arXiv subjects

Shang-Jen Su

Publications and source records attributed to Shang-Jen Su.

3 recordsLinked to original sources

arXiv2026

A Quantum-Memory-Free Quantum Secure Direct Communication Protocol Based on Privacy Amplification of Coded Sequences

We develop an information-theoretic analysis of Quantum-Memory-Free (QMF) Quantum Secure Direct Communication (QSDC) under collective attacks as an alternative to the use of a conventional Quantum Key Distribution (QKD) protocol in conjunction with one-time pads. Our main contributions are: 1) a QMF-QSDC protocol that only relies on universal hashing of coded sequences without wiretap coding; 2) a set of privacy amplification theorems for extracting secrecy from coded classical sequences against quantum side-information. These tools open the way to the design of effective QMF-QSDC protocols.

quant-ph↗

arXiv2025

Joint Communication and Sensing with Bipartite Entanglement over Bosonic Channels

We consider a joint communication and sensing problem over an optical link in which a low-power transmitter simultaneously communicates with a receiver and identifies the range of a defect producing a backscattered signal. We model the system as a lossy thermal-noise bosonic channel, in which the target location, modeled as a beamsplitter, affects the timing of the backscattered signal. Motivated by the envisioned deployment of entanglement-enabled quantum networks, we allow the transmitter to exploit shared entanglement to assist both sensing and communication. Since entanglement is known to enhance sensing, as demonstrated in Quantum Illumination (QI), and to increase communication rates through entanglement-assisted communication, the transmitter faces a trade-off in allocating its entanglement resources between the two tasks. Our main result is a characterization of these trade-offs in the form of an achievable rate/error-exponent region, which can outperform time-sharing and demonstrates a quantum advantage.

quant-ph↗

arXiv2024

Quantum Ring States

Quantum ring states are non-Gaussian mixed states generated by uniformly modulating the phase of one arm of a bipartite Gaussian quantum resource and transmitting the modulated arm through a lossy thermal bosonic channel. For resources such as two-mode squeezed vacuum (TMSV) states and split coherent states, the continuous phase modulation produces classical states that are diagonal in the Fock basis and fully characterized by photon-number distributions involving hypergeometric functions. We precisely characterize how well states obtained with a finite m-ary phase-shift keying (PSK) modulation approximate quantum ring states. We also leverage bounds on hypergeometric functions to develop closed-form and surprisingly tight bounds for information-theoretic quantities involving quantum ring states, such as the von Neumann entropy and the associated Holevo information. We demonstrate the usefulness of quantum ring states by revisiting several canonical problems and deriving new results including: 1) closed-form achievable communication rates with PSK modulation for lossy thermal bosonic channels over a broad range of channel parameters; 2) improved achievable covert throughputs for one-way and round-trip lossy thermal bosonic channels.

quant-ph↗