Ramón Aguado

Direct manipulation of a superconducting spin qubit strongly coupled to a transmon qubit

  1. Marta Pita-Vidal,
  2. Arno Bargerbos,
  3. Rok Žitko,
  4. Lukas J. Splitthoff,
  5. Lukas Grünhaupt,
  6. Jaap J. Wesdorp,
  7. Yu Liu,
  8. Leo P. Kouwenhoven,
  9. Ramón Aguado,
  10. Bernard van Heck,
  11. Angela Kou,
  12. and Christian Kraglund Andersen
Spin qubits in semiconductors are currently one of the most promising architectures for quantum computing. However, they face challenges in realizing multi-qubit interactions over extended
distances. Superconducting spin qubits provide a promising alternative by encoding a qubit in the spin degree of freedom of an Andreev level. Such an Andreev spin qubit could leverage the advantages of circuit quantum electrodynamic, enabled by an intrinsic spin-supercurrent coupling. The first realization of an Andreev spin qubit encoded the qubit in the excited states of a semiconducting weak-link, leading to frequent decay out of the computational subspace. Additionally, rapid qubit manipulation was hindered by the need for indirect Raman transitions. Here, we exploit a different qubit subspace, using the spin-split doublet ground state of an electrostatically-defined quantum dot Josephson junction with large charging energy. Additionally, we use a magnetic field to enable direct spin manipulation over a frequency range of 10 GHz. Using an all-electric microwave drive we achieve Rabi frequencies exceeding 200 MHz. We furthermore embed the Andreev spin qubit in a superconducting transmon qubit, demonstrating strong coherent qubit-qubit coupling. These results are a crucial step towards a hybrid architecture that combines the beneficial aspects of both superconducting and semiconductor qubits.
arxiv pdf

Singlet-doublet transitions of a quantum dot Josephson junction detected in a transmon circuit

  1. Arno Bargerbos,
  2. Marta Pita-Vidal,
  3. Rok Žitko,
  4. Jesús Ávila,
  5. Lukas J. Splitthoff,
  6. Lukas Grünhaupt,
  7. Jaap J. Wesdorp,
  8. Christian K. Andersen,
  9. Yu Liu,
  10. Leo P. Kouwenhoven,
  11. Ramón Aguado,
  12. Angela Kou,
  13. and Bernard van Heck
We realize a hybrid superconductor-semiconductor transmon device in which the Josephson effect is controlled by a gate-defined quantum dot in an InAs/Al nanowire. Microwave spectroscopy
of the transmon’s transition spectrum allows us to probe the ground state parity of the quantum dot as a function of gate voltages, external magnetic flux, and magnetic field applied parallel to the nanowire. The measured parity phase diagram is in agreement with that predicted by a single-impurity Anderson model with superconducting leads. Through continuous time monitoring of the circuit we furthermore resolve the quasiparticle dynamics of the quantum dot Josephson junction across the phase boundaries. Our results can facilitate the realization of semiconductor-based 0−π qubits and Andreev qubits.
arxiv pdf

A perspective on semiconductor-based superconducting qubits

  1. Ramón Aguado
Following the demonstration of semiconductor-based Josephson junctions which are fully tuneable by electrical means, new routes have been opened for the study of hybrid semiconductor-superconductor
qubits. These include semiconductor-based transmon qubits, single-spin Andreev qubits, and fault-tolerant topological qubits based on Majorana zero modes. In this perspective, we review recent progress in the path towards such novel qubit designs. After a short introduction and a brief digression about the historical roadmap that has led to the experimental state-of-the art, the emphasis is placed on superconducting qubits based on semiconductor nanowires
arxiv pdf