Silicon Chip Creates Two-Qubit Processor.
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Category: quantum physics – Page 708
Nearly a century after its founding, physicists and philosophers still don’t know—but they’re working on it.
- By Anil Ananthaswamy on September 3, 2018
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In 2018, Canada is ranked tenth in the world in nominal GDP. It is a rich developed country. Despite having an economy that is 11 times smaller than the USA or 7 times smaller than China, Canada has world competitive or world-leading projects in quantum computing, artificial intelligence, molecular nanotechnology, nuclear fusion and nuclear-molten salt.
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When it comes to fundamental physics, things can get spooky. At least that’s what Albert Einstein said when describing the phenomenon of quantum entanglement—the linkage of particles in such a way that measurements performed on one particle seem to affect the other, even when separated by great distances. “Spooky action at a distance” is how Einstein described what he couldn’t explain.
While quantum mechanics includes many mysterious phenomena like entanglement, it remains the best fundamental physical theory describing how matter and light behave at the smallest scales. Quantum theory has survived numerous experimental tests in the past century while enabling many advanced technologies: modern computers, digital cameras and the displays of TVs, laptops and smartphones. Quantum entanglement itself is also the key to several next-generation technologies in computing, encryption and telecommunications. Yet, there is no clear consensus on how to interpret what quantum theory says about the true nature of reality at the subatomic level, or to definitively explain how entanglement actually works.
According to Andrew Friedman, a research scientist at the University of California San Diego Center for Astrophysics and Space Sciences (CASS), “the race is on” around the globe to identify and experimentally close potential loopholes that could still allow alternative theories, distinct from quantum theory, to explain perplexing phenomena like quantum entanglement. Such loopholes could potentially allow future quantum encryption schemes to be hacked. So, Friedman and his fellow researchers conducted a “Cosmic Bell” test with polarization-entangled photons designed to further close the “freedom-of-choice” or “free will” loophole in tests of Bell’s inequality, a famous theoretical result derived by physicist John S. Bell in the 1960s. Published in the Aug. 20 issue of Physical Review Letters, their findings are consistent with quantum theory and push back to at least 7.
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After their recent pioneering experiments to couple light and matter to an extreme degree, Rice University scientists decided to look for a similar effect in matter alone. They didn’t expect to find it so soon.
Rice physicist Junichiro Kono, graduate student Xinwei Li and their international colleagues have discovered the first example of Dicke cooperativity in a matter-matter system, a result reported in Science this week.
The discovery could help advance the understanding of spintronics and quantum magnetism, Kono said. On the spintronics side, he said the work will lead to faster information processing with lower power consumption and will contribute to the development of spin-based quantum computing. The team’s findings on quantum magnetism will lead to a deeper understanding of the phases of matter induced by many-body interactions at the atomic scale.
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One Universe Is Not Enough
Posted in quantum physics
The team of Li Chengfeng, Zhou Zongquan and others from the CAS Key Lab of Quantum Information developed a multi-degree-of-freedom (DOF) multiplexed solid-state quantum memory, and demonstrated photon pulse operation functions with time and frequency DOFs. The results were published in Nature Communications recently.
The reliable storage and coherent manipulation of quantum states with matter-systems enable the construction of large-scale quantum networks based on a quantum repeater. To achieve useful communication rates, highly multi-mode quantum memories will be required to construct a multiplexed quantum repeater.
The team presented the first demonstration of the on-demand storage of orbital-angular-momentum states with weak coherent pulses at the single-photon-level in a rare-earth-ion doped crystal. Through the combination of this 3-dimensional spatial DOF with 2-dimensional temporal and 2-dimensional spectral DOFs, the team created a multiple-DOF memory with high multi-mode capacity up to 3×2×2=12.
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