Entanglement and quantum non-locality

• Rainer Kaltenbaek

Room: 122:026 Since its development, quantum physics has quickly become one of the most successful physical theories ever devised. Despite of that, some of the most basic concepts of quantum physics even today remain a topic of discussion. One of these central concepts is that of quantum superposition, which will be the main topic of a second talk. However, it also is a prerequisite for quantum entanglement. The notion of entanglement was originally coined by Erwin Schrödinger, and the concept was immediately seized by Einstein, Podolsky and Rosen (EPR) in an argument for what they called the “incompleteness” of quantum theory. Bell and others later formalized this argument in what is now known as Bell-type inequalities. This inequality has to be fulfilled by the predictions of any theory fulfilling the two basic assumptions of EPR's definition of a complete physical theory: locality and realism. Such theories are therefore called local-realistic models. Yet, quantum theory can violate those inequalities and, by now, many experiments have shown that nature itself also violates Bell-type inequalities, confirming the predictions of quantum theory. Due to this fact, quantum theory and any theory that wants to accurately predict experimental results has to violate at least one of the two assumptions of local-realistic models: either realism or locality. Because many physicists still find it hard to part with the classical notion of realism, the notion of quantum non-locality appeared. Here, we will discuss the concepts, the realization and the implications of experiments testing quantum theory against local realism.

Quantum optomechanics, the quantum/classical border & space

• Rainer Kaltenbaek

Room: 122:026 Already before physicists started to discuss entanglement with all its consequences and applications, they argued about an even more fundamental concept: quantum superposition. One of the clearest visualizations of this concept is the double- slit experiment. As Feynman once stated, this simple experiment contains the heart of quantum theory. In this experiment a source emits a particle towards some distant detection screen where the particle's position can be measured. Between the screen and the source there is an inpenetrable wall that has two open slits through which particles can pass. When many runs of this experiment are performed, one will get a distribution of particle positions measured on the screen. According to quantum physics, if it is impossible even in principle to know which slit each particle went through, this distribution will exhibit an interference pattern as if the particles, in some way, behaved like interfering waves (“matter waves”). The explanation of quantum physics for the occurrence of the interference pattern is that each particle is in a superposition of passing through one or the other slit. Such interference has been shown to occur experimentally for increasingly heavy particles. While the concept may be easier to grasp (or to shrug away) for microscopic particles, Schrödinger demonstrated in a thought experiment that quantum theory, in principle, allows for quantum superposition states even of macroscopic objects like a cat in a superposition of being dead or alive. Here, we will discuss experimental efforts using matter-wave interference and quantum optomechanics in order to test quantum superposition for increasingly massive objects. Such experiments probe the boundaries between the macroscopic, classical world and the microscopic, quantum world. We will also discuss recent investigations that indicate that this quest may eventually lead us to perform experiments in space.

Analogue Gravity: theory & experiment, Part I

• Silke Weinfurtner

Room: 122:026 A major problem of quantum field theory in curved spacetime, and quantum gravity more generally, is the lack of sufficient observational and experimental guidance. To address this issue we utilise the possibility to explore various phenomena of classical and quantum field theory in curved spacetimes in table-top experiments. The overall programme is based on the existence of analogue models for gravity, demonstrating that certain effects predicted within quantum field theory in curved spacetimes can be mimicked in easy-to-access physical systems, such as fluids, superfluids and fibre optics. In contrast to many other studies in quantum field theory in curved spacetimes and quantum gravity, the project objectives are not only theoretical, but also of experimental nature. In detail I will discuss how we study Hawking radiation, the Penrose effect and cosmological particle production in analogue gravity experiments.

Analogue Gravity: theory & experiment, Part II

• Silke Weinfurtner

Room: 122:026 A major problem of quantum field theory in curved spacetime, and quantum gravity more generally, is the lack of sufficient observational and experimental guidance. To address this issue we utilise the possibility to explore various phenomena of classical and quantum field theory in curved spacetimes in table-top experiments. The overall programme is based on the existence of analogue models for gravity, demonstrating that certain effects predicted within quantum field theory in curved spacetimes can be mimicked in easy-to-access physical systems, such as fluids, superfluids and fibre optics. In contrast to many other studies in quantum field theory in curved spacetimes and quantum gravity, the project objectives are not only theoretical, but also of experimental nature. In detail I will discuss how we study Hawking radiation, the Penrose effect and cosmological particle production in analogue gravity experiments.

History of quantum computing

• Marie Ericsson

Room: 122:026 In the first lecture I will talk about the history of quantum theory and the theoretical development of quantum computation. I will talk about superposition and entanglement, important concepts to understand the power of quantum computing. The different algorithms that are available for a quantum computer, such as searching algorithm and factoring algorithm, will be discussed as well as quantum cryptography that help us to share secrets when we cannot use RSA, the traditional crypto system used today that quantum computers can break.

