Majorana particles may block intruders on sensitive networks in the future

The signature of the long-sought-after Majorana particle – a particle that has unusual properties believed to render it resistant to external interference – has been found by a group of researchers led by UCLA and funded by the U.S. Army. What they’ve found may just be the key to blocking intruders on sensitive communications networks in the future.

Majorana particles, predicted more than 80 years ago by Italian theoretical physicist Ettore Majorana, could become critical building blocks for quantum computers.

The group’s discovery solves a long-standing physics problem and also opens up a new way to control Majorana fermions (building blocks of matter) for achieving robust topological quantum computing, according to Joe Qiu, manager of the Solid-State Electronics Program within the Engineering Sciences Directorate at the Army Research Office, an element of the U.S. Army Research Laboratory located in Durham, North Carolina.

Quantum computers are of great interest to the U.S. Army because of their potential to solve problems much faster and more efficiently than classical computers. Quantum computers’ ability to process large amounts of data would enable significant improvements in situational awareness for warfighters.

Prior experimental approaches based on semiconductor nanowires on superconductors “produced inconclusive signals that could also be attributed to other effects,” ­Qiu says. “The UCLA experiment using stacked layers of magnetic topological insulator and superconductor demonstrated the clearest and most unambiguous evidence of the Majorana particles as predicted by theory so far.”

The group’s research leading up to the discovery of the Majorana particles involved a close interdisciplinary collaboration between a team of researchers including electrical engineers, physicists, and material scientists from UC, Irvine; UC, Davis; and Stanford University.

Kang L. Wang, a UCLA distinguished professor of electrical engineering, physics, and materials science and engineering, as well as UCLA’s Raytheon Chair Professor of Physical Science and Electronics, led the work.

“The Majorana particle is its own antiparticle – carrying zero electrical charge – so it’s viewed as the best candidate to carry a quantum bit, or qubit, the unit of data that would be the foundation of quantum computers. Unlike ‘bits’ of data in standard computers, which can be represented as either 0s or 1s, qubits have the ability to be both 0s and 1s, a property that would give quantum computers exponentially more computing power than today’s best computers,” explains Qiu.

The Majorana particle is of interest for quantum computing largely because its ­neutral charge makes it resistant to external interference, which means it can leverage and sustain a quantum property known as “entanglement.” Entanglement allows two physically separate particles to concurrently encode information, potentially generating enormous computing power.

You can imagine “bits of data in standard computers as cars traveling both ways on two-lane highways,” Wang says. “A quantum computer could have many lanes and many levels of ‘traffic,’ and the cars could hop between levels and travel in both directions at the same time, in every lane and on every level. We need stable, armored quantum ‘cars’ to do this, and Majorana particles are those supercars.”

The researchers set up a superconductor (a material that allows electrons to flow freely across its surfaces without resistance) and placed above it a thin film of a new quantum material (a topological insulator) to give the engineers the ability to manipulate particles into a specific pattern. After sweeping a very small magnetic field across their setup, they found the Majorana particles’ distinct quantized signal: a telltale fingerprint that revealed a specific type of quantum particles within the electrical traffic between the two materials.

These particles “show up and behave like halves of an electron, although they aren’t pieces of electrons,” says Qing Lin He, a UCLA postdoctoral scholar and one of the lead researchers. “We observed quantum behavior, and the signal we saw clearly showed the existence of these particles.”

In their experiment, Majorana particles traveled along the topological insulator’s edges in a distinct braid-like pattern. The next step, the researchers say, is to explore the use of Majorana particles in quantum braiding, in effect to “knit them together” to enable information to be stored and processed at super-high speeds.

The Majorana particles’ unique properties appear to make them “especially useful for topological quantum computers,” says Lei Pan, a UCLA doctoral student in electrical engineering who is one of the lead researchers. “While conventional quantum systems have sophisticated schemes to correct errors, information encoded in a topological quantum computer cannot be easily corrupted.”