26/09/2014Speaker: Time & Venue: Title & Abstract: |
RQTech SeminarJoel Lindkvist (Chalmers University of Technology, Gothemburg, Sweden) 14:00, Venue: C27 Physics Relativistically moving quantum clocks and superconducting circuits We consider a localized quantum field as a fundamental model of a quantum clock moving in spacetime. Using this model, we investigate the role of clock size as well as quantum effects on time dilation. Moreover, it is shown that motion affects the precision of the clock. In superconducting circuits, relativistic motion can be simulated by modifying the magnetic flux through a superconducting quantum interference device (SQUID). In particular, we can simulate a moving cavity containing a quantum field, allowing us to experimentally investigate our clock model. |

05/02/2014Speaker: Time & Venue: Title & Abstract: |
RQTech SeminarStefano Pirandola 15:00, Venue: B13 Physics Applications of quantum hypothesis testing We review a recent formulation of quantum hyphotesis testing in terms of quantum channel discrimination. Considering the framework of bosonic systems and Gaussian states, we discuss how this model of quantum discrimination can be identified with practical technological applications,such as the quantum illumination of targets and the quantum reading of optical memories. |

05/02/2014Speaker: Time & Venue: Title & Abstract: |
RQTech SeminarSabine Hossenfelder 12:00, Venue: B21 Physics News from Quantum Gravity Phenomenology I will talk about recent developments in the search for experimental signatures for quantum gravitational effects. Some of the topics that I will cover are the prospects of finding Planck scale effects in gamma ray bursts, in neutral Kaon oscillations, or with massive quantum oscillators. I will also comment on the possibility of finding holographic noise and on Bekenstein's proposed table top experiment. This is not a review talk; it is a hand selected assortment of topics I think are interesting. |

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RQTech SeminarNicole Yunger Halpern 16:30, Venue: Keighton Auditorium Simple thermo, general tools: The resource theory of informational non equilibrium How can thermodynamics, which involves vast numbers of particles, de- scribe cutting-edge technology, which involves miniscule scales? Small-system thermodynamics is modeled by a resource theory like that of pure bipartite entanglement. When all Hamiltonians are totally degenerate, this model becomes a resource theory of information, or nonuniformity. I will explain the nonuniformity theory, the insights it offers into thermodynamics, and its intrinsic interest (arXiv:1309.6586). Two mathematical tools structure the nonuniformity theory: Lorenz curves and smooth single-shot entropies. After introducing these tools, which generalize to broader contexts, I will illustrate how they simplify proofs and provide geometric insights. This research pro- gram is intended to help advance small-scale thermodynamics and to inform applications such as nanoscale engines. RQI SeminarDaniel Oi (University of Strathclyde, Glasgow) 14:00, Venue: C05, Physics Fundamental Physics with Nano Satellites: Overview and ProspectsWhat could you do with a kilogram or three in space? Could you test the laws of Nature? This may not be as far fetched an idea as at first glance. Although traditional space missions are characterized by huge costs and long development times, recently a paradigm shift has occurred where miniaturized but highly advanced satellites can be launched at a fraction of the cost and time bringing space-based experiments within the reach of small research groups. CubeSats, one of the most widely adopted form of such nano satellites, has a basic spacecraft configuration of 1kg in a 10cm x 10cm x10cm cube. Though it will be a challenge to deliver the capability within this envelope to mount fundamental physics missions, developments both in nanosat space hardware and experiments make it an exciting possibility. RQI SeminarStefano Liberati (SISSA, Trieste, Italy) 14:00, Venue: C05, Physics Gravity, an unexpected journey: from thermodynamics to emergent gravity and back... In