A bridge to the quantum world: Dirac electrons found in unique material

December 4, 2012, University of Michigan

In a discovery that helps clear a new path toward quantum computers, University of Michigan physicists have found elusive Dirac electrons in a superconducting material.

Quantum computers use atoms themselves to perform processing and . They promise dramatic increases in computing power because of their ability to carry out scores of calculations at once. They could factor numbers dramatically faster than conventional computers, and would be game-changers for computer security.

The combination of properties the researchers identified in a shiny, black material called copper-doped bismuth selenide adds the material to an elite class that could serve as the silicon of the quantum era. Copper-doped bismuth selenide is a .

Superconductors can—at cold enough temperatures—conduct electricity indefinitely from one kickstart of energy. They have no . Dirac electrons, named after the English physicist whose equation describes their behavior, are particles with such high energy that they straddle the realms of classical and .

"They're a bridge between the worlds," said Lu Li, assistant professor of physics in the College of Literature, Science, and the Arts and leader of a study published in the current edition of .

Other research teams had theorized that copper-doped bismuth selenide contained Dirac electrons, but no one had ever detected them. Li and his colleagues were able to observe the electrons' tell-tale quantum oscillations in the material by cooling it to cryogenic temperatures and exposing it to a strong magnetic field. Materials rotate under intense magnetic fields, and the researchers could detect the quantum oscillations by varying the strength of the magnetic field and the temperature.

In quantum computers, "qubits" stand in for the 0s and 1s of conventional computers' binary code. A conventional bit can be either a 0 or a 1. A can be both at the same time—until you measure it. Measuring a quantum system perturbs it into picking just one phase, which eliminates its most enticing attribute.

As one of the major hurdles to developing practical quantum computers, research groups are exploring ways to get around this so-called "local noise" problem. The new class of materials that copper-doped bismuth belongs to—topological superconductors—present a new possibility. The Dirac electrons within them have the ability to clump together into a new kind of qubit that changes the properties of the material in a way that's detectable to an observer, but not to the qubits. So the qubits can carry on calculating without knowing they're being measured.

"Schrödinger's cat can stay alive and dead at the same time," said Li, referring to Austrian physicist Erwin Schrödinger's famous thought experiment about quantum mechanics. "The so-called qubit is no longer the object we're looking at. This material could be a promising way to make quantum computers."

Explore further: The age of quantum information

More information: prl.aps.org/abstract/PRL/v109/i22/e226406

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3.5 / 5 (2) Dec 04, 2012
The cats out of the bag.
3 / 5 (4) Dec 04, 2012
WTF: `Dirac electrons' ? An electron is an electron. Dirac's only added attribute is zitterbewegung. No mention of such is made in the article. I smell hype.
4.5 / 5 (6) Dec 04, 2012
Yes, the terminology used in the article is odd. There's no such thing as a 'Dirac electron.' Dirac's equation describes an oscillation expected to be found in all electrons.

Perhaps a more sensible explanation (in words, at least; no doubt mathematics would be better) is that the researchers have explored a method for generating high-energy electrons within a superconducting matrix and measuring their Dirac oscillations to glean clues as to their quantum states without disturbing those states...?

Hard to tell, really. The article is opaque and strangely written.
1 / 5 (5) Dec 04, 2012
The existence of such particle can be understood quite easily in my explanation of superconductivity, which arises from high compression of electrons within atom lattice. The repulsive forces of individual electrons overlap and compensate mutually and as the result such an electrons are moving freely. The charge is mediated across sea of such electrons in similar way like the pressure waves of wagons inside of long train or like the ripples at the water surface. Dirac fermions are denomination for the state of particles, the mass of which doesn't depend on speed. They're moving with constant speed which is close to the speed of light and their rest mass is effectively close to zero in similar way, like for the waves of light.
1 / 5 (4) Dec 04, 2012
The name "Dirac fermion" comes just from fact, the description of electrons moving with the high speed requires the introduction of relativistic effects (Lorentz transform) into quantum equation, which was first done with P.A.Dirac. I'm interested about it particularly because in AWT the fast moving charged particles should interact strongly with vacuum fluctuations and they should induce for example the gravitational beams and antigravity effects, which were observed first with Podkletnov. For superconductive paddle the vacuum should behave like the thin atmosphere filled with low-energy neutrinos and it should reflect the gravitational/scalar waves (mirror for superluminal telescopes penetrating the materials) and exhibit dragging and antigravity effects. Unfortunately the mainstream physics is completely mentally separated from physics of longitudinal waves in vacuum, being based on deterministic transverse waves only. Whole half of physics is still missing in this way.
1 / 5 (4) Dec 04, 2012
IMO these effects should be observable even at room temperature, because we have room temperature superconductors developed already. The conductivity of these samples is low, because they do consist of mutually isolated superconductive islands (pseudogap state) - but it doesn't make problem just for above applications, because the Dirac electrons are already presented there.
1 / 5 (3) Dec 04, 2012
An electron is an electron. Dirac's only added attribute is zitterbewegung
Yes, but what the zitterbewegung actually is? The (quantum wave of) free electrons are undulating mostly in three dimensions. When their motion is constrained mutually, then the electrons have no other option, than to undulate mostly in forth dimension like particle wave closed inside of tight potential box. Such a trapped electron interacts strongly not with transverse waves of vacuum, but rather with scalar waves, because it's scalar wave by itself. It manifests for example with high optical transparency of Dirac electrons - they do absorb/reflect gravitational waves instead. For example, the optical absorption of graphene is driven with fine structure constant only.
5 / 5 (4) Dec 05, 2012
When one speaks of Dirac electrons in a condensed matter context, it means that an electrons energy has a linear dependece on it's wave vector. For free massless particles the Dirac equation gives the same kind of dependence. This why Diracs name pops up here.
I can't see why this would be a problem, or warrant spouting out nonsense.

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