arXiv subjects

Jiyoung Yun

Publications and source records attributed to Jiyoung Yun.

9 recordsLinked to original sources

arXiv2026

Structured Masked Diffusion for Joint Multiuser Decoding

In joint multiuser decoding, a receiver recovers a set of messages from a single noisy aggregate of many simultaneous transmissions. Classical decoders rely on rule-based mechanisms such as successive interference cancellation, joint belief propagation, or list recovery, all of which become brittle or expensive as ambiguity increases. We propose CIDER, a learned multiuser decoder with masked-diffusion refinement steps. CIDER uses demixing to prevent duplicate-row collapse and uses parity-aware propagation to provide soft guidance from the code constraints. In higher-load regimes, we further improve reliability via a lightweight quality-guided remasking step that selectively re-decodes low-confidence sequences. On commonly used error-correcting codes, CIDER matches or improves on FFT-accelerated joint belief propagation-style decoding in symbol error rate while running more than $6\times$ to over $100\times$ faster, with the speedup widening as the blocklength grows. Code is available at https://github.com/jiyunyoung/CIDER.

cs.IT↗

arXiv2025

Enhancing Sum Capacity via Quantum and No-Signaling Cooperation Between Transmitters

We consider communication over discrete memoryless interference channels or multiple access channels without feedback, where transmitters exploit classical, quantum, or no-signaling cooperation. Previous works have shown that, for channels associated with pseudo-telepathy games, quantum or no-signaling cooperation can increase the sum capacity. However, a full characterization of channels admitting such an improvement remains open. Motivated by common features of previously studied examples, we propose a broader class of game-induced channels. In these channels, each input is a question-answer pair from a nonlocal game. When the inputs satisfy the game's winning condition, the channel has lower conditional output uncertainty, and the channel decomposes into parallel weakly symmetric subchannels with a unique capacity-achieving input distribution. We show that, for this class, quantum or no-signaling cooperation strictly increases the sum capacity whenever the associated game is a quantum or no-signaling pseudo-telepathy game, respectively. The proposed class recovers several previously studied channels and includes new examples.

quant-ph↗

arXiv2025

Protocol for Purifying Noisy Preparation and Measurements of Qubits

Noise affecting qubit preparation and measurements accounts for a significant fraction of errors in quantum information processing. This is especially critical in tasks like variational quantum algorithms, quantum error correction, and entanglement distribution through repeaters. In this work, we present a protocol to purify noisy SPAM, effectively suppressing these errors to an arbitrarily low level. For instance, in a realistic scenario where qubits contain error rates around $0.05$ in both preparation and measurement, the protocol can suppress error rates up to $10^{-3}$ with two ancillas and $10^{-6}$ with four ancillas. We show how to distill error-free SPAM by repeating noisy SPAMs. The protocol is also feasible with superconducting qubits. We envisage that our results can be used to realize quantum information tasks in computing and communication with negligible SPAM errors.

quant-ph↗

arXiv2025

Purification of Noisy Measurements and Faithful Distillation of Entanglement

We consider entanglement distillation with noisy operations in which quantum measurements that constitute a general quantum operation are particularly noisy. We present a protocol for purifying noisy measurements and show that imperfect local operations can distill entanglement. The protocol works for arbitrary noisy measurements in general and is cost-effective and resource-efficient with single additional qubit per party to resolve the distillation of entanglement. The purification protocol is feasible with currently available quantum technologies and readily applied to entanglement applications.

quant-ph↗

arXiv2024

Double-sided van der Waals epitaxy of topological insulators across an atomically thin membrane

Atomically thin van der Waals (vdW) films provide a novel material platform for epitaxial growth of quantum heterostructures. However, unlike the remote epitaxial growth of three-dimensional bulk crystals, the growth of two-dimensional (2D) material heterostructures across atomic layers has been limited due to the weak vdW interaction. Here, we report the double-sided epitaxy of vdW layered materials through atomic membranes. We grow vdW topological insulators (TIs) Sb$_2$Te$_3$ and Bi$_2$Se$_3$ by molecular beam epitaxy on both surfaces of atomically thin graphene or hBN, which serve as suspended 2D vdW "$\textit{substrate}$" layers. Both homo- and hetero- double-sided vdW TI tunnel junctions are fabricated, with the atomically thin hBN acting as a crystal-momentum-conserving tunnelling barrier with abrupt and epitaxial interface. By performing field-angle dependent magneto-tunnelling spectroscopy on these devices, we reveal the energy-momentum-spin resonant tunnelling of massless Dirac electrons between helical Landau levels developed in the topological surface states at the interface.

