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A List Candidates for Quantum Computing Without Obstacle Brings Mysterious Surprise

Impressions of a neutron artist colliding with a sample of superconducting uranium nitteruride in an experiment at Oak Ridge National Laboratory. Uranium (dark gray) and tellurium (brown) crystals are suspected of hosting spin triplet superconductivity, a state marked by (blue) electron pairs with spins pointing in the same direction. In neutron scattering experiments, incoming neutrons destroy a pair by reversing one spin in the opposite direction (red), revealing clear evidence of the quantum mechanical state of the pair. Credit: Jill Hemman / ORNL

Mysterious results require physicists to rethink “spin triplet” superconductivity.

Rice University-led research has forced physicists to rethink the superconductivity of the A-list material, diterrutic uranium, in the global competition to create fault-tolerant quantum computers. ..

Uranium diterrudate crystals are a rare “Spin triplet“Shape of superconductivityHowever, the mysterious experimental results released this week Nature It overturned the main explanation of how the state of matter can occur in matter.Neutron scattering experiments by physicists at Rice, Oak Ridge National Laboratory, University of California, San Diego, National High Magnetic Field Laboratory Florida State University We have revealed clear signs of antiferromagnetic spin fluctuations associated with the superconductivity of ditellurized uranium.

Spin triplet superconductivity has not been observed in solid materials, but physicists have long suspected that it results from an ordered state that is ferromagnetic. The race to find spin triplet matter has intensified in recent years as it can host elusive quasiparticles called. Majorana fermion You can make it using it Error-free quantum computer..

“People have spent billions of dollars looking for them,” said Pengcheng Dai, co-author of Rice Studies, about Majorana fermions. Fictitious quasiparticle You can make it using it Topological qubit Free from troubled decoherence Qubits of today’s quantum computers..

“With spin triplet superconductors, we could use it to create topology qubits,” said Die, a professor of physics and astronomy and a member of the Rice Quantum Initiative. “Spin singlet superconductors can’t do that. That’s why people are very interested in this.”

Pengcheng Dai, Chunruo Duan, Qimiao Si

Rice University physicists (from left) Pengcheng Dai, Chunruo Duan, and Qimiao Si have long suspected hosting a rare “spin triplet” type of superconductivity. Co-authored a study that clarified.Credits: Photo by Jeff Fitlow / Rice University

Superconductivity occurs when electrons form a pair and move as one, like a couple rotating across a dance floor. Electrons naturally hate each other, but their tendency to avoid other electrons can be overcome by their inherent desire for the presence of low energies. Pairing can guide electrons to a pair if they can achieve a sloth-like state (only possible at very low temperatures) than they can achieve on their own.

Soothing comes in the form of fluctuations in their physical environment. In a normal superconductor such as lead, the fluctuation is the vibration of the atomic lattice of lead atoms inside the superconducting wire. Physicists have not yet identified the variability that results in unconventional superconductivity in materials such as ditellurized uranium. However, decades of research have found a phase change (the moment of the watershed where electrons spontaneously rearrange) at the critical point where pairing begins.

In quantum mechanics equations, these spontaneously ordered arrangements are expressed in terms known as ordinal parameters. The name spin triplet refers to the spontaneous collapse of the three contrasts in these ordered arrangements. for example, Electrons spin Always like a small bar magnet. One order parameter is related to the upward or downward spin axis (think North Pole). Ferromagnetic order means that all spins point in the same direction, and antiferromagnetic order means that they are arranged alternately up and down and up and down.In Confirmed only Spin triplet, Superfluid helium-3The, order parameter has more than 18 components.

“Everything else Superconductivity It’s a spin singlet, “said Dai, who is also a member of Rice’s Quantum Materials Center (RCQM). “In the spin singlet, there is one spin-up and one spin-down, and when applied with a magnetic field, superconductivity can easily be destroyed.”

