Deep Lall

Emulating two qubits with a four-level transmon qudit for variational quantum algorithms

  1. Shuxiang Cao,
  2. Mustafa Bakr,
  3. Giulio Campanaro,
  4. Simone D. Fasciati,
  5. James Wills,
  6. Deep Lall,
  7. Boris Shteynas,
  8. Vivek Chidambaram,
  9. Ivan Rungger,
  10. and Peter Leek
Using quantum systems with more than two levels, or qudits, can scale the computation space of quantum processors more efficiently than using qubits, which may offer an easier physical
implementation for larger Hilbert spaces. However, individual qudits may exhibit larger noise, and algorithms designed for qubits require to be recompiled to qudit algorithms for execution. In this work, we implemented a two-qubit emulator using a 4-level superconducting transmon qudit for variational quantum algorithm applications and analyzed its noise model. The major source of error for the variational algorithm was readout misclassification error and amplitude damping. To improve the accuracy of the results, we applied error-mitigation techniques to reduce the effects of the misclassification and qudit decay event. The final predicted energy value is within the range of chemical accuracy. Our work demonstrates that qudits are a practical alternative to qubits for variational algorithms.
arxiv pdf

Efficient qutrit gate-set tomography on a transmon

  1. Shuxiang Cao,
  2. Deep Lall,
  3. Mustafa Bakr,
  4. Giulio Campanaro,
  5. Simone Fasciati,
  6. James Wills,
  7. Vivek Chidambaram,
  8. Boris Shteynas,
  9. Ivan Rungger,
  10. and Peter Leek
Gate-set tomography enables the determination of the process matrix of a set of quantum logic gates, including measurement and state preparation errors. Here we propose an efficient
method to implement such tomography on qutrits, using only gates in the qutrit Clifford group to construct preparation and measurement fiducials. Our method significantly reduces computational overhead by using the theoretical minimum number of measurements and directly parametrizing qutrit Hadamard gates. We demonstrate qutrit gate-set tomography on a superconducting transmon, and find good agreement of average gate infidelity with qutrit randomized benchmarking.
arxiv pdf