Note: this is the third part of a four-part article on the Five-Sigma criterion in particle physics. See part 1 and part 2 to make more sense of the discussion below.
In the previous installment of this longish article, I have introduced some of the issues that may affect the correct interpretation of a statistically significant effect.
A pre-emptive warning to the reader: the article below is too long to publish as a single post. I have broken it out in four installments. After reading the text below you should continue with part II, part III, and part IV (which includes a summary).
Here's a development that could have significant implications for electrochemistry, biochemistry, electrical engineering and many other fields: a Nature Materials paper is about computer simulations which find that the electrical conductivity of many materials increases with a strong electrical field in a universal way.
Electrical conductivity is a measure of how strongly a given material conducts the flow of electric current and is generally understood in terms of Ohm's law, which states that the conductivity is independent of the magnitude of an applied electric field, i.e. the voltage per meter. This law is widely obeyed in weak applied fields, which means that most material samples can be ascribed a definite electrical resistance, measured in Ohms.
You have decided to start a graduate study in physics. Where should you apply? And how to decide which offer to take?
A diarrhea of lists attempt to rank "the world’s best universities". Mostly these lists are based on some aggregate of different metrics. Yet, for a postgraduate degree your focus should be on one and only one metric: you want to surround yourself with the best brains. If you're good, the place to hone your skills is there where you get the opportunity to learn from the best. There where you can join those that are making impact in their field of research.
What are the high-impact universities in physics?
Do you remember the X(3872) ? This is a hadron containing charm and anticharm quarks, which was observed to decay into a J/Psi meson, a positive, and a negative pion. When it was discovered, by the Belle experiment in 2003, the X caused a lot of interest among spectroscopists, because it is an "exotic" charmonium state: its nature is not totally clear, as it might be interpreted as a "molecule" of two charmed mesons loosely bound together. Or maybe a four-quark system ? Or just conventional charmonium, a bit at odds with the expected set of spin-parity states but otherwise just a honest meson ?
Researchers have used an atomic clock as a quantum simulator, mimicking the behavior of a different, more complex quantum system, joining a growing list of physical systems that can be used for modeling and perhaps eventually explaining the quantum mechanical behavior of exotic materials such as high-temperature superconductors, which conduct electricity without resistance.
All but the smallest, most trivial quantum systems are too complicated to simulate on classical computers, hence the interest in quantum simulators. Sharing some of the features of experimental quantum computers—a hot research topic—quantum simulators are "special purpose" devices designed to provide insight into specific challenging problems.
In the past few weeks the Tevatron and LHC experiments have updated their results on some of the most important Standard Model parameters. Of these, notably the top quark mass is one where the Tevatron is still doing slightly better than the LHC, due to the longer running time of the CDF and DZERO experiments, which allowed for a more precise calibration of the jet energy scale - the largest systematic uncertainty in this kind of business.
I have updated you on the matter tangentially in the previous two posts, where I discussed the overall compatibility of top and W boson masses with the Standard Model predictions, where the latter depend on the now well-known mass of the Higgs boson. Here instead I want to focus briefly on the top quark mass.
For quantum physicists working on future systems, entangling quantum systems is a key resource for upcoming quantum computers and simulators.
Physicists have crafted a new, reliable method to verify entanglement in the laboratory using a minimal number of assumptions about the system and measuring devices - it witnesses the presence of useful entanglement, a ‘verification without knowledge’.
Quantum computation, quantum communication and quantum cryptography often require entanglement. For many of these upcoming quantum technologies, entanglement – this hard to grasp, counter-intuitive aspect in the quantum world – is a key ingredient. Therefore, experimental physicists often need to verify entanglement in their systems.
Two days ago I showed how the measurements produced in the course of the last decade have allowed us to "zoom into" the parameter space of the Standard Model, pinpointing the W boson, top quark, and Higgs boson masses to a very narrow 3-D volume of phase space.