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Category: particle physics – Page 406

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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For the first time, scientists from the ALPHA collaboration at CERN reported successfully manipulating antimatter with the use of a laser system — potentially changing antimatter research and guide future experiments on the field.

Antimatter basically refers to the opposite of matter. Specifically, antimatter has sub-atomic particles whose properties (such as electric charge) are the opposite of normal matter. Most of the challenges surrounding the detection and observation of antimatter come from the fact that it immediately “annihilates” when it comes into contact with normal matter.

The ALPHA collaboration scientists report their findings in the article “Laser cooling of antihydrogen atoms,” appearing in the latest journal Nature, March 31.

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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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Circa 2020

Researchers at UC Berkeley have developed a rapid test for SARS-CoV-2 that uses an enzyme to cleave viral RNA, initiating a fluorescent signal that can be detected using a smartphone camera, and which can provide a quantitative measurement of the level of viral particles in the sample. The test produce a result in as little as 30 minutes and does not require bulky or expensive laboratory equipment.

Rapid testing is key to measuring and stopping the spread of COVID-19, but current tests, such as PCR, are time consuming and require expensive laboratory equipment, creating a bottleneck in obtaining results. Researchers have been developing alternatives, and this latest technology was rapidly repurposed when the pandemic began. Originally intended to detect HIV in blood samples, the Berkeley researchers have pivoted to allow the device to detect SARS-CoV-2 in nasal swab samples.

The test relies on CRISPR-Cas, originally developed as a gene editing technology. When a pre-programmed Cas13 enzyme is added to the sample, it can cleave RNA sequences from the SARS-CoV-2 virus. This results in other nearby sequences being cleaved also, including a probe that releases fluorescent light when cleaved. The device uses a laser to excite this fluorescence and a smartphone camera can then detect the light, providing a quantitative measurement of the viral particles present in the sample.

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“Conditional witnessing” technique makes many-body entangled states easier to measure.

Quantum error correction – a crucial ingredient in bringing quantum computers into the mainstream – relies on sharing entanglement between many particles at once. Thanks to researchers in the UK, Spain and Germany, measuring those entangled states just got a lot easier. The new measurement procedure, which the researchers term “conditional witnessing”, is more robust to noise than previous techniques and minimizes the number of measurements required, making it a valuable method for testing imperfect real-life quantum systems.

Quantum computers run their algorithms on quantum bits, or qubits. These physical two-level quantum systems play an analogous role to classical bits, except that instead of being restricted to just “0” or “1” states, a single qubit can be in any combination of the two. This extra information capacity, combined with the ability to manipulate quantum entanglement between qubits (thus allowing multiple calculations to be performed simultaneously), is a key advantage of quantum computers.

The problem with qubits

However, qubits are fragile. Virtually any interaction with their environment can cause them to collapse like a house of cards and lose their quantum correlations – a process called decoherence. If this happens before an algorithm finishes running, the result is a mess, not an answer. (You would not get much work done on a laptop that had to restart every second.) In general, the more qubits a quantum computer has, the harder they are to keep quantum; even today’s most advanced quantum processors still have fewer than 100 physical qubits.

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Physics World

Quantum mechanics describes this frustration by suggesting that the orientation of the spins is not rigid. Instead, it constantly changes direction in a fluid-like way to produce an entangled ensemble of spin-ups and spin-downs. Thanks to this behaviour, a spin liquid will remain in a liquid state even at temperatures near absolute zero, where most materials usually freeze solid.

The holon and the spinon

To describe this behaviour in mathematical terms, the late Nobel laureate Philip W Anderson, who predicted the existence of spin liquids in 1973, proposed that in the quantum regime, an electron might in fact be composed of two distinct particles. The first, known as a “holon”, would bear the electron’s negative charge, while the second “spinon” particle would carry its spin. Anderson later suggested that this spin-charge separation might provide a microscopic mechanism to explain the high superconducting transition temperatures (Tc) that were observed in copper oxides, or cuprates, beginning in the late 1980s.

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This year, physicists gave us an early view of a third kingdom of quasiparticles that only arise in two dimensions.

The rest of the particles in the universe are bosons, a group that includes particles like photons (the messengers of light and radiation) and gluons (which “glue” quarks together). Unlike fermions, two or more bosons can exist in the same state at the same time.

This article appeared in Discover’s annual state of science issue as Anyons Join the Particle Party.

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This Stone Predates the Sun.

Recent analysis of a stone found in the Libyan Desert Glass area of southwest Egypt, has sparked debate and a rethink of the current consensus on the formation of the solar system.

In a study, due to be published next month, a team of international researchers announced the resulting analysis of a stone that was subsequently named Hypatia after the ancient female astronomer of Alexandria.

Utilizing techniques from electron scanning microscopy, to proton induce X-ray emission and micro-Raman spectroscopy – the results revealed compounds not found anywhere on our planet, solar system or any known meteorite. As well, a lack of silicates was found which sets it apart from interplanetary dust particles and all known cometary material. Previous analysis of noble gas and nitrogen isotope studies suggest an extraterrestrial origin, which along with these new results strongly suggests a pre-solar origin and could indicate a high degree of heterogeneity in the solar nebula.

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When particles are cooled down to temperatures just above absolute zero, they form a BEC – a state of matter in which all the particles occupy the same quantum state and thus act in unison, like a superfluid. A BEC made up of tens of thousands of particles therefore behaves as if it were just one single giant quantum particle.

An international team of researchers led by Carlos Anton-Solanas and Christian Schneider from the University of Oldenburg, Germany; Sven Höfling of the University of Würzburg, Germany; Sefaattin Tongay at Arizona State University, US; and Alexey Kavokin of Westlake University in China, has now generated a BEC from quasiparticles known as exciton-polaritons in atomically thin crystals. These quasiparticles form when excited electrons in solids couple strongly with photons.

“Devices that can control these novel light-matter states hold the promise of a technological leap in comparison with current electronic circuits,” explains Anton-Solanas, who is in the quantum materials group at Oldenburg’s Institute of Physics. “Such optoelectronic circuits, which operate using light instead of electric current, could be better and faster at processing information than today’s processors.”

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