All Outputs (16)

General upper bounds on fluctuations of trajectory observables (2023)
Journal Article

Thermodynamic uncertainty relations (TURs) are general lower bounds on the size of fluctuations of dynamical observables. They have important consequences, one being that the precision of estimation of a current is limited by the amount of entropy pr... Read More about General upper bounds on fluctuations of trajectory observables.

Projected Least-Squares Quantum Process Tomography (2022)
Journal Article

We propose and investigate a new method of quantum process tomography (QPT) which we call projected least squares (PLS). In short, PLS consists of first computing the least-squares estimator of the Choi matrix of an unknown channel, and subsequently... Read More about Projected Least-Squares Quantum Process Tomography.

Large deviations, central limit, and dynamical phase transitions in the atom maser (2022)
Journal Article

The theory of quantum jump trajectories provides a new framework for understanding dynamical phase transitions in open systems. A candidate for such transitions is the atom maser, which for certain parameters exhibits strong intermittency in the atom... Read More about Large deviations, central limit, and dynamical phase transitions in the atom maser.

Parameter estimation and system identification for continuously-observed quantum systems (2022)
Journal Article

This paper gives an overview of parameter estimation and system identification for quantum input–output systems by continuous observation of the output field. We present recent results on the quantum Fisher information of the output with respect to u... Read More about Parameter estimation and system identification for continuously-observed quantum systems.

Fast state tomography with optimal error bounds (2020)
Journal Article

Projected least squares is an intuitive and numerically cheap technique for quantum state tomography: compute the least-squares estimator and project it onto the space of states. The main result of this paper equips this point estimator with rigorous... Read More about Fast state tomography with optimal error bounds.

A comparative study of estimation methods in quantum tomography (2019)
Journal Article

As quantum tomography is becoming a key component of the quantum engineering toolbox, there is a need for a deeper understanding of the multitude of estimation methods available. Here we investigate and compare several such methods: maximum likelihoo... Read More about A comparative study of estimation methods in quantum tomography.

Local asymptotic equivalence of pure states ensembles and quantum Gaussian white noise (2018)
Journal Article
Butucea, C., Guţă, M., & Nussbaum, M. (2018). Local asymptotic equivalence of pure states ensembles and quantum Gaussian white noise. Annals of Statistics, 46(6B), 3676-3706. https://doi.org/10.1214/17-aos1672

Quantum technology is increasingly relying on specialised statistical inference methods for analysing quantum measurement data. This motivates the development of “quantum statistics”, a field that is shaping up at the overlap of quantum physics and “... Read More about Local asymptotic equivalence of pure states ensembles and quantum Gaussian white noise.

Catching and reversing quantum jumps and thermodynamics of quantum trajectories (2018)
Journal Article
Garrahan, J. P., & Guta, M. (2018). Catching and reversing quantum jumps and thermodynamics of quantum trajectories. Physical Review A, 98(5), Article 052137. https://doi.org/10.1103/PhysRevA.98.052137

A recent experiment by Minev et. al [arXiv:1803.00545] demonstrated that in a dissipative (artificial) 3-level atom with strongly intermittent dynamics it is possible to " catch and reverse " a quantum jump " mid-flight " : by the conditional applica... Read More about Catching and reversing quantum jumps and thermodynamics of quantum trajectories.

Minimax estimation of qubit states with Bures risk (2018)
Journal Article
Acharya, A., & Guţă, M. (2018). Minimax estimation of qubit states with Bures risk. Journal of Physics A: Mathematical and Theoretical, 51(17), 1-27. https://doi.org/10.1088/1751-8121/aab6f2

The central problem of quantum statistics is to devise measurement schemes for the estimation of an unknown state, given an ensemble of n independent identically prepared systems. For locally quadratic loss functions, the risk of standard procedures... Read More about Minimax estimation of qubit states with Bures risk.

