Quantum superposition of three macroscopic states and superconducting qutrit detector

TL;DR

This paper introduces a superconducting qutrit system utilizing a three-well potential with atomic-size contacts, demonstrating advantages over qubits for quantum computing applications.

Contribution

It reports the design and implementation of a novel rf SQUTRID superconducting qutrit with a three-well potential and high energy splitting, advancing quantum detector technology.

Findings

Achieved a 1.5 K energy splitting at the 30th energy level.

Demonstrated good isolation from electromagnetic noise.

Utilized atomic-size Nb-Nb contact for adiabatic quantum dynamics.

Abstract

Superconducting quantum coherent circuits have opened up a novel area of fundamental low-temperature science since they could potentially be the element base for future quantum computers. Here we report a quasi-three-level coherent system, the so-called superconducting qutrit, which has some advantages over a two-level information cell (qubit), and is based on the qutrit readout circuit intended to measure individually the states of each qubit in a quantum computer. The designed and implemented radio-frequency superconducting qutrit detector (rf SQUTRID) with atomic-size ScS-type contact utilizes the coherent-state superposition in the three-well potential with energy splitting Delta E_01/k_B=1.5 K at the 30th quantized energy level with good isolation from the electromagnetic environment. The reason why large values of Delta E_01 (and thus using atomic-size Nb-Nb contact) are required is to ensure an adiabatic limit for the quantum dynamics of magnetic flux in the rf SQUTRID.