Physicists are using quantum math to understand what happens when black holes collide. In a surprise, they’ve shown that a single particle can describe a collision’s entire gravitational wave.
Category: quantum physics – Page 570
ATLAS observes pairs of tau particles in heavy-ion collisions
Today at the Quark Matter 2022 conference, the ATLAS Collaboration announced the observation of tau-lepton pairs created when particles of light – or photons – interact during lead-ion collisions. The result opens a new avenue for measuring how magnetic the tau lepton is – a property sensitive to new particles beyond the Standard Model.
In everyday life, two crossing beams of light follow the rules of classical electrodynamics and do not deflect, absorb or disrupt one another. But, in quantum electrodynamics, things are different. Lead ions accelerated to high energy by the LHC are surrounded by an enormous flux of photons. For a short moment, these photons can interact and transform into a particle–antiparticle pair, such as a pair of tau leptons. These interactions are called ultra-peripheral collisions, which ATLAS physicists used to observe light-by-light scattering in 2019.
Rather than colliding head-on at the centre of the ATLAS detector, the accelerated lead ions pass by each other unscathed. This provides a uniquely clean environment for physicists to study collisions of photons into a pair of tau leptons. Further, the rate of tau-lepton creation scales to the fourth power of the number of protons in the ion, which is 82 for lead.
The side effects of quantum error correction and how to cope with them
It is well established that quantum error correction can improve the performance of quantum sensors. But new theory work cautions that unexpectedly, the approach can also give rise to inaccurate and misleading results—and shows how to rectify these shortcomings.
Quantum systems can interact with one another and with their surroundings in ways that are fundamentally different from those of their classical counterparts. In a quantum sensor, the particularities of these interactions are exploited to obtain characteristic information about the environment of the quantum system—for instance, the strength of a magnetic and electric field in which it is immersed. Crucially, when such a device suitably harnesses the laws of quantum mechanics, then its sensitivity can surpass what is possible, even in principle, with conventional, classical technologies.
Unfortunately, quantum sensors are exquisitely sensitive not only to the physical quantities of interest, but also to noise. One way to suppress these unwanted contributions is to apply schemes collectively known as quantum error correction (QEC). This approach is attracting considerable and increasing attention, as it might enable practical high-precision quantum sensors in a wider range of applications than is possible today. But the benefits of error-corrected quantum sensing come with major potential side effects, as a team led by Florentin Reiter, an Ambizione fellow of the Swiss National Science Foundation working in the group of Jonathan Home at the Institute for Quantum Electronics, has now found. Writing in Physical Review Letters, they report theoretical work in which they show that in realistic settings QEC can distort the output of quantum sensors and might even lead to unphysical results.
Quantum Mereology: Factorizing Hilbert Space into Subsystems with Quasi-Classical Dynamics
We study the question of how to decompose Hilbert space into a preferred tensor-product factorization without any pre-existing structure other than a Hamiltonian operator, in particular the case of a bipartite decomposition into “system” and “environment.” Such a decomposition can be defined by looking for subsystems that exhibit quasi-classical behavior. The correct decomposition is one in which pointer states of the system are relatively robust against environmental monitoring (their entanglement with the environment does not continually and dramatically increase) and remain localized around approximately-classical trajectories. We present an in-principle algorithm for finding such a decomposition by minimizing a combination of entanglement growth and internal spreading of the system. Both of these properties are related to locality in different ways.
Why Quantum Computing Is Closer Than You Think
When I first started looking into quantum computing I had a fairly pessimistic view about its near-term commercial prospects, but I’ve come to think we’re only a few years away from seeing serious returns on the technology.
10 Difficult Problems Quantum Computers can Solve Easily
ab initio calculations
Classical computing is of very little help when the task to be accomplished pertains to ab initio calculations. With quantum computing in place, you have a quantum system simulating another quantum system. Furthermore, tasks such as modelling atomic bonding or estimating electron orbital overlaps can be done much more precisely.
Why Going Faster-Than-Light Leads to Time Paradoxes
►Is faster-than-light (FTL) travel possible? In most discussions of this, we get hung up on the physics of particular ideas, such as wormholes or warp drives. But today, we take a more zoomed out approach that addresses all FTL propulsion — as well as FTL messaging. Because it turns out that they all allow for time travel. Join us today as we explore why this is so and the profound consequences that ensue. Special thanks to Prof Matt.
Written & presented by Prof David Kipping. Special thanks to Prof Matt Buckley for fact checking and his great blog article that inspired this video (http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel)
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::References::
► Alcubierre, M., 1994, “The warp drive: hyper-fast travel within general relativity”, Classical and Quantum Gravity, 11 L73: https://arxiv.org/abs/gr-qc/0009013
► Pfenning, M. & Ford, L., 1997, “The unphysical nature of Warp Drive”, Classical and Quantum Gravity, 14, 1743: https://arxiv.org/abs/gr-qc/9702026
► Finazzi, S., Liberati, S., Barceló, C., 2009, “Semiclassical instability of dynamical warp drives”, Physical Review D., 79, 124017: https://arxiv.org/abs/0904.0141
► McMonigal, B., Lewis, G., O’Byrne, P., 2012, “Alcubierre warp drive: On the matter of matter”, Physical Review D., 85, 064024: https://arxiv.org/abs/1202.5708
► Everett, A., 1996, “Warp drive and causality”, Physical Review D, 53, 7365: https://journals.aps.org/prd/abstract/10.1103/PhysRevD.53.
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