arXiv subjects

R. J. P. T. de Keijzer

Publications and source records attributed to R. J. P. T. de Keijzer.

3 recordsLinked to original sources

arXiv2025

Variational method for learning Quantum Channels via Stinespring Dilation on neutral atom systems

Real-world quantum systems interact with their environments, leading to the irreversible dynamics described by the Lindblad equation. Solutions to the Lindblad equation give rise to quantum channels $Φ_t$ that characterize the evolution of density matrices as $ρ(t) = Φ_t(ρ_0)$. In many quantum experiments, the observation windows are limited by experimental instability or technological constraints. Nevertheless, extending the evolution of the state beyond this window may be valuable for identifying sources of decoherence and dephasing or determining the steady state of the evolution. In this work, we propose a method to approximate an arbitrary target quantum channel by variationally constructing equivalent unitary operations on an extended system, leveraging the Stinespring dilation theorem. We also present an experimentally feasible approach to extrapolate the quantum channel in discrete time steps beyond the period covered by the training data. Our approach takes advantage of the unique capability of neutral-atom quantum computers to spatially transport entangled qubits, an essential feature for implementing our method. The approach demonstrates significant predictive power for approximating non-trivial quantum channels.

quant-ph↗

arXiv2023

Recapture Probability for anti-trapped Rydberg states in optical tweezers

In a neutral atom quantum computer, the qubits are individual neutral atoms trapped in optical tweezers. Excitations to Rydberg states form the basis for the entanglement procedure that is at the basis of multi-qubit quantum gates. However, these Rydberg atoms are often anti-trapped, leading to decoherence and atom loss. In this work, we give a quantum mechanical description of the anti-trapping loss rates and determine the recapture probability after Rydberg excitation, distinguishing between having the laser traps turned on and off. We find that there is ample time ($\approx$ 30 $μ$s, in a Strontium-88 system) needed for the wave functions to expand out off the trap. Therefore, even with traps on, $\approx$ 100% recapture probabilities can be expected for times in which significant entanglement operations between atoms can be performed. We find that for 2D radial traps with bosonic Strontium-88 atoms, the time in which perfect recapture can be achieved, is of the same order of magnitude for traps on, and off.

quant-ph↗

arXiv2022

Optimization of the Variational Quantum Eigensolver for Quantum Chemistry Applications

This work studies the variational quantum eigensolver algorithm, designed to determine the ground state of a quantum mechanical system by combining classical and quantum hardware. Methods of reducing the number of required qubit manipulations, prone to induce errors, for the variational quantum eigensolver are studied. We formally justify the qubit removal process as sketched by Bravyi, Gambetta, Mezzacapo and Temme [arXiv:1701.08213 (2017)]. Furthermore, different classical optimization and entangling methods, both gate based and native, are surveyed by computing ground state energies of H$_2$ and LiH. This paper aims to provide performance-based recommendations for entangling methods and classical optimization methods. Analyzing the VQE problem is complex, where the optimization algorithm, the method of entangling, and the dimensionality of the search space all interact. In specific cases however, concrete results can be shown, and an entangling method or optimization algorithm can be recommended over others. In particular we find that for high dimensionality (many qubits and/or entanglement depth) certain classical optimization algorithms outperform others in terms of energy error.

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