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Category: quantum physics – Page 306

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According to computational complexity theory, mathematical problems have different levels of difficulty in the context of their solvability. While a classical computer can solve some problems ℗ in polynomial time—i.e., the time required for solving P is a polynomial function of the input size—it often fails to solve NP problems that scale exponentially with the problem size and thus cannot be solved in polynomial time. Classical computers based on semiconductor devices are, therefore, inadequate for solving sufficiently large NP problems.

In this regard, quantum computers are considered promising as they can perform a large number of operations in parallel. This, in turn, speeds up the NP problem-solving process. However, many physical implementations are highly sensitive to thermal fluctuations. As a result, quantum computers often demand stringent experimental conditions such extremely low temperatures for their implementation, making their fabrication complicated and expensive.

Fortunately, there is a lesser-known and as-yet underexplored alternative to quantum computing, known as probabilistic computing. Probabilistic computing utilizes what are called “stochastic nanodevices,” whose operations rely on thermal fluctuations, to solve NP problems efficiently. Unlike in the case of quantum computers, thermal fluctuations facilitate problem solving in probabilistic computing. As a result, probabilistic computing is, in fact, easier to implement in real life.

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Quantum objects make up classical objects. But the two behave very differently. The collapse of the wave-function prevents classical objects from doing the weird things quantum objects do; like quantum entanglement or quantum tunneling. Is the universe as a whole a quantum object or a classical one? Artyom Yurov and Valerian Yurov argue the universe is a quantum object, interacting with other quantum universes, with surprising consequences for our theories about dark matter and dark energy.

1. The Quantum Wonderland

If scientific theories were like human beings, the anthropomorphic quantum mechanics would be a miracle worker, a brilliant wizard of engineering, capable of fabricating almost anything, be it a laser or a complex integrated circuit. At the same token, this wizard of science would probably look and act crazier than a March Hair and Mad Hatter combined. The fact of the matter is, the principles of quantum mechanics are so bizarre and unintuitive, they seem to be utterly incompatible with our inherent common sense. For example, in the quantum realm, a particle does not journey from point A to point B along some predetermined path. Instead, it appears to traverse all possible trajectories between these points – every single one! In this strange realm the items might vanish right in front of an impenetrably high barrier – only to materialize on the other side (this is called quantum tunneling).

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In a new breakthrough, researchers at the University of Copenhagen, in collaboration with Ruhr University Bochum, have solved a problem that has caused quantum researchers headaches for years. The researchers can now control two quantum light sources rather than one. Trivial as it may seem to those uninitiated in quantum, this colossal breakthrough allows researchers to create a phenomenon known as quantum mechanical entanglement. This in turn, opens new doors for companies and others to exploit the technology commercially.

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Neuromorphic computing approaches become increasingly important as we address future needs for efficiently processing massive amounts of data. The unique attributes of quantum materials can help address these needs by enabling new energy-efficient device concepts that implement neuromorphic ideas at the hardware level. In particular, strong correlations give rise to highly non-linear responses, such as conductive phase transitions that can be harnessed for short-and long-term plasticity. Similarly, magnetization dynamics are strongly non-linear and can be utilized for data classification. This Perspective discusses select examples of these approaches and provides an outlook on the current opportunities and challenges for assembling quantum-material-based devices for neuromorphic functionalities into larger emergent complex network systems.

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In a new study, scientists have observed long-lived excitons in a topological material, opening intriguing new research directions for optoelectronics and quantum computing.

Excitons are charge-neutral quasiparticles created when light is absorbed by a semiconductor. Consisting of an excited electron coupled to a lower-energy electron vacancy or hole, an exciton is typically short-lived, surviving only until the electron and hole recombine, which limits its usefulness in applications.

“If we want to make progress in quantum computing and create more sustainable electronics, we need longer exciton lifetimes and new ways of transferring information that don’t rely on the charge of electrons,” said Alessandra Lanzara, who led the study. Lanzara is a senior faculty scientist at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and a UC Berkeley physics professor. “Here we’re leveraging topological material properties to make an exciton that is long lived and very robust to disorder.”

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We present an algorithm of quantum engineering of large-amplitude $$\ge 5$$ high-fidelity $$\ge 0.99$$ even/odd Schrödinger cat states (SCSs) using a single mode squeezed vacuum (SMSV) state as resource. Set of $$k$$ beam splitters (BSs) with arbitrary transmittance and reflectance coefficients sequentially following each other acts as a hub that redirects a multiphoton state into the measuring modes simultaneously measured by photon number resolving (PNR) detectors. We show that the multiphoton state splitting guarantees significant increase of the success probability of the SCSs generator compared to its implementation in a single PNR detector version and imposes less requirements on ideal PNR detectors.

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