Information geometry and local asymptotic normality for multi-parameter estimation of quantum Markov dynamics (2017)
Journal Article
Guţă, M., & Kiukas, J. (in press). Information geometry and local asymptotic normality for multi-parameter estimation of quantum Markov dynamics. Journal of Mathematical Physics, 58, https://doi.org/10.1063/1.4982958

This paper deals with the problem of identifying and estimating dynamical parameters of continuous-time Markovian quantum open systems, in the input-output formalism. First, we characterise the space of identifiable parameters for ergodic dynamics, a... Read More about Information geometry and local asymptotic normality for multi-parameter estimation of quantum Markov dynamics.

Statistical analysis of compressive low rank tomography with random measurements (2017)
Journal Article
Acharya, A., & Guţă, M. (in press). Statistical analysis of compressive low rank tomography with random measurements. Journal of Physics A: Mathematical and Theoretical, 50(19), https://doi.org/10.1088/1751-8121/aa682e

We consider the statistical problem of 'compressive' estimation of low rank states (r«d ) with random basis measurements, where r, d are the rank and dimension of the state respectively. We investigate whether for a fixed sample size N, the estimatio... Read More about Statistical analysis of compressive low rank tomography with random measurements.

Identification of single-input–single-output quantum linear systems (2017)
Journal Article
Levitt, M., & Guţă, M. (in press). Identification of single-input–single-output quantum linear systems. Physical Review A, 95(3), Article 033825. https://doi.org/10.1103/PhysRevA.95.033825

The purpose of this paper is to investigate system identification for single-input–single-output general (active or passive) quantum linear systems. For a given input we address the following questions: (1) Which parameters can be identified by measu... Read More about Identification of single-input–single-output quantum linear systems.

Towards a Theory of Metastability in Open Quantum Dynamics (2016)
Journal Article
Macieszczak, K., Guţă, M., Lesanovsky, I., & Garrahan, J. P. (2016). Towards a Theory of Metastability in Open Quantum Dynamics. Physical Review Letters, 116(24), Article 240404. https://doi.org/10.1103/PhysRevLett.116.240404

© 2016 American Physical Society. By generalizing concepts from classical stochastic dynamics, we establish the basis for a theory of metastability in Markovian open quantum systems. Partial relaxation into long-lived metastable states - distinct fro... Read More about Towards a Theory of Metastability in Open Quantum Dynamics.

Fisher informations and local asymptotic normality for continuous-time quantum Markov processes (2015)
Journal Article
Catana, C., Bouten, L., & Guţă, M. (2015). Fisher informations and local asymptotic normality for continuous-time quantum Markov processes. Journal of Physics A: Mathematical and Theoretical, 48(36), Article 365301. https://doi.org/10.1088/1751-8113/48/36/365301

We consider the problem of estimating an arbitrary dynamical parameter of an open quantum system in the input–output formalism. For irreducible Markov processes, we show that in the limit of large times the system-output state can be approximated by... Read More about Fisher informations and local asymptotic normality for continuous-time quantum Markov processes.

Sanov and central limit theorems for output statistics of quantum Markov chains (2015)
Journal Article
Horssen, M. V., & Guţă, M. (2015). Sanov and central limit theorems for output statistics of quantum Markov chains. Journal of Mathematical Physics, 56(2), Article 022109. https://doi.org/10.1063/1.4907995

In this paper, we consider the statistics of repeated measurements on the output of a quantum Markov chain. We establish a large deviations result analogous to Sanov’s theorem for the multi-site empirical measure associated to finite sequences of con... Read More about Sanov and central limit theorems for output statistics of quantum Markov chains.

Equivalence classes and local asymptotic normality in system identification for quantum Markov chains (2014)
Journal Article
Guţă, M., & Kiukas, J. (2015). Equivalence classes and local asymptotic normality in system identification for quantum Markov chains. Communications in Mathematical Physics, 335(3), https://doi.org/10.1007/s00220-014-2253-0

We consider the problem of identifying and estimating dynamical parameters of an ergodic quantum Markov chain, when only the stationary output is accessible for measurements. The starting point of the analysis is the fact that the knowledge of the ou... Read More about Equivalence classes and local asymptotic normality in system identification for quantum Markov chains.