Microwave interferometry, cooling, and amplitude spectroscopy with a superconducting artificial atom

Dr. William D. Oliver, MIT Lincoln Laboratory and the Research Laboratory for Electronics

CSB 601

Abstract

Superconducting persistent-current qubits are quantum-coherent artificial atoms with multiple energy levels. In the presence of large-amplitude harmonic excitation, the qubit state can be driven through one or more of the energy-level avoided crossings. The resulting Landau-Zener-Stueckelberg (LZS) transitions mediate a rich array of quantum-coherent phenomena as a function of the driving amplitude and frequency.

In this talk, we present three demonstrations of LZS-mediated quantum coherence in a strongly-driven niobium persistent-current qubit. The first is Stueckelberg interferometry [1], with which we observed quantum interference fringes in the transition rates for n-photon transitions, with n = 150. The second is microwave-induced cooling [2], by which we achieved effective qubit temperatures < 3 mK, a factor 10x-100x lower than the dilution refrigerator ambient temperature. The third is amplitude spectroscopy [3], a spectroscopy approach that monitors the system response to amplitude rather than frequency. This allowed us to probe the energy spectra of our artificial atom from 0.01 ^ 120 GHz, while driving it at a fixed frequency 0.16 GHz.

These experiments exhibit a remarkable agreement with theory, and are extensible to other solid-state qubit modalities. In addition to our interest in these techniques for fundamental studies of quantum coherence in strongly-driven systems, we anticipate they will find application to qubit control and state-preparation methods for quantum information science and technology [4].

[1] W.D. Oliver, et al., Science 310, 1653 (2005)
[2] S.O. Valenzuela, et al., Science (2006)
[3] D.M. Berns et al., Nature 455, 51 (2008)
[4] A.J. Kerman and W.D. Oliver, PRL 101, 070501 (2008)

The work at Lincoln Laboratory was sponsored by the Air Force under Air Force Contract FA8721-05-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the author(s) and are not necessarily endorsed by the United States Government.=

Speaker Biography

William D. Oliver is a Staff Member at MIT Lincoln Laboratory, where he leads the laboratory's Cryogenic Electronics program, and a Research Affiliate with the Research Laboratory for Electronics (RLE), where he collaborates with the Orlando group. Since arriving at Lincoln in 2003, Will's research has focused on the fabrication and measurement of superconducting flux qubits for quantum information processing applications, and the development of cryogenic semiconducting and superconducting digital electronics for high-performance classical computation. Before coming to Lincoln, Will earned a Ph.D. at Stanford developing experimental techniques to realize quantum optical phenomena and entanglement with electrons in two-dimensional electron gas systems. He previously spent two years at the MIT Media Laboratory developing an interactive computer music installation called the Singing Tree as part of Tod Machover's Brain Opera.

William D. Oliver received degrees in Electrical Engineering (BS) and Japanese (BA) from the University of Rochester in 1995, the S.M. degree from the Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology in 1997, and the PhD degree in Electrical Engineering with a PhD minor in Physics from Stanford University in 2003.