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Won-Young Hwang

Publications and source records attributed to Won-Young Hwang.

At least 19 recordsLinked to original sources
arXiv2026

Enhanced Precision in Entangled Quantum Clocks with Phase Estimation Algorithm

We present an enhanced entangled-quantum-clock protocol that incorporates a quantum phase estimation algorithm to directly estimate proper-time differences as an unknown phase. By employing highly entangled multi-clock states, the achievable uncertainty scales inversely with the total number of quantum clocks, achieving the Heisenberg limit $O(1/N)$ while remaining completely immune to dynamical phase noise. Furthermore, we discuss the feasibility of utilizing this ultra-high precision protocol for gravitational wave detection, highlighting its potential for quantum-enhanced relativistic sensing and fundamental physics tests.

quant-ph↗
arXiv2025

Quantum Statistics of Two Identical Particles and Modified Hong-Ou-Mandel Interferometer

We propose an experimental scheme to probe the quantum statistics of two identical particles. The transition between the quantum and classical statistics of two identical particles is described by the particles having identical multiple internal energy levels. We show that effective distinguishability emerges as the thermal energy increases with respect to the energy level spacing, and the mesoscopic regime bridges quantum indistinguishability and classical distinguishability. A realistic experimental approach is proposed using a two-particle interferometer, where the particles reach statistical equilibrium before the two-particle distribution is measured. The unitarity of the scattering/separation process ensures the preservation of the equilibrium distribution and allows a direct measurement of the two-particle statistical distribution. Our results show the transition between quantum and classical behavior of the two-particle distribution, which can be directly probed by a realistic experiment.

quant-ph↗
arXiv2018

$ψ$-Epistemic Models and Bell Theorem

We consider a question in what condition a mixed state which can be decomposed in different ways cannot be described by a single set of hidden variables. The condition is closely related with Bell theorem.

quant-ph↗
arXiv2016

General tradeoff relations of quantum nonlocality in the Clauser-Horne-Shimony-Holt scenario

General tradeoff relations present in nonlocal correlations of bipartite systems are studied, regardless of any specific quantum states and measuring directions. Extensions to multipartite scenarios are possible and very promising. Tsirelson's bound can be derived out in particular. The close connection with uncertainty relations is also presented and discussed.

quant-ph↗
arXiv2014

A Coherent View on Entropy

Informational entropy is often identified as physical entropy. This is surprising because the two quantities are differently defined and furthermore the former is a subjective quantity while the latter is an objective one. We describe the problems and then present a possible view that reconciles the two entropies. Informational entropy of a system is interpreted as physical entropy of a whole composed of both the system and "memories" containing information about the system.

quant-ph↗
arXiv2013

Optimal Discrimination of Qubit States - Methods, Solutions, and Properties

We show a geometric formulation for minimum-error discrimination of qubit states, that can be applied to arbitrary sets of qubit states given with arbitrary a priori probabilities. In particular, when qubit states are given with equal \emph{a priori} probabilities, we provide a systematic way of finding optimal discrimination and the complete solution in a closed form. This generally gives a bound to cases when prior probabilities are unequal. Then, it is shown that the guessing probability does not depend on detailed relations among given states, such as angles between them, but on a property that can be assigned by the set of given states itself. This also shows how a set of quantum states can be modified such that the guessing probability remains the same. Optimal measurements are also characterized accordingly, and a general method of finding them is provided.

quant-ph↗
arXiv2013

An Instructional Scaffolding for Intuitive Explanation of "Why does not a spinning top collapse?"

