Nicholas J.C. Papadopoulos, PhD Candidate

Research & Projects

Project 1

Reductive Quantum Phase Estimation

N. J. C. Papadopoulos, J. T. Reilly, J. D. Wilson, and M. J. Holland, “Reductive quantum phase estimation,” Phys. Rev. Res., vol. 6, p. 033 051, 3 Jul. 2024. doi: 10.1103/PhysRevResearch.6.033051.

Abstract

Estimating a quantum phase is a necessary task in a wide range of fields of quantum science. To accomplish this task, two well-known methods have been developed in distinct contexts, namely, Ramsey interferometry (RI) in atomic and molecular physics and quantum phase estimation (QPE) in quantum computing. We demonstrate that these canonical examples are instances of a larger class of phase estimation protocols, which we call reductive quantum phase estimation (RQPE) circuits. Here, we present an explicit algorithm that allows one to create an RQPE circuit. This circuit distinguishes an arbitrary set of phases with a smaller number of qubits and unitary applications, thereby solving a general class of quantum hypothesis testing to which RI and QPE belong. We further demonstrate a tradeoff between measurement precision and phase distinguishability, which allows one to tune the circuit to be optimal for a specific application.

Presentation

ReductiveQuantumPhaseEstimation_Presentation.pdf

Project 2

Increasing Interference Detection in Quantum Cryptography using the Quantum Fourier Transform

N. J. C. Papadopoulos and K. Linvill, “Increasing interference detection in quantum cryptography using the quantum fourier transform,” in 2025 Future of Information and Communication Conference (FICC), 2025. url: https://arxiv.org/abs/2404.12507.

Abstract

Quantum key distribution (QKD) and quantum message encryption protocols promise a secure way to distribute information while detecting eavesdropping. However, current protocols may suffer from significantly reduced eavesdropping protection when only a subset of qubits are observed by an attacker. In this paper, we present two quantum cryptographic protocols leveraging the quantum Fourier transform (QFT) and show their higher effectiveness even when an attacker measures only a subset of the transmitted qubits. The foremost of these protocols is a novel QKD method that leverages this effectiveness of the QFT while being more practical than previously proposed QFT-based protocols, most notably by not relying on quantum memory. We additionally show how existing quantum encryption methods can be augmented with a QFT-based approach to improve eavesdropping detection. Finally, we provide equations to analyze different QFT-based detection schemes within these protocols so that protocol designers can make custom schemes for their purpose.

Presentation

QFT_Cryptography_Presentation.pdf

Project 3

Spectrum Sharing Dynamic Protection Area Neighborhoods for Radio Astronomy

N. Papadopoulos, M. Lofquist, A. W. Clegg, and K. Gifford, “Spectrum sharing dynamic protection area neighborhoods for radio astronomy,” in 2023 IEEE Wireless Communications and Networking Conference (WCNC), 2023, pp. 1–6. doi: 10.1109/WCNC55385.2023.10118800.

Abstract

To enforce incumbent protection through a spectrum access system (SAS) or future centralized shared spectrum system, dynamic protection area (DPA) neighborhood distances are employed. These distances are distance radii, in which citizen broadband radio service devices (CBSDs) are considered as potential interferers for the incumbent spectrum users. The goal of this paper is to create an algorithm to define DPA neighborhood distances for radio astronomy (RA) facilities with the intent to incorporate those distances into existing SASs and to adopt for future frameworks to increase national spectrum sharing. This paper first describes an algorithm to calculate sufficient neighborhood distances. Verifying this algorithm by recalculating previously calculated and currently used neighborhood distances for existing DPAs then proves its viability for extension to radio astronomy facilities. Applying the algorithm to the Hat Creek Radio Observatory (HCRO) with customized parameters results in distance recommendations, 112 kilometers for category A (devices with 30 dBm/10 MHz max EIRP) and 144 kilometers for category B (devices with 47 dBm/10MHz max EIRP), for HCRO’s inclusion into a SAS and shows that the algorithm can be applied to RA facilities in general. Calculating these distances identifies currently used but likely out-of-date metrics and assumptions that should be revisited for the benefit of spectrum sharing.

Presentation

WCNC Presentation

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