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Prof. Howard Carmichael
University of Auckland, New Zealand

Abstract

Quantum jumps are emblematic of all things quantum. Certainly that is so in the popular mind…and more than an echo from the past, "quantum jumps" still hold a prominent place in the lexicon of physics today. What, however, is the character of these "jumps" on close inspection? Discontinuous and discrete, as in Bohr’s original conception…or perhaps a version of Schrödinger’s continuous evolution, which might be "tracked", even interrupted and turned around? This seminar re-visits the jumps of single trapped ions from the mid-1980s [1] where quantum trajectory theory favours the latter option. I present the theoretical prediction and its recent experimental verification [2]: real-time monitoring tracks the jumps of an artificial atom in a superconducting circuit—the continuous path is reconstructed and the jumps interrupted and turned around.

[1] W. Nagourney et al., Phys. Rev. Lett. 56, 2797 (1986); T. Sauter et al., Phys. Rev. Lett. 57, 1696 (1986); J. C. Bergquist et al., Phys. Rev. Lett. 57, 1699 (1986).
[2] Z. K. Minev, S. O. Mundhada, S. Shankar, P. Rheinhold, R. Gutiérrez-Jáuregui, R. J. Schoelkopf, M. Mirrahimi, H. J. Carmichael, and M. H. Devoret, “To catch and reverse a quantum jump mid-flight,”  Nature 570, 200 (2019).