## What does quantum mechanics tell us about reality? Part II

This blog post follows on from a previous post, “What does quantum mechanics tell us about reality”, in which I tried to give a balanced and non-technical overview of some of the interpretations of quantum mechanics. In this post I will take a different approach: this will be a slightly biased, critical, and more technical follow-up. I recommend reading the earlier post first, but those already familiar with the interpretations of quantum mechanics should be able to dive straight into this.

In the Schrödinger’s cat thought experiment, a cat is placed in a box with a device that contains a radioactive atom and a vial of poison. If the atom decays, then the device is designed to release the poison, thus killing the cat. It is now well known that such an atom can be put into a state in which it has decayed, and not decayed simultaneously – this is known as a superposition state. Now, if this system is studied using the central equation in quantum mechanics, the Schrödinger equation, then the following result will be found: if the atom is in a superposition state, then this will lead to the cat being in a superposition state. The cat will be dead and alive simultaneously! Now suppose you open the box – what will you find? The Schrödinger equation again predicts that, if the cat was in a superposition of being dead and alive, then when you open the box you will also enter into a superposition. You will be in a superposition of either seeing the dead cat, whilst simultaneously seeing the alive cat.

How much coal do I need to put into my steam engine to get to Glasgow? How efficient can I make my power station? What’s the best way to cool down a cup of tea? The fundamental answers to these questions lies within the field of thermodynamics.

On the other side of the spectrum, scientists are asking seemingly disparate questions within the field of quantum information. How much entanglement do I need to pass on this message? How can I stop my quantum computer from losing its quantum-ness? What’s the best way I can make a quantum superposition?

Now it may seem that there can be no possible link between the answers to these questions. That a steam engine has nothing to do with quantum entanglement, well that is mostly true. However, all of questions are concerned with the same problem, the extractability and conservation of a given resource. On the thermodynamic scale, engineers want to know how heat and work behave. On the quantum scale, theorists and experimentalists alike are interested in defining and conserving the quantum-ness of a given system.

In order to bridge a gap between these fields, Continue reading

## What does quantum mechanics tell us about reality?

In this blog post I will introduce a core philosophical issue at the heart of quantum mechanics, and some of the most popular resolutions to this problem. This will be a non-technical introduction – I will try to avoid jargon and unnecessary details. But for those who like the gritty details, a second blog post will soon follow in which I will give a more technical and thorough (but also slightly biased) discussion of the same issues.

## The Entanglement picture

Entanglement by Pamela Ott (1999, 58x71cm, acrylic) http://hottr6.com/ott/index.html

I first came across the Entanglement picture about 11 years ago. Nearing the end of my year-long visit to the Centre for Quantum Computation in Cambridge (UK), I was returning to Salerno (Italy) to start working on my PhD thesis. As my dissertation was entitled Entanglement of Gaussian states, I decided to include some pictures related to (quantum) entanglement at the beginning of each part. The first few hits for “entanglement” found at the time on Google Images eventually made the cut (check the final version at https://arxiv.org/abs/quant-ph/0702069) However, one of the images in particular captured my imagination – and stole my heart – so much that I chose it for the best spot: Part II, showcasing the bulk of my original results on bipartite entanglement. The image was a relatively low-res photo of a painting entitled, quite aptly, Entanglement, and taken from the website of its creator, American artist Pamela (Pam) Ott: http://www.hottr6.com/ott/.

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## Do not get discouraged by the struggles of academia. There are plenty of success stories!

paper of ours featured on the cover of J. Phys. A (2014)

I have recently been appointed to the the Editorial Board of Journal of Physics A: Mathematical and Theoretical (in short, J. Phys. A).  J. Phys. A is a highly respected journal with a long history of seminal contributions to mathematical and theoretical physics, belonging to the non-profit Institute of Physics (IOP) Publishing family. I have enjoyed publishing in J. Phys. A over the years (including two Topical Reviews) and always experienced a very constructive peer review process; my students love it as well. We had our latest (the first for me) Editorial Board meeting a month ago in Edinburgh and it was a really pleasant and interesting experience, also because I got to spend the week-end there with my family and the weather was surprisingly nice 🙂

The publishers of the IOP blog JPhys+ interviewed me recently about my career, current research and what it is I find so appealing about the topics I study. The full text of the Q&A interview with Phil Brown, originally appeared here, is copied below.

