Breakdown of gauge invariance in ultrastrong-coupling cavity QED

By D. D. Bernardis, Philipp Pilar, T. Jaako, S. Liberato, Peter Rabl. Physical Review A, 2018

161 citations recorded by the source corpus.

We revisit the derivation of Rabi- and Dicke-type models, which are commonly used for the study of quantum light-matter interactions in cavity and circuit QED. We demonstrate that the validity of the two-level approximation, which is an essential step in this derivation, depends explicitly on the choice of gauge once the system enters the ultrastrong-coupling regime. In particular, while in the electric dipole gauge the two-level approximation can be performed as long as the Rabi frequency remains much smaller than the energies of all higher-lying levels, it can dramatically fail in the Coulomb gauge, even for systems with an extremely anharmonic spectrum. We extensively investigate this phenomenon both in the single-dipole (Rabi) and multidipole (Dicke) case, and consider the specific examples of dipoles confined by double-well and square-well potentials, and of circuit QED systems with flux qubits coupled to an LC resonator.

Subfields: Artificial Intelligence, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/e98f5757712976b4a18cf82694c240d5aa1342ab

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Artificial Intelligence

1. F. García-Vidal
2. T. Ebbesen
3. C. Ciuti
4. A. Imamoğlu
5. Jonathan Keeling
6. J. Feist
7. Dieter Jaksch
8. C. Climent

In Atomic and Molecular Physics, and Optics

1. F. García-Vidal
2. T. Ebbesen
3. J. Feist
4. Javier Galego
5. C. Climent
6. E. Demler
7. C. Ciuti
8. A. Imamoğlu

Citations in the corpus

• Introduction to the Dicke Model: From Equilibrium to Nonequilibrium, and Vice Versa (2018, background): “Very recent works 41] have also noted that since the two-level approximation has a different meaning in different gauges, its validity at strong coupling is not gauge invariant: as such([40]) shows that only in the dipole gauge can the two-level approximation be trusted.”
• Cavity Casimir-Polder Forces and Their Effects in Ground-State Chemical Reactivity (2018, background): “[64] Daniele De Bernardis, Philipp Pilar, Tuomas Jaako, Simone De Liberato, and Peter Rabl, “Breakdown of Gauge Invariance in Ultrastrong-Coupling Cavity QED,” Phys.”
• Manipulating matter by strong coupling to vacuum fields (2021, background): “In particular, we note the problems related to gauge invariance when describing the light-matter coupling in approximated models (56, 57) and the role of spatial inhomogeneity of the cavity EM modes in the occurrence of phase transitions affecting the ground state (58, 59).”
• Quantum Electrodynamic Control of Matter: Cavity-Enhanced Ferroelectric Phase Transition (2020, background): “Two essential elements of our analysis place it outside the recently discussed no-go theorems for the superradiant transition [44,45,55,56,58].”