Qubit Zoo

The superconducting quasicharge qubit

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Introduces and demonstrates the blochnium (quasicharge qubit): a single Josephson junction shunted by a large superinductance, operated in the regime where the charge dispersion is exponentially flat. The qubit behaves as a “dual” of the transmon — protected against flux noise rather than charge noise.

Key Results

  • Single junction + superinductance (granular aluminum, ~1 μH)
  • Exponentially suppressed flux dispersion (dual of transmon’s charge insensitivity)
  • Coherence limited by dielectric loss, not flux noise
  • T₁ ~ 2 μs, T₂ ~ 1 μs (first demonstration)

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