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Item type:Publication, Access status: with files , Randomized quantum measurements beyond the Clifford group(2026); Randomized quantum measurements with the multi-qubit Clifford group can reconstruct many properties from the same experimental data. However, their implementation is beyond the capabilities of near-term devices. This thesis analyzes randomized protocols beyond group designs, with a focus on shadow estimation and randomized benchmarking. We provide an analytic characterization of shadow estimation with short random quantum circuits, and extend randomized benchmarking to photonic platforms to benchmark passive Gaussian transformations.Publicationtype: Doctoral Thesis38 30 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Engineering qubit dynamics in open systems with photonic synthetic lattices(American Physical Society (APS), 2025-06-06); ; ; ; The evolution of a quantum system interacting with an environment can be described as a unitary process acting on both the system and the environment. In this framework, the system's evolution can be predicted by tracing out the environmental degrees of freedom. Here, we establish a precise mapping between the global unitary dynamics and the quantum operation involving the system, wherein the system is a single qubit, and the environment is modeled as a discrete lattice space. This approach enables the implementation of arbitrary noise operations on single-polarization qubits using a minimal set of three liquid-crystal metasurfaces, whose transverse distribution of the optic axes can be patterned to reproduce the target process. We experimentally validate this method by simulating common noise processes, such as phase errors and depolarization. Besides providing a practical solution for quantum state purification, this work demonstrates a versatile approach for the simulation of open qubit dynamics, with potential implications for quantum error correction and environment-induced quantum phase transitions.Publicationtype: Journal Article45 15 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Bosonic Randomized Benchmarking with Passive Transformations(American Physical Society (APS), 2025-04-07); ; ; Randomized benchmarking (RB) is the most commonly employed protocol for the characterization of unitary operations in quantum circuits due to its reasonable experimental requirements and robustness against state preparation and measurement (SPAM) errors. So far, the protocol has been limited to discrete or fermionic systems, whereas extensions to bosonic systems have been unclear for a long time due to challenges arising from the underlying bosonic Hilbert space. In this work, we close the gap for bosonic systems and develop an RB protocol to benchmark passive Gaussian transformations on any particle-number subspace, hich we call passive bosonic RB. The protocol is built on top of the recently developed filtered RB framework [J. Helsen et al., PRX Quantum 3, 020357 (2022), M. Heinrich et al., Randomized benchmarking with random quantum circuits, arxiv:2212.06181 [quant-ph]] and is designed to isolate the multitude of exponential decays arising for passive bosonic transformations. We give explicit formulas and a Julia implementation for the necessary postprocessing of the experimental data. We also analyze the sampling complexity of passive bosonic RB by deriving analytical expressions for the variance. They show a mild scaling with the number of modes, suggesting that passive bosonic RB is experimentally feasible for a moderate number of modes. We focus on experimental settings involving Fock states and particle-number-resolving measurements, but also discuss Gaussian settings, deriving the first results for heterodyne measurements.Publicationtype: Journal Article20 24 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Closed-form analytic expressions for shadow estimation with brickwork circuits(2023-09); ; ; Properties of quantum systems can be estimated using classical shadows, which implement measurements based on random ensembles of unitaries. Originally derived for global Clifford unitaries and products of single-qubit Clifford gates, practical implementations are limited to the latter scheme for moderate numbers of qubits. Beyond local gates, the accurate implementation of very short random circuits with two-local gates is still experimentally feasible and, therefore, interesting for implementing measurements in near-term applications. In this work, we derive closed-form analytical expressions for shadow estimation using brickwork circuits with two layers of parallel two-local Haar-random (or Clifford) unitaries. Besides the construction of the classical shadow, our results give rise to sample-complexity guarantees for estimating Pauli observables. We then compare the performance of shadow estimation with brickwork circuits to the established approach using local Clifford unitaries and find improved sample complexity in the estimation of observables supported on sufficiently many qubits.Publicationtype: Journal Article56