Single-shot parity readout of a minimal Kitaev chain
Nick van Loo (TU Delft - QuTech Advanced Research Centre, TU Delft - QRD/General, Kavli institute of nanoscience Delft)
Francesco Zatelli (TU Delft - QRD/Kouwenhoven Lab, TU Delft - QuTech Advanced Research Centre, Kavli Institute of Nanoscience Discovery)
Bart Roovers (TU Delft - QRD/Kouwenhoven Lab, TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft)
Guanzhong Wang (TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QRD/Wimmer Group)
Thomas Van Caekenberghe (Kavli institute of nanoscience Delft)
Alberto Bordin (TU Delft - QuTech Advanced Research Centre, TU Delft - QRD/Kouwenhoven Lab, Kavli institute of nanoscience Delft)
David van Driel (TU Delft - QuTech Advanced Research Centre, TU Delft - BUS/Quantum Delft, Kavli institute of nanoscience Delft)
Yining Zhang (TU Delft - QRD/Goswami Lab, Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre)
Wietze D. Huisman (Kavli institute of nanoscience Delft, TU Delft - QRD/Goswami Lab, TU Delft - QuTech Advanced Research Centre)
Ghada Badawy (Eindhoven University of Technology)
Erik P.A.M. Bakkers (Eindhoven University of Technology)
Grzegorz P. Mazur (TU Delft - QRD/Wimmer Group, TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft)
Leo P. Kouwenhoven (TU Delft - QuTech Advanced Research Centre, TU Delft - QN/Kouwenhoven Lab, TU Delft - QRD/Kouwenhoven Lab, Kavli institute of nanoscience Delft)
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Abstract
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 chains3, 4–5. 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.