Transitions between the quasienergy states of weakly nonlinear quantum systems

Eugene Oks

P. V. Elyutin

The motion of a one-dimensional quantum weakly anharmonic system under the influence of harmonic external field is treated in the range where the transition frequency between the neighboring levels is close to the frequency of the harmonic field (quantum nonlinear resonance). The case of the strong external field, in which the Rabi frequency for the transitions is large in comparison with the field frequency, is studied. The expression for compact wavepackets of quasienergy states that change their content and width periodically (and, possibly, strongly), is obtained.

P. V. Elyutin, Timur V. Filippov

Vittorio Peano, Michael Thorwart

We analyze the driven resonantly coupled Jaynes-Cummings model in terms of a quasienergy approach by switching to a frame rotating with the external modulation frequency and by using the dressed atom picture. A quasienergy surface in phase space emerges whose level spacing is governed by a rescaled effective Planck constant. Moreover, the well-known multiphoton transitions can be reinterpreted as resonant tunneling transitions from the local maximum of the quasienergy surface. Most importantly, the driving defines a quasienergy well which is nonperturbative in nature. The quantum-mechanical quasienergy state localized at its bottom is squeezed. In the Purcell-limited regime, the potential well is metastable and the effective local temperature close to its minimum is uniquely determined by the squeezing factor. The activation occurs in this case via dressed spin-flip transitions rather than via quantum activation as in other driven nonlinear quantum systems such as the quantum Duffing oscillator. The local maximum is, in general, stable. However, in presence of resonant coherent or dissipative tunneling transitions the system can escape from it and a stationary state arises as a statistical mixture of quasienergy states being localized in the two basins of attraction. This gives rise to a resonant or an antiresonant nonlinear response of the cavity at multiphoton transitions. The model finds direct application in recent experiments with a driven superconducting circuit quantum electrodynamics setup.

Artur Mikhailovich Ishkhanyan, M. Hakobyan

Qiongtao Xie, Wenhua Hai

We investigate nonlinear Floquet states and quasienergies of a Bose-Einstein condensate in a double-well potential subject to a high-frequency driving field. A multiple time scale method is used to obtain the nonlinear Floquet states and quasienergies in both weak and strong nonlinearity regimes. It is shown that there are more nonlinear Floquet states without linear counterparts in the strong nonlinearity regime than in the weak nonlinearity regime, and they are phase-locked to an integer multiple of the external driving frequency. The validity of the effective description in the two different regimes is discussed. The stability criterion for these nonlinear Floquet states is found analytically and confirmed numerically.