Generation and manipulation of magnonic Schrödinger cat states for quantum information science

Project Information

SPINCAT

Grant agreement ID: 101018193

DOI

10.3030/101018193

Project closed

EC signature date 25 February 2021

Start date 1 May 2021

End date 30 April 2023

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 187 572,48

EU contribution

€ 187 572,48

Coordinated by

UNIVERSITEIT UTRECHT
Netherlands

Periodic Reporting for period 1 - SPINCAT (Generation and manipulation of magnonic Schrödinger cat states for quantum information science)

Reporting period: 2021-05-01 to 2023-04-30

Summary of the context and overall objectives of the project

With the rapid accumulation of information in modern society, it becomes more and more important to find efficient means to store and process big data. Traditional electronic devices suffer from the problems of large energy consumption and Joule heating. To overcome these problems, spintronics and quantum information sciences rise in the last few decades and have shown great potential to innovate our computing technologies. This project investigates the interplay of spintronics and quantum information and aims to take advantage of both fields to build a hybrid quantum system for studying exotic quantum phenomena and for performing multi-functional quantum information tasks. The major issues of this interdisciplinary field are how to generate, manipulate and detect the robust quantum state of spins and further entangle it to the existing quantum platforms, for example, photons, phonons, and qubits, as shown in the figure attached. Under this background, we set the objectives of our project as follows:

(1) Identify the generation, manipulation, and decoherence channels of magnon quantum states including single magnon states, squeezed states, and Schrodinger cat states.
(2) Build a theoretical framework to study the dynamics of magnon quantum states, taking the decoherence effects of magnons into account.
(3) Propose new methods and materials to control the magnon quantum states and their applications in quantum information.
(4) Set up the framework of quantum magnonics and disseminate the field to a wide community.

Note that we are in the stage of the second quantum revolution that people are using basic principles of quantum mechanics to innovate our computing, simulation, and teleportation technologies. European has launched the well-known Quantum Technologies Flagship, and the Netherlands launched the Quantum Delta Program to build an excellent quantum ecosystem. The successful realization of my project will first strengthen the fundamental aspects of quantum information using hybrid quantum systems based on magnonic platforms. Further, it can bring considerable added value to the application of solid-state platforms for quantum computing, quantum communication, and quantum simulation and thus extend the current horizon of spintronics and quantum information science.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

1. Build the framework of quantum magnonics

In this work, we built the framework of quantum magnonics, review its history and developments, and outlooked its future directions including the new physics in hybrid quantum systems based on magnonics, the experimental detection of magnonic quantum states, and the fabrication of magnonic quantum devices. Our review provides a solid and comprehensive introduction to the motivation and key concepts of quantum magnonics and has become a valuable reference for both junior and experienced researchers working in the field of quantum optics, magnetism, and quantum information.

This review was published in Physics Reports and was well received by the community. It obtained 120+ citations in one year and was selected as ESI highly cited and hot paper. I presented this work to worldwide researchers on the Cassyni platform, which attracted an audience of thousands. Further, I introduced the field of quantum magnonics in the conferences JEMS 2022, IEEE NAP-2022, and Spintronics Netherlands 2022.

2. Control over the magnetic squeezed state by electric means in 2D magnets

Two-dimensional layered van der Waals (vdW) magnets have demonstrated their potential to study both fundamental and applied physics due to their remarkable electronic properties. However, the connection of vdW magnets to spintronics and quantum information science remains to be explored. In this work, we investigated the quantum correlations of magnons in a layered vdW magnet and identified an entanglement channel of magnons across the magnetic layers. The magnons excited on the two layers form a two-mode squeezed state with a finite entanglement. The strength of the entanglement can be effectively tuned and even deterministically switched on and off by both magnetic and electric means. Such a tunable entanglement channel can mediate the electrically controllable entanglement of two distant qubits, which also provides a protocol to indirectly measure the entanglement of magnons.

This work was published in Physical Review Applied. I presented this work to the community in Korrelationstage 2021 as an invited talk.

3. Identify the pure dephasing mechanisms of magnon quantum states

A wide class of magnon quantum states has been proposed and demonstrated recently. However, the decoherence mechanism of these quantum states is not clear. In this work, by considering exchange interaction and spin-phonon coupling in an ordered magnet, we evaluated the pure dephasing time of magnons and found it to be smaller than the magnon lifetime at temperatures of a few kelvins. By examining magnonic cat states as an example, we showed how pure dephasing of magnons destroys and limits the survival of quantum superpositions.

This work was published in Physical Review B. I presented this work in Magnetism Meet 2022 as an invited talk, in Quantum Spintronics 2022 as a poster, and in JEMS 2022 as an oral talk.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Now we are in the stage of the second quantum revolution that people are using basic principles of quantum mechanics to innovate our computing, simulation, and teleportation technologies. My project focuses on the fundamental aspects of quantum information using hybrid quantum systems based on magnonic platforms. In general, the progress presented below will first deepen our fundamental knowledge of the quantum effects of magnons in hybrid quantum systems and further bring considerable added value to the application of solid-state platforms for quantum computing, quantum communication, and quantum simulation.

1. Build the theoretical framework to study magnon quantum states

Here we first identified the dephasing channels of magnons based on the scattering between magnons and phonons. Further, to account for the dephasing dynamics of magnons, we formulated a master equation approach based on the Lindblad formalism. This approach provides a fully quantum-mechanical description of magnon dephasing, which is completely missing in the classical equation of motion for magnetization, and it can be extended to address other dephasing mechanisms in near-future experiments. Our findings provide guidance to measure this timescale in experiments and further benefit the design of magnon quantum states with long coherence time.

2. Manipulate magnon quantum states in low-dimensional materials

Here we considered the quantum correlations of magnetic excitations (magnons) in a layered van der Waals magnet. We first identified a hidden entanglement channel of magnons across the two magnetic layers and showed that it can be efficiently tuned by electric means through gate voltage. This feature is unique in a vdW magnet with competing exchange and anisotropy strength and is absent in normal bulk magnets. As an application potential, we demonstrated that such a tunable entanglement channel can mediate the entanglement of two distant qubits. This may readily enable the electric control of two or more quits, which is a desirable knob in solid-state platforms with wide applicability and low-energy consumption. Thus, it may open up new opportunities for vdW magnets for quantum information science.

scheme-qm.jpg