this talk we shall discuss some tantalising connections between gravitation, thermodynamics and quantum entanglement which seem to suggest a new perspective in which spacetime and its dynamics could be emergent phenomena. Condensed matter analogues of gravity are in this sense a fruitful tool for exploring the rich implications of this new paradigm. We shall in particular discuss the possible nature of the cosmological constant in this framework and the kind of phenomenology one might seek for in testing this idea. RQI SeminarRaymond Rivers (Imperial College, London) 14:00, Venue: B21, Physics Tunable condensates: metrics, fluctuations and defectsWe explore parallels between magnetic field quenches of tunable cold Fermi gases and particle production, defect production and stochastic gravity in the early universe. In particular, I. We suggest that, with current experimental techniques, the constraints of causal horizons can lead to the spontaneous creation of vortices in fast quenches from the BEC to the BCS regime by a method akin to that for the creation of topological defects in the very early universe. II. On the other hand, in rapid quenches from the BCS to the BEC regime, we discuss to what extent quasi-particle production in the condensate mimics that of particle production in Freedman-Robinson-Walker (FRW) metrics in the early universe, as proposed by several authors. III. We look for parallels between stochastic soundcone fluctuations in the condensates with lightcone fluctuations due to quantum gravity. RQI Seminar
Andrea Di Falco (University of St. Andrews) 14:00, Venue: B21, Physics Synthetic Optical Materials for Photonics Applications The current advances in photonics have given us ways to control and manipulate light virtually at will. We have learnt how to bend it, slow it down and even stop it, confine it in dimensions smaller that its wavelength and ultimately determine its path. This progress has been generated by enabling technologies, like that of photonic crystals and metamaterials, which allow the design of the properties of matter at the nanoscale. In this talk I will present the portfolio of techniques developed at the University of St Andrews to fabricate synthetic optical materials, like chaotic broadband resonators and flexible metamaterials, and discuss their potential applications. Joint RQI, Philosophy & Cold Atoms SeminarEmily Adlam (University of Oxford) 16:00, Venue: B21, Physics Interpretations of Quantum Mechanics Despite being an extraordinarily successful theory, quantum mechanics as it stands is manifestly incomplete, because there is no consensus about how the mathematical formalism can be read as a description of physical reality. Consequently, there exists considerable debate over how we should ‘interpret’ quantum mechanics – that is, what it tells us about how the world really works. In this talk I will discuss a range of proposed interpretations, including Niels Bohr’s ‘Copenhagen interpretation,’ theories of spontaneous, consciousness-based and gravitational collapse, the Everett (many-worlds) interpretation, and the de Broglie-Bohm interpretation, briefly touching on the principal advantages and difficulties associated with each. RQI Seminar
Luis Cortés Barbado (Instituto de Astrofísica de Andalucía, CSIC, Granada) 14:00, Venue: B21, Physics Hawking radiation as perceived by different observers In this talk, I will introduce a method for studying the perception of Hawking radiation by different observers outside a black hole, and for different vacuum states of the radiation field. The analysis is performed in terms of an effective-temperature function that varies along the trajectory of each observer. Among other results, I will show that - It is not necessary to strictly form an horizon for obtaining Hawking radiation;
- Not all observers crossing the horizon of a black hole in free-fall will fail to detect radiation;
- The radiation temperature perceived by a generic observer outside the black hole (when it is possible to talk about a temperature) can be calculated directly from the local characteristics of its trajectory in a way which has a clear physical interpretation.
