Superconducting Qubit Interferometry

Claudia Quintana, Karl D. Petersson, Louis W. McFaul +3 more

William D. Oliver, Yang Yu, Janice C. Lee +3 more

We demonstrate Mach-Zehnder-type interferometry in a superconducting flux qubit. The qubit is a tunable artificial atom, the ground and excited states of which exhibit an avoided crossing. Strongly driving the qubit with harmonic excitation sweeps it through the avoided crossing two times per period. Because the induced Landau-Zener transitions act as coherent beamsplitters, the accumulated phase between transitions, which varies with microwave amplitude, results in quantum interference fringes for n = 1 to 20 photon transitions. The generalization of optical Mach-Zehnder interferometry, performed in qubit phase space, provides an alternative means to manipulate and characterize the qubit in the strongly driven regime.

Sahel Ashhab

Michael Hatridge

P. Y. Wen, O. V. Ivakhnenko, M. A. Nakonechnyi +7 more

We investigate the Landau-Zener-St\"uckelberg-Majorana interferometry of a superconducting qubit in a semi-infinite transmission line terminated by a mirror. The transmon-type qubit is at the node of the resonant electromagnetic (EM) field, ``hiding'' from the EM field. We modulate the resonant frequency of the qubit by applying a sinusoidal flux pump. We perform spectroscopy by measuring the reflection coefficient of a weak probe in the system. Remarkable interference patterns emerge in the spectrum, which can be interpreted as multiphoton resonances in the dressed qubit. Our calculations agree well with the experiments.

Gianluigi Catelani