arXiv subjects

Dharmaraj Ramachandran

Publications and source records attributed to Dharmaraj Ramachandran.

4 recordsLinked to original sources

arXiv2025

Entanglement dynamics via Geometric phases in Trapped-ions

Trapped-ion systems are a leading platform for quantum computing. The Mølmer-Sørensen (MS) gate is a widely used method for implementing controlled interactions in multipartite systems. However, due to unavoidable interactions with the environment, quantum states undergo non-unitary evolution, leading to significant deviations from ideal dynamics. Common techniques such as Quantum Process Tomography (QPT) and Bell State Tomography (BST) are typically employed to evaluate MS gate performance and to characterize noise in the system. In this letter, we propose leveraging the geometric phase as a tool for performance assessment and noise identification in the MS gate. Our findings indicate that the geometric phase is particularly sensitive to environmental noise occurring around twice the clock pulse time. Given that geometric phase measurements do not require full-state tomography, this approach offers a practical and experimentally feasible method to detect entanglement and classify the nature of noise affecting the system.

quant-ph↗

arXiv2025

Robust entanglement measure for mixed quantum states

We introduce an entanglement measure, the Modified Bloch Norm (MBN), for finite-dimensional bipartite mixed states, based on the improved Bloch matrix criteria. MBN is demonstrated to be effective in analyzing the dynamics of bound entanglement--a valuable resource for quantum protocols where free entanglement may not be available. Through examples, we illustrate the applications of MBN in accurately estimating the Entanglement Sudden Death (ESD) time and detecting behavior such as the freezing of bound entanglement. Additionally, we show that the error rate for entanglement measured using state estimation from a limited number of measurement copies is significantly lower when using MBN compared to negativity. This demonstrates the robustness of MBN under practical constraints.

quant-ph↗

arXiv2024

A Riemannian Genuine Measure of Entanglement for Pure States

While several measures exist for entanglement of multipartite pure states, a true entanglement measure for mixed states still eludes us. A deeper study of the geometry of quantum states may be the way to address this issue, on which context we come up with a measure for pure states based on a geodesic distance on the space of quantum states. Our measure satisfies all the desirable properties of a ``Genuine Measure of Entanglement" (GME), and in comparison with some of the other existing measures, shows better smoothness and discriminance.

quant-ph↗

arXiv2024

A Sharp Geometric Measure of Entanglement

Despite their elegance and widespread use, the current Geometric Measures (GMs) of entanglement exhibit a significant limitation: they fail to effectively distinguish Local Unitary (LU) inequivalent states due to the inherent nature of their definition. We illustrate the impact of this limitation using the fidelity of the teleportation protocol as an example. To address this issue, we introduce the Sharp Geometric Measure (SGM) by modifying the standard definition of the Geometric Measure. We show that the closed-form expression of the SGM can be equivalently derived using the Riemannian structure of both the composite state space and the reduced density operator space. Furthermore, we define a measure of Genuine Multipartite Entanglement (GME) derived from the SGM, which we term GMS. We demonstrate that GMS resolves two key limitations of some existing GME measures, thereby establishing its utility and effectiveness in quantifying GME.

quant-ph↗