백경현 교수

We focus here on the uncertainty of an observable $Y$ caused by a precise measurement of $X$. We illustrate the effect by analyzing the general scenario of two successive measurements of spin components $X$ and $Y$. We derive an optimized entropic uncertainty limit that quantifies the necessary amount of uncertainty observed in a subsequent measurement of $Y$. We compare this bound to recently derived error-disturbance relations and discuss how the bound quantifies the information of successive

Abstract In this work we investigate how to quantify the coherence of quantum measurements. First, we establish a resource theoretical framework to address the coherence of measurement and show that any statistical distance can be adopted to define a coherence monotone of measurement. For instance, the relative entropy fulfills all the required properties as a proper monotone. We specifically introduce a coherence monotone of measurement in terms of off-diagonal elements of positive-operator-val

Under the scenario of generalized measurements, it can be questioned how much of quantum uncertainty can be attributed to measuring device, independent of the uncertainty in the measured system. On the course to answer the question, we suggest a new class of entropic uncertainty relation that differentiates quantum uncertainty from device imperfection due to the unsharpness of measurement. In order to quantify the unsharpness, we suggest and analyze the quantity that characterizes the uncertaint

We propose a non-Gaussianity measure of a multimode quantum state based on the negentropy of quadrature distributions. Our measure satisfies desirable properties as a non-Gaussianity measure, i.e., faithfulness, invariance under Gaussian unitary operations, and monotonicity under Gaussian channels. Furthermore, we find a quantitative relation between our measure and the previously proposed non-Gaussianity measures defined via quantum relative entropy and the quantum Hilbert-Schmidt distance. Thi

We suggest an improved version of the Robertson--Schr\"odinger uncertainty relation for canonically conjugate variables by taking into account a pair of characteristics of states: non-Gaussianity and mixedness quantified by using fidelity and entropy, respectively. This relation is saturated by both Gaussian and Fock states and provides a strictly improved bound for any non-Gaussian states or mixed states. For the case of Gaussian states, it is reduced to the entropy-bounded uncertainty relation

We introduce a measure of quantum non-Gaussianity (QNG) for those quantum states not accessible by a mixture of Gaussian states in terms of quantum relative entropy. Specifically, we employ a convex-roof extension using all possible mixed-state decompositions beyond the usual pure-state decompositions. We prove that this approach brings a QNG measure fulfilling the properties desired as a proper monotone under Gaussian channels and conditional Gaussian operations. As an illustration, we explicit

Abstract Quantum state discrimination (QSD) is a fundamental task in quantum information processing with numerous applications. We present a variational quantum algorithm that performs the minimum-error QSD, called the variational quantum state discriminator (VQSD). The VQSD uses a parameterized quantum circuit that is trained by minimizing a cost function derived from the QSD, and finds the optimal positive-operator valued measure (POVM) for distinguishing target quantum states. The VQSD is cap

To analyze the joint measurability of given measurements, we introduce a Hermitian operator-valued measure, called $W$ measure, such that it has marginals of positive operator-valued measures. We prove that $W$ measure is a positive operator-valued measure (POVM) if and only if its marginal POVMs are jointly measurable. The proof suggests employing a negative $W$ measure as an indicator of nonjoint measurability. This translates the joint measurability problem to unconstrained convex minimizatio

We derive entropic uncertainty relations for successive generalized measurements by using general descriptions of quantum measurement within two distinctive operational scenarios. In the first scenario, by merging two successive measurements into one we consider successive measurement scheme as a method to perform an overall composite measurement. In the second scenario, on the other hand, we consider it as a method to measure a pair of jointly measurable observables by marginalizing over the di

인계 난연제인 트리페닐 포스페이트 (TPP)와 열적, 기계적 성질이 우수하고 네트워크 구조를 형성하는 노블락 형의 에폭시 수지를 이용하여 마이크로캡슐을 제조하였다. 유용성 인계 난연제인 TPP는 고분자 압출 공정 가공 시 고분자 수지에서 기화 및 방출로 인하여 난연제의 손실과 고분자 복합재의 젖음성 문제들을 야기시킨다. 이를 해결하기 위해 TPP를 마이크로캡슐화하였다. 즉, 본 공정은 캡슐의 심물질인 TPP와 벽막 물질인 노블락 형의 에폭시 레진을 혼합된 유화제와 함께 수중유형 (O/W) 상태로 역상유화시키고 제조된 유화액을 인시츄 중합법으로 가교반응을 진행하였다. 혼합된 유화제의 비율과 양 그리고 TPP 함량에 따른 실험을 진행하였으며 마이크로캡슐의 형성 및 열적 특성의 확인을 위해 DSC와 TGA에 의해 분석하였다. 또한 캡슐 입자의 형태학적 고찰을 위해 SEM과 TEM을 이용하여 캡슐의 크기 및 모폴로지 등을 분석하였다. 혼합된 유화제의 비율이 플로닉 F127과 소디움 도데실벤

Quantum technology offers great advantages in many applications by exploiting quantum resources like nonclassicality, coherence, and entanglement. In practice, an environmental noise unavoidably affects a quantum system and it is thus an important issue to protect quantum resources from noise. In this paper, we investigate the manipulation of quantum resources possessing the so-called tensorization property and identify the fundamental limitations on concentrating and preserving those quantum re

Abstract Quantum search algorithms offer a remarkable advantage of quadratic reduction in query complexity using quantum superposition principle. However, how an actual architecture may access and handle the database in a quantum superposed state has been largely unexplored so far; the quantum state of data was simply assumed to be prepared and accessed by a black-box operation—so-called oracle, even though this process, if not appropriately designed, may adversely diminish the quantum query adv

Abstract We suggest generalized robustness for quantifying nonlocality and derive its equivalence to the maximum violation ratio of Bell inequalities defined as vectors with non-negative elements. We investigate its properties by comparing it with white-noise and standard robustness measures. As a result, we show that white-noise robustness does not fulfill monotonicity under local operations and shared randomness, whereas the other measures do. To compare the standard and generalized robustness

In this work we investigate how to quantify the coherence of quantum measurements. First, we establish a resource theoretical framework to address the coherence of measurement and show that any statistical distance can be adopted to define a coherence monotone of measurement. For instance, the relative entropy fulfills all the required properties as a proper monotone. We specifically introduce a coherence monotone of measurement in terms of off-diagonal elements of Positive-Operator-Valued Measu