Kavli Affiliate: Ke Wang
| First 5 Authors: Bibek Bhandari, Bibek Bhandari, , ,
| Summary:
We theoretically explore an alternative circuit for Kerr-cat qubits based on
symmetrically threaded Superconducting Quantum Interference Devices (SQUID).
The Symmetrically Threaded SQUIDs (STS) architecture employs a simplified
flux-pumped design that suppresses two-photon dissipation, a dominant loss
mechanism in high-Kerr regimes, by engineering the drive Hamiltonian’s flux
operator to generate only even-order harmonics. By fulfilling two critical
criteria for practical Kerr-cat qubit operation, the STS emerges as an ideal
platform: (1) a static Hamiltonian with diluted Kerr nonlinearity (achieved via
the STS’s middle branch) and (2) a drive Hamiltonian restricted to even
harmonics, which ensures robust two-photon driving with reduced dissipation.
For weak Kerr nonlinearity, we find that the coherent state lifetime
($T_alpha$) is similar between STS and SNAIL circuits. However, STS Kerr-cat
qubits exhibit enhanced resistance to higher-order photon dissipation, enabling
significantly extended $T_alpha$ even with stronger Kerr nonlinearities
($sim$10 MHz). In contrast to SNAIL, STS Kerr-cat qubits display a $T_alpha$
dip under weak two-photon driving for high Kerr coefficient. We demonstrate
that this dip can be suppressed by applying drive-dependent detuning, enabling
Kerr-cat qubit operation with only eight Josephson junctions (of energies 80
GHz); fewer junctions suffice for higher junction energies. We further validate
the robustness of the STS design by studying the impact of strong flux driving
and asymmetric Josephson junctions on $T_alpha$. With the proposed design and
considering a cat size of 10 photons, we predict $T_alpha$ of the order of
tens of milliseconds, even in the presence of multi-photon heating and
dephasing effects.
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