arXiv subjects

Małgorzata Strzałka

Publications and source records attributed to Małgorzata Strzałka.

5 recordsLinked to original sources

arXiv2026

Entanglement with a mode observable via a tunable interaction with a qubit

We study the possibility of detection of ``spin-boson'' entanglement by qubit only measurements. Such entanglement is impossible to detect by previously proposed schemes that involve a fixed system-environment interaction, because of inherent symmetries within the coupling and the initial state of the environment. We take advantage of the possibility of tuning of qubit-environment coupling, that is available in some qubit realizations. As an example we study a superconducting transmon qubit interacting with a microwave cavity, which is one of such systems and is, furthermore, essential in the context of quantum information processing. We propose suitable Hamiltonian parameters for the preparation and measurement phases of the detection scheme that allow for an experimental test, and verify that the reported signal is nonnegligibly large still at finite temperatures.

quant-ph↗

arXiv2026

Signatures of quantum noise in the operation of Deutsch's algorithm

We use Deutsch's algorithm as a stand in for more complex quantum algorithms in order to determine how quantum properties of an environment manifest themselves in results that can be obtained on quantum computers. We model pure dephasing in two different ways; one keeps the full density matrix of the qubits and environments (quantum) while the other uses Kraus operators (classical). We find that a single run of the algorithm yields the same effect in both cases, but running the algorithm twice leads to stark differences. Taking correlations and interplay between different decoherence processes into account leads to a slowing of decoherence effects for balanced functions. For constant functions, the effect is much more pronounced, and there is a qualitative change in the dependence of measurement outcomes on decoherence. We present results obtained on one of the IBM Quantum processors, which fully reproduce the predicted effect regardless of the assumptions made in the derivation. We further illustrate the findings on NV center spin qubits, which show more complex behavior due to a small size of the environment.

quant-ph↗

arXiv2023

Qubit-environment entanglement in time-dependent pure dephasing

We show that the methods for quantification of system-environment entanglement that were recently developed for interactions that lead to pure decoherence of the system can be straightforwardly generalized to time-dependent Hamiltonians of the same type. This includes the if-and-only-if criteria of separability, as well as the entanglement measure applicable to qubit systems, and methods of detection of entanglement by operations and measurements performed solely on the system without accessing the environment. We use these methods to study the nature of the decoherence of a qubit-oscillator system. Qubit-oscillator entanglement is essential for developing bosonic quantum technology with quantum non-Gaussian states and its applications in quantum sensing and computing. The dominating bosonic platforms, trapped ions, electromechanics, and superconducting circuits, are based on the time-dependent gates that use such entanglement to achieve new quantum sensors and quantum error correction. The step-like time-dependence of the Hamiltonian that is taken into account allows us to capture complex interplay between the build-up of classical and quantum correlations, which could not be replicated in time-independent scenarios.

quant-ph↗

arXiv2021

Detection of entanglement during pure dephasing evolutions for systems and environments of any size

W generalize the scheme for detection of qubit-environment entanglement to qudit-environment systems. This is of relevance for many-qubit systems and the quantification of the operation of quantum algorithms under the influence of external noise, since only decoherence that is not entangling in its nature can be effectively described by quantum channels and similar methods in more complicated scenarios. The generalization involves an increase of the class of entangled states which are not detected by the scheme, but the type of entanglement which cannot be detected is also least likely to qualitatively influence decoherence. We exemplify the operation of the scheme on a realistically modelled NV-center spin qutrit interacting with an environment of nuclear spins.

quant-ph↗

arXiv2019

Qubit-environment Negativity versus Fidelity of conditional environmental states for an NV-center spin qubit interacting with a nuclear environment

We study the evolution of qubit-environment entanglement, quantified using Negativity, for NV-center spin qubits interacting with an environment of $^{13}$C isotope partially polarized nuclear spins in the diamond lattice. We compare it with the evolution of the Fidelity of environmental states conditional on the pointer states of the qubit, which can serve as a tool to distinguish between entangling and non-entangling decoherence in pure-dephasing scenarios. The two quantities show remarkable agreement during the evolution in a wide range of system parameters, leading to the conclusion that the amount of entanglement generated between the qubit and the environment is proportional to the trace that the joint evolution leaves in the environment.

quant-ph↗