Anti-dynamical Casimir effect with an ensemble of qubits

•Effective Hamiltonian is deduced for resonant modulations in the dispersive regime.•Two system excitations can be coherently annihilated due to external modulation.•Three photons are destroyed while one matter excitation is created, or vice versa.•The transition rates and resonant modulation frequencies are evaluated analytically.

We consider the interaction between a single cavity mode and N≫1N≫1 identical qubits, assuming that any system parameter can be rapidly modulated in situ   by external bias. It is shown that, for the qubits initially in the ground states, three photons can be coherently annihilated in the dispersive regime for harmonic modulation with frequency 3ω0−Ω03ω0−Ω0, where ω0ω0 (Ω0Ω0) is the bare cavity (qubit) frequency. This phenomenon can be called “Anti-dynamical Casimir effect”, since a pair of excitations is destroyed without dissipation due to the external modulation. For the initial vacuum cavity state, three qubit excitations can also be annihilated for the modulation frequency 3Ω0−ω03Ω0−ω0.