====== Welcome to QuIC! ====== The **Centre for Quantum Information and Communication** (QuIC) has been active in quantum information sciences since 2001, with research contributions ranging from fundamental physics questions, such as quantum measurement, quantum entanglement, or quantum nonlocality, to more information-flavored topics, such as quantum communication, quantum cryptography, or quantum algorithms. It has invented and contributed to the demonstration of the first continuous-variable (Gaussian) quantum cryptographic protocol, and has developed the first quantum adiabatic algorithm with a quantum speedup (quantum adiabatic search). Recently, it also has contributed to establish the fundamental limit on the transmission rate via Gaussian bosonic channels (the quantum extension of Shannon's famous channel capacity formula), and has discovered a quantum two-photon interference effect in the amplification of light akin to the Hong-Ou-Mandel effect. It currently holds two patents, and has published numerous scientific papers, among which two in the journal //Nature//, one in //Nature Physics//, two in //Nature Photonics//, and three in //Nature Communications//. //Nicolas J. Cerf, group leader.// Applications are invited for a postdoctoral position in quantum foundations and quantum information. The researcher will work with Dr. Ognyan Oreshkov on topics ranging from entanglement to causal structures and quantum reference frames. The position is for up to two years, finishing at the end of 2025. For application instructions, see [[https://www.quantiki.org/position/postdoctoral-position-quantum-foundations-and-information-ulb|announcement]]. Please direct informal enquiries to [[ognyan.oreshkov@ulb.be|Dr. Ognyan Oreshkov]]. {{:time-delocalised.jpg?150|}} Julian Wechs and Ognyan Oreshkov from QuIC and Cyril Branciard from the CNRS have shown for the first time that an exotic type of process violating causal inequalities can be realised with known physics. A violation of a causal inequality proves under theory-independent assumptions that certain variables in an experiment cannot be assigned a definite causal order. The new study, published in [[https://www.nature.com/articles/s41467-023-36893-3|Nature Communications]], shows that such processes can be realised in standard quantum mechanics using variables delocalised in time. The finding may have far-reaching implications for our understanding of causality in physics. \\ See [[https://actus.ulb.be/fr/presse/communiques-de-presse/recherche/des-variables-delocalisees-dans-le-temps-allant-a-lencontre-des-inegalites-causales|press release]]. {{:causalloops.jpg?160|}} Ognyan Oreshkov from QuIC and colleagues Jonathan Barrett and Robin Lorenz from the University of Oxford have developed a theory of causality in quantum theory, according to which cause-effect relations can sometimes form cycles. This theory offers a novel understanding of exotic processes in which events do not have a definite causal order. The study has been published in [[https://www.nature.com/articles/s41467-020-20456-x|Nature Communications]]. \\ See [[https://www.eurekalert.org/news-releases/783860|press release]]. {{:hom-1.png?130|}} Nicolas Cerf from QuIC and Michael Jabbour from the University of Cambridge have uncovered an unsuspected quantum interference mechanism, which originates from the indistinguishability of identical bosons in time. The famous Hong–Ou–Mandel effect describes the “bunching” of identical bosons at the output of a half-transparent beam splitter resulting from the symmetry of the wave function. The study, published in the [[https://www.pnas.org/doi/full/10.1073/pnas.2010827117|Proceedings of the National Academy of Sciences]], establishes that this effect turns, under partial time reversal, into an interference effect in a quantum amplifier that can be ascribed to time-like indistinguishability (bosons from the past and future cannot be distinguished). This hitherto unknown effect is a genuine manifestation of quantum physics and may be observed whenever two identical bosons participate in Bogoliubov transformations, which play a role in many facets of physics. \\ See [[https://phys.org/news/2020-12-quantum.html|press release]]. [[members:oreshkov|{{:members:oreshkov:ognyan_small.jpg?85|}}]] The QuIC center is happy to welcome Ognyan Oreshkov as a tenured F.R.S.-FNRS researcher, starting in October 2017. Ognyan received his Ph.D. from the University of Southern California and has held several postdoctoral positions in Europe, including in Barcelona, Vienna, Brussels, and Oxford. He previously received a Marie Curie Intra-European Fellowship and an F.R.S.-FNRS Postdoctoral Fellowship. Ognyan has been awarded a tenured Research Associate mandate for a project on indefinite causal structure in quantum theory. See {{:fnrs-news-110.pdf|FNRS news}} (issue of September 2017). {{:npjqi.png?235|}} An improved method for calculating the entropy of quantum information carriers may help solve hard problems in quantum communication theory. QuIC researchers have investigated the entropy generation of Gaussian quantum transformations by adapting for this purpose the ‘replica’ method, a trick developed by statistical physicists for the description of random media such as spin glasses. These results are published in [[http://www.nature.com/npjqi|npj Quantum Information]] (Nature Partner Journal) and are advertised in the journal homepage (see full article at [[http://www.nature.com/articles/npjqi20158|doi:10.1038/npjqi.2015.8]]) {{:raul.png?85|}} Starting October 2015, the QuIC center will host a new permanent researcher: Raúl García-Patrón Sánchez, who was a Return Fellow from BELSPO (Belgian Science Policy Office) after several years of postdoctoral experience in Germany and the USA, has recently been awarded a Research Associate tenured position from the F.R.S.