RQI SeminarFriedrich König (University of St Andrews) 14:00, Venue: B21, Physics Artificial event horizons in optical fibers The geometry of black holes can be viewed as if space were a medium moving towards their singularities. Where the flow is superluminal such that nothing can escape, horizons are formed. Laboratory analogues of black holes are based on this picture: the black hole resembles a river -- a moving medium -- flowing towards a waterfall, the singularity. Waves on the river propagating upstream at speed c' play the role of light where c' represents c, the speed of light. Suppose as the river approaches the waterfall the flow speed exceeds c'. Clearly, beyond this, no wave can propagate upstream. This point of no return is the horizon. According to quantum physics, the black hole emits waves in thermal equilibrium. The waves consist of correlated pairs of quanta. Laboratory analogues would allow for the observation of the emission of these photon pairs. As Hawking radiation from astronomical black holes seems impossible to detect,analogue systems thus seem the only possibility at hand to explore the intriguing physics of Hawking radiation experimentally. In my talk I will explain how optical event horizons can be created in optical fibers using ultrashort pulses of light. I will report on experimental findings and progress towards the observation of analogue Hawking radiation. RQI SeminarChristoph Westbrook (Laboratoire Charles Fabry de l'Institut d'Optique, Palaiseau) 14:00, Venue: B21, Physics Acoustic analog of the dynamical Casimir effect Although we often picture the quantum vacuum as containing virtual quanta whose observable ef- fects are only indirect, it is a remarkable prediction of quantum field theory that the vacuum can generate real particles when boundary conditions are suddenly changed. Thus the ’dynamical Casimir effect’ results in the spontaneous generation of photon pairs in an empty cavity whose boundaries are rapidly moving. Bose Einstein condensates are attractive candidates in which to study acoustic analogs to such phenomena [1], because their low temperatures promise to reveal quantum effects. I will discuss an experiment to observe an acoustic analog to the dynamical Casimir effect by modulating the confinement of a Bose-Einstein condensate. Correlated pairs of Bogoliubov quanta, both phonon-like and particle-like, are excited by this modulation in a process that formally resembles parametric down conversion. [1] I. Carusotto, R. Balbinot, A. Fabbri and A. Recati, Euro Phys. J. D 56, 391 (2010), e-print: arXiv:0907.2314 [cond-mat.quant-gas] (2009). RQI SeminarMyungshik Kim (Imperial College, London) 14:00, Venue: C27, Physics Planck scale nanomechanics Abstract: tba RQI SeminarJason Doukas (University of Nottingham) 13:00, Venue: B21, Physics Localized detection of the Unruh effect: Entanglement degradation across the horizonThe Unruh effect is a fundamental result of the application of quantum field theory to curved spacetimes. It states that accelerated observers experience the vacuum as a thermal state of particles at a temperature proportional to the acceleration. The subject of the Unruh effect has received renewed interest in the last decade, as the quantum optics community have begun to realize that the Unruh transformation is an example of a basic and well-known class of Gaussian unitary operations known as two-mode squeezing operations. Two mode squeezed states, are entangled states that are routinely generated by parametric-down conversion in non-linear crystals. It has been the focus of the newly emerging field of Relativistic Quantum Information theory to characterize how this Unruh squeezing operator in conjunction with the existence of event horizons can degrade the entanglement that accelerated observers see. However, when looking at entanglement seen between accelerated and inertial observers, previous studies had misinterpreted the dependence of initial state with that of the acceleration. This misinterpretation can be traced back to the use of global field modes like Unruh modes, where the inability to control the size and location of their observation left the physical interpretation of these models unclear. In this talk I will discuss a recent series of works I have done in collaboration, which re-investigates the problem of entanglement degradation due to acceleration in a localized setting. I will discuss how the approach enables one for the first time to solve the acceleration degradation problem and leads to new insights into the degradation process. Joint RQI & Cold Atoms SeminarAngela White (University of Newcastle) 14:00, Venue: B21, Physics Signature changing events and emergent space-times in Bose-Einstein condensatesMotivated by the 'no-boundary' proposal of Hartle and Hawking, that the initial condition appropriate at the big bang is a signature changing event, in which the universe changed from four space-like dimensions (Euclidean signature universe [+,+,+,+]) to one time-like and three space-like dimensions (Lorentzian signature universe [-,+,+,+]) we explore signature change in an analogue gravity framework. Signature changing emergent geometries are shown to arise in a Bose-Einstein condensate, achieved via a change in atomic interactions from repulsive (Lorentzian signature) to attractive (Euclidean signature). The particle production from a finite-duration Euclidean signature event is calculated both in the hydrodynamic limit and beyond that limit by the inclusion of quantum pressure. A combination of trans-Planckian physics and signature change results from the inclusion of ultraviolet modes in this analysis, modifying the total particle production. We also propose that such a signature changing region could be applied as an amplifier for a pre-existing quasi-particle spectrum. This provides a method to address the outstanding problem of detectability of quasi-particle spectrums resulting from analogue cosmological particle production processes in Bose-gases. Joint RQI & Cold Atoms SeminarSilke Weinfurtner (SISSA, Trieste) 14:00, Venue: B21, Physics Quantum Gravity LaboratoryA 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 I am proposing to explore various phenomena of semi-classical gravity and quantum gravity in table-top experiments. The overall programme is based on the existence of analogue gravity models for semi-classical quantum 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 and superfluids. In addition, I will explore the possibility of adapting the general principles underlying analogue gravity models to full quantum gravity, combining tools and concepts from quantum information theory with discrete quantum gravity. In contrast to many other proposals in quantum gravity, the project objectives are not only theoretical (analytical and numerical studies), but also of experimental nature. The specific scientific goals are to study the robustness and universality of (rotating) black hole phenomena in water channel flows, cosmological particle production in Bose-Einstein condensate, and the emergence of a smooth geometry as an ensemble average of binary encodings of triangulated manifolds. Furthermore, I demonstrate how to construct a power-counting renormalizable theory of gravity, generally referred to as Horava-Lifshitz gravity, using concepts from condensed matter physics such as quantum critical phenomena. Last but not least I will combine all of the above and discuss the intriguing similarities arising from Horava-Lifshitz, Einstein-aether and discrete gravity. Joint RQI & Cold Atoms Seminar
Göran Johansson (Chalmers University, Göteborg) 14:00, Venue: B21, Physics Microwave Quantum Optics in Superconducting Circuits – Photon Routing and Observation of the Dynamical Casimir EffectIn this presentation, I will address recent advances in the field of microwave quantum optics using superconducting circuits. My focus will be on the emerging subfield of propagating microwave photonics. This field relies on the fact that the coupling between an artificial superconducting atom (quantum bit) and a microwave photon propagating in a one-dimensional transmission line can be made strong enough to observe quantum coherent effects, without using any cavity to confine the microwave photons. In particular, I will discuss a recent result, demonstrating the possibility to switch single microwave photons on a nanosecond timescale [1], using electromagnetically induced transparency from Autler-Townes splitting, in a single artificial atom. Here, one can also note that anti-bunching was very recently observed in this system [2]. In the second part of my presentation, I will turn to the possibility of studying more fundamental physics phenomena in this type of systems. In 1970, Gerald Moore predicted the generation of photons from an oscillating mirror, moving close to the speed of light [3]. The effect was named the dynamical Casimir effect (DCE), from its resemblance to the static Casimir effect. One can study the DCE using a single one-dimensional transmission line terminated with a quickly tunable boundary condition (inductance) [4,5], and in this system the DCE was after 40 years finally observed experimentally [6]. If there is time I will also discuss two different measures of non-classicality, which could be used on the DCE radiation [7]. [1] Io-Chun Hoi, C. M. Wilson, G. Johansson, T. Palomaki, B. Peropadre, P. Delsing, Phys. Rev. Lett. 107, 073601 (2011). [2] Io-Chun Hoi, Tauno Palomaki, Göran Johansson, Joel Lindkvist, Per Delsing, C. M. Wilson, Phys. Rev. Lett. 108, 263601 (2012). [3] G. Moore, J. Math. Phys. 11, 2679–2691 (1970). [4] J. R. Johansson, G. Johansson, C. M. Wilson, and Franco Nori, Phys. Rev. A 82, 052509 (2010). [5] J. R. Johansson, G. Johansson, C. M. Wilson, and Franco Nori, Phys. Rev. Lett. 103, 147003 (2009). [6] C. M. Wilson, G. Johansson, A. Pourkabirian, M. Simoen, J. R. Johansson, T. Duty, F. Nori and P. Delsing, Nature 479, 376-379 (2011). [7] J. R. Johansson, G. Johansson, C. M. Wilson, P. Delsing, F. Nori, e-print arXiv:1207.1988 (2012) |