Events: Global events at Chalmers University of TechnologyFri, 07 Feb 2020 16:00:21 +0100 Properties of Semiconductor Moire Crystals<p>Kollektorn, lecture room, Kemivägen 9, MC2-huset</p><p>​​Welcome to a Graphene Centre Seminar with Xiaoqin (Elaine) Li, Austin, Texas USA</p><strong>Abstra​ct:</strong><div><span style="font-size:14px"><span></span>A new type of superlattice, known as the moiré superlattice, form when two monolayers of van der Waals materials are stacked to form a heterostructure. A periodic energy modulation, as well as distinct optical selection rules, give rise to rich optical properties that remain largely unexplored in semiconductor moiré crystals. I will discuss how the moiré potential in twisted transition metal dichalcogenide bilayers changes the exciton resonances and diffusion in a manner controllable by the twist angle. Additional insights are obtained by comparing heterostructures prepared with either chemical vapor deposition or mechanical stacking. There are many exciting opportunities for exploring fundamental condensed matter physics and novel optoelectronic devices such as an array of single-photon emitters in these moiré crystals.</span><br /></div> workshop on gender biases<p>SB-L200, Sven Hultins Gata 6, Campus Johanneberg</p><p>​&quot;I’ve never experienced gender as a problem</p><div><br /></div> Welcome to a WiSE workshop with Nanna Gillberg, researcher and author engaged in equality, digitalisation and medialisation. The workshop aims to uncover the history and contemporary expressions of our unconscious gender biases to show how biases and their effects can be eradicated.  ​​​<div><br /><div><span style="background-color:initial">While all formal barriers to gender equality have been eliminated, it is expected to take another 185 years to achieve gender equality in Sweden. The delay is due to the informal gender organising mechanisms that still prevail. These are found in our minds in the form of notions of what it means to be a woman and a man, as well as built into our societal structures. Generally, we are not aware of the notions on gender that we carry around and which are also embedded in society’s division of labour, responsibility, power, and resources. Ingrained in our culture and our structures, they have become invisible and are taken for granted. In spite of their invisible status, the informal mechanisms make their mark in practice in a number of ways. Both men and women for example are more prone to relating to and identifying with men than women and find it easier to see competence and authority in men. Men’s approval carries more weight than that of women. This workshop uncovers the history and contemporary expressions of our unconscious gender biases to show how biases and their effects can be eradicated.</span><div> </div> <div><strong>Nanna Gillberg</strong> (<a href="">​</a>) is a researcher at Gillberg Neuropsychiatric Center at the Sahlgenska Accademy and at the Gothenburg Research Institute at the School of Business, Economics and Law, University of Gothenburg. Her research focuses on how digitalization and medialization affect norms and values, social climate and economic value creation. She is author of several books among which &quot;Jag har aldrig märkt att kön har haft någon betydelse&quot; in which she highlights the informal mechanisms give rise contributes to gender inequality despite all the legislations, official rhetoric and political initiatives taken to end it.</div> <div><br /></div> <div>The workshop is open to anyone with an interest in female role models within academia - especially from Chalmers, Sahlgrenska University Hospital, Sahlgrenska Academy, Gothenburg University, Borås University, and MedTech West.<br /></div> <div><br /></div> <div><a href="" target="_blank"><img class="ms-asset-icon ms-rtePosition-4" src="/_layouts/images/icgen.gif" alt="" />More information and registration</a></div> <div><br /></div> <div><div><img src="/SiteCollectionImages/Institutioner/E2/Kalendarium/WiSE/WiSE_250px.jpg" class="chalmersPosition-FloatLeft" alt="" style="margin:5px" /><br /><br />WiSE – Women in Science – aims to create a supportive network for young female researchers during their academic career. WiSE is a joint project between MedTech West and the department of Electrical Engineering at Chalmers University of Technology.