Universal quantum processor already exists and just waits for the proper programming

TL;DR

This paper demonstrates a method to perform quantum gate operations using a controllable two-level system interacting with harmonic oscillators, proposing a universal quantum processor architecture that can be implemented with existing experimental setups.

Contribution

It introduces a Turing machine-like quantum processing scheme where a fully controllable two-level system enables universal gate operations on harmonic oscillators.

Findings

Demonstrates C-NOT gate operation between harmonic oscillator states.

Proposes a quantum processor architecture using microwave cavities and Josephson junctions.

Shows feasibility of performing multiple gate operations with current technology.

Abstract

A possibility of performing the C-NOT gate operation at the ground and the first excited states of two harmonic oscillators interacting via a two-level system subject to complete control is demonstrated. The system resembles Turing machine, where the result of interaction between oscillators and the two level system is restricted to a certain fixed unitary transformation matrix, while all the control required for the implementation of the gate is provided via manipulations with the two-level system, which remains the only fully-controllable part of the entire system. Each gate operation requires a "Turing programming", - it can be realized as a series of > 63 elementary unitary operations. The result shows a way how one can construct a quantum processor in a multimode microwave cavity equipped with a fully controlled two-level system, such as Josephson junction chip. Parameters of already existing experimental devises could allow one to perform up to 15 gate operations in an ensemble of about 10 qubits.