Bias-preserving and error-detectable entangling operations in a superconducting dual-rail system

  1. Nitish Mehta,
  2. James D. Teoh,
  3. Taewan Noh,
  4. Ankur Agrawal,
  5. Richard Chamberlain,
  6. Tzu-Chiao Chien,
  7. Jacob C. Curtis,
  8. Bassel Heiba Elfeky,
  9. S. M. Farzaneh,
  10. Benjamin Gudlewski,
  11. Trevor Keen,
  12. Nishaad Khedkar,
  13. Cihan Kurter,
  14. Richard Li,
  15. Gangqiang Liu,
  16. Pinlei Lu,
  17. Heather McCarrick,
  18. Anirudh Narla,
  19. Sitakanta Satapathy,
  20. Tali Shemma,
  21. Ruby A. Shi,
  22. Daniel K. Weiss,
  23. Jose Aumentado,
  24. Chan U Lei,
  25. Joseph O. Yuan,
  26. Shantanu O. Mundhada,
  27. S. Harvey Moseley Jr.,
  28. Kevin S. Chou,
  29. and Robert J. Schoelkopf
For useful quantum computation, error-corrected machines are required that can dramatically reduce the inevitable errors experienced by physical qubits. While significant progress has
been made in approaching and exceeding the surface-code threshold in superconducting platforms, large gains in the logical error rate with increasing system size remain out of reach. This is due both to the large number of required physical qubits and the need to operate far below threshold. Importantly, by exploiting the biases and structure of the physical errors, this threshold can be raised. Erasure qubits achieve this by detecting certain errors at the hardware level. Dual-rail qubits encoded in superconducting cavities are a promising erasure qubit wherein the dominant error, photon loss, can be detected and converted to an erasure. In these approaches, the complete set of operations, including two qubit gates, must be high performance and preserve as much of the desirable hierarchy or bias in the errors as possible. Here, we design and realize a novel two-qubit gate for dual-rail erasure qubits based on superconducting microwave cavities. The gate is high-speed (∼500 ns duration), and yields a residual gate infidelity after error detection below 0.1%. Moreover, we experimentally demonstrate that this gate largely preserves the favorable error structure of idling dual-rail qubits, making it ideal for error correction. We measure low erasure rates of ∼0.5% per gate, as well as low and asymmetric dephasing errors that occur at least three times more frequently on control qubits compared to target qubits. Bit-flip errors are practically nonexistent, bounded at the few parts per million level. This error asymmetry has not been well explored but is extremely useful in quantum error correction and flag-qubit contexts, where it can create a faster path to effective error-corrected systems.

Characterizing losses in InAs two-dimensional electron gas-based gatemon qubits

  1. William M. Strickland,
  2. Jaewoo Lee,
  3. Lukas Baker,
  4. Krishna Dindial,
  5. Bassel Heiba Elfeky,
  6. Mehdi Hatefipour,
  7. Peng Yu,
  8. Ido Levy,
  9. Vladimir E. Manucharyan,
  10. and Javad Shabani
The tunnelling of cooper pairs across a Josephson junction (JJ) allow for the nonlinear inductance necessary to construct superconducting qubits, amplifiers, and various other quantum
circuits. An alternative approach using hybrid superconductor-semiconductor JJs can enable a superconducting qubit architecture with full electric field control. Here we present continuous-wave and time-domain characterization of gatemon qubits based on an InAs 2DEG. We show that the qubit undergoes a vacuum Rabi splitting with a readout cavity and we drive coherent Rabi oscillations between the qubit ground and first excited states. We measure qubit coherence times to be T1= 100 ns over a 1.5 GHz tunable band. While various loss mechanisms are present in III-V gatemon circuits we detail future directions in enhancing the coherence times of qubit devices on this platform.

Quasiparticle dynamics in epitaxial Al-InAs planar Josephson junctions

  1. Bassel Heiba Elfeky,
  2. William M. Strickland,
  3. Jaewoo Lee,
  4. James T. Farmer,
  5. Sadman Shanto,
  6. Azarin Zarassi,
  7. Dylan Langone,
  8. Maxim G. Vavilov,
  9. Eli M. Levenson-Falk,
  10. and Javad Shabani
Quasiparticle (QP) effects play a significant role in the coherence and fidelity of superconducting quantum circuits. The Andreev bound states of high transparency Josephson junctions
can act as low-energy traps for QPs, providing a mechanism for studying the dynamics and properties of both the QPs and the junction. We study the trapping and clearing of QPs from the Andreev bound states of epitaxial Al-InAs Josephson junctions incorporated in a superconducting quantum interference device (SQUID) galvanically shorting a superconducting resonator to ground. We use a neighboring voltage-biased Josephson junction to inject QPs into the circuit. Upon the injection of QPs, we show that we can trap and clear QPs when the SQUID is flux-biased. We examine effects of the microwave loss associated with bulk QP transport in the resonator, QP-related dissipation in the junction, and QP poisoning events. By monitoring the QP trapping and clearing in time, we study the dynamics of these processes and find a time-scale of few microseconds that is consistent with electron-phonon relaxation in our system and correlated QP trapping and clearing mechanisms. Our results highlight the QP trapping and clearing dynamics as well as the associated time-scales in high transparency Josephson junctions based fabricated on Al-InAs heterostructures.