arXiv subjects

Steven van Enk

Publications and source records attributed to Steven van Enk.

5 recordsLinked to original sources

arXiv2023

Quantum state transfer and input-output theory with time reversal

Being able to reliably transfer the quantum state from one system to another is crucial to developing quantum networks. A standard way to accomplish this transfer of information is by making use of an intermediate information carrier (e.g., a photon) that is emitted by the first system and absorbed by the second. For such a scenario one can develop an effective description by eliminating the intermediate degrees of freedom, which yields an effective direct coupling between the two systems. If, however, the spectral properties of the two systems are different, the photon's time-frequency shape needs to be appropriately modified before it reaches the second system. We study here the effective description that results when we thus manipulate the intermediate photon. We examine a unitary transformation, $U$, that time reverses, frequency translates, and stretches the photon wave packet. We find that the concomitant modifications to the effective description can best be understood in terms of a change to the state's time argument, $ρ(t) = ρ_1(\tilde{t}) \otimes ρ_2(t)$, where $\tilde{t}$ is a fictitious time for the first system that is stretched and runs backward. We apply this theory to three-level $Λ$-systems inside optical cavities, and we numerically illustrate how performing the unitary transformation $U$ results in improved quantum state transfer.

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arXiv2017

The Born rule as a parallel transport equation: Detecting multiqudit state-preparation and measurement correlations

In the context of quantum tomography, we recently introduced a quantity called a partial determinant \cite{jackson2015detecting}. PDs (partial determinants) are explicit functions of the collected data which are sensitive to the presence of state-preparation-and-measurement (SPAM) correlations. Importantly, this is done without any need to estimate state-preparation or measurement parameters. In the present work, we wish to better explain our theoretical perspective behind the PD. Further, we would like to demonstrate that there is an overwhelming variety of applications and generalizations of the PD. In particular we will construct methods for detecting SPAM correlations in multiqudit systems. The relationship between the PDs of each method and the correlations they are sensitive to is topological. We give a classification of all such methods but focus on explicitly detailing only the most scalable methods, $\mathcal{O}(d^4)$.

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arXiv2017

Non-holonomic tomography I: The Born rule as a connection between experiments

In the context of quantum tomography, we recently introduced a quantity called a partial determinant \cite{jackson2015detecting}. PDs (partial determinants) are explicit functions of the collected data which are sensitive to the presence of state-preparation-and-measurment (SPAM) correlated errors. As such, PDs bypass the need to estimate state-preparation or measurement parameters individually. In the present work, we suggest a theoretical perspective for the PD. We show that the PD is a holonomy and that the notions of state, measurement, and tomography can be generalized to non-holonomic constraints. To illustrate and clarify these abstract concepts, direct analogies are made to parallel transport, thermodynamics, and gauge field theory. This paper is the first of a two part series where the second paper [2] is about scalable applications of the PD to multiqudit systems.

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arXiv2017

Non-holonomic tomography II: Detecting correlations in multiqudit systems

In the context of quantum tomography, quantities called a partial determinants\cite{jackson2015detecting} were recently introduced. PDs (partial determinants) are explicit functions of the collected data which are sensitive to the presence of state-preparation-and-measurement (SPAM) correlations. In this paper, we demonstrate further applications of the PD and its generalizations. In particular we construct methods for detecting various types of SPAM correlation in multiqudit systems | e.g. measurement-measurement correlations. The relationship between the PDs of each method and the correlations they are sensitive to is topological. We give a complete classification scheme for all such methods but focus on the explicit details of only the most scalable methods, for which the number of settings scale as $\mathcal{O}(d^4)$. This paper is the second of a two part series where the first paper[2] is about theoretical perspectives of the PD and its interpretation as a holonomy.

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arXiv2013

Error models in quantum computation: an application of model selection

Threshold theorems for fault-tolerant quantum computing assume that errors are of certain types. But how would one detect whether errors of the "wrong" type occur in one's experiment, especially if one does not even know what type of error to look for? The problem is that for many qubits a full state description is impossible to analyze, and a full process description is even more impossible to analyze. As a result, one simply cannot detect all types of errors. Here we show through a quantum state estimation example (on up to 25 qubits) how to attack this problem using model selection. We use, in particular, the Akaike Information Criterion. The example indicates that the number of measurements that one has to perform before noticing errors of the wrong type scales polynomially both with the number of qubits and with the error size.

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