Coherent cancellation of tunneling and quantum information protection: the Delta variant of the Kerr-cat qubit - Part 2/3

Encoding and manipulating quantum information with logical cat qubits is a promising means to perform quantum error correction, but controlling undesired parametric processes, while preserving quantum control, remains an outstanding challenge. The Kerr-cat qubit, created by squeeze-driving a weakly nonlinear Kerr oscillator, provides a double-well system with minimal spurious parametric processes. The tunnel effect is expected to be cancelled in its ground state manifold. The logical errors induced by incoherent well-flipping are then dominated by tunneling through excited states under incoherent excitations. A key question is, how does this incoherent well-flipping affect the qubit manifold? Moreover, can the cancellation of tunneling be extended to the higher excited states?

In this two-part talk, we will present experimental results, measuring the passage through zero of the tunneling amplitude in the ground and excited state spectrum as a function of squeezing drive strength and frequency. This quantum error correction strategy leads to a 500x enhancement of well-flipping lifetimes while maintaining coherent control, and high-fidelity quantum non-demolition readout.

Part 2 addresses the cancellation excited state tunneling due to quantum interference effects.