Measurement of a superconducting qubit with a microwave photon counter

Data image from the paper. It shows rainbow-colored curve lines.


The superconducting qubit group at WQI introduced an approach to measurement based on a microwave photon counter demonstrating raw single-shot measurement fidelity of 92% [Science, 361, 1239 (2018)]. This scheme provides access to the classical outcome of projective quantum measurement at the millikelvin stage and could form the basis for a scalable quantum-to-classical interface, see this article for broader perspective on this technology.

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Effects of charge noise on a pulse-gated singlet-triplet qubit

schematic of a quantum dot qubit and the available electron paths

We study the dynamics of a pulse-gated semiconductor double quantum dot qubit. In our experiments, the qubit coherence times are relatively long, but the visibility of the quantum oscillations is low. We show that these observations are consistent with a theory that incorporates decoherence arising from charge noise that gives rise to detuning fluctuations of the double dot.


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Quasiparticle poisoning of superconducting microwave resonators

graph of Steady-state QP density as a function of bias e V / ?”

Nonequilibrium quasiparticles represent a significant source of decoherence in superconducting quantum circuits. Here we investigate the mechanism of quasiparticle poisoning in devices subjected to local quasiparticle injection.

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