arXiv subjects

Seungchan Seo

Publications and source records attributed to Seungchan Seo.

6 recordsLinked to original sources

arXiv2026

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↗

arXiv2026

Mitigation of Crosstalk Errors in Quantum Measurements

In the present-day quantum information technologies, measurements are performed not only at the end of quantum state evolution but also between quantum circuits to connect short-depth quantum circuits, for instance, variational quantum algorithms. Furthermore, measurements also contain crosstalk errors, which cannot be factorized into individual readout errors. In this work, we investigate methods for mitigating measurement errors across multiple qubits, particularly measurement crosstalk that cannot be corrected by methods for correcting individual readout errors. We present mitigation protocols that generally suppress these errors by up to a percentage level across multiple qubits. We first demonstrate that mitigating measurement errors of individual qubits cannot eliminate measurement crosstalk errors. We then present methods for mitigating measurement readout errors across multiple qubits, accounting for crosstalk noise. Both methods rely on quantum detector tomography. We also present proof-of-principle demonstrations of measurement error mitigation on IBM quantum hardware.

quant-ph↗

arXiv2026

Practical and Efficient Verification of Entanglement with Incomplete Measurement Settings

In this work, we present a practical and efficient framework for verifying entangled states when only a tomographically incomplete measurement setting is available-specifically, when access to observables is severely limited. We show how the experimental estimation of a small number of observables can be directly exploited to construct a large family of entanglement witnesses, enabling the efficient identification of entangled states. Moreover, we introduce an optimization approach, formulated as a semidefinite program, that systematically searches for those witnesses best suited to reveal entanglement under the given measurement constraints. We demonstrate the practicality of the approach in a proof-of-principle experiment with photon-polarization qubits, where entanglement is certified using only a fraction of the full measurement data. These results reveal the maximal usefulness of incomplete measurement settings for entanglement verification in realistic scenarios.

quant-ph↗

arXiv2024

Machine-learning certification of multipartite entanglement for noisy quantum hardware

Entanglement is a fundamental aspect of quantum physics, both conceptually and for its many applications. Classifying an arbitrary multipartite state as entangled or separable -- a task referred to as the separability problem -- poses a significant challenge, since a state can be entangled with respect to many different of its partitions. We develop a certification pipeline that feeds the statistics of random local measurements into a non-linear dimensionality reduction algorithm, to determine with respect to which partitions a given quantum state is entangled. After training a model on randomly generated quantum states, entangled in different partitions and of varying purity, we verify the accuracy of its predictions on simulated test data, and finally apply it to states prepared on IBM quantum computing hardware.

quant-ph↗

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↗

arXiv2021

Measurement Crosstalk Errors in Cloud-Based Quantum Computing

Quantum technologies available currently contain noise in general, often dubbed noisy intermediate-scale quantum (NISQ) systems. We here present the verification of noise in measurement readout errors in cloud-based quantum computing services, IBMQ and Rigetti, by directly performing quantum detector tomography, and show that there exist measurement crosstalk errors. We provide the characterization and the quantification of noise in a quantum measurement of multiple qubits. We remark that entanglement is found as a source of crosstalk errors in a measurement of three qubits.

quant-ph↗