Quantum control of cavities using an improved SNAP protocol without coherent errors

Superconducting microwave cavities provide high coherence times, enable flexible manipulation of quantum states and are thus a promising platform for quantum information processing. In this setup the selective number-dependent arbitrary phase (SNAP) gates [1] form an important class of gates, which can impart arbitrarily chosen phases to the different Fock states of the cavity.

Recently, effort has been taken to increase the fidelity of the SNAP gate, in particular to reduce the incoherent errors by exploiting error-transparency [2]. Based on geometrical arguments, we have developed a scheme to completely suppress the coherent errors above a certain threshold for the pulse time. For typical applications, this threshold is lower than the pulse times employed so far by a factor of 3 to 5, allowing to reduce also the incoherent errors. Furthermore, our approach is compatible with the scheme proposed in [2], and their combination promises to yield higher fidelities than both of them individually.

[1] RW Heeres, B Vlastakis, E Holland et al., Phys. Rev. Lett. 115, 137002 (2015).
[2] P Reinhold, S Rosenblum, W Ma et al., Nat. Phys. 16, 822–826 (2020).