Heiko Rieger

Department of Physics,
Universität des Saarlandes

Biophysics of Killing – Theory and Experiment

Cytotoxic Tlymphocytes and natural killer cells are the main cytotoxic killer cells of the human body to eliminate pathogen-infected or tumorigenic cells. Various processes are involved in a successful killing event: activation of the killer cell, migration and search for the target, formation of a synapse and polarization upon contact with the target, transport of cytotoxic agents towards the synapse, and finally elimination of the target via necrosis or apoptosis. In this talk I will review various biophysical aspects of killing that were studied in collaboration with experimental groups from biology and medicine. Topics include the analysis of search strategies of migrating killer cells; the mechanistic understanding of the molecular motor driven cytoskeleton rotation towards the synapse during polarization; the efficiency of the spatial organization of the cytoskeleton for search problems occurring in intra-cellular cargo transport; and the stochastic analysis of different killing strategies via inducing necrosis or apoptosis.

Oct. 21 (Wed), 2020, 5PM KST
(Oct. 21 (Wed), 2002, 10AM CEST)

Hyukjoon Kwon

Department of Physics,
Imperial College London

Quantum computing and quantum error correction: new perspectives beyond conventional approaches

Along with the development of quantum theory, people have asked whether we can utilize quantum principles for practical purposes. The discovery of new technological advances in a wide range of fields, including communication, cryptography, computation, and sensing tasks, has opened a new research area, quantum information science. In particular, quantum computing lies at the core of such advances as it opens a new possibility to solve complex problems that even the fastest classical computers cannot simulate. The major issues regarding quantum computing are to find the most efficient design of a quantum circuit to protect quantum information from a noisy environment and to fully understand where the computational power of quantum computers comes from.

In this talk, we review the underlying principles of quantum computation and its unique feature to correct errors using entanglement. While the stabilizer formalism provides a powerful toolkit to detect and correct errors in various types of quantum systems, uncorrectable errors can be accumulated throughout a quantum circuit. We show that the fundamental limitation of quantum error-correction can be formulated by the dissipated amount of quantum information throughout a quantum circuit. Furthermore, we construct a universal recovery map to recover quantum information close to the optimal rate. This approach of approximate quantum error-correction opens a new possibility to lower the threshold value required for fault-tolerant quantum computation, beyond the stabilizer formalism. We also introduce a new viewpoint to understand the origin of quantum computational advantages by characterizing classical simulabilty of a quantum circuit based on the negativity in quasi-probability distribution.

Oct. 28 (Wed), 2020, 5PM KST
(Oct. 28 (Wed), 2020, 8AM BST)

Christopher Jarzynski

Department of Chemistry and Biochemistry,
University of Maryland, College Park

Scaling down the laws of thermodynamics

Thermodynamics provides a robust conceptual framework and set of laws that govern the exchange of energy and matter. Although these laws were originally articulated for macroscopic objects, nanoscale systems also exhibit “thermodynamic¬-like” behavior – for instance, biomolecular motors convert chemical fuel into mechanical work, and single molecules exhibit hysteresis when manipulated using optical tweezers. To what extent can the laws of thermodynamics be scaled down to apply to individual microscopic systems, and what new features emerge at the nanoscale? I will describe some of the challenges and recent progress – both theoretical and experimental – associated with addressing these questions. Along the way, my talk will touch on non-equilibrium fluctuations, “violations” of the second law, the thermodynamic arrow of time, nanoscale feedback control, strong system-environment coupling, and quantum thermodynamics.

Nov. 3 (Tue), 2020, 10AM KST
(Nov. 2 (Mon), 2020, 8PM EDT)

Mike Hinczewski

Department of Physics,
Case Western Reserve University

Steering evolution: shortcuts to adiabaticity in cellular populations

Shortcuts to adiabaticity provide powerful tools for the control of quantum systems, allowing adiabatic evolution over finite time intervals. These methods also have direct mathematical analogues in classical stochastic systems. In this talk, we will explore the implementation of these ideas in the context of microbial evolution, where populations of cells undergo random mutations and compete via natural selection. The pace and unpredictability of this evolution are critically relevant in a variety of modern challenges, including combating drug resistance in pathogens and cancer. Great progress has been made in quantitative modeling of evolution as diffusion along fitness landscapes, allowing a degree of prediction for future evolutionary histories. Yet fine-grained control of the speed and the distributions of these trajectories remains elusive. We show how one particular form of adiabatic shortcut, known as counterdiabatic driving, gives us a novel tool for evolutionary control: it allows us to calculate a protocol for a set of external control parameters (i.e. varying drug concentrations / types, temperature, nutrients) that can guide the probability distribution of genetic variants in a population along a specified path and time interval. The method is validated on simulations based on experimental fitness data from a set of mutations of the malarial dihydrofolate reductase gene, showing varying degrees of resistance to anti-malarial drugs. Because the underlying mathematical framework is not unique to evolution, we also discuss extending these ideas to other stochastic processes in biology, including ecology and stem cell development.

