Quantum Network with Magnonic and Mechanical Nodes

A quantum network consisting of magnonic and mechanical nodes connected by light is proposed. Recent years have witnessed a significant development in cavity magnonics based on collective spin excitations in ferrimagnetic crystals, such as yttrium iron garnet (YIG). Magnonic systems are considered to be a promising building block for a future quantum network. However, a major limitation of the system is that the coherence time of the magnon excitations is limited by their intrinsic loss (typically in the order of $1\mu \mathrm{s}$ for YIG). Here, we show that by coupling the magnonic system to a mechanical system using optical pulses, an arbitrary magnonic state (either classical or quantum) can be transferred to and stored in a distant long-lived mechanical resonator. The fidelity depends on the pulse parameters and the transmission loss. We further show that the magnonic and mechanical nodes can be prepared in a macroscopic entangled state. These demonstrate the quantum state transfer and entanglement distribution in such a novel quantum network of magnonic and mechanical nodes. Our work shows the possibility to connect two separate fields of optomagnonics and optomechanics, and to build a long-distance quantum network based on magnonic and mechanical systems.

Popular Summary

The past decade has witnessed a significant development in cavity magnonics based on collective spin excitations in ferrimagnetic crystals, such as yttrium iron garnet (YIG). Magnonic systems are considered to be a promising building block for realizing a hybrid quantum network, benefiting from their excellent ability to coherently interact with various quantum systems, including microwave or optical photons, phonons, and superconducting qubits. However, a major limitation of the system is that the coherence time of the magnons is limited by their intrinsic loss, in the order of one microsecond for YIG.

Here it is shown that this obstacle can be eliminated by connecting the magnonic system to a distant mechanical system via optical pulses through a fiber. Such a magnon-photon-phonon remote network allows for transferring an arbitrary magnonic quantum state to a long-lived mechanical node, which acts as a quantum memory. It is also shown that the magnonic and mechanical nodes can be prepared in a macroscopic nonlocal entangled state. Here is proof that such a configuration can realize the basic functions of a quantum network, i.e., quantum state transfer and entanglement distribution among different nodes.

This work offers a promising vision for realizing a future hybrid quantum network based on magnonic systems and shows the possibility to connect two separate research fields of optomagnonics and optomechanics. It may find potential applications in quantum networks and quantum information processing based on magnonics and in the study of macroscopic quantum mechanics.

Figure 1

(a) An optomagnonic system of a YIG sphere supporting two WGMs and a magnon mode. (b) Mode frequencies of the optomagnonic Stokes BLS. (c) Mode frequencies of the optomagnonic anti-Stokes BLS.

Figure 2

(a) A cavity optomechanical system: a cavity mode couples to a mechanical resonator via radiation pressure. (b) A red-detuned drive field to activate the optomechanical anti-Stokes process for realizing state swap. (c) A blue-detuned drive field to activate the optomechanical Stokes process for realizing two-mode squeezing.

Figure 3

Sketch of the distant magnon-to-phonon state transfer protocol (a) and the corresponding mode frequencies (c). The nonlocal magnon-phonon entanglement protocol (b) and the associated mode frequencies (d).

Figure 4

The transmission loss modeled by a beam splitter (BS), of which the reflection denotes the loss and the transmission represents the pulse after suffering the loss.

Figure 5

Magnon-phonon entanglement (logarithmic negativity $E_N$) versus the squeezing $r$ for different conversion efficiencies $W$. From upper to lower curves: $W=1$, 0.8, 0.5, and 0.2.