmetric nonlinear ion chain, revealing a fragile phase with unique dissipative excitations and potential observable signatures in trapped ion experiments.

Contribution

It introduces the concept of quantum fragility in PT-symmetric nonlinear ion chains and analyzes their unique dissipative vibrational modes.

Findings

Identification of a quantum fragile regime dominated by nonlinearity

Discovery of momentum-dependent phonon velocities and dissipative spectra

Discussion of observable signatures in trapped ion systems

Abstract

We theoretically study the quantum dynamics of transverse vibrations of a one-dimensional chain of trapped ions in harmonic potentials interacting via a Reggeon-type cubic nonlinearity that is nonunitary but preserves PT symmetry. We propose the notion of quantum fragility for the dissipative structural phase transition that spontaneously breaks the PT symmetry. In the quantum fragile regime, the nonlinearity dominates the response to mechanical perturbations and the chain supports neither the ordinary quantum phonons of a Luttinger liquid, nor the supersonic solitons that arise in classical fragile critical points in the absence of fluctuations. Quantum fluctuations, approximately captured within a one-loop renormalization group, give rise to mechanical excitations with a strongly momentum-dependent phonon velocity and dissipative spectral behavior. Observable signatures of the quantum fragile chain in trapped ion systems are discussed.