Regensburg 2016 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 27: Transport: Quantum Coherence and Quantum Information Systems - Theory 1
(Joint session of HL, MA and TT organized by TT)
TT 27.4: Talk
Tuesday, March 8, 2016, 10:15–10:30, H22
Theory and practice of dressed coherent states in circuit QED — •Frank Wilhelm1 and Luke C. G. Govia1,2 — 1Theoretical Physics, Saarland University, Campus E 2.6, 66123 Saarbrücken, Germany — 2Department of Physics, McGill University, Montreal, Canada
In the dispersive regime of
qubit-cavity coupling, classical cavity drive populates the cavity, but leaves
the qubit state unaffected. However, the dispersive Hamiltonian is derived
after both a frame transformation and an approximation. Therefore, to connect
to external experimental devices, the inverse frame transformation from the
dispersive frame back to the lab frame is necessary. We show that in the lab
frame the system is best described by an entangled state known as the dressed
coherent state, and thus even in the dispersive regime, entanglement is
generated between the qubit and the cavity. Also, we show that further qubit
evolution depends on both the amplitude and phase of the dressed coherent
state. This provides a limitation to readout in the dispersive regime.
We show that only in the limit of infinite measurement time is this protocol
QND, as the formation of a dressed coherent state in the qubit-cavity system
applies an effective rotation to the qubit state. We show how this rotation can
be corrected by a unitary operation, leading to improved qubit initialization
by measurement and unitary feedback.
L. C. G. Govia and F.K. Wllhelm,
Phys. Rev. Appl. 4, 054001 (2015)
L. C.G. Govia and F.K. Wilhelm, arXiv: 1506.04997