This is because the magnetic field pushes the spins and aligns them in the same direction. The stronger the field, the stronger the push.

“The problem with urangetellide is Fields needed to destroy Superconductivity is 40 Tesla, “said Dai. “It’s huge. For 40 years, people thought that the only possibility that it would happen was that the spins were already aligned in one direction when you put the field. That is, it’s ferromagnetism. It’s the body. “

In this study, lead author of the study, Die and Postdoctoral Fellow of Rice, Chun Luo Duan, collaborated with Florida co-author Ryan Baumbach. Brian Maple tested and prepared a sample for a neutron scattering experiment at Oak Ridge’s Spalling Neutron Source.

“What neutrons do can come with a certain amount of energy and momentum to invert the spin of a Cooper pair from an up-up state to an up-down state,” Dai said. “We show how the pair is formed. From this neutron spin resonance, we can basically determine the electron pair energy,” says another obvious quantum mechanical wavefunction function that explains the pair. He said the trait.

Dai said there are two possible explanations for this result. Isn’t the diterrud uranium a spin triplet superconductor, or spin triplet superconductivity arises from antiferromagnetic spin fluctuations in a way physicists have never imagined.Die said for decades Experimental evidence Refers to the latterHowever, this seems to violate conventional knowledge about superconductivity. So Die teamed up with Kimyao Shi, a colleague of Rice, a theoretical physicist who specializes in new quantum phenomena such as unconventional superconductivity.

Si, the co-author of the study, has spent much of the last five years, Theory of multi-orbital pairing He co-developed with a former PhD.Student Emilian Nika Explain contradictory experimental results In some types of unconventional superconductors, including heavy fermion materials, a class containing ditellurized uranium.

In multi-orbital pairing, the electrons in some shells are more likely to pair than in other shells. Si recalled that he thought that uranium could contribute to electron pairs from any of the seven orbitals with 14 possible states.

“The first thing that came to my mind was multi-orbital,” he said. “It’s not possible if you have only one band or one orbit, but orbits bring a new dimension to the possible unconventional combinations of superconductors. They are like a palette of colors. Colors are internal. It is a quantum number f electron Uranium-based heavy fermion materials are naturally set to these colors. They lead to new possibilities beyond the “Periodic Table of Pairing States”. One of these new possibilities turned out to be spin triplet pairing. “

Si and Nica, currently enrolled at Arizona State University, have shown that antiferromagnetic correlations can lead to plausible, low-energy spin triplet pairing states.

“Spin-triplet pairing is almost impossible because the pair is formed as a spin-singlet to reduce energy,” says Si. “In uranium diterlate, spin-orbit interaction can alter the energy landscape in a way that the spin triplet pairing state is more competitive with the spin singlet state.”

Reference: “Resonance from antiferromagnetic spin fluctuations to UTe superconductivity2Chunruo Duan, RE Baumbach, Andrey Podlesnyak, Yuhang Deng, Camilla Moir, Alexander J. Breindel, M. BrianMaple, EM Nica, Qimiao Si, Pengcheng Dai, December 22, 2021 Nature..
DOI: 10.1038 / s41586-021-04151-5

Si is Professor Harry C. and Olga K. Wis of Rice’s Department of Physics and Astronomy and Director of RCQM. Additional co-authors include Andrey Podolsnjak and Yuhan Den of Oak Ridge, and Camilla More and Alexander Blinder of the University of California, San Diego.

This study was conducted by the Department of Energy Science, Department of Basic Energy Science (DE-SC0012311, DE-SC0016568, DE-SC0018197, DEFG02-04-ER46105), Robert A. Welch Foundation (C-1839, C-1411), National Science. DOE Science Department user facility at the Spalling Neutron Sources of the Foundation (1644779, 1810310, 1607611), Florida, Arizona State University, and Oak Ridge National Laboratory.



A List Candidates for Quantum Computing Without Obstacle Brings Mysterious Surprise

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