arXiv subjects

Kirill Dubovitskii

Publications and source records attributed to Kirill Dubovitskii.

2 recordsLinked to original sources

arXiv2024

Theory of quasiparticle-induced errors in driven-dissipative Schrödinger cat qubits

Understanding the mechanisms of qubit decoherence is a crucial prerequisite for improving the qubit performance. In this work we discuss the effects of residual Bogolyubov quasiparticles in Schrödinger cat qubits, either of the dissipative or Kerr type. The major difference from previous studies of quasiparticles in superconducting qubits is that the Schrödinger cat qubits are operated under non-equilibrium conditions. Indeed, an external microwave drive is needed to stabilize "cat states", which are superpositions of coherent degenerate eigenstates of an effective stationary Lindbladian in the rotating frame. We present a microscopic derivation of the master equation for cat qubits and express the effect of the quasiparticles as dissipators acting on the density matrix of the cat qubit. This enables us to determine the conditions under which the quasiparticles give a substantial contribution to the qubit errors.

cond-mat.mes-hall↗

arXiv2022

Partial randomized benchmarking

In randomized benchmarking of quantum logical gates, partial twirling can be used for simpler implementation, better scaling, and higher accuracy and reliability. For instance, for two-qubit gates, single-qubit twirling is easier to realize than full averaging. We analyze such simplified, partial twirling and demonstrate that, unlike for the standard randomized benchmarking, the measured decay of fidelity is a linear combination of exponentials with different decay rates (3 for two qubits and single-bit twirling). The evolution with the sequence length is governed by an iteration matrix, whose spectrum gives the decay rates. For generic two-qubit gates one slowest exponential dominates and characterizes gate errors in three channels. Its decay rate is close, but different from that in the standard randomized benchmarking, and we find the leading correction. Using relations to the local invariants of two-qubit gates we identify all exceptional gates with several slow exponentials and analyze possibilities to extract their decay rates from the measured curves.

quant-ph↗