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Transmitting quantum information using electron spin

In the realm of quantum information science, researchers are constantly exploring innovative ways to extend the boundaries of information storage beyond the conventional binary system of “one” and “zero.”

The electron’s spin, nature’s perfect quantum bit, has emerged as a promising candidate for achieving this goal.

Riding the magnon waves

A team of researchers from Lawrence Berkeley National Laboratory (Berkeley Lab), consisting of Joseph Orenstein, Yue Sun, Jie Yao, and Fanghao Meng, has made significant progress in utilizing magnon wave packets to transport quantum information over substantial distances in antiferromagnetic materials.

Their findings, published in a paper in Nature Physics, challenge the conventional understanding of how such excitations propagate in antiferromagnets.

Understanding magnon wave packets

Magnon wave packets are collective excitations of electron spins in magnetic materials. They can be thought of as quantized spin waves that propagate through the material, carrying information about the spin state of the electrons. Here are some key points to help you better understand magnon wave packets:

Spin waves

In magnetic materials, electron spins are coupled to each other through exchange interactions. When an electron’s spin is perturbed, it can cause a ripple-like effect, influencing the spins of neighboring electrons. This collective excitation is called a spin wave.

Quantization of spin waves

Just like other waves, such as light or sound, spin waves can be quantized. The quantized version of a spin wave is called a magnon. Magnons are quasi-particles that represent the collective excitation of electron spins in a magnetic material.

Magnon wave packets

A magnon wave packet is a localized excitation of magnons that can propagate through the material. It is formed by the superposition of different magnon modes with similar frequencies and wave vectors. Magnon wave packets can be created by various means, such as laser pulses or microwave excitation.

Quantum information carriers

Magnon wave packets can carry information about the spin state of the electrons in the material. This makes them promising candidates for use in quantum information processing and transmission. By manipulating and detecting magnon wave packets, researchers can encode, process, and transmit quantum information.

Propagation in magnetic materials

The properties of magnon wave packets, such as their speed and distance of propagation, depend on the type of magnetic material they are in. In antiferromagnetic materials, where neighboring electron spins are oriented in alternating directions, magnon wave packets have been shown to propagate faster and over longer distances than predicted by conventional models.

Applications in quantum information science

The ability of magnon wave packets to carry and transmit quantum information has potential applications in various fields, such as quantum computing, quantum sensing, and quantum communication. By harnessing the properties of magnon wave packets, researchers aim to develop novel quantum devices and technologies that can revolutionize the way we process and transmit information.

Electron spin and quantum information technologies

Electron spins, responsible for magnetism in materials, can be thought of as tiny bar magnets. In antiferromagnetic materials, neighboring spins are oriented in alternating directions, resulting in no net magnetization.

The ability to transmit quantum information with fidelity over distance is crucial for the development of quantum technologies, including computers, sensors, and other devices.

Challenging existing models

To investigate the movement of magnon wave packets through an antiferromagnetic material, Orenstein’s group employed pairs of laser pulses to perturb the antiferromagnetic order in one location while probing at another.

The resulting snapshots revealed that magnon wave packets propagate in all directions, similar to ripples on a pond created by a dropped pebble.

The Berkeley Lab team’s findings in the antiferromagnet CrSBr (chromium sulfide bromide) showed that magnon wave packets propagate faster and over longer distances than predicted by existing models.

These models assume that each electron spin couples only to its neighbors, similar to a system of spheres connected to near neighbors by springs. However, the observed speed of propagation was orders of magnitude faster than these models would suggest.

Role of long-range interactions

Orenstein explained the discrepancy between the observed propagation speed and the existing models by considering the long-range interactions between electron spins.

However, recall that each spinning electron is like a tiny bar magnet. If we imagine replacing the spheres by tiny bar magnets representing the spinning electrons, the picture changes completely,” Orenstein noted.

“Now, instead of local interactions, each bar magnet couples to every other one throughout the entire system, through the same long-range interaction that pulls a refrigerator magnet to the fridge door,” he concluded.

Quantum information and the future of technology

In summary, this breakthrough research conducted by Joseph Orenstein and his colleagues at Berkeley Lab highlights the potential of magnon wave packets in antiferromagnetic materials for quantum information storage and transmission.

By challenging conventional models and revealing the role of long-range interactions in the propagation of magnon wave packets, their work brings us closer to the development of advanced quantum technologies.

As scientists continues to drive innovation across the quantum research ecosystem, from theory to application, we can expect to see more discoveries that will shape the future of quantum devices and revolutionize the way we store, process, and transmit information.

The full study was published in the journal Nature Physics.


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