Implementations of quantum computation and why we don't have a quantum computer (or do we?)

• Marie Ericsson

Room: 122:026 In the second lecture I will talk about different implementations for quantum computations and compare the different systems researchers are using. I will then talk about the problems we have when we want to implement quantum algorithms and ways to overcome them, like quantum error corrections. In the end we will discuss the limitations of quantum computers and if there are other ways of computations beyond quantum computations?

Quantum information: from pure science to today’s technologies, Part I

• Raymond Laflamme

Room: 122:026 Around 1980, Charley Bennett (IBM) apparently asked Richard Feynman if the uncertainty principles in quantum mechanics would limit the precision at which we will be able to compute. Feynman thought about it and quickly realised that not only there are no inherent limitations to the precision at which we can compute but quantum mechanics offers an opportunity to simulate quantum systems something which is apparently exponentially hard to do. That was one the first realisation that quantum information can be much more than its classical counterpart. Over the last 30 years, quantum information science has grown from pure theoretical science to new surprising applications, devices and technologies. Quantum computers, one the most coveted of these technologies, promise to fundamentally change how we process information. The quest towards a quantum computer has already brought deep insights into our quantum world and new ways to control and harness the unusual quantum behaviour for computation. Yet, some of the most interesting insights have come along the road to this holy grail in computing. We’ve discovered spinoffs of these ideas that have led to new and improved quantum technologies. During this presentation, I will share examples of quantum technologies – technologies where some are still in the labs, but some are in the market today. For example, I will show how a challenge with the inhomogeneity of magnetic field in quantum computing led to a device used today in oil exploration. I will also share how a superconducting qubit, led to a sensor that is much more precise than its classical counterpart. In each example, I will provide an overview of the technology, explain the science behind the technology, and how quantum information was used to solve a particular problem.

Quantum information: from pure science to today’s technologies, Part II

• Raymond Laflamme

Room: 122:026 Around 1980, Charley Bennett (IBM) apparently asked Richard Feynman if the uncertainty principles in quantum mechanics would limit the precision at which we will be able to compute. Feynman thought about it and quickly realised that not only there are no inherent limitations to the precision at which we can compute but quantum mechanics offers an opportunity to simulate quantum systems something which is apparently exponentially hard to do. That was one the first realisation that quantum information can be much more than its classical counterpart. Over the last 30 years, quantum information science has grown from pure theoretical science to new surprising applications, devices and technologies. Quantum computers, one the most coveted of these technologies, promise to fundamentally change how we process information. The quest towards a quantum computer has already brought deep insights into our quantum world and new ways to control and harness the unusual quantum behaviour for computation. Yet, some of the most interesting insights have come along the road to this holy grail in computing. We’ve discovered spinoffs of these ideas that have led to new and improved quantum technologies. During this presentation, I will share examples of quantum technologies – technologies where some are still in the labs, but some are in the market today. For example, I will show how a challenge with the inhomogeneity of magnetic field in quantum computing led to a device used today in oil exploration. I will also share how a superconducting qubit, led to a sensor that is much more precise than its classical counterpart. In each example, I will provide an overview of the technology, explain the science behind the technology, and how quantum information was used to solve a particular problem.

Discussion

• Michael Schirber

Room: 122:026

Tabletop String Theory, Part I

• Lárus Thorlacius (Nordita)

Room: 122:026 String theory provides novel theoretical tools for the study of strongly coupled field theories through the so- called gauge theory/gravity correspondence. These methods and ideas may provide useful insight into strongly correlated systems in condensed matter physics, where conventional theories of weakly interacting quasi-particles break down. They also suggest that quantum gravity can be explored via experiments in suitably engineered materials or optical lattices. In these lectures I will describe how the original gauge theory/gravity correspondence comes about in the study of extended objects called Dirichlet branes in string theory. I'll then discuss a more general correspondence with reduced symmetry, which is expected to be more relevant to the real world, and outline some potential applications to quantum critical systems of interest in condensed matter physics.

Tabletop String Theory

• Lárus Thorlacius (Nordita)

Room: 122:026 String theory provides novel theoretical tools for the study of strongly coupled field theories through the so- called gauge theory/gravity correspondence. These methods and ideas may provide useful insight into strongly correlated systems in condensed matter physics, where conventional theories of weakly interacting quasi-particles break down. They also suggest that quantum gravity can be explored via experiments in suitably engineered materials or optical lattices. In these lectures I will describe how the original gauge theory/gravity correspondence comes about in the study of extended objects called Dirichlet branes in string theory. I'll then discuss a more general correspondence with reduced symmetry, which is expected to be more relevant to the real world, and outline some potential applications to quantum critical systems of interest in condensed matter physics.