Nov. 11 (Wed), 2020, 10AM KST
(Nov. 10 (Tue), 2020, 8PM EDT)

Sidney Redner

Santa Fe Institute

Is Basketball Scoring Just a Random Walk?

Watching basketball is nearly the same as watching repeating coin tossings! By analyzing recently available data from recent NBA basketball seasons, basketball scoring during a game is well described by a continuous-time anti-persistent random walk, with essentially no temporal correlations between successive scoring events. We show how to calibrate this model to account for many statistical season-long metrics of NBA basketball. As further fillustrations of this random-walk picture, we show that the distribution of times when the last lead change occurs and the distribution of times when the score difference is maximal are both given by the celebrated arcsine law---a beautiful and surprising property of random walks. We also use the random-walk picture to construct the criterion for when a lead of a specified size is "safe" as a function of the time remaining in the game. The obvious application to game-time betting is left as an exercise for the interested.

Nov. 18 (Wed), 2020, 10AM KST
(Nov. 17 (Tue), 2020, 6PM MDT)

Valerio Scarani

National University of Singapore

Measuring and using quantum uncertainty

What pretty much everyone knows about quantum mechanics is that "one cannot measure position and momentum at the same time". This is popularly understood as meaning that our instruments won't ever be precise enough (Heisenberg himself fell into this trap when he tried to make it palatable to a large audience). Physicists however mean something much more radical: they claim that position and momentum are "really" not simultaneously determined, and that a measurement would not reveal a pre-existing value. There is "intrinsic randomness" in the physical world. On what can such a radical claim be based? Since 1964, we know that intrinsic randomness is not just a preference: it can actually be proved by observing a "violation of Bell inequalities". Just like apples fall to the ground for Aristotle, Newton and Einstein alike, so this violation is a phenomenon: even if quantum theory is replaced by something else in the future, the phenomenon is here to stay -- and so is the evidence for intrinsic randomness in nature. In this talk, I shall present this story, and complete it with its latest development: the evidence for intrinsic randomness provided by quantum physics leads to the actual certification of randomness and cryptography without any other assumption than the obvious ones (those of the kind: you should be in a safe location when you read a secret message). This level of certification is called "device-independent" and has been a major topic in quantum information science since more than a decade.

Dec. 2 (Wed), 2020, 4PM KST

(Dec. 2 (Wed), 2020, 3PM SST)

Francesco Buscemi

Department of Mathematical Informatics,
Nagoya University

Quantum entanglement is all over the places nowadays, but what is it really? Why was it introduced in the first place? What are the observable phenomena that it entails? How can we "verify" the presence of entanglement is a certain setup? And what are the implications of all this in the development of quantum information technologies? In this colloquium I will try to explain why these questions matter, both from a foundational and from a practical viewpoint, and propose my understanding of the subject, which is based on the notion of "semi-quantum nonlocal games".

Nov. 24 (Tue), 2020, 4PM KST
(Nov. 24 (Tue), 2020, 4PM JST)

Changmin Lee

KIAS

Cryptography for next generation computation

New trends in computational science have emerged. Data analysis and quantum computers are one of them. Data analysis is an essential technique in the Fourth Industrial revolution. However, data analysis has the potential to invade individual privacy. On the other hand, after the breakthrough in quantum computers, existing solutions for digital signature and internet protocol are threatened. As a result, new cryptographic schemes for next generation have been constructed. Lattices are a major mathematical platform to build new cryptosystems. It is expected that these cryptosystems will soon be standardized and deployed, replacing the historical solutions. Recently, lattices over the number fields (a.k.a algebraic lattices) get highlighted rather than lattices over the integers because such lattices over additional structures allow efficient operations. This talk briefly covers privacy issues in terms of data analysis and a quantum computer, thereafter introduces a basic notion of algebraic lattices.

Dec. 16 (Wed), 2020, 4PM KST