-FNRS (Fund for Scientific Research). See {{:fnrs-news-102.pdf|FNRS news}} (issue of September 2015). {{:clock-in-mirror.jpg?130|}} The laws of classical mechanics are independent of the direction of time, but whether the same is true in quantum mechanics has long been a subject of debate. While it is agreed that the laws that govern isolated quantum systems are time-symmetric, measurement changes the state of a system according to rules that appear to hold forward in time only (e.g. Born’s rule). Two QuIC researchers have developed a time-symmetric operational formulation of quantum mechanics, which offers new insights into the so-called “psychological” arrow of time (the fact that we remember the past but not the future). This study, recently published in [[http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3414.html|Nature Physics]], reexamines the notions of causality and free choice in the context of an operational theory (i.e. a theory centered on events). It may open new perspectives on the role of causal structures in quantum mechanics and potentially even be extended to an operational quantum theory without any predefined time.\\ See {{::pr-naturephysicsquantumtheory.pdf|press release}}. {{::info-quant.jpg?140|}} The massive data transfer over the Internet, which is vital to our information society, would not be possible without the crucial role played by optical communications. Every time a message, an image or a video is sent over the Internet, the corresponding sequence of bits is encoded into light pulses that are transmitted through optical fibers up to a receiver, which converts the light signal back to the original sequence of bits. The ever-increasing demand for data naturally raises the question of what are the ultimate physical limits on the achievable bit-rate over optical links. Two QuIC researchers have found, together with Italian and Russian colleagues, the long-awaited answer to this question in an article published in [[http://www.nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2014.216.html|Nature Photonics]]. They establish the fundamental limit on the transmission rate via Gaussian photonic channels that results from quantum physics, thereby extending the famous channel capacity formula due to Claude Shannon, the father of information theory. This news has been covered in Belgium in {{:fnrs-news-99.pdf|FNRS news}} (issue of December 2014), in {{:gsquare-14.pdf|G Square}} (issue of March 2015). See also {{:athena-305.pdf|Athena magazine}}. {{:cewqo_2014.png?300|}} The [[http://cewqo14.ulb.ac.be/|21st Central European Workshop on Quantum Optics]] has been held in Brussels from 23rd to 27th of June 2014, in the Palace of the Academies. Started in the 90s within a European project aimed at collaborating with Central-European countries, this series of workshops has evolved into a central annual gathering of European researchers working in quantum optics, its applications to quantum information, and foundations of quantum mechanics. It provides them with an opportunity to share their latest results and to listen to leading researchers invited to come from the other parts of the Globe. For two decades the workshop traveled all over the continent reaching its geographical edges. This 21st edition has come to the "Capital of Europe". {{:g-van-assche.jpg?95|}} Gilles Van Assche, a former PhD student at QuIC, is member of the team of four cryptographers who designed the [[http://keccak.noekeon.org/|Keccak]] algorithm, selected as the winner of the [[http://csrc.nist.gov/groups/ST/hash/sha-3/index.html|SHA-3 Cryptographic Hash Algorithm Competition]] by the [[http://www.nist.gov/index.html|National Institute of Standards and Technology]] (NIST). In the review process, the cryptographic community provided an enormous amount of expert feedback and NIST winnowed the original 64 candidates down to the five finalist candidates. These finalists were further reviewed in a third public conference in March 2012, and NIST finally announced //Keccak// as the winner of this competition on October 2nd, 2012. //Keccak// will now become NIST’s new SHA-3 hash algorithm. See the [[http://www.nist.gov/itl/csd/sha-100212.cfm|press release]]. The [[http://www.nobelprize.org/nobel_prizes/physics/laureates/2012/press.html|2012 Nobel Prize in Physics]] has been awarded to Serge Haroche (Collège de France and ENS, Paris, France) and David J. Wineland (NIST and University of Colorado, Boulder, USA) for the development of “ground-breaking experimental methods that enable measuring and manipulation of individual quantum systems”. Haroche and Wineland have carried out pioneering experiments in the field of quantum optics, independently developing approaches to examine, control, and count quantum particles. Wineland works with trapped ions and measures them with light, whereas Haroche controls and measures photons. Besides reporting multiple breakthroughs in fundamental science, their experiments have led to the construction of extreme precision atomic clocks and paved the way for researchers making the first steps towards building computers based on quantum physics.