Dispersive measurements of superconducting qubit coherence with a fast latching readout

By Irfan Siddiqi, R Patil Vijay, M. Metcalfe, E. Boaknin, Luigi Frunzio, Robert J. Schoelkopf, Michel H. Devoret. 2005

143 citations recorded by the source corpus.

The "quantronium" is a superconducting qubit consisting of a split Cooper pair box in which a large tunnel junction is inserted. This circuit has a special bias point where the Larmor frequency is, to first order, insensitive to fluctuations in the bias parameters -- the charge of the box island and the phase of the large junction. At this optimal working point, the state of the qubit can be determined by dispersive measurements that probe the second derivative of the state energy with respect to these bias parameters. We use the quantronium phase degree of freedom to perform a non-linear, dispersive measurement of its inductive response using bifurcation amplification. This novel readout projects the state of the qubit in a few nanoseconds, and its latching property allows us to record the resulting information in a few hundred nanoseconds. We have measured, using this technique, Rabi oscillations and Ramsey fringes with an improved signal to noise ratio and contrast. The speed of this new readout scheme also opens the door for a new class of experiments which would characterize the relaxation processes associated with the measurement protocol.

Subfields: Artificial Intelligence, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/048f1145c58f4cda964417c7bb9a408924257555

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Citations in the corpus

Quantum non-demolition measurement of a superconducting two-level system (2006, methodology): “Exploiting the nonlinearity of such a resonator based on Josephson junctions, leads to fast and efficient detection of the qubit state, as demonstrated in experiments on a charge-phase qubit by Siddiqi et al.(18) and Boulant et al.”
Resolving photon number states in a superconducting circuit (2006, methodology): “While these effects are large in the present experiment, an independent measurement of the qubit could be introduced using a second cavity or Josephson-bifurcation amplifier[24], allowing the realization of a quantitative photon statistics analyzer.”
Microwave photonics with superconducting quantum circuits (2017, methodology): “To resolve the measured weak signal, various amplifiers, such as the Josephson bifurcation amplifier [97,98,102,103], the Josephson ring amplifier [104], or parametric amplifiers [105] are used (a more extensive overview of amplifiers is given in Section 9.”