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Category: quantum physics

An international team led by researchers at Princeton University has uncovered a new pattern of ordering of electric charge in a novel superconducting material.

The researchers discovered the new type of ordering in a material containing atoms arranged in a peculiar structure known as a kagome lattice. While researchers already understand how the electron’s spin can produce magnetism, these new results provide insights into the fundamental understanding of another type of quantum order, namely, orbital magnetism, which addresses whether the charge can spontaneously flow in a loop and produce magnetism dominated by extended orbital motion of electrons in a lattice of atoms. Such orbital currents can produce unusual quantum effects such as anomalous Hall effects and be a precursor to unconventional superconductivity at relatively high temperatures. The study was published in the journal Nature Materials.

“The discovery of a novel charge order in a kagome superconductor with topological band-structure which is also tuneable via a is a major step forward that could unlock new horizons in controlling and harnessing quantum topology and superconductivity for future fundamental physics and next-generation device research,” said M. Zahid Hasan, the Eugene Higgins Professor of Physics at Princeton University, who led the research team.

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Circa 2017

The future Internet is very likely the mixture of all-optical Internet with low power consumption and quantum Internet with absolute security. The optical regular Internet would be used by default, but switched over to quantum Internet when sensitive data need to be transmitted. PT and and its counterpart in the quantum limit SPT would be the core components for both OIP and QIP in future Internet. Compared with electronic transistors, PTs/SPTs potentially have higher speed, lower power consumption and compatibility with fibre-optic communication systems.

Several schemes for PT6,7,8,9,10 and SPT11,12,13,14,15,16,17 have been proposed or even proof-of-principle demonstrated. All these prototypes exploit optical nonlinearities, i.e., photon-photon interactions18. However, photons do not interact with each other intrinsically, so indirect photon-photon interactions via electromagnetically induced transparency (EIT)19, photon blockade20 and Rydberg blockade21 were intensively investigated in this context over last two decades in either natural atoms22,23 or artificial atoms including superconducting boxes24,25 and semiconductor quantum dots (QDs)12,13. PT can seldom work in the quantum limit as SPT with the gain greater than 1 because of two big challenges, i.e., the difficulty to achieve the optical nonlinearities at single-photon levels and the distortion of single-photon pulse shape and inevitable noise produced by these nonlinearities26. The QD-cavity QED system is a promising solid-state platform for information and communication technology (ICT) due to their inherent scalability and matured semiconductor technology. But the photon blockade resulting from the anharmonicity of Jaynes-Cummings energy ladder27 is hard to achieve due to the small ratio of the QD-cavity coupling strength to the system dissipation rates12,13,28,29,30,31,32 and the strong QD saturation33. Moreover, the gain of this type of SPT based on the photon blockade is quite limited and only 2.2 is expected for In(Ga)As QDs12,13.

In this work, a different PT and SPT scheme exploiting photon-spin interactions rather than photon-photon interactions is proposed based on a linear quantum-optical effect — giant optical Faraday rotation (GFR) induced by a single QD-confined spin in a single-sided optical microcavity34. This spin-cavity transistor is genuinely a quantum transistor in three aspects: it is based on a quantum effect, i.e., the linear GFR; it has the duality as a quantum gate for QIP and a classical transistor for OIP; it can work in the quantum limit as a SPT to amplify a single-photon state to Schrödinger cat state. Therefore this new-concept transistor can be more powerful than the traditional electronic transistors. Theoretically the maximum gain can reach ~105 in the state-of-the-art pillar microcavity, several orders of magnitude greater than previous PT/SPT schemes6,7,8,9,10,11,12,13,14,15,16,17. The large gain is attributed to the linear GFR that is robust against classical and quantum fluctuations and the long spin coherence time compared with the cavity lifetime. The maximal speed which is determined by the cavity lifetime has the potential to break the terahertz (THz) barrier for electronic transistors35,36. Based on this versatile spin-cavity transistor, optical Internet1, quantum computers (QCs)37,38 (either spin-cavity hybrid QCs or all-optical QCs), and quantum Internet4 could become reality even with current semiconductor technology.

