The world may undergo a transformation thanks to quantum computing. It promises to be considerably faster for certain and important activities than the zero-or-one binary technology that powers today’s equipment, from supercomputers in research labs to smartphones in our pockets. But creating a reliable network of qubits—or quantum bits—to store information, access it, and carry out computations is essential for creating quantum computers.
But the qubit systems that have been made public so far all share a similar flaw: they are frequently delicate and susceptible to external disruptions. A single errant photon can cause problems. The ultimate response to this problem could be the development of fault-tolerant qubits, which would be unaffected by outside disturbances.
Substantial development in this endeavor has been disclosed by a team from the University of Washington led by scientists and engineers. The researchers say that in trials with semiconductor material flakes that were each only a single layer of atoms thick, they were able to identify “fractional quantum anomalous Hall” (FQAH) states. Their findings were reported in a pair of papers on June 14 in Nature and on June 22 in Science.
Due to the fact that FQAH states can support anyons—weird “quasiparticles” with only a small fraction of an electron’s charge—the team’s findings represent a first and encouraging step in the construction of a specific form of the fault-tolerant qubit. It is possible to create “topologically protected” qubits, which are stable against any minor, local disruptions, using certain types of anyons.
“This really establishes a new paradigm for studying quantum physics with fractional excitations in the future,” said Xiaodong Xu, the principal investigator behind these findings and the Boeing Distinguished Professor of Physics and a professor of materials Science and Engineering at the UW.
The fractional quantum Hall state (FQAH state) is a rare phase of matter that exists in two-dimensional systems. Electrical conductivity is limited in these states to precise fractions of the conductance quantum, a constant. Fractional quantum Hall systems, however, frequently require strong magnetic fields to maintain their stability, rendering them unsuitable for use in quantum computing. Such a condition is not necessary for the FQAH state, which the team claims is stable even “at zero magnetic fields.”
The researchers had to create an artificial lattice with exotic properties in order to host such an exotic phase of matter. They created a modest, mutual “twist” angle between two atomically thin flakes of the semiconductor material molybdenum ditelluride (MoTe2). This arrangement created an artificial “honeycomb lattice” for the electrons.
The arrangement developed an inherent magnetic when scientists cooled the stacked slices to a few degrees above absolute zero. The strong magnetic field generally needed for the fractional quantum Hall state is replaced by intrinsic magnetism. The discovery of the FQAH effect signatures by the researchers using lasers as probes represents a significant advance in the understanding of anyons and their potential for quantum computing.
The team, which also includes researchers from Boston College, the Massachusetts Institute of Technology, the National Institute for Materials Science in Japan, and the University of Hong Kong, sees their system as a potent tool for understanding anyons, which differ greatly from common particles like electrons in terms of their properties.
Anyone is a quasiparticle or “excitation” that resembles particles and can function as a portion of an electron. Researchers aim to find “non-Abelian” anyons, which could be employed as topological qubits, an even more exotic variation of this sort of quasiparticle in subsequent experiments with their experimental setup. It is possible to create an entangled quantum state by “braiding” or wrapping the non-Abelian anyons around one another. The fundamental building block of topological qubits, which represent a significant improvement over the capabilities of existing quantum computers, is the quantum state in which information is basically “spread out” over the entire system and resilient to local perturbations.
Eric Anderson, a doctorate student in physics at the University of Washington, is the lead author of the Science publication and the co-lead author of the Nature paper. “This type of topological qubit would be fundamentally different from those that can be created now,” Anderson said. Non-Abelian anyons’ peculiar nature would make them far more reliable as a quantum computing platform.
FQAH states developed as a result of the simultaneous occurrence of three essential characteristics in the researchers’ experimental design:
Despite the fact that MoTe2 is not magnetic, a “spontaneous spin order”—also known as ferromagnetism—emerged when the system was charged with positive charges.
Topology: The electrical charges’ “twisted bands,” which resemble a Möbius strip, help to make the system topological.
Charges in their experimental system interact vigorously enough to keep the FQAH condition stable.
The team believes that this novel strategy will lead to the discovery of non-Abelian anyons.
Jiaqi Cai, the co-lead author of the Nature publication and co-author of the Science piece, a doctorate student in physics at the University of Washington, called the detected fingerprints of the fractional quantum anomalous Hall effect “inspiring.” The system’s productive quantum states could lead to new quantum gadgets as well as a lab-on-a-chip for studying new physics in two dimensions.
“Our work provides clear evidence of the long-sought FQAH states,” said Xu, who is also a member of the UW’s Molecular Engineering and Sciences Institute, Institute for Nano-Engineered Systems, and Clean Energy Institute. We are now developing electrical transport experiments that could offer clear, conclusive proof of fractional excitations in the absence of a magnetic field.
The team thinks this strategy will make it easier to study and manipulate these peculiar FQAH states, advancing the development of quantum computers.
