Entanglement Dynamics in a Two Transmon Qubit System under Continuous Measurement and Postselection

TL;DR

This paper explores how continuous measurement and postselection influence entanglement dynamics in a coupled transmon system, revealing slowed entanglement decay and PT-symmetry phase transitions.

Contribution

It introduces a detailed stochastic master equation approach, incorporating realistic detector inefficiencies, and uncovers the impact of exceptional points on entanglement.

Findings

Postselection significantly slows entanglement decay.

Identification of PT-symmetry phases affecting system dynamics.

Analysis of realistic detector inefficiencies on monitoring outcomes.

Abstract

We investigate the role of continuous measurement and postselection in the dynamics and entanglement of a transmon-cavity-transmon coupled system. In the dispersive regime, characterized by a large detuning between the transmons and the cavity, the two transmons interact via virtual excitation of the cavity, giving rise to an effective transmon-transmon coupling. In addition to this coherent interaction, each transmon undergoes spontaneous emission, which is continuously monitored through independent detection channels. By incorporating realistic detector inefficiencies, we analyze both efficient and imperfect monitoring scenarios and demonstrate that postselection significantly slows down the decay of entanglement compared to the unmonitored case. We formulate the stochastic master equation for the coupled system, derive the corresponding postselected master equation, and investigate the dynamics through the Liouvillian superoperator spectrum. In the interaction frame, we identify the emergence of an exceptional point and characterize the associated broken and unbroken PT-symmetric phases. We show how these phases influence the system dynamics and the corresponding entanglement behavior. Our results provide insight into how continuous measurement and postselection affect entanglement in dissipative quantum systems, with potential applications in quantum information processing.