</div> <div><a href="/en/departments/e2/network/wise/Pages/default.aspx"><img class="ms-asset-icon ms-rtePosition-4" src="/_layouts/images/ichtm.gif" alt="" />Read more about WiSE​​​​​​​​</a></div></div> <div><br /></div> </div></div> feedback of a mechanical oscillator<p>Kollektorn, lecture room, Kemivägen 9, MC2-huset</p><p>​Welcome to a Linnaeus Colloquium by Tobias Kippenberg, Institute of Physics Swiss Federal Institute of Technology Lausanne, EPFL, Switzerland</p><strong>Abstract:</strong><div> <div>In real-time quantum feedback protocols (1), the record of a continuous measurement is used to stabilize a desired quantum state. Recent years have seen spectacular advances in a variety of well-isolated micro-systems, including microwave photons(2) and superconducting qubits(3). By contrast, the ability to stabilize the quantum state of a tangibly massive object, such as a nano-mechanical oscillator, remains a difficult challenge. The main obstacle is environmental decoherence, which places stringent requirements on the timescale in which the state must be  measured. Using cavity optomechanical coupling(4, 5) we report on a position sensor that is capable of resolving the zero-point motion of a solid-state, 4.3 MHz frequency nanomechanical oscillator in the timescale of its thermal decoherence(6), a basic requirement for preparing its ground-state using feedback as well as (Markovian) quantum feedback. The sensor is based on evanescent coupling to a high-Q optical microcavity(7), and achieves an imprecision 40 dB below that at the standard quantum limit for a weak continuous position measurement(8), while maintaining an imprecision-back-action product within a factor of 5 of the Heisenberg uncertainty limit. As a demonstration of its utility, we use the measurement as an error signal with which to feedback cool the oscillator. Using radiation pressure as an actuator, the oscillator is cold-damped(9) with unprecedented efficiency: from a cryogenic bath temperature of 4.4 K to an effective value of 1.1 mK, corresponding to a mean phonon number of 5 (i.e., a ground state probability of 16%). The measurement reveals strong backaction-imprecision correlations, which we observe as quantum mechanical sideband asymmetries, as well as pondermotive squeezing of the light field(10). Our results set a new benchmark for the performance of a linear position sensor, and signal the emergence of mechanical oscillators as practical subjects for measurement-based quantum control.  We moreover demonstrate the existence of such quantum correlations due to the optomechanical interaction at room temperature (11) and demonstrate that the correlations enable quantum enhanced force sensing (termed “variational measurements”). This scheme, rather than utilizing squeezed vacuum, uses the quantum correlations produced in the interferometer for enhanced force sensing. Closing, we will describe recent progress which uses soft clamping and strain engineering, which has enabled to attain mechanical quality factor exceeding 800 million at room temperature, implying a mechanical oscillator undergoing more than hundreds of oscillations during the thermal decoherence time. These results signal the emergence of room temperature quantum feedback, and room temperature quantum control of mechanical oscillators. Time permitting, I will also show emerging hybrid optomechanical technologies, ranging from non-reciprocal photonic circuits using optomechanics, to quantum limited amplifiers based on ground state cooled mechanical oscillators.</div> <div><strong>References:</strong></div> <div>1.<span style="white-space:pre"> </span>H. Wiseman, Quantum theory of continuous feedback. Physical Review A 49, 2133 (1994).</div> <div>2.<span style="white-space:pre"> </span>C. Sayrin et al., Real-time quantum feedback prepares and stabilizes photon number states. Nature 477, 73 (Sep 1, 2011).</div> <div>3.<span style="white-space:pre"> </span>R. Vijay et al., Stabilizing Rabi oscillations in a superconducting qubit using quantum feedback. Nature 490, 77 (Oct 4, 2012).</div> <div>4.<span style="white-space:pre"> </span>T. Kippenberg, H. Rokhsari, T. Carmon, A. Scherer, K. Vahala, Analysis of Radiation-Pressure Induced Mechanical Oscillation of an Optical Microcavity. Physical Review Letters 95,  (2005).</div> <div>5.<span style="white-space:pre"> </span>M. Aspelmeyer, T. J. Kippenberg, F. Marquardt, Cavity optomechanics. Reviews of Modern Physics 86, 1391 (December 30, 2014, 2014).</div> <div>6.<span style="white-space:pre"> </span>D. J. Wilson et al., Measurement and control of a mechanical oscillator at its thermal decoherence rate. Nature doi:10.1038/nature14672,  (2015, 2014).</div> <div>7.<span style="white-space:pre"> </span>E. Gavartin, P. Verlot, T. J. Kippenberg, A hybrid on-chip optomechanical transducer for ultrasensitive force measurements. Nature nanotechnology 7, 509 (Aug, 2012).</div> <div>8.<span style="white-space:pre"> </span>A. A. Clerk, M. H. Devoret, S. M. Girvin, F. Marquardt, R. J. Schoelkopf, Introduction to quantum noise, measurement, and amplification. Reviews of Modern Physics 82, 1155 (2010).</div> <div>9.<span style="white-space:pre"> </span>M. Pinard, P. Cohadon, T. Briant, A. Heidmann, Full mechanical characterization of a cold damped mirror. Physical Review A 63,  (2000).</div> <div>10.<span style="white-space:pre"> </span>V. Sudhir, D. Wilson, A. Ghadimi, T. J. Kippenberg, Appearance and disappearance of quantum correlations in measurement-based feedback control of a mechanical oscillator. Phys. Rev.  X  (2017).</div> <div>11.<span style="white-space:pre"> </span>V. Sudhir, D. Wilson,  T. J. Kippenberg, Room temperature quantum correlations of a mechanical oscillator. Phys. Rev.  