## Understanding resources in the quantum world

If you have ever asked a quantum researcher about their subject, you will have realised that our first response is to tell you that the quantum world is weird, spooky, and counter-intuitive. It cannot be explained easily because we only just about understand it ourselves! After a bit more conversation, you’ll find us telling you that all these weird features are actually very useful: we talk about a potential for new technologies that can harness the quantum, from quantum computers to cryptography. The idea is to treat these quantum features as useful resources that help us to do things in an improved way. To do this, we need to carefully construct a framework that allows us to rigorously characterise these resources. Such a framework is called a quantum resource theory.

In this post, I will give a short explanation of resource theories. We begin by outlining the concept generally, but then focus on two particular examples of resources. The first example considers the resource of money in a fictional bank account, while the second example moves properly into the quantum world with the familiar resource of quantum entanglement.

Posted in Entanglement, Quantum research | 1 Comment

## Computers designing quantum optics experiments

Quantum states can exhibit bizarre but powerful properties, such as being in a superposition or containing correlations not possible in classical physics. If these properties can be controlled, then they can be exploited in quantum technologies to dramatically transform computing, enable secure cryptography, and unlock new ways of observing the universe. Quantum optics is a particularly fertile field for testing and developing these technologies – but how exactly can we design a quantum optics experiment to produce useful quantum states of light that can be put to good use? The usual methods involve painstaking calculations, clever insights, and utilising knowledge built up from years of experience and careful reading of previous researchers’ work. But the counter-intuitive nature of the quantum world, whilst enabling disruptive new technologies, can make it particularly challenging to design quantum experiments that can engineer useful states – our usual intuitions can fail us here. Indeed, while the current techniques used by researchers have led to a host of impressive and exciting results, we are far from finding the optimal methods to manipulate and control quantum states.

## Can we freeze something at room temperature? Yes, quantum coherence!

Happy 2017 from the Quanta Rei team! We close the current year with a guest post from our former member, long-time friend and collaborator Dr Rosario Lo Franco |RLF>

From the dawn of agriculture until the industrial revolution, all over the world, human beings have been facing the problem of food preservation. We are now quite familiar with many techniques, most of which utilised in our own kitchens, to reach this fundamental goal for our existence on Earth. Efficient and very employed procedures are, for instance: drying, salting, smoking, cooling and freezing. Let us focus on the last one, which works well for a very wide variety of foods. We are aware that, in order to preserve foods for long times by freezing, our freezers and refrigerators must be able to maintain temperatures well under zero Celsius degrees, typically −18° C or below (0° Fahrenheit or below). Air at the poles of our planet would be an extremely efficient freezer for foods, although it is not a very pleasant environment where to live (the average temperatures at North Pole and South Pole are, respectively: 0° C (32° F) and −28.2° C (−18° F) during summer; −40° C (−40° F) and −60° C (−76° F) during winter). There is therefore a continuous technological development in engineering efficient and eco-friendly freezing machines to assure a trustable and lasting food preservation. If someone comes and tells us that it is possible to preserve food by freezing at room temperature we wold not believe them, unless we are in front of Marvel’s Iceman (see picture aside).

## Rise and fall of the Ice King

Few people might have heard about Frederic Tudor before, but sometime in the early 1800s this Bostonian whiz kid had an idea that changed the world for ever. As most life-changing ideas, this was simple, groundbreaking, and completely crazy.

When young Tudor visited the West Indies for the first time, he was delighted by the warm Caribbean weather. He may have been sunbathing or walking on the beach when the idea struck him like a lightning. It was a new business model, completely overlooked, and extremely profitable: Why not cut ice in Boston, ship it to the tropics and sell it to local restaurants? They could start selling chilled drinks, or even ice-cream. Most people there had never seen ice before. They would go crazy about it!

I can imagine young Tudor considering with excitement the feasibility of his idea. Ice was free. At least in Boston. And there was plenty. One only needed to cut it in blocks. Ships were affordable at the time and, to keep the ice from melting, one could insulate it with sawdust, which was also essentially free. Believe it or not, nobody had thought about large scale commercial ice ventures before. Back then, ice was only used in small quantities wherever it was naturally available. But the idea of getting people to actually pay for ice was simply revolutionary.

Posted in Miscellanea, Thermodynamics | 1 Comment

## Would you rather be monogamous or faithful?

“When two systems enter into temporary physical interaction due to known forces between them, and when after a time of mutual influence the systems
separate again, then they can no longer be described in the same way as before. I would not call that one but rather the characteristic trait of quantum mechanics,the one that enforces its entire departure from classic lines of thought. By the interaction the two systems have become entangled”
[E. Schroedinger, 1935]

Being a physicist or a mathematician and living in the normal world is not a simple task. This is not only about physical aspect, conventions, or appearances.

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