Demonstration of conditional gate operation using superconducting charge qubits

TL;DR

This paper demonstrates a conditional quantum gate operation using coupled superconducting charge qubits, marking progress toward universal quantum computing with solid-state devices.

Contribution

It presents the first implementation of a C-NOT gate in superconducting charge qubits using a pulse technique.

Findings

Successful demonstration of a C-NOT gate operation

Preparation and transformation of input states confirmed

Progress toward universal solid-state quantum gates

Abstract

Since the first demonstration of coherent control of a quantum state of a superconducting charge qubit a variety of Josephson-junction-based qubits have been implemented with remarkable progress in coherence time and read-out schemes. Although the current level of this solid-state device is still not as advanced as that of the most advanced microscopic-system-based qubits, these developments, together with the potential scalability, have renewed its position as a strong candidate as a building block for the quantum computer. Recently, coherent oscillation and microwave spectroscopy in capacitively-coupled superconducting qubits have been reported. The next challenging step toward quantum computation is a realization of logic gates. Here we demonstrate a conditional gate operation using a pair of coupled superconducting charge qubits. Using a pulse technique, we prepare different input states and show that they can be transformed by controlled-NOT (C-NOT) gate operation in the amplitude of the states. Although the phase evolution during the gate operation is still to be clarified, the present results are a major step toward the realization of a universal solid-state quantum gate.