ELFT HÍRADÓ

[Janos Asboth <asboth.janos AT wigner.mta.hu>]

*WIGNER SZFI Seminar*
Quantum Rifling: Revisiting the Stern-Gerlach experiment with a twist

*Daniel Szombati*
University of Queensland, Australia

Tuesday, 14 May 2019 10:00, KFKI Campus, Bldg. 1, 2nd floor, Conference Room

Quantum mechanics postulates that a measurement forces the wavefunction of
a qubit to collapse to one of its two eigenstates. The result of the
measurement can then be recorded as a discrete outcome designating the
particular eigenstate the qubit collapsed to. I will show that this
well-accustomed picture of quantum measurement breaks down when the qubit
is strongly driven during measurement. More specifically, when the
evolution speed exceeds a threshold defined by the characteristic
measurement time, the outcome does not contain any information about the
initial state of the qubit, and thus the measurement does not generate any
back-action. We call this phenomenon “quantum rifling” (in analogy with the
way a bullet is made to spin before it leaves the barrel of a gun), as the
fast spinning of the Bloch vector protects it from collapsing into either
of its two eigenstates. We study this phenomenon with two superconducting
qubits coupled to one and the same detector and demonstrate that quantum
rifling allows us to measure either one of the qubits on demand while
protecting the state of the other one from the measurement back-action.

Everyone is welcome to attend.

János Asbóth
szfi-seminar AT wigner.mta.hu