arXiv subjects

En-Jui Chang

Publications and source records attributed to En-Jui Chang.

9 recordsLinked to original sources

arXiv2026

Discrete-variable assisted error correction of continuous-variable quantum information

Robust continuous-variable (CV) quantum information processing requires correcting realistic errors in bosonic systems, but all existing schemes rely on auxiliary Gottesman-Kitaev-Preskill (GKP) states which the preparation and operation are demanding in many platforms. In this work, we propose a novel CV quantum error correction (QEC) scheme that utilizes a broadly accessible resource: discrete-variable (DV) ancilla. Our scheme extracts information about CV displacement to the DV ancilla, measuring that allows counteracting the unwanted displacement error. We show that a simple single-qubit ancilla can already suppress CV infidelity by more than 20%. By concatenating with DV QEC codes, our scheme is robust against the physical errors in hybrid CV-DV systems, and yields a new class of oscillator-in-oscillator code that does not involve GKP states. Our work facilitates the implementation of CV QEC on realistic platforms.

quant-ph↗

arXiv2025

Overlapped-repetition Shor codes achieving fourfold asymptotic rate

Introducing controlled overlap among a few repetition blocks yields a fourfold asymptotic rate improvement while preserving an average stabilizer weight of $4$. Substituting the overlapped outer layer with an LDPC code further produces a family of constructions with asymptotic rate $2/d$. We also describe a constant-excitation variant that suppresses collective coherent errors without additional overhead, as well as a bosonic generalization that extends the framework to oscillator encodings. The resulting family achieves a code rate intermediate between that of the rotated surface code (average stabilizer weight $4$) and the BB code (average stabilizer weight $6$), while remaining free of the performance degradation typical of iterative decoders.

cs.IT↗

arXiv2025

Quantum keystroke logging

Superdense coding has long been regarded as a secure quantum communication protocol. It is natural to assume that employing logical quantum states with error-correcting capability would not compromise this security. However, in the context of GKP-based quantum communication, we propose a vulnerability that we term quantum keystroke logging. Specifically, consider a large organization that prepares and transmits logical Bell states without ever assembling the full encoded Bell state. Even under this restriction, the organization can still extract the input information without detection, thereby realizing a form of quantum keystroke logging.

quant-ph↗

arXiv2025

Quantum dual extended Hamming code immune to collective coherent errors

Collective coherent (CC) errors are inevitable, as every physical qubit undergoes free evolution under its kinetic Hamiltonian. These errors can be more damaging than stochastic Pauli errors because they affect all qubits coherently, resulting in high-weight errors that standard quantum error-correcting (QEC) codes struggle to correct. In quantum memories and communication systems, especially when storage durations are long, CC errors often dominate over stochastic noise. Trapped-ion platforms, for example, exhibit strong CC errors with minimal stochastic Pauli components. In this work, we address the regime where immunity to CC errors, high code rate (due to limited qubit availability), and moderate distance (sufficient for correcting low-weight errors) are all essential. We construct a family of constant-excitation (CE) stabilizer codes with parameters $[[2^{r+1}, 2^r - (r+1), 3]]$. The smallest instance, the $[[8,1,3]]$ code, improves the code rate and error threshold of the best previously known CE code by factors of approximately two and four, respectively.

quant-ph↗

arXiv2025

High-rate extended binomial codes for multiqubit encoding

We introduce a class of bosonic quantum error-correcting codes, termed \emph{extended binomial codes}, which generalize the structure of one-mode binomial codes by incorporating ideas from high-rate qubit stabilizer codes. These codes are constructed in close analogy to $[[n,k,d]]$ qubit codes, where the parameter $n$ corresponds to the total excitation budget rather than the number of physical qubits. Our construction achieves a significant reduction in average excitation per mode while preserving error-correcting capabilities, offering improved compatibility with hardware constraints in the strong-dispersive regime. We demonstrate that extended binomial codes not only reduce the mean excitation required for encoding but also simplify syndrome extraction and logical gate implementation, particularly the logical $\bar{X}$ operation. These advantages suggest that extended binomial codes offer a scalable and resource-efficient approach for bosonic quantum error correction.

quant-ph↗

arXiv2024

High-Rate Amplitude-Damping Shor Codes with Immunity to Collective Coherent Errors

We introduce a family of high-rate amplitude-damping (AD) Shor Codes, designed to effectively correct AD errors while maintaining immunity to collective coherent (CC) errors. The proposed $[[(w+1)(w+K), K]]$ AD codes can approximately correct up to $w$ AD errors, with flexible parameters $(w, K)$, and we provide a rigorous proof that these codes satisfy the approximate quantum error correction conditions. These codes leverage structured stabilizer measurements, enabling efficient detection of AD errors using only local operations and ancillary qubits. We further construct a family of CC-AD Shor codes by concatenating these AD codes with the dual-rail code.

quant-ph↗

arXiv2024

How to surpass no-go limits in Gaussian quantum error correction and entangled Gaussian state distillation?

Gaussian quantum information processing with continuous-variable (CV) quantum information carriers holds significant promise for applications in quantum communication and quantum internet. However, applying Gaussian state distillation and quantum error correction (QEC) faces limitations imposed by no-go results concerning local Gaussian unitary operations and classical communications. This paper introduces a Gaussian QEC protocol that relies solely on local Gaussian resources. A pivotal component of our approach is CV gate teleportation using entangled Gaussian states, which facilitates the implementation of the partial transpose operation on a quantum channel. Consequently, we can efficiently construct a two-mode noise-polarized channel from two noisy Gaussian channels. Furthermore, this QEC protocol naturally extends to a nonlocal Gaussian state distillation protocol.

quant-ph↗

arXiv2018

Holographic Superconductors: An Analytic Method Revisit

We study a non-minimal holographic superconductors model in both non-backreaction and fullbackreaction cases using an analytic method. We calculate the condensate of the dilaton and the critical temperature of the phase transition. We also study the properties of the electric conductivity in various parameters.

hep-th↗

arXiv2018

Holographic Entanglement Entropy in Boundary Quantum Field Theory

We study the holographic entanglement entropy in a (d+1)-dimensional boundary quantum field theory at both the zero and finite temperature. The phase diagrams for the holographic entanglement entropy at various temperatures are obtained by solving the entangled surfaces in the different homology. We also verify the Araki-Lieb inequality and illustrate the entanglement plateau.

hep-th↗