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Category: quantum physics – Page 320

Fluorescence exclusively occurs from the lowest excited state of a given multiplicity according to Kasha’s rule. However, this rule is not obeyed by a handful of anti-Kasha fluorophores whose underlying mechanism is still understood merely on a phenomenological basis. This lack of understanding prevents the rational design and property-tuning of anti-Kasha fluorophores. Here, we propose a model explaining the photophysical properties of an archetypal anti-Kasha fluorophore, azulene, based on its ground-and excited-state (anti)aromaticity. We derived our model from a detailed analysis of the electronic structure of the ground singlet, first excited triplet, and quintet states and of the first and second excited singlet states using the perturbational molecular orbital theory and quantum-chemical aromaticity indices.

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In a paper published today (Sept. 18) in Nature Communications, researchers from the Paul-Drude-Institut in Berlin, Germany, and the Instituto Balseiro in Bariloche, Argentina, demonstrated that the mixing of confined quantum fluids of light and GHz sound leads to the emergence of an elusive phonoriton quasi-particle—in part a quantum of light (photon), a quantum of sound (phonon) and a semiconductor exciton. This discovery opens a novel way to coherently convert information between optical and microwave domains, bringing potential benefits to the fields of photonics, optomechanics and optical communication technologies.

The research team’s work draws inspiration from an everyday phenomenon: the transfer of energy between two coupled oscillators, such as, for instance, two pendulums connected by a spring. Under specific coupling conditions, known as the strong-coupling (SC) regime, energy continuously oscillates between the two pendulums, which are no longer independent, as their frequencies and decay rates are not those of the uncoupled ones. The oscillators can also be photonic or electronic quantum states: the SC regime, in this case, is fundamental for quantum state control and swapping.

In the above example, the two pendulums are assumed to have the same frequency, i.e., in resonance. However, hybrid quantum systems require coherent information transfer between oscillators with largely dissimilar frequencies. Here, one important example is in networks of quantum computers. While the most promising quantum computers operate with microwave qubits (i.e., at few GHz), quantum information is efficiently transferred using near infrared photons (100ds THz).

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A shadowy form of light within a universe of hypothetical particles is getting some serious consideration as a means of discovering the identity of dark matter.

According to a comprehensive new analysis under quantum chromodynamics, the dark photon is a much better fit for the observed results of particle collider experiments than the standard model of particle physics, by quite a wide margin.

In fact, a team of researchers led by physicist Nicholas Hunt-Smith of the ARC Centre of Excellence for Dark Matter Particle Physics and the University of Adelaide in Australia calculated a confidence level of 6.5 sigma, suggesting the odds that dark photons don’t explain the observations are in the ballpark of one in a billion.

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Quantum behavior is a strange, fragile thing that hovers on the edge of reality, between a world of possibility and a Universe of absolutes. In that mathematical haze lies the potential of quantum computing; the promise of devices that could quickly solve algorithms that would take classic computers too long to process.

For now, quantum computers are confined to cool rooms close to absolute zero (−273 degrees Celsius) where particles are less likely to tumble out of their critical quantum states.

Breaking through this temperature barrier to develop materials that still exhibit quantum properties at room temperatures has long been the goal of quantum computing. Though the low temperatures help keep the particle’s properties from collapsing out of their useful fog of possibility, the bulk and expense of the equipment limits their potential and ability to be scaled up for general use.

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Quantum computing has provided new insights into a fundamental aspect of photochemical reactions that has previously proven difficult to study. The findings could improve scientists’ understanding of light-driven processes such as photosynthesis, smog formation and ozone destruction.

Photochemical processes occur when atomic nuclei and their electrons take on different configurations after absorbing a photon. Some of these reactions are guided by a quantum phenomenon called a conical intersection, where the potential energy surfaces that describe a molecule in its ground state and in its excited state converge. In these situations, quantum mechanical interference can prevent certain molecular transformations from taking place – a constraint known as a geometric phase. This limits the path that the reaction can take and affects the reaction outcome. The geometric phase has been known about since the 1950s, but due to the femtosecond timescales involved, it has never been directly observed in a molecular system.

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Kevin Slagle, Quantum 7, 1113 (2023). Although tensor networks are powerful tools for simulating low-dimensional quantum physics, tensor network algorithms are very computationally costly in higher spatial dimensions. We introduce $\textit{quantum gauge networks}$: a different kind of tensor network ansatz for which the computation cost of simulations does not explicitly increase for larger spatial dimensions. We take inspiration from the gauge picture of quantum dynamics, which consists of a local wavefunction for each patch of space, with neighboring patches related by unitary connections. A quantum gauge network (QGN) has a similar structure, except the Hilbert space dimensions of the local wavefunctions and connections are truncated. We describe how a QGN can be obtained from a generic wavefunction or matrix product state (MPS). All $2k$-point correlation functions of any wavefunction for $M$ many operators can be encoded exactly by a QGN with bond dimension $O(M^k)$. In comparison, for just $k=1$, an exponentially larger bond dimension of $2^{M/6}$ is generically required for an MPS of qubits. We provide a simple QGN algorithm for approximate simulations of quantum dynamics in any spatial dimension. The approximate dynamics can achieve exact energy conservation for time-independent Hamiltonians, and spatial symmetries can also be maintained exactly. We benchmark the algorithm by simulating the quantum quench of fermionic Hamiltonians in up to three spatial dimensions.

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A new record time for quantum coherence is reported, with a single-photon qubit encoded for 34 milliseconds. This is 55% longer than the previous record set in 2020.

In classical computing – such as the PC, smartphone, or other device you are currently using – information is processed with bits, which exist in a binary state of either a 0 or a 1. Quantum computing, by contrast, involves the processing of information with quantum bits, or qubits, which can exist in a “superposition” of both 0 and 1 simultaneously. This allows quantum computers to do certain types of calculations much faster than classical computers.

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Magnets, those everyday objects we stick to our fridges, all share a unique characteristic: they always have both a north and a south pole. Even if you tried breaking a magnet in half, the poles would not separate—you would only get two smaller dipole magnets. But what if a particle could have a single pole with a magnetic charge?

For over a century, physicists have been searching for such . A new study on the preprint server arXiv from the ATLAS collaboration at the Large Hadron Collider (LHC) places new limits on these hypothetical particles, adding new clues for the continuing search.

In 1931, physicist Paul Dirac proved that the existence of magnetic monopoles would be consistent with quantum mechanics and require—as has been observed—the quantization of the electric charge. In the 1970s, magnetic monopoles were also predicted by new theories attempting to unify all the fundamental forces of nature, inspiring physicist Joseph Polchinski to claim that their existence was “one of the safest bets that one can make about physics not yet seen.” Magnetic monopoles might have been present in the but diluted to an unnoticeably tiny density during the early exponential expansion phase known as cosmic inflation.

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