X  (2017).</div> <div>12.<span style="white-space:pre"> </span>A. Ghadimi et al., Elastic strain engineering for ultralow mechanical dissipation, Science (2018)</div> <div><br /></div></div> Higher Education 2020<p>Wallenberg Conference Center, Medicinaregatan, Göteborg</p><p>Welcome to the conference Rethinking Higher Education 2020! Students, teachers, researchers and other professionals are invited to a one-day conference on Saturday 28 March 2020 to discuss how to put the Sustainable Development Goals (SDGs) into action in our educational programs, research, and collaborations with society.​</p><span style="font-family:verdana,arial,helvetica,sans-serif;font-size:13px">This conference is the second in a series, building on the conference &quot;Rethinking Higher Education&quot; held at Karolinska Institutet in March 2019. This conference offers an exciting forum for carrying forward the results from the first conference in 2019 where participants identified how universities can take responsibility for, and be inspired by, the Sustainable Development Goals in our activities.</span><br style="font-family:verdana,arial,helvetica,sans-serif;font-size:13px" /><div><br /> </div> <div>​<span></span>Arjen Wals, Professor of Transformative Learning for Socio-Ecological Sustainability at Wageningen University, is confirmed as a keynote speaker. A tentative programme is available at the conference website.<br style="font-family:verdana,arial,helvetica,sans-serif;font-size:13px" /></div> <div><span style="font-family:verdana,arial,helvetica,sans-serif;font-size:13px"><br /></span> </div> <div><span style="font-family:verdana,arial,helvetica,sans-serif;font-size:13px">Learn more about the conference at <a href=""></a> </span><br style="font-family:verdana,arial,helvetica,sans-serif;font-size:13px" /></div> <br style="font-family:verdana,arial,helvetica,sans-serif;font-size:13px" /><font face="verdana, arial, helvetica, sans-serif"><span style="font-size:13px"><span></span>Rethinking Higher Education 2020 is organised by the University of Gothenburg and Chalmers University of Technology in collaboration with Karolinska Institutet and the Royal Swedish Academy of Sciences.</span></font> pathways of hot electrons in graphene<p>Kollektorn, lecture room, Kemivägen 9, MC2-huset</p><p>​Welcome to a Graphene Centre Seminar with Bernard Placais, CNRS, Paris, France.</p> devices in bilayer graphene<p>Kollektorn, lecture room, Kemivägen 9, MC2-huset</p><p>​​​Welcome to a Graphene Centre Seminar with​ Klaus Ensslin, ETH, Zurich , Switzerland</p> optics, extraordinary momentum and spin in evanescent waves, optical analog of topological insulators, and the quantum spin Hall effect of light<p>Kollektorn, lecture room, Kemivägen 9, MC2-huset</p><p>​Welcome to a Linnaeus Colloquium with Franco Nori, RIKEN, Japan</p><strong>Abstract:</strong><br /><div><div>This talk provides a brief overview to some aspects of parity-time symmetric optics, extraordinary momentum and spin in evanescent waves, optical analog of topological insulators, and the quantum spin Hall effect of light.  </div> <div> </div> <div>1.<span style="white-space:pre"> </span>Parity-Time-Symmetric Optics </div> <div>Optical systems combining balanced loss and gain provide a unique platform to implement classical analogues of quantum systems described by non-Hermitian parity–time (PT)-symmetric Hamiltonians [1]. Such systems can be used to create synthetic materials with properties that cannot be attained in materials having only loss or only gain. We report PT-symmetry breaking in coupled optical resonators. We observed non-reciprocity in the PT-symmetry-breaking phase due to strong field localization, which significantly enhances nonlinearity. In the linear regime, light transmission is reciprocal regardless of whether the symmetry is broken or unbroken. We show that in one direction there is a complete absence of resonance peaks whereas in the other direction the transmission is resonantly enhanced, which is associated with the use of resonant structures. Our results could lead to a new generation of synthetic optical systems enabling onchip manipulation and control of light propagation. </div> <div> </div> <div>2.<span style="white-space:pre"> </span>The quantum spin Hall effect of light: photonic analog of 3D topological insulators. </div> <div>Maxwell’s equations, formulated 150 years ago, ultimately describe properties of light, from classical electromagnetism to quantum and relativistic aspects. The latter ones result in remarkable geometric and topological phenomena related to the spin-1 massless nature of photons. By analyzing fundamental spin properties of Maxwell waves, we show [2] that free-space light exhibits an intrinsic quantum spin Hall effect —surface modes with strong spin-momentum locking. These modes are evanescent waves that form, for example, surface plasmon-polaritons at vacuum-metal interfaces. Our findings illuminate the unusual transverse spin in evanescent waves and explain recent experiments that have demonstrated the transverse spin-direction locking in the excitation of surface optical modes. This deepens our understanding of Maxwell’s theory, reveals analogies with topological insulators for electrons, and offers applications for robust spindirectional optical interfaces.  