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A new on-chip device that is very good at mediating interactions between light and atoms in a vapour has been developed by researchers in Germany and the UK. Flavie Davidson-Marquis at Humboldt University of Berlin and colleagues call their device a “quantum-optically integrated light cage” and say that it could be used for wide range of applications in quantum information technology.

Hybrid quantum photonics is a rapidly growing area of research that integrates different optical systems within miniaturized devices. One area of interest is the creation of devices for the control, storage and retrieval of the quantum states of light using individual atoms. This is usually done by integrating on-chip photonic devices with miniaturized cells containing warm vapours of alkali atoms. However, this approach faces challenges due to inefficient vapour filling times, high losses of quantum information near cell surfaces and limited overlaps between the wavelengths of light used in optical circuits and the wavelengths of atomic transitions.

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Researchers from University of Copenhagen have developed a new technique that keeps quantum bits of light stable at room temperature instead of only working at-270 degrees. Their discovery saves power and money and is a breakthrough in quantum research.

As almost all our private information is digitalized, it is increasingly important that we find ways to protect our data and ourselves from being hacked.

Quantum Cryptography is the researchers’ answer to this problem, and more specifically a certain kind of qubit — consisting of single photons: particles of light.

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Given the importance of the Kirkwood–Dirac quasiprobability’s nonclassical values, two natural questions arise: Under what conditions does this quasiprobability behave anomalously? And how anomalous can its behaviour get? That’s what we wanted to explore.

What did you do in the paper?

We pinned down conditions under which the Kirkwood–Dirac quasiprobability assumes nonclassical values. Using these conditions, one can calculate which experiments can exhibit certain types of quantum advantages. We also put a “ceiling” on how much nonclassicality one Kirkwood–Dirac quasiprobability distribution can contain.

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In search for a unifying quantum gravity theory that would reconcile general relativity with quantum theory, it turns out quantum theory is more fundamental, after all. Quantum mechanical principles, some physicists argue, apply to all of reality (not only the realm of ultra-tiny), and numerous experiments confirm that assumption. After a century of Einsteinian relativistic physics gone unchallenged, a new kid of the block, Computational Physics, one of the frontrunners for quantum gravity, states that spacetime is a flat-out illusion and that what we call physical reality is actually a construct of information within [quantum neural] networks of conscious agents. In light of the physics of information, computational physicists eye a new theory as an “It from Qubit” offspring, necessarily incorporating consciousness in the new theoretic models and deeming spacetime, mass-energy as well as gravity emergent from information processing.

In fact, I expand on foundations of such new physics of information, also referred to as [Quantum] Computational Physics, Quantum Informatics, Digital Physics, and Pancomputationalism, in my recent book The Syntellect Hypothesis: Five Paradigms of the Mind’s Evolution. The Cybernetic Theory of Mind I’m currently developing is based on reversible quantum computing and projective geometry at large. This ontological model, a “theory of everything” of mine, agrees with certain quantum gravity contenders, such as M-Theory on fractal dimensionality and Emergence Theory on the code-theoretic ontology, but admittedly goes beyond all current models by treating space-time, mass-energy and gravity as emergent from information processing within a holographic, multidimensional matrix with the Omega Singularity as the source.

There’s plenty of cosmological anomalies of late that make us question the traditional interpretation of relativity. First off, what Albert Einstein (1879 — 1955) himself called “the biggest blunder” of his scientific career – t he rate of the expansion of our Universe, or the Hubble constant – is the subject of a very important discrepancy: Its value changes based how scientists try to measure it. New results from the Hubble Space Telescope have now “raised the discrepancy beyond a plausible level of chance,” according to one of the latest papers published in the Astrophysical Journal. We are stumbling more often on all kinds of discrepancies in relativistic physics and the standard cosmological model. Not only the Hubble constant is “constantly” called into question but even the speed of light, if measured by different methods, and on which Einsteinian theories are based upon, shows such discrepancies and turns out not really “constant.”

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