ИСТИНА

In recent years, there has been noticeable progress in creating quantum registers based on Josephson transitions of various types [1]: phase, flux, charge etc. The classification of types of superconducting qubits is based on the dominance of their various energy parameters, which is in some sense analogous to the classification of atoms in the periodic table of elements [2]. According to a number of characteristics (high coherence, scalability, fast control), charge transmon qubits are considered the most promising [3], in which the Josephson energy significantly exceeds the electrostatic energy. Transmon qubits were developed in [3] and they are micron superconducting islands separated by a thin layer of dielectric. To reduce the effect of noise between the islands, a large capacity is switched on, which makes the electrostatic significantly smaller than the Josephson one. In turn, this allows us to strongly localize the phase, and consider the lower levels of the anharmonic Josephson oscillator as a qubit. In fact, the transmon consists of a pair of parallel connected Josephson junctions, which allows you to control the effective Josephson energy of SQUID by manipulating the distance between levels, i.e. to implement quantum logic-the Pauli Z-operation. Other operations ( X - and Y-rotations) can be performed by applying two phase-shifted Rabi pulses. It is important to note that the small anharmonicity parameter of the Josephson SQUID imposes a restriction on the duration and amplitude of microwave pulses [3]. This fact limits the speed of transmon registers, so various approaches are currently being discussed to avoid using high-frequency electronics for implementing computational algorithms. In this paper, it is shown that one of the ways to solve the above problem to speed up operations on transmon qubits can be the use of digital devices of superconducting electronics (Rapid Single Flux Quantum) [4-5] using unipolar pulses of large amplitude (fluxon). We show that the effect of rectangular pulses on a nonlinear oscillator is qualitatively different from Rabi pulses: it is characterized by a different parameter that is responsible for the rate of transitions. In addition, one of the problems that this work aims to solve is the study of the stability of States of a qubit when it is affected by Rabi - and rectangular unipolar pulses with respect to leakage under such non-stationary perturbations in high energy states. However, the use of short picosecond pulses is sufficient for arbitrary rotations along the Bloch sphere and performing basic quantum logical operations. 1. P. Krantz et. al Applied Physics Reviews 6, 021318 (2019) 2. J. Clarke, F. K. Wilhelm, Nature 453, 1031 (2008). 3. J. Koch et. al Phys. Rev. A 76, 042319 (2007) 4. R. McDermott and M. G. Vavilov Phys. Rev. Appl. 2,014007 (2014). 5. K. Li, R. McDermott, and M. G. Vavilov Phys. Rev. Appl. 12, 014044 (2019).