cond-mat.mtrl-sci↗

arXiv2024

Static Quantum Errors and Purification

State preparation that initializes quantum systems in a fiducial state and measurements to read outcomes after the evolution of quantum states, both essential elements in quantum information processing in general, may contain noise from which errors, in particular, referred to as static errors, may appear even with noise-free evolution. In this work, we consider noisy resources such as faulty manufacturing and improper maintenance of systems by which static errors in state preparation and measurement are inevitable. We show how to suppress static errors and purify noiseless SPAM by repeatedly applying noisy resources. We present the purification protocol for noisy initialization and noisy measurements and verify that a few qubits are immediately cost-effective to suppress error rates up to $10^{-3}$. We also demonstrate the purification protocol in a realistic scenario. The results are readily feasible with current quantum technologies.

quant-ph↗

arXiv2024

Analog-Digital Beam Focusing for Line of Sight Wide-Aperture MIMO with Spherical Wavefronts

Enhancing high-speed wireless communication in the future relies significantly on harnessing high frequency bands effectively. These bands predominantly operate in line-of-sight (LoS) paths, necessitating well-configured antenna arrays and beamforming techniques for optimal spectrum utilization. Maximizing the potential of LoS multiple-input multiple-output (MIMO) systems, which are crucial for achieving high spectral efficiency, heavily depends on this. As the costs and power demands of mixed-signal devices in high frequency bands make a fully-digital architecture impractical for large-scale MIMO setups, our focus shifts to a hybrid analog-digital hardware configuration. Yet, analog processors' limitations restrict flexibility within arrays, necessitating a nuanced understanding of hardware constraints for optimal antenna configuration design. We explore array design that optimizes the spectral efficiency of hybrid systems, considering hardware constraints. We propose an optimal antenna configuration, leveraging the prolate matrix structure of the LoS channel between two planar arrays. Building on the optimal array configuration, we introduce a low-complexity explicit analog-digital beam focusing scheme that exploits the asymptotic behavior of the LoS channel matrix in the near-field region. Simulation results validate that the proposed antenna configuration and beam focusing scheme achieves near-optimal performance across a range of signal-to-noise ratios with low computational complexity, even under arbitrary rotations relative to the communication link.

cs.IT↗

arXiv2023

Nonlocal and quantum advantages in network coding for multiple access channels

In this work, we consider two-sender, one-receiver communication over a discrete memoryless multiple-access channel without feedback, where two senders may cooperate on channel coding by using preshared resources, such as shared randomness, quantum states and measurements, or nonlocal correlations. We present the capacity region when senders employ cooperative encoding with quantum and nonlocal resources, extending beyond shared randomness, and derive a sum rate that serves as a lower bound to the sum capacity; the lower bound is computable by exploiting specific strategies. We also compute the sum capacities for two instances. One is when senders apply local resources for cooperative encoding. The other is when senders exploit nonclassical resources for encoding against channels constructed by referring to nonlocal games; in this way, correlated noise other than independent errors occurs on code words. Comparing the exact sum capacities and lower bounds, we show that nonlocal and quantum resources for cooperative encoding enable higher sum capacities over local ones. The Clauser-Horne-Shimony-Holt and magic square games are considered for constructing multiple-access channels, and we demonstrate the usefulness of nonlocal and quantum resources to achieve higher-sum capacities.

quant-ph↗

arXiv2020

Non-Local Network Coding in Interference Channels

In a network, a channel introduces correlations to the parties that aim to establish a communication protocol. In this work, we present a framework of non-local network coding by exploiting a Bell scenario and show the usefulness of non-local and quantum resources in network coding. Two-sender and two-receiver interference channels are considered, for which network coding is characterized by two-input and four-outcome Bell scenarios. It is shown that non-signaling (quantum) correlations lead to strictly higher channel capacities in general than quantum (local) correlations. It is also shown that, however, more non-locality does not necessarily imply a higher channel capacity. The framework can be generally applied to network communication protocols.

quant-ph↗