Bradley K. Mitchell

High-Fidelity Qutrit Entangling Gates for Superconducting Circuits

  1. Noah Goss,
  2. Alexis Morvan,
  3. Brian Marinelli,
  4. Bradley K. Mitchell,
  5. Long B. Nguyen,
  6. Ravi K. Naik,
  7. Larry Chen,
  8. Christian Jünger,
  9. John Mark Kreikebaum,
  10. David I. Santiago,
  11. Joel J. Wallman,
  12. and Irfan Siddiqi
Ternary quantum information processing in superconducting devices poses a promising alternative to its more popular binary counterpart through larger, more connected computational spaces
and proposed advantages in quantum simulation and error correction. Although generally operated as qubits, transmons have readily addressable higher levels, making them natural candidates for operation as quantum three-level systems (qutrits). Recent works in transmon devices have realized high fidelity single qutrit operation. Nonetheless, effectively engineering a high-fidelity two-qutrit entanglement remains a central challenge for realizing qutrit processing in a transmon device. In this work, we apply the differential AC Stark shift to implement a flexible, microwave-activated, and dynamic cross-Kerr entanglement between two fixed-frequency transmon qutrits, expanding on work performed for the ZZ interaction with transmon qubits. We then use this interaction to engineer efficient, high-fidelity qutrit CZ† and CZ gates, with estimated process fidelities of 97.3(1)% and 95.2(3)% respectively, a significant step forward for operating qutrits on a multi-transmon device.
arxiv pdf

Scalable High-Performance Fluxonium Quantum Processor

  1. Long B. Nguyen,
  2. Gerwin Koolstra,
  3. Yosep Kim,
  4. Alexis Morvan,
  5. Trevor Chistolini,
  6. Shraddha Singh,
  7. Konstantin N. Nesterov,
  8. Christian Jünger,
  9. Larry Chen,
  10. Zahra Pedramrazi,
  11. Bradley K. Mitchell,
  12. John Mark Kreikebaum,
  13. Shruti Puri,
  14. David I. Santiago,
  15. and Irfan Siddiqi Singh
The technological development of hardware heading toward universal fault-tolerant quantum computation requires a large-scale processing unit with high performance. While fluxonium qubits
are promising with high coherence and large anharmonicity, their scalability has not been systematically explored. In this work, we propose a superconducting quantum information processor based on compact high-coherence fluxoniums with suppressed crosstalk, reduced design complexity, improved operational efficiency, high-fidelity gates, and resistance to parameter fluctuations. In this architecture, the qubits are readout dispersively using individual resonators connected to a common bus and manipulated via combined on-chip RF and DC control lines, both of which can be designed to have low crosstalk. A multi-path coupling approach enables exchange interactions between the high-coherence computational states and at the same time suppresses the spurious static ZZ rate, leading to fast and high-fidelity entangling gates. We numerically investigate the cross resonance controlled-NOT and the differential AC-Stark controlled-Z operations, revealing low gate error for qubit-qubit detuning bandwidth of up to 1 GHz. Our study on frequency crowding indicates high fabrication yield for quantum processors consisting of over thousands of qubits. In addition, we estimate low resource overhead to suppress logical error rate using the XZZX surface code. These results promise a scalable quantum architecture with high performance for the pursuit of universal quantum computation.
arxiv pdf