High-Coherence Kerr-cat qubit in 2D architecture

  1. Ahmed Hajr,
  2. Bingcheng Qing,
  3. Ke Wang,
  4. Gerwin Koolstra,
  5. Zahra Pedramrazi,
  6. Ziqi Kang,
  7. Larry Chen,
  8. Long B. Nguyen,
  9. Christian Junger,
  10. Noah Goss,
  11. Irwin Huang,
  12. Bibek Bhandari,
  13. Nicholas E. Frattini,
  14. Shruti Puri,
  15. Justin Dressel,
  16. Andrew Jordan,
  17. David Santiago,
  18. and Irfan Siddiqi
The Kerr-cat qubit is a bosonic qubit in which multi-photon Schrodinger cat states are stabilized by applying a two-photon drive to an oscillator with a Kerr nonlinearity. The suppressed
bit-flip rate with increasing cat size makes this qubit a promising candidate to implement quantum error correction codes tailored for noise-biased qubits. However, achieving strong light-matter interactions necessary for stabilizing and controlling this qubit has traditionally required strong microwave drives that heat the qubit and degrade its performance. In contrast, increasing the coupling to the drive port removes the need for strong drives at the expense of large Purcell decay. By integrating an effective band-block filter on-chip, we overcome this trade-off and realize a Kerr-cat qubit in a scalable 2D superconducting circuit with high coherence. This filter provides 30 dB of isolation at the qubit frequency with negligible attenuation at the frequencies required for stabilization and readout. We experimentally demonstrate quantum non-demolition readout fidelity of 99.6% for a cat with 8 photons. Also, to have high-fidelity universal control over this qubit, we combine fast Rabi oscillations with a new demonstration of the X(90) gate through phase modulation of the stabilization drive. Finally, the lifetime in this architecture is examined as a function of the cat size of up to 10 photons in the oscillator achieving a bit-flip time higher than 1 ms and only a linear decrease in the phase-flip time, in good agreement with the theoretical analysis of the circuit. Our qubit shows promise as a building block for fault-tolerant quantum processors with a small footprint.

Empowering high-dimensional quantum computing by traversing the dual bosonic ladder

  1. Long B. Nguyen,
  2. Noah Goss,
  3. Karthik Siva,
  4. Yosep Kim,
  5. Ed Younis,
  6. Bingcheng Qing,
  7. Akel Hashim,
  8. David I. Santiago,
  9. and Irfan Siddiqi
High-dimensional quantum information processing has emerged as a promising avenue to transcend hardware limitations and advance the frontiers of quantum technologies. Harnessing the
untapped potential of the so-called qudits necessitates the development of quantum protocols beyond the established qubit methodologies. Here, we present a robust, hardware-efficient, and extensible approach for operating multidimensional solid-state systems using Raman-assisted two-photon interactions. To demonstrate its efficacy, we construct a set of multi-qubit operations, realize highly entangled multidimensional states including atomic squeezed states and Schrödinger cat states, and implement programmable entanglement distribution along a qudit array. Our work illuminates the quantum electrodynamics of strongly driven multi-qudit systems and provides the experimental foundation for the future development of high-dimensional quantum applications.