A new single-shot readout scheme for transmon qubits
speaker: Florian Ong (SPEC, CEA-Saclay F-91191, Gif-sur-Yvette Cedex (France))abstract: Abstract:A new single-shot readout scheme for transmon qubits
The transmon is a promising superconducting qubit 1 consisting of a Cooper-pair box made insensitive to charge noise. When a floating transmon is embedded in (and is capacitively coupled to) a coplanar waveguide resonator, it is well isolated from the environment, which limits its decoherence. Such a setup enables to perform circuit QED experiments in the microwave domain 2. When the frequency detuning between the resonator and the qubit is larger than their coupling strength (dispersive regime), the resonance frequency of the cavity depends on the state of the qubit and this cavity pull can be measured without strongly perturbing the qubit. A way to readout the qubit is to measure the phase of a microwave pulse reflected onto the cavity. However, with a linear cavity the phase shift between states 0 and 1 is small and the signal-to-noise ratio is limited by the HEMT cryogenic amplifier. To overcome this limitation we have added a non-linear element, to obtain a Cavity Josephson Bifurcation Amplifier (CJBA) 3, which consists of a lambda2 cavity containing a simple Josephson junction in its center. When the resonator is strongly driven slightly below its resonance frequency, it exhibits a bifurcation between two metastable dynamical states. The phase shift of the reflected pulse is now amplified such that the phase can be used to map the qubit states onto the metastable states of the oscillator. This new readout scheme should allow single-shot qubit state discrimination while perturbing only weakly the qubit during measurement. We present preliminary results, and study the quantum non-demolition (QND) character of this readout scheme.
1 Koch et al., Phys. Rev. A 76, 042319 (2007) 2 Wallraff et al., Nature 431, 162 (2004) 3 Boaknin et al., arXiv:cond-mat0702445v1
timetable:
Fri 5 Dec, 9:30 - 9:50, Sala Stemmi
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