High Precision, Not High Energy: Using Atomic, Molecular, and Optical Physics to Look Beyond the Standard Model, Part I

• Chad Orzel

Room: 122:026 The Standard Model of particle physics is one of the most successful theories in the history of science, but we know from phenomena like matter-antimatter asymmetry, dark matter and dark energy, and neutrino masses that the Standard Model is not complete. While the best-known searches for physics beyond the Standard Model involve particle accelerators and detectors the size of office buildings, there are smaller experiments in labs around the world looking for signs of new physics with atoms, molecules, and lasers. While the effects of exotic particles are tiny at the atomic scale, the unparalleled precision of modern spectroscopic techniques makes it possible to detect even such minuscule effects, and these measurements provide some of the tightest constraints we know of on physics beyond the Standard Model. In these talks, I will review the basics of the interaction between atoms and light, and how such systems have been used to detect exotic effects. I will also discuss the operation of atomic clocks, and how the development of frequency measurements accurate to 17 decimal places allows physicists to changes in the constants of nature, violations of fundamental symmetries, and other exotic phenomena using experimental apparatus that fits comfortably within a single room. The first talk will cover the background, history, basics of atomic physics, and a simple example of exotic physics (parity-violating transitions). The second will cover atomic clocks, and ultra-high-precision frequency measurements for things like changing fundamental constants and EDM's.

High Precision, Not High Energy: Using Atomic, Molecular, and Optical Physics to Look Beyond the Standard Model, Part II

• Chad Orzel

Room: 122:026 The Standard Model of particle physics is one of the most successful theories in the history of science, but we know from phenomena like matter-antimatter asymmetry, dark matter and dark energy, and neutrino masses that the Standard Model is not complete. While the best-known searches for physics beyond the Standard Model involve particle accelerators and detectors the size of office buildings, there are smaller experiments in labs around the world looking for signs of new physics with atoms, molecules, and lasers. While the effects of exotic particles are tiny at the atomic scale, the unparalleled precision of modern spectroscopic techniques makes it possible to detect even such minuscule effects, and these measurements provide some of the tightest constraints we know of on physics beyond the Standard Model. In these talks, I will review the basics of the interaction between atoms and light, and how such systems have been used to detect exotic effects. I will also discuss the operation of atomic clocks, and how the development of frequency measurements accurate to 17 decimal places allows physicists to changes in the constants of nature, violations of fundamental symmetries, and other exotic phenomena using experimental apparatus that fits comfortably within a single room. The first talk will cover the background, history, basics of atomic physics, and a simple example of exotic physics (parity-violating transitions). The second will cover atomic clocks, and ultra-high-precision frequency measurements for things like changing fundamental constants and EDM's.

What is topological matter, and why do we care? Part I

• Eddy Ardonne (Nordita)

Room: 122:026 We are all familiar with the fact that when liquid water is cooled down, it turns into ice at some point. We say that water and ice are two different phases of matter. In this lecture, we will explore phases of matter that are called “topological.” By using some simple examples, we will explain the nature of topological phases of matter, and explain why they are called topological. The first topological phase was discovered in 1980, in a certain semi-conductor system at very low temperature, and in a high magnetic field. It was discovered rather recently, in 2007, that topological phases can also exist without magnetic field. We will discuss these so-called topological insulators and how they were discovered.One of the fascinating properties of topological phases is that the particles living inside such phases can be smaller, in a sense, than the particles that make up the phase in the first place! This “fractionalization” phenomenon has led to an intense search for topological matter, because it might be possible to utilize them as building blocks for quantum computers. We will briefly discuss this potential application.

What is topological matter, and why do we care? Part II

• Eddy Ardonne (Nordita)

Room: 122:026 We are all familiar with the fact that when liquid water is cooled down, it turns into ice at some point. We say that water and ice are two different phases of matter. In this lecture, we will explore phases of matter that are called “topological.” By using some simple examples, we will explain the nature of topological phases of matter, and explain why they are called topological. The first topological phase was discovered in 1980, in a certain semi-conductor system at very low temperature, and in a high magnetic field. It was discovered rather recently, in 2007, that topological phases can also exist without magnetic field. We will discuss these so-called topological insulators and how they were discovered.One of the fascinating properties of topological phases is that the particles living inside such phases can be smaller, in a sense, than the particles that make up the phase in the first place! This “fractionalization” phenomenon has led to an intense search for topological matter, because it might be possible to utilize them as building blocks for quantum computers. We will briefly discuss this potential application.