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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Measurement Device Independent Entanglement Witness of Continuous Variable States

Benjamin Lindegren Larsen, Shuro Izumi, Jonas Schou Neergaard-Nielsen, Ulrik L. Andersen

Published Jun 26, 2023• 0 citations
Publisher

Abstract

We experimentally demonstrated a protocol for measurement device independent entanglement witness (MDI-EW) presented in [1]. A measurement device independent (MDI) protocol will allow two parties (Alice and Bob) to verify that they share an entangled state via the help of trusted input states without making any assumption on the measurement device using only the statistics of the output of the measurement device. Verification of entanglement between states is important as entangled states are a commonly used resource in several aspects of quantum information science such as quantum key distribution. Experimental implementation of MDI-EW in discrete variables have previously been demonstrated in [2], [3].

DOI
10.1109/cleo/europe-eqec57999.2023.10232266

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We experimentally demonstrated a protocol for measurement device independent entanglement witness (MDI-EW) presented in [1]. A measurement device independent (MDI) protocol will allow two parties (Alice and Bob) to verify that they share an entangled state via the help of trusted input states without making any assumption on the measurement device using only the statistics of the output of the measurement device. Verification of entanglement between states is important as entangled states are a commonly used resource in several aspects of quantum information science such as quantum key distribution. Experimental implementation of MDI-EW in discrete variables have previously been demonstrated in [2], [3].
Measurement-device-independent entanglement witness (MDI-EW) will always give an affirmative certification for witnessing entanglement with untrusted measurement apparatuses. Using the MDI-EW method, we propose a measurement-device-independent quantum secret sharing (MDI-QSS) protocol that Charlie can securely distribute a key between the two agents Alice and Bob. A tight bound for collective attacks can provide good bounds on the long-distance MDI-QSS with source flaws. Then we show through numerical simulations that using single-photon source a secure QSS over 136 km can be achieved.
Quantum entanglement serves as an essential resource for quantum information technology. In many realistic quantum information tasks, it is necessary to reliably verify entanglement even when the measurement devices are unreliable. In this Letter, we experimentally demonstrate measurement-device-independent verification of continuous-variable (CV) entanglement. We show that the conventional CV entanglement witness may falsely identify a separable state as a CV entangled state when the measurement devices are unreliable. To eliminate such need for trusted measurement devices, we implement a measurement-device-independent entanglement witness for verifying CV entanglement and demonstrate its resilience against local oscillator power and phase modifications. Our Letter sheds light on advancing high-security quantum information processing and its practical implementation in quantum networks.
Imperfections in experimental measurement schemes can lead to falsely identifying, or over estimating, entanglement in a quantum system. A recent solution to this is to define schemes that are robust to measurement imperfections-measurement-device-independent entanglement witness (MDI-EW). This approach can be adapted to witness all entangled qubit states for a wide range of physical systems and does not depend on detection efficiencies or classical communication between devices. Here we extend the theory to remove the necessity of prior knowledge about the two-qubit states to be witnessed. Moreover, we tested this model via a novel experimental implementation for MDI-EW that significantly reduces the experimental complexity. By applying it to a bipartite Werner state, we demonstrate the robustness of this approach against noise by witnessing entanglement down to an entangled state fraction close to 0.4.
Entanglement is the key resource in quantum information processing, and an entanglement witness (EW) is designed to detect whether a quantum system has any entanglement. However, prior knowledge of the target states should be known first to design a suitable EW, which weakens this method. Nevertheless, a recent theory shows that it is possible to design a universal entanglement witness (UEW) to detect negative-partial-transpose (NPT) entanglement in unknown bipartite states with measurement-device-independent (MDI) characteristic. The outcome of a UEW can also be upgraded to be an entanglement measure. In this study, we experimentally design and realize an MDI UEW for two-qubit entangled states. All of the tested states are well-detected without any prior knowledge. We also show that it is able to quantify entanglement by comparing it with concurrence estimated through state tomography. The relation between them is also revealed. The entire experimental framework ensures that the UEW is MDI.
Entanglement is one of the most puzzling features of quantum theory and of great importance for the new field of quantum information. The determination whether a given state is entangled or not is one of the most challenging open problems of the field. Here we report on the experimental demonstration of measurement-device-independent (MDI) entanglement detection using witness method for general two qubits photon polarization systems. In the MDI settings, there is no requirement to assume perfect implementations or neither to trust the measurement devices. This experimental demonstration can be generalized for the investigation of properties of quantum systems and for the realization of cryptography and communication protocols.
Measurement-device-independent entanglement witnesses (MDI-EWs) enable the detection of entanglement without relying on characterized measurements. However, entanglement criteria for MDI-EWs typically assume the idealized condition that the laboratory input states are precisely the desired ones. In this work, we remove this idealization by considering the realistic scenario in which laboratory input states may be imprecise. We specify a class of MDI-EWs, termed sensitive MDI-EWs, whose entanglement criteria fail under any nonzero imprecision in the input states. We derive sufficient conditions for an MDI-EW to be classified as sensitive, revealing that a large class of MDI-EWs exhibit this sensitivity, consistent with the intuition that sensitive MDI-EWs are common. Additionally, we demonstrate that two well-known MDI-EWs for Werner states are sensitive according to our criteria, one of which recovers the result from a previous study [Phys. Rev. A 104, 012429 (2021)]. Moreover, we clarify the concept of laboratory input states in a way that makes imprecisions experimentally measurable and propose a systematic approach for modifying the criterion of any MDI-EW to accommodate small imprecisions, thus enhancing experimental relevance. A simple MDI-EW example is provided, where our modified criterion is already optimal. This work bridges the gap between idealized theoretical models and practical experimental conditions, paving the way for more robust and accessible entanglement detection in real-world settings.