Ali Javadi-Abhari

Native two-qubit gates in fixed-coupling, fixed-frequency transmons beyond cross-resonance interaction

  1. Ken Xuan Wei,
  2. Isaac Lauer,
  3. Emily Pritchett,
  4. William Shanks,
  5. David C. McKay,
  6. and Ali Javadi-Abhari
Fixed-frequency superconducting qubits demonstrate remarkable success as platforms for stable and scalable quantum computing. Cross-resonance gates have been the workhorse of fixed-coupling,
fixed-frequency superconducting processors, leveraging the entanglement generated by driving one qubit resonantly with a neighbor’s frequency to achieve high-fidelity, universal CNOTs. Here, we use on-resonant and off-resonant microwave drives to go beyond cross-resonance, realizing natively interesting two-qubit gates that are not equivalent to CNOTs. In particular, we implement and benchmark native ISWAP, SWAP, ISWAP‾‾‾‾‾‾‾√, and BSWAP gates. Furthermore, we apply these techniques for an efficient construction of the B-gate: a perfect entangler from which any two-qubit gate can be reached in only two applications. We show these native two-qubit gates are better than their counterparts compiled from cross-resonance gates. We elucidate the resonance conditions required to drive each two-qubit gate and provide a novel frame tracking technique to implement them in Qiskit.
arxiv pdf

Optimized Surface Code Communication in Superconducting Quantum Computers

  1. Ali Javadi-Abhari,
  2. Pranav Gokhale,
  3. Adam Holmes,
  4. Diana Franklin,
  5. Kenneth R. Brown,
  6. Margaret Martonosi,
  7. and Frederic T. Chong
, and several-hundred-qubit"]machines are around the corner. Machines of this scale have the capacity to demonstrate quantum supremacy, the tipping point where QC is faster than the fastest classical alternative for a particular problem. Because error correction techniques will be central to QC and will be the most expensive component of quantum computation, choosing the lowest-overhead error correction scheme is critical to overall QC success. This paper evaluates two established quantum error correction codes—planar and double-defect surface codes—using a set of compilation, scheduling and network simulation tools. In considering scalable methods for optimizing both codes, we do so in the context of a full microarchitectural and compiler analysis. Contrary to previous predictions, we find that the simpler planar codes are sometimes more favorable for implementation on superconducting quantum computers, especially under conditions of high communication congestion.
arxiv pdf