Free Evolution of Superposition States in a Single Cooper Pair Box

TL;DR

This paper demonstrates the fabrication and measurement of a single Cooper-pair box coupled with an RF-SET, revealing charge quantization and enabling control of quantum states through fast pulsing, with insights into dephasing and relaxation times.

Contribution

It introduces a novel integrated device combining a Cooper-pair box with an RF-SET for charge state measurement and control.

Findings

Observed 2e charge quantization in the SCB

Extracted charging and Josephson energies from spectroscopy

Measured dephasing and relaxation times of quantum states

Abstract

We have fabricated a single Cooper-pair box (SCB) in close proximity to a single electron transistor (SET) operated in the radio-frequency mode (RF-SET) with an inductor and capacitor lithographed directly on chip. The RF-SET was used to measure the charge state of the SCB revealing a 2e periodic charge quantization. We performed spectroscopy measurements to extract the charging energy (EC) and the Josephson coupling energy (EJ). Control of the temporal evolution of the quantum charge state was achieved by applying fast DC pulses to the SCB gate. The dephasing and relaxation times were extracted from these measurements