"Why does not a spinning top collapse?" is a puzzling question. Standard solution using angular momentum and torque is not intuitive enough. Thus intuitive explanations for the question have been proposed. We provide scaffolding for an intuitive explanation for the question. Accelerated point-masses in the top exert forces on the frame, which balances the effect due to gravity. The explanation is supplemented by the two following points. A more rigorous conceptual framework of the explanation is provided. A full calculation of trajectory is given. Nutation of spinning top is a difficult issue to understand physically. However, the nutation can also be understood by the intuitive explanation. We discuss another intuitive explanation.

physics.class-ph↗
arXiv2013

Optical Activity and Mirror-Symmetry

A misconception that non-chiral molecules have no optical activity at all is widespread. However, at molecular level even non-chiral molecules have optical activity. Optical activity of a non-chiral molecule is canceled out by that of another molecule in its mirror image in normal liquids. We describe the canceling mechanism by using mirror-symmetry of physical laws without resorting to detailed formulas. The description will be helpful for overcoming the misconception. Optical activity can be understood from the opposite viewpoint by the description. Aligned non-chiral molecules have optical activity.

physics.chem-ph↗
arXiv2013

No-signaling Quantum Key Distribution: Solution by Linear Programming

We outline a straightforward approach for obtaining a secret key rate using only no-signaling constraints and linear programming. Assuming an individual attack, we consider all possible joint probabilities. Initially, we study only the case where Eve has binary outcomes, and we impose constraints due to the no-signaling principle and given measurement outcomes. Within the remaining space of joint probabilities, by using linear programming, we get bound on the probability of Eve correctly guessing Bob's bit. We then make use of an inequality that relates this guessing probability to the mutual information between Bob and a more general Eve, who is not binary-restricted. Putting our computed bound together with the Csiszár-Körner formula, we obtain a positive key generation rate. The optimal value of this rate agrees with known results, but was calculated in a more straightforward way, offering the potential of generalization to different scenarios.

quant-ph↗
arXiv2012

Quantum State Discrimination with General Figures of Merit

We solve the problem of quantum state discrimination with "general (symmetric) figures of merit" for an even number of symmetric quantum bits with use of the no-signaling principle. It turns out that conditional probability has the same form for any figure of merit. Optimal measurement and corresponding conditional probability are the same for any monotonous figure of merit.

quant-ph↗
arXiv2012

How to Device-Independently Generate States for Which Unambiguous State Discrimination is Impossible

We describe how to device-independently generate a set of quantum states for which unambiguous state discrimination is not possible. First, we derive a formula that a certain non-signaling black box must satisfy. Then, we describe how to generate a set of quantum states. Devices for generating states and possible measurements on the states can be put into a black box. Because this black box is non-signaling, it satisfies the formula. Using the formula, we prove that unambiguous state discrimination is not possible for the generated states. Because we did not consider internal mechanisms but only outcomes, our argument is valid for any (imperfect) devices.

quant-ph↗
arXiv2012

Comment on "Security Proof for Cryptographic Protocols Based Only on Monogamy of Bell's Inequality Violations"

Recently, Pawlowski [Phys. Rev. A 82, 032313 (2010)] claimed to have proven the security of a quantum key distribution by using only the monogamy of Bell's inequality violations. In the proof, however, he tacitly assumed that the eavesdropper's outcome is binary. The assumption cannot be justified because Eve's (eavesdropper's) power can only be limited by natural principle. We provide a counter-example for a step of the proof.

quant-ph↗
arXiv2011

No-signaling Principle Can Determine Optimal Quantum State Discrimination

We provide a general framework of utilizing the no-signaling principle in derivation of the guessing probability in the minimum-error quantum state discrimination. We show that, remarkably, the guessing probability can be determined by the no-signaling principle. This is shown by proving that in the semidefinite programming for the discrimination, the optimality condition corresponds to the constraint that quantum theory cannot be used for a superluminal communication. Finally, a general bound to the guessing probability is presented in a closed form.

quant-ph↗
arXiv2010

Optimal Quantum State Estimation with Use of the No-Signaling Principle

A simple derivation of the optimal state estimation of a quantum bit was obtained by using the no-signaling principle. In particular, the no-signaling principle determines a unique form of the guessing probability independently of figures of merit, such as the fidelity or information gain. This proves that the optimal estimation for a quantum bit can be achieved by the same measurement for almost all figures of merit.

quant-ph↗