Josiah Cochran

Experimental signatures of a σzσx beam-splitter interaction between a Kerr-cat and transmon qubit

  1. Josiah Cochran,
  2. Haley M. Cole,
  3. Hebah Goderya,
  4. Zhuoqun Hao,
  5. Yao-Chun Chang,
  6. Theo Shaw,
  7. Aikaterini Kargioti,
  8. and Shyam Shankar
Quantum error correction (QEC) requires ancilla qubits to extract error syndromes from data qubits which store quantum information. However, ancilla errors can propagate back to the
data qubits, introducing additional errors and limiting fault-tolerance. In superconducting quantum circuits, Kerr-cat qubits (KCQs), which exhibit strongly biased noise, have been proposed as ancillas to suppress this back-action and enhance QEC performance. Here, we experimentally demonstrate a beamsplitter interaction between a KCQ and a transmon, realizing an effective σzσx coupling that can be employed for parity measurements in QEC protocols. We characterize the interaction across a range of cat sizes and drive amplitudes, confirming the expected scaling of the interaction rate. These results establish a step towards hybrid architectures that combine transmons as data qubits with noise-biased bosonic ancillas, enabling hardware-efficient syndrome extraction and advancing the development of fault-tolerant quantum processors.
arxiv pdf

Dual on-chip SQUID measurement protocol for flux detection in large magnetic fields

  1. Josiah Cochran,
  2. Giovanni Franco-Rivera,
  3. Denghui Zhang,
  4. Lei Chen,
  5. Zhen Wang,
  6. and Irinel Chiorescu
Sensitive magnetometers that can operate in high magnetic fields are essential for detecting magnetic resonance signals originating from small ensembles of quantum spins. Such devices
have potential applications in quantum technologies, in particular quantum computing. We present a novel experimental setup implementing a differential flux measurement using two DC-SQUID magnetometers. The differential measurement allows for cancellation of background flux signals while enhancing sample signal. The developed protocol uses pulsed readout which minimizes on-chip heating since sub-Kelvin temperatures are needed to preserve quantum spin coherence. Results of a proof of concept experiment are shown as well.
arxiv pdf