Two topical papers unleash 'signals' for topological quantum computing ......

Quantum computing could revolutionize our world.

For specific and critical tasks, it promises to be several times faster than the binary technology of 0s or 1s on which today's machines (from the supercomputers in the lab to the smartphones in our pockets) are based. However, developing a quantum computer depends on building a stable network of quantum bits (or quantum bits) to store information, access it, and perform computations.

However, the quantum bit platforms announced so far share a common problem: they are often fragile and vulnerable to outside interference. Even a single stray photon can cause trouble.

The development of fault-tolerant quantum bits (which would be immune to external interference) may be the ultimate solution to this challenge.

Now, a team led by scientists and engineers at the University of Washington has announced significant progress in this quest. In two papers published June 14 in Nature and June 22 in Science, the researchers report that in experiments on sheets of semiconductor material, each just one atomic layer thick, they detected the "fractional quantum anomalous Hall (FQAH) effect. (FQAH)".

The group's discovery marks a promising first step in building a fault-tolerant quantum bit, since FQAH states can carry arbitrons - "particle-like" particles with only an electronic charge. Some types of arbitrons can be used to make topological quantum bits that are stable to any small, localized disturbance.

Xiaodong Xu, the lead researcher behind these discoveries, said, "This really establishes a new paradigm for future studies of quantum physics with fractional excitations."

The FQAH states are associated with fractional quantum Hall states - a peculiar phase of matter that exists in two-dimensional systems. In these states, the conductivity is limited to an exact fraction of a constant called the conductance quantum. But fractional quantum Hall systems typically require huge magnetic fields to keep them stable, making them impractical for use in quantum computing.

The team says the FQAH state has no such requirements; it is stable even "in a zero-field" environment.

Controlling such a peculiar phase of matter required the researchers to build an artificial lattice with peculiar properties. They stacked two atomically thin slices of the semiconductor material molybdenum ditelluride (MoTe2) at a small "twist" angle relative to each other; this configuration formed a synthetic "honeycomb lattice" for the electrons.

When the researchers cooled the stacked slices above absolute zero, an intrinsic magnetic field emerged in the system, replacing the strong magnetic field normally required for fractional quantum Hall states. Using a laser as a probe, the researchers detected the signature of the FQAH effect, a major step forward in unleashing arbitrary quantum forces in quantum computing.

The team, which also includes scientists from the University of Hong Kong, the National Institute for Materials Science (NIMS) in Japan, Boston College and the Massachusetts Institute of Technology, considers their system a powerful platform to develop a deeper understanding of arbitrons.

Arbitrons are quasiparticles that can act as part of an electron. In future work on their experimental system, the researchers hope to discover a more exotic version of this type of quasiparticle: non-abelian arbitrons, which can be used as topological quantum bits.

By twisting or "weaving" non-abelian arbitrons around each other, an entangled quantum state can be created. In this quantum state, information is essentially "dispersed" throughout the system and is resistant to local interference - the basis for topological quantum bits and a significant advance on the capabilities of current quantum computers.

These types of topological quantum bits would be fundamentally different from those that can be created today, and the "strange" properties of non-abelian arbitrators would make them even more powerful as a quantum computing platform.

Electron differentiation: In the fractional quantum anomalous Hall stage, the strongly interacting charges can "differentiate" into three parts.

The FQAH state emerges when all three key properties are present simultaneously in the researchers' experimental setup:

- Magnetism: Although MoTe2 is not a magnetic material, a form of magnetism called ferromagnetism emerged when the scientists loaded the system with a positive charge.

- Topology: The charges in their system have "twisted bands" (similar to Möbius bands), which help make the system topological.

- Interactions: The charges in their experimental system have strong enough interactions to stabilize the FQAH state.

With this new approach, the team hopes to discover non-abelian arbitrators.

Commenting on the results, Jiaqi Cai, a doctoral student in physics at the University of Washington and co-first author of the Nature paper and co-author of the Science paper, said, "The observed signature of the fractional quantum anomalous Hall effect is encouraging, and the fruitful quantum states in this system could become a lab-on-a-chip for discovering new physics in two dimensions, as well as a new devices for quantum applications."

The team members added, "Our work provides clear evidence for the long-sought FQAH state, and we are currently performing electrical transport measurements, which could provide direct and unambiguous evidence for fractional excitation at zero magnetic field."

The team believes that with their approach, investigating and manipulating these unusual FQAH states could become commonplace: this would accelerate the journey to quantum computing.

Reference links:

[1] https://phys.org/news/2023-06-quantum-magnetic.html

[2]https://www.nature.com/articles/s41586-023-06289-w

[3]https://www.science.org/doi/10.1126/science.adg4268