Time molecules with periodically driven interacting qubits

Abstract

We provide numerical evidence for a temporal quantum-mechanical interference phenomenon: time molecules (TMs). A variety of such stroboscopic states are observed in the dynamics of two interacting qubits subject to a periodic sequence of pi-pulses with the period T. The TMs appear periodically in time and have a large duration, delta t (TM) T. All TMs are characterized by almost zero value of the total polarization and a strong enhancement of the entanglement entropy S up to the maximum value of S ln 2 indicating the presence of corresponding Bell state. Moreover, the TMs demonstrate a stroboscopic switching between the two maximally entangled Bell states and a slow leakage into other eigenstates. The TMs are generated by the commensurability of the Floquet eigenvalues and the presence of maximally entangled Floquet eigenstates. The TMs remain stable with detuned system parameters and with an increased number of qubits. In particular, we observed the TMs in the dynamics of three interacting qubits, and these TMs show a stroboscopic switching between the four Greenberger-Horne-Zeilinger states. The TMs can be observed in microwave experiments with an array of superconducting qubits.