Jen-Hao Yeh

Full control of superconducting qubits with combined on-chip microwave and flux lines

  1. Riccardo Manenti,
  2. Eyob A. Sete,
  3. Angela Q. Chen,
  4. Shobhan Kulshreshtha,
  5. Jen-Hao Yeh,
  6. Feyza Oruc,
  7. Andrew Bestwick,
  8. Mark Field,
  9. Keith Jackson,
  10. and Stefano Poletto
As the field of quantum computing progresses to larger-scale devices, multiplexing will be crucial to scale quantum processors. While multiplexed readout is common practice for superconducting
devices, relatively little work has been reported about the combination of flux and microwave control lines. Here, we present a method to integrate a microwave line and a flux line into a single „XYZ line“. This combined control line allows us to perform fast single-qubit gates as well as to deliver flux signals to the qubits. The measured relaxation times of the qubits are comparable to state-of-art devices employing separate control lines. We benchmark the fidelity of single-qubit gates with randomized benchmarking, achieving a fidelity above 99.5%, and we demonstrate that XYZ lines can in principle be used to run parametric entangling gates.
arxiv pdf

Implementation of a generalized CNOT gate between fixed-frequency transmons

  1. Shavindra P. Premaratne,
  2. Jen-Hao Yeh,
  3. F. C. Wellstood,
  4. and B. S. Palmer
We have embedded two fixed-frequency Al/AlOx/Al transmons, with ground-to-excited transition frequencies at 6.0714 GHz and 6.7543 GHz, in a single 3D Al cavity with a fundamental mode
at 7.7463 GHz. Strong coupling between the cavity and each transmon results in an effective qubit-qubit coupling strength of 26 MHz and a -1 MHz dispersive shift in each qubit’s transition frequency, depending on the state of the other qubit. Using the all-microwave SWIPHT (Speeding up Waveforms by Inducing Phases to Harmful Transitions) technique, we demonstrate the operation of a generalized controlled-not (CNOT) gate between the two qubits, with a gate time τ_g=907 ns optimized for this device. Using quantum process tomography we find that the gate fidelity is 83%-84%, somewhat less than the 87% fidelity expected from relaxation and dephasing in the transmons during the gate time.
arxiv pdf