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Category: quantum physics – Page 1,110

Proposed test would offer strongest evidence yet that the quantum state is real

(Phys.org)—Physicists are getting a little bit closer to answering one of the oldest and most basic questions of quantum theory: does the quantum state represent reality or just our knowledge of reality?

George C. Knee, a theoretical physicist at the University of Oxford and the University of Warwick, has created an algorithm for designing optimal experiments that could provide the strongest evidence yet that the quantum state is an ontic state (a state of ) and not an epistemic state (a state of knowledge). Knee has published a paper on the new strategy in a recent issue of the New Journal of Physics.

While physicists have debated about the nature of the quantum state since the early days of quantum theory (with, most famously, Bohr being in favor of the ontic interpretation and Einstein arguing for the epistemic one), most modern evidence has supported the view that the quantum state does indeed represent reality.

Quantum matter — shaken, but not stirred

A team of researchers led by physics professor Immanuel Bloch has experimentally realized an exotic quantum system which is robust to mixing by periodic forces (Nature Physics, “Periodically driving a many-body localized quantum system”).

martini

When James Bond asks the barkeeper for a Martini (“shaken, not stirred”), he takes it for granted that the ingredients of the drink are miscible. If he were to place the order in a bar in the quantum realm, however, Agent 007 might be in for a surprise!

Quantum Systems, Channels, Information: A Mathematical Introduction [Repost]

Published: 2012/11/01 | ISBN: 311027325X | PDF | 349 pages | 12.06 MB

The subject of this book is theory of quantum system presented from information science perspective. The central role is played by the concept of quantum channel and its entropic and information characteristics. Quantum information theory gives a key to understanding elusive phenomena of quantum world and provides a background for development of experimental techniques that enable measuring and manipulation of individual quantum systems. This is important for the new efficient applications such as quantum computing, communication and cryptography. Research in the field of quantum informatics, including quantum information theory, is in progress in leading scientific centers throughout the world. This book gives an accessible, albeit mathematically rigorous and self-contained introduction to quantum information theory, starting from primary structures and leading to fundamental results and to exiting open problems.

A quantum leap for computers

More on the QC Blueprint which enables others to use as a reference when building a QC.

According to Prof Winfried Hensinger of the University of Sussex in the United Kingdom, he and his team have the first practical design for a quantum computer. Like millions of others, I have struggled to come to an understanding of quantum mechanics and how a quantum computer might work.

It would use qubits rather than standard on/off or 1 and 0 bits used in traditional computers. A qubit can have a state of anywhere between zero and one, including all the “states” in between. Theoretically, a quantum computer can perform a very large number of calculations simultaneously using the ideas of super positioning and quantum entanglement. The theory is that all the necessary calculations are carried out at virtually the same time, e.g. working out all the factors of a very large number. This kind of problem can take a regular computer quite a while.

Prof Hensinger claims he has produced a “how to build it” template, published in Science Advances journal, with a scalable construction plan which you can read here: www.advances.sciencemag.org/content/3/2/e1601540.full. It involves ions, long wave radiation, overlapping fields, vacuum chambers and other pieces of exacting technology. To be honest, I have never quite understood how you program in the questions and read the answers from quantum computers.

NSCI Seminar: Quantum Applications and Microsoft’s unique approach to Quantum Computing

Sharing in case folks would like to listen in.

Microsoft’s Station Q was founded in 2006. The focus of the team has always been topological quantum computing. By taking a full systems architecture approach, we have reached the point where we now able to start engineering a scalable quantum computer. The goal is to be able to solve major problems in areas of interest (e.g., Chemistry, Materials and Machine Learning). This talk will focus on the types of applications that we will be trying to solve as well as the unique approach to quantum computation that we’ve developed. For reference, see:

Current Approach: https://arxiv.org/abs/1610.05289 Chemistry Application: https://arxiv.org/abs/1605.03590 Other papers: https://arxiv.org/find/all/1/all:+wecker_d/0/1/0/all/0/1

Quantum Entanglement is Just as Einstein Predicted

I never doubt the theory.

We owe a lot to Einstein, and this week physicists have confirmed another of his theories by unraveling and proving that quantum entanglement does in fact exist. Under the standard quantum theory, nothing has a definitive state until it’s measured, and when two particles interact they become entangled. Being entangled means no longer do the particles have their probabilities but one that includes both particles together. Even though two photons become entangled, they can still travel light years apart from each other, but they will always remain linked.

Shell-Dependent Photoluminescence Studies Provide Mechanistic Insights into the Off-Grey-On Transitions of Blinking Quantum Dots

The majority of quantum dot (QD) blinking studies have used a model of switching between two distinct fluorescence intensity levels, “on” and “off”. However, a distinct intermediate intensity level has been identified in some recent reports – a so-called “grey” or “dim” state, which has brought this binary model into question. While this grey state has been proposed to result from the formation of a trion, it is still unclear under which conditions it is present in a QD. By performing shell-dependent blinking studies on CdSe QDs, we report that the populations of the grey state and the on state are strongly dependent on both the shell material and its thickness. We found that adding a ZnS shell did not result in a significant population of the grey state. Using ZnSe as the shell material resulted in a slightly higher population of the grey state, although it was still poorly resolved. However, adding a CdS shell resulted in the population of a grey state, which depended strongly on its thickness up to 5 ML. Interestingly, while the frequency of transitions to and from the grey state showed a very strong dependence on CdS shell thickness, the brightness of and the dwell time in the grey state did not. Moreover, we found that the grey state acts as an on-pathway intermediate state between on and off states, with the thickness of the shell determining the transition probability between them. We also identified two types of blinking behavior in QDs, one that showed long-lived but lower intensity on states and another that showed short-lived but brighter on states that also depended on the shell thickness. Intensity-resolved single QD fluorescence lifetime analysis was used to identify the relationship between the various exciton decay pathways and the resulting intensity levels. We used this data to propose a model in which multiple on, grey and off states exist whose equilibrium populations vary with time that give rise to the various intensity levels of single QDs, and which depends on shell composition and thickness.

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