Field-theoretical basics on superconductivity

A. Zawadowski, G. Pócsik

Börje Johansson

Irina A Solovykh, Andrey V Pashchenko, Natalya A Maleeva +3 more

Increasing the efficiency of quantum processors is possible by moving from two-level qubits to elements with a larger computational base. An example would be a transmon-based superconducting atom, but the new basic elements require new approaches to control. To solve the control problem, we propose the use of nonclassical fields in which the number of photons is comparable to the number of levels in the computational basis. Using theoretical analysis, we have shown that (i) our approach makes it possible to efficiently populate on demand even relatively high energy levels of the qudit starting from the ground state; (ii) by changing the difference between the characteristic frequencies of the superconducting atom and a single field mode, we can choose which level to populate; and (iii) even the highest levels can be effectively populated on a sub-nanosecond time scale. We also propose the quantum circuit design of a real superconducting system in which the predicted rapid control of the transmon-based qudit can be demonstrated.

J. R. Schrieffer

Nikolay V. Kolotinskiy, Daniil E. Bazulin, Victor K. Kornev

We discuss design issues and present Nb-based layout designs of two basic cells for broadband active electrically small antennas based on superconducting quantum arrays. The cells are the differential array circuit and bi-SQUID. The cell layouts realize parameter values answering results of the in-depth theoretical analysis performed earlier for attaining the high-linearity voltage response to magnetic signal. The layouts are to give reference approaches to the antenna circuit designs to be fabricated using niobium process.

Roman V. Zakharov, Olga V. Tikhonova, N. V. Klenov +3 more

Abstract A basic element of a quantum network based on two single‐mode waveguides is proposed with different frequencies connected by a solid‐state qubit. Using a simple example of a possible superconducting implementation, the usefulness of the simplifications used in the general theoretical consideration has been justified. The non‐classical field in a single‐mode with a frequency of is fed to the input of a qubit controller and transformed into a non‐classical field in an output single‐mode with a frequency of . The interface can establish a quantum connection between solid‐state and photonic flying qubits with adjustable pulse shapes and carrier frequencies. This allows quantum information to be transferred to other superconducting or atomic‐based quantum registers or chips. The peculiarities of the wave‐qubit interactions are described, showing how they help to control the quantum state of the non‐classical field. On this basis, the operating principles of solid‐state and flying qubits for the future quantum information platforms are considered.