Reduced Visibility of Rabi Oscillations in Superconducting Qubits

TL;DR

This paper investigates why Rabi oscillations in superconducting qubits often have low visibility, identifying background charge fluctuations and higher energy state transitions as key factors reducing coherence.

Contribution

It demonstrates how background charge fluctuators and higher energy states diminish Rabi oscillation visibility, providing a detailed theoretical analysis of these effects.

Findings

Charge fluctuators significantly reduce visibility at certain Rabi frequencies

Higher excited states dominate and suppress oscillations at larger Rabi frequencies

Probability of quasiparticle excitations is calculated for typical experiments

Abstract

Coherent Rabi oscillations between quantum states of superconducting micro-circuits have been observed in a number of experiments, albeit with a visibility which is typically much smaller than unity. Here, we show that the coherent coupling to background charge fluctuators [R.W. Simmonds et al., Phys. Rev. Lett. 93, 077003 (2004)] leads to a significantly reduced visibility if the Rabi frequency is comparable to the coupling energy of micro-circuit and fluctuator. For larger Rabi frequencies, transitions to the second excited state of the superconducting micro-circuit become dominant in suppressing the Rabi oscillation visibility. We also calculate the probability for Bogoliubov quasi-particle excitations in typical Rabi oscillation experiments.