arXiv subjects

Nicholas J. C. Papadopoulos

Publications and source records attributed to Nicholas J. C. Papadopoulos.

5 recordsLinked to original sources

arXiv2026

Stabilizer Code-Generic Universal Fault-Tolerant Quantum Computation

Fault-tolerant quantum computation allows quantum computations to be carried out while resisting unwanted noise. Several error-correcting codes have been developed to achieve this task, but none alone are capable of universal quantum computation. This universality is highly desired and often achieved using additional techniques such as code concatenation, code switching, magic state distillation, or pieceable fault tolerance, which can be costly and only work for specific codes. This work proposes a new direction by implementing logical Clifford and T gates through novel ancilla-mediated protocols to construct a universal fault-tolerant quantum gate set. Unlike traditional techniques, our implementation is deterministic, does not consume ancilla registers, does not modify the underlying data codes or registers, and is generic over all stabilizer codes. Thus, any single code becomes capable of universal quantum computation by leveraging helper codes in ancilla registers and mid-circuit measurements. Furthermore, since these logical gates are stabilizer code-generic, these implementations enable communication between heterogeneous stabilizer codes. These features collectively open the door to countless possibilities for existing and yet undiscovered codes as well as their scalable, heterogeneous coexistence.

quant-ph↗

arXiv2026

BloQBench: A Blockchain Benchmarking Framework for Quantum Supremacy

As quantum computing matures, characterizing its practical workloads and verifying quantum supremacy presents a significant challenge. Current benchmarking and claims rely on trust-based verification methods that lack public auditability. We propose a decentralized benchmarking framework implemented via an Ethereum smart contract to provide verifiable assurance in these claims. This framework generates classically intractable puzzles that, crucially, require absolutely no pre-computed secrets. By utilizing the blockchain as an immutable public ledger, independent observers can mathematically verify that any provided solution to the puzzle must have been computationally derived via quantum hardware rather than classically spoofed. Furthermore, we demonstrate how this verifiable benchmarking metric can be utilized as an automation trigger. As a practical example of such a trigger, we focus on the ability for blockchains to automatically switch to quantum-secure signature schemes upon the successful demonstration of cryptographic quantum supremacy. We demonstrate these principles with BloQBench, which implements the concept using integer factorization as the generated puzzle and Lamport signatures as the trigger-based effect. This approach demonstrates a novel use of distributed ledgers for quantum workload characterization, providing a transparent, automated metric for measuring quantum supremacy while managing the performance and complexity trade-offs of post-quantum technology transitions.

cs.CR↗

arXiv2025

Southwest Tree: A Low-Memory Data Structure for Partial Accumulations by Non-Commutative Invertible Operations

The task of accumulating a portion of a list of values, whose values may be updated at any time, is widely used throughout various applications in computer science. While it is trivial to accomplish this task without any constraints, trivial solutions often sacrifice time complexity in either accumulating or updating the values, one being constant time and the other being linear. To even out the complexity, two well-known data structures have been used to accomplish this task, namely the Segment Tree and the Binary Indexed Tree, which are able to carry out both tasks in O(log_2 N) time for a list of N elements. However, the Segment Tree suffers from requiring auxiliary memory to contain additional values, while the Binary Indexed Tree is unable to handle non-commutative accumulation operations. Here, we present a data structure, called the Southwest Tree, that accomplishes these tasks for non-commutative, invertible accumulation operations in O(log_2 N) time and uses no additional memory to store the structure apart from the initial input array.

cs.DS↗

arXiv2024

Increasing Interference Detection in Quantum Cryptography using the Quantum Fourier Transform

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.

quant-ph↗

arXiv2024

Reductive Quantum Phase Estimation

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 fewer 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 trade-off between measurement precision and phase distinguishability, which allows one to tune the circuit to be optimal for a specific application.

quant-ph↗