14:00 ~ 15:00

Seung-Woo Lee: Information trade-off relations in Quantum Measurements

15:30 ~ 16:30

Myung-Joong Hwang: Dynamical scaling laws of Loschmidt Echo and Out-of-Time-Ordered Correlators

A system exhibiting a quantum phase transition may exhibit critical behavior not only in their ground state, but also in their non-equilibrium dynamics. Understanding the latter through the lens of universality is an important challenge. In this context, I will present recent works where we formulate dynamical scaling laws of two important quantities characterizing non-equilibrium dynamics near a critical point, namely, the Loschmidt Echo (LE) and the Out-of-Time-Ordered Correlator (OTOC). First, I will demonstrate the decay of Loschmidt echo, a dynamical analogue of quantum fidelity measuring the overlap between a ground state and a time-evolved quantum state following a sudden quench, follows power-law scaling in the system size and the distance from a critical point with equilibrium critical points. It has long been pointed out that the Loschmidt echo may exhibit a sharp decay near a critical point, but our work provides a quantitative dynamical scaling law governing such a critical decay of Loschmidt echo. In addition, such dynamical scaling is also formulated for the OTOC and its implication for the quantum chaotic property of a system such as butterfly velocity. I will outline the construction of dynamical scaling functions and demonstrate numerically the validity of the predicted scaling laws with a diverse range of critical models such as Ising spin models with a short and long range interaction and non-integrable model such as next-nearest neighbor Ising model.

17:00 ~ 18:00

Abolfazl Bayat: A quantum information perspective for both quantum phase transitions and many-body localization

A quantum phase transition may occur in the ground state of a system at zero temperature when a controlling field or interaction is varied. The resulting quantum fluctuations which trigger the transition produce scaling behavior of various observables, governed by universal critical exponents. A particularly interesting class of such transitions appears in systems with quantum impurities where the notion of a conventional order parameter is generically missing in these systems due to the absence of spontaneous symmetry breaking.

On the other hand, many-body localization has become an important phenomenon for illuminating a potential rift between non-equilibrium quantum systems and statistical mechanics. Unlike quantum phase transitions, the many-body localization is a property of the whole spectrum. However, the nature of the transition between ergodic and localized phases in models displaying many-body localization is not yet well understood.

Here, we provide insight on both impurity quantum phase transition and many-body localization using quantities developed in quantum information technologies, namely Schmidt gap and entanglement negativity. In particular, we show that the Schmidt gap can play the role of order parameter in both transitions and entanglement negativity can detect the diverging length scale in such systems.

9:30 ~ 10:30

Jaehak Lee: Quantum non-Gaussianity and secure communication

I introduce quantum non-Gaussianity in bosonic system. It is of crucial importance to identify quantum non-Gaussian states that cannot be produced by Gaussian resources and their statistical mixtures. I propose a quantum non-Gaussianity measure, which is defined by a convex roof of quantum relative entropy, and investigate the properties of the measure. Further, I introduce the critical role played by their quantum non-Gaussianity in quantum communications, addressing communication security. I investigate the no-cloning bound of non-Gaussian states with unknown displacement. I show that the no-cloning bound decreases as non-Gaussianity increases, but it becomes harder to achieve the bound by quantum teleportation.

11:00 ~ 12:00

Jinhyoung Lee: Negative probability and nonclassicality by statistical distance

14:00 ~ 15:00

Wonmin Son: Dimensionality induced entanglement in macroscopic dimer systems

15:30 ~ 16:30

Yonghae Lee: Quantum state exchange and entanglement cost

We first introduce some quantum communication tasks using quantum entanglement as a non-local resource, such as quantum teleportation, quantum state merging, and quantum state redistribution. We explain that the least amounts of entanglement needed for these tasks are given by some entropic measures. Then we consider a quantum communication task between two users Alice and Bob, in which Alice and Bob exchange their respective quantum information by means of local operations and classical communication assisted by shared entanglement. Here, we assume that Alice and Bob may have quantum side information, not transferred, and classical communication is free. In this talk, we call this task as quantum state exchange, and we present general upper and lower bounds for the least amount of entanglement required for this task. We show that the least amount of entanglement can be negative when Alice and Bob make use of their quantum side information, and study how the users deal with their symmetric information in order to reduce the amount of entanglement.

17:00 ~ 18:00

Jeongho Bang: Learning-with-errors (LWE) problem on Noisy Intermediate-Scale Quantum Computers

9:30 ~ 10:30

Ho-Joon Kim: Coherence concentration is irrecoverable

Quantum coherence is an undeniable characteristic that comes from quantumness, which can be quantitatively formulated in the quantum resource theory framework. We investigate whether the coherence of pure states can be concentrated and then recovered without error with the incoherent operation. Although the resource theory of quantum coherence is known to be reversible in this case, we find that the concentration-recovery process is doomed to have an inevitable error in general: Moreover, the optimal error is a constant. Relaxing to an approximate recovery with a bounded error, we figure out the optimal number of approximately recovered copies of the initial state. Furthermore, when it comes to conversion between arbitrary two pure states, we obtain the condition for perfect recovery in terms of the first and second moments of the coherence contents in the states.

11:00 ~ 12:00

Hyukjoon Kwon: Rényi Entanglement Entropy Inequalities in Nondeterministic LOCC Transformations

Entanglement is a quantum resource which does not increase by a local operation and classical communication (LOCC) protocol. Nevertheless, a nondeterministic LOCC protocol allows the increment of entanglement with the probability smaller than unity, preventing the degree of entanglement from increasing on average. We establish the bounds of probability to raise a degree of the Rényi entanglement entropy in the nondeterministic LOCC. The probability distribution of the outcome Rényi entanglement entropy is proven to satisfy the inequality stronger than the LOCC monotonicity condition. We also demonstrate the exponential decay of the probability to raise the degree of entanglement, which can be easily observed in a system with a large Schmidt rank. Our results are not limited to the specific type of entanglement manipulation protocol, such as distillation of the maximally entangled state, but can widely be applied to any LOCC protocols aiming to generate moderately entangled states. Finally, we discuss a generalisation of our result for mixed quantum states.

14:00 ~ 15:00

Cédric Bény: Relevant components of channels

The effect of a quantum channel can be reversed on a cluster of states provided it does't degrade their distinguishability to a common reference state. Using linearized distinguishability metrics, we can generalize this relationship to a hierarchy of state clusters whose distinguishability is degraded by specific amounts: the channel's singular values. This provides a useful representation of the channel with applications to quantum error correction, quantum field theory, classical machine learning and more.

15:30 ~ 16:30

Jaeyoon Cho: Holographic entanglement in free-fermion systems

In this talk, I discuss about an on-going work on the "derivation" of the celebrated holographic entanglement entropy formula by Ryu and Takayanagi in free-fermion systems.