24 papers
The Classical Boundary of Quantum Computation: History-Resolved Causal Stochastic Machines and the Cost of Classicalization
Kyoungho Cho, Junghee Ryu, Minsu Kim +1
What separates quantum computation from classical computation when a classical model may retain every branch history and arbitrary causal memory? We study this question using histo…
Passive Pauli Toggling of Polarization Qubits in Optical Fibers: Error Bounds and QKD Performance
Bongjune Kim, Jeongho Bang
Polarization qubits offer a direct route to fiber-based quantum communication, yet the fiber that carries them also scrambles their reference frame through uncontrolled birefringen…
Phase-Flag Access and No-Go Constraints on Quotient-Space Real Quantum Mechanics
Jeongho Bang, Kyoungho Cho, Kyunghyun Baek
Barrios Hita et al. [Phys. Rev. Lett. 136, 240202 (2026)] proposed a quotient-space formulation of quantum mechanics over the real numbers and concluded that complex numbers are on…
Hayden--Preskill recovery at finite temperature on a quantum processor: dynamics and initial state from the SYK model
Jeongho Bang, Moongul Byun, Kyoungho Cho +2
In the original Hayden--Preskill recovery, the post-injection scrambler and initial state are {\it not related}. We extend this setup in two ways: by using a SWAP gate so that the…
Exact No Signaling in Time without Temporal Classicality
Minsu Kim, Jeongho Bang, Han Seb Moon
No signaling in time (NSIT) has often been treated as the clean operational remnant of noninvasive measurability. If an earlier measurement leaves every later marginal unchanged, t…
Hidden Complex Structure in Quotient-Space Real Quantum Mechanics
Jeongho Bang, Kyoungho Cho, Kyunghyun Baek
Barrios Hita et al. [Phys. Rev. Lett. , 240202 (2026)] argued that quantum mechanics can be formulated over the real numbers by replacing the tensor-product postulate wit…
Breaking the One-Dimensional Expressibility-Trainability Tradeoff
Kyoungho Cho, Yu-Seong Jeon, Jinhyoung Lee +1
Expressive parameterized quantum circuits (PQCs) are often designed under a dilemma: the growth of expressibility and entangling power (EP) that improves Hilbert-space coverage is…
First-Quantized Relativistic Quantum Simulation with Periodic and Dirichlet Boundary Conditions
Jeongho Bang, Timothy P. Spiller, Kyunghyun Baek +2
In this work, we present a methodology for first-quantized relativistic quantum simulation on one-dimensional finite domains under the two boundary conditions most commonly used in…
No Reference-Free Generalization in Quantum Machine Learning
Jeongho Bang
Quantum machine learning is often motivated by the exponentially large state space of quantum systems, but this promise leaves a basic generalization problem unresolved: how can a…
Quantum Occam Learning: Sample-Supported Expressibility for Circuit-Based Quantum Learning
Jeongho Bang, Kyoungho Cho, Jeongwoo Jae
A central principle in quantum machine learning is that an ansatz should be expressive enough to represent the quantum data of interest. Yet, the expressibility is statistically me…
Learning with Active Quantum Subspaces: Scalable Hybrid Advantage without Full Quantum Data-Encoding
Jeongho Bang, Wooyeong Song, Kyoungho Cho +2
We study whether quantum learning advantage can persist without fully embedding a large classical input into a highly superposed quantum state. To address this question, we introdu…
Causal Fisher-Information Inequalities: Classical Causal Model Falsification and Metrological Advantage
Jeongho Bang, Su-Yong Lee
Fisher-information inequalities have recently been used as operational witnesses of nonclassical metrological behavior, but their physical meaning is often tied to a particular nar…
Neural Information Causality: A Random-Access Capacity Law for Representation Learning
Jeongho Bang, Marcin Pawłowski
How can a learned representation remain useful when the question it must answer is chosen only after encoding? Preserving information is essential, but does not by itself ensure ac…
Finite Imaginary-Time Evolution for Polynomial Unconstrained Binary Optimization
Jaehee Kim, Juhyeon Kim, Gwonhak Lee +4
Imaginary-time evolution is a standard primitive for ground-state preparation but is nonunitary, precluding direct quantum implementation. We develop Finite Imaginary-Time Evolutio…
Universality cost of non-Gaussian enhancement in continuous-variable quantum teleportation: A fidelity--deviation trade-off
Kyoungho Cho, Bongjune Kim, Jeongho Bang
Continuous-variable (CV) quantum teleportation is usually benchmarked by average fidelity, but when the teleportation is repeatedly used within optical networks or measurement-base…
Single-shot measurement learning as a self-certifying estimator for quantum-enhanced sensing
Jeongho Bang
Single-shot measurement learning (SSML) learns a compensation unitary from a one-bit success/failure record and halts after a prescribed run of consecutive successes. We recast SSM…
Sharpening Worst-Case Error Assessment for Fault-Tolerant Quantum Computing: Fidelity and Its Deviation
Kyoungho Cho, Ilkwon Sohn, Yongsoo Hwang +1
Gate fidelity -- an average fidelity over all possible input states -- is the workhorse metric for benchmarking quantum gates or circuits, yet fault-tolerant quantum computing ulti…
A rigorous hybridization of variational quantum eigensolver with classical neural network
Minwoo James Kim, Kyoung Keun Park, Kyungmin Lee +2
Combining variational quantum process with classical neural learning offers a flexible route to improve ground-state estimation. We establish an integrated framework that connects…
Quantum Amplitude-Amplification Eigensolver: A State-Learning-Assisted Approach beyond Energy-Gradient-Based Heuristics
Kyunghyun Baek, Seungjin Lee, Joonsuk Huh +4
Ground-state estimation lies at the heart of a broad range of quantum simulations. Most near-term approaches are cast as variational energy minimization and thus inherit the challe…
Relativistic Quantum Simulation under Periodic and Dirichlet Boundary Conditions: A First-Quantised Framework for Near-Term Devices
Jaewoo Joo, Timothy P. Spiller, Kyunghyun Baek +1
We present a new recipe for relativistic quantum simulation using the first quantisation approach, under periodic (PBC) and Dirichlet (DBC) boundary conditions. The wavefunction is…
Fundamental limits to contrast reversal of survival probability correlations
Kyoungho Cho, Jeongho Bang
In measurement design, it is common to engineer anti-contrast readouts -- two measurements that respond as differently as possible to the same inputs so that contributions that aff…
Subspace Variational Quantum Simulation: Fidelity Lower Bounds as Measures of Training Success
Seung Park, Dongkeun Lee, Jeongho Bang +2
We propose an iterative variational quantum algorithm to simulate the time evolution of arbitrary initial states within a given subspace. The algorithm compresses the Trotter circu…
Quantum Simulation of Dynamical Transition Rates in Open Quantum Systems
Robson Christie, Kyunghyun Baek, Jeongho Bang +1
Estimating transition rates in open quantum systems is hampered by computing-resource demands that grow rapidly with system size. We present a quantum-simulation framework that ena…
Quantum superposing algorithm for quantum encoding
Jaehee Kim, Taewan Kim, Kyunghyun Baek +3
Efficient encoding of classical data into quantum state -- currently referred to as quantum encoding -- holds crucial significance in quantum computation. For finite-size databases…