<p>Protecting qubits from noise is essential for building reliable quantum computers. Topological qubits offer a route to this goal by encoding quantum information non-locally, using pairs of Majorana zero modes. These modes form a shared fermionic state whose occupation—either even or odd—defines the fermionic parity that encodes the qubit<sup><CitationRef CitationID="CR1">1</CitationRef></sup>. Notably, this parity can only be accessed by a measurement that couples two Majoranas to each other. A promising platform for realizing such qubits is the Kitaev chain<sup><CitationRef CitationID="CR1">1</CitationRef></sup>, implemented in quantum dots coupled using superconductors<sup><CitationRef CitationID="CR2">2</CitationRef></sup>. Even the minimal two-site chain hosts a pair of Majorana modes, often called ‘poor man’s Majoranas’, which are spatially separated but offer limited protection compared with longer chains<sup><CitationRef AdditionalCitationIDS="CR4" CitationID="CR3">3</CitationRef>–<CitationRef CitationID="CR5">5</CitationRef></sup>. Here we introduce a measurement technique that reads out their parity through quantum capacitance. Our method couples two Majoranas and resolves their parity in real time, visible as random telegraph switching with lifetimes exceeding a millisecond. Simultaneous charge sensing confirms that the two parity states are charge neutral and remain indistinguishable to a probe that does not couple the modes. These results establish the essential readout step for time-domain control of Majorana qubits, resolving a long-standing experimental challenge.</p>

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Single-shot parity readout of a minimal Kitaev chain

  • Nick van Loo,
  • Francesco Zatelli,
  • Gorm O. Steffensen,
  • Bart Roovers,
  • Guanzhong Wang,
  • Thomas Van Caekenberghe,
  • Alberto Bordin,
  • David van Driel,
  • Yining Zhang,
  • Wietze D. Huisman,
  • Ghada Badawy,
  • Erik P. A. M. Bakkers,
  • Grzegorz P. Mazur,
  • Ramón Aguado,
  • Leo P. Kouwenhoven

摘要

Protecting qubits from noise is essential for building reliable quantum computers. Topological qubits offer a route to this goal by encoding quantum information non-locally, using pairs of Majorana zero modes. These modes form a shared fermionic state whose occupation—either even or odd—defines the fermionic parity that encodes the qubit1. Notably, this parity can only be accessed by a measurement that couples two Majoranas to each other. A promising platform for realizing such qubits is the Kitaev chain1, implemented in quantum dots coupled using superconductors2. Even the minimal two-site chain hosts a pair of Majorana modes, often called ‘poor man’s Majoranas’, which are spatially separated but offer limited protection compared with longer chains35. Here we introduce a measurement technique that reads out their parity through quantum capacitance. Our method couples two Majoranas and resolves their parity in real time, visible as random telegraph switching with lifetimes exceeding a millisecond. Simultaneous charge sensing confirms that the two parity states are charge neutral and remain indistinguishable to a probe that does not couple the modes. These results establish the essential readout step for time-domain control of Majorana qubits, resolving a long-standing experimental challenge.