Perfect intrinsic squeezing at the superradiant phase transition critical point

Abstract

Some of the most exotic properties of the quantum vacuum are predicted in ultrastrongly coupled photon–atom systems; one such property is quantum squeezing leading to suppressed quantum fluctuations of photons and atoms. This squeezing is unique because (1) it is realized in the ground state of the system and does not require external driving, and (2) the squeezing can be perfect in the sense that quantum fluctuations of certain observables are completely suppressed. Specifically, we investigate the ground state of the Dicke model, which describes atoms collectively coupled to a single photonic mode, and we found that the photon–atom fluctuation vanishes at the onset of the superradiant phase transition in the thermodynamic limit of an infinite number of atoms. Moreover, when a finite number of atoms is considered, the variance of the fluctuation around the critical point asymptotically converges to zero, as the number of atoms is increased. In contrast to the squeezed states of flying photons obtained using standard generation protocols with external driving, the squeezing obtained in the ground state of the ultrastrongly coupled photon–atom systems is resilient against unpredictable noise.

Terahertz spin dynamics in rare-earth orthoferrites

“…Building upon the same line of theory, Hayashida et al [338] further discovered perfect intrinsic vacuum squeezing at an SRPT critical point. They started from a standard Dicke Hamiltonian, performed the Holstein–Primakov transformation, and defined the two-mode annihilation operator and the associated quadrature in a way similar to Eqs.…”

“…(b) Diagram of an individual atom. (c) Static cavity and matter fields (upper) [338] and polariton frequencies versus coupling strength (lower) calculated from the Dicke model. (d) Same as the lower panel of (c), but for the Hopfield model (full Hamiltonian retaining the A2-term).…”

“…Perfect intrinsic squeezing at an SRPT critical point [338] . Minimized quadrature fluctuation (red) versus coupling strength shows perfect suppression at the SRPT transition point.…”