Related work can be found in [3]. </div></div> <div><br /></div> <div><a href="/en/departments/mc2/calendar/Documents/franco_nori.pdf"><img class="ms-asset-icon ms-rtePosition-4" src="/en/departments/mc2/calendar/_layouts/images/icpdf.png" alt="" />Abstract and references (pdf</a>)</div> <div><br /></div> ​ 2nd International Conference on Negative CO2 Emissions<p>Chalmers Student Union Building, Chalmers Campus Johanneberg</p><p>​The 2nd International Conference on Negative CO2 Emissions will be held May 12-15, 2020, at Chalmers University of Technology, Gothenburg, Sweden. The purpose of this conference series is to bring together a wide range of scientists, experts and stakeholders, in order to engage in various aspects of research relating to negative CO2 emissions. This will include various negative emission technologies, climate modelling, climate policies and incentives. The main topics of the conference, around which the sessions will be built, include:</p><ul><li>​<span style="font-size:14px"><span style="background-color:initial">BECCS</span></span></li> <li><span style="font-size:14px">Biospheric storage</span></li> <li><span style="font-size:14px">Cross-cutting sessions</span></li> <li><span style="font-size:14px">Direct air capture</span></li> <li><span style="font-size:14px">Enhanced weathering</span></li> <li><span style="font-size:14px">Modeling</span></li> <li><span style="background-color:initial">Ocean alkalization</span></li></ul> <span></span> <div><span style="font-size:14px"></span><span></span><div><span style="font-size:14px"><strong>Background</strong></span></div> <div><span style="font-size:14px">The objective of the Paris Agreement is to limit global warming to well below 2ºC, and to pursue efforts to limit the temperature increase to 1.5ºC. The carbon budget is the amount of carbon dioxide that we can emit while still limiting global temperature rise to a given level, for example 1.5ºC.</span></div></div> <div><br /></div> <div><span style="background-color:initial;font-size:14px"></span><strong>Read more and sign up to the conference:</strong><br /><a href=""><img class="ms-asset-icon ms-rtePosition-4" src="/_layouts/images/icgen.gif" alt="" />The 2nd International Conference on Negative CO2 Emissions​</a><br /></div> Bands in Flatlands<p>Kollektorn, lecture room, Kemivägen 9, MC2-huset</p><p>​Welcome to a Graphene Centre Seminar with ChunNing (Jeanie) Lau, Ohio, USA</p> and reversing a quantum jump mid-flight<p>Kollektorn, lecture room, Kemivägen 9, MC2-huset</p><p>Joint Linnaeus and GPC Colloquium with Michel Devoret, Yale University, USA​</p><div><span style="font-weight:700"><img src="/SiteCollectionImages/Institutioner/MC2/Föreläsningar/M%20Devoret.jpg" class="chalmersPosition-FloatRight" alt="" style="margin:5px;height:235px;width:200px" />Abstract:</span></div> <div>Measurements in quantum physics, unlike their classical physics counterparts, can fundamentally yield discrete and random results. Historically, Niels Bohr was the first to hypothesize that quantum jumps occurred between two discrete energy levels of an atom. Experimentally, quantum jumps were only directly observed many decades later, in an atomic ion driven by a weak deterministic force under strong continuous energy measurement. The times at which the discontinuous jump transitions occur are reputed to be fundamentally unpredictable. Despite the non-deterministic character of quantum physics, is it possible to know if a quantum jump is about to occur? </div> <div>Our work<span style="font-size:10.5px;line-height:0;vertical-align:baseline;top:-0.5em">1</span> provides a positive answer to this question: we experimentally show that the jump from the ground state to an excited state of a superconducting artificial three-level atom can be tracked as it follows a predictable “flight” by monitoring the population of an auxiliary energy level coupled to the ground state. The experimental results demonstrate that the evolution of the jump — once completed — is continuous, coherent, and deterministic. Based on these insights and aided by real-time monitoring and feedback, we then pinpoint and reverse one such quantum jump “mid-flight”, thus deterministically preventing its completion. Our findings, which agree with theoretical predictions essentially without adjustable parameters, lend support to the modern formulation of quantum trajectory theory; most importantly, they may provide new ground for the exploration of real-time intervention techniques in the control of quantum systems, such as the early detection of error syndromes.</div> <div><br /></div> <div>1.<span style="white-space:pre"> </span>Z. Minev et al., Nature 570, 200–204 (2019)</div> <div><br /></div>