Certifying Quantum Devices Without Spatial Separation Achieved

Researchers have long sought innovative approaches to certify quantum devices, leading to the concept of self-testing. A new protocol achieves this feat without assuming compatibility conditions or spatial separation between subsystems. This approach relies on observing sequential correlations leading to the maximal violation of a temporal inequality derived from non-contextuality inequalities. The proposed protocol certifies two-qubit entangled states and measurements, making it robust to small experimental errors or noise.

Can Quantum Devices Be Certified Without Spatial Separation?

In recent years, the quest for fault-tolerant quantum computing has led researchers to explore innovative approaches to certify quantum devices. One such method is self-testing, which relies on observing measurement statistics to verify the properties of a quantum system without requiring spatial separation between its subsystems. In this article, we will delve into a new protocol that achieves this feat without assuming compatibility conditions or spatial separation.

The concept of self-testing was first introduced in 2020 by researchers who demonstrated a scheme based on observing measurement statistics that demonstrate Kochen-Specker contextuality. This approach has since been shown to certify two-qubit entangled states and measurements without the need for spatial separation between the subsystems. However, this protocol relies on a set of compatibility conditions on the measurements, which are crucial to demonstrating Kochen-Specker contextuality.

In this work, we propose a new self-testing protocol that certifies the same two-qubit states and measurements without assuming these compatibility conditions or requiring spatial separation between the subsystems. Our protocol is based on observing sequential correlations leading to the maximal violation of a temporal inequality derived from non-contextuality inequalities. Moreover, our protocol is robust to small experimental errors or noise.

What Are Topological Qubits?

Topological qubits are a type of quantum bit that can be used to achieve fault-tolerant quantum computation. These qubits are encoded as the subspace of a high-dimensional space of suitable physical systems, such as Majorana fermions. The circuit model of quantum computing can be replaced by Pauli-based computing, which makes use of only a minimal number of Pauli measurements. This approach can be realized using topological qubits.

In order to perform any quantum information processing task, it is essential to certify how close the relevant quantum devices are to the ideal ones. There are various certification methods that have been explored to achieve this goal, including tomography and self-testing. While certifying quantum devices, it is desirable to use methods that make use of a limited number of resources and minimize assumptions on the quantum devices.

The Importance of Certification

Before performing any quantum information processing task, it is crucial to certify how close the relevant quantum devices are to the ideal ones. This is because quantum devices can be prone to errors or noise, which can significantly impact the accuracy and reliability of the results. By certifying the properties of a quantum device, researchers can ensure that the device is operating within acceptable limits and make necessary adjustments to optimize its performance.

In this context, self-testing protocols like the one proposed in this work offer a promising approach to certify quantum devices without requiring spatial separation between their subsystems. This protocol relies on observing sequential correlations leading to the maximal violation of a temporal inequality derived from non-contextuality inequalities. Moreover, our protocol is robust to small experimental errors or noise.

The Role of Temporal Inequality

Temporal inequality plays a crucial role in the proposed self-testing protocol. This inequality is derived from non-contextuality inequalities and provides a measure of the maximum violation that can be achieved by observing sequential correlations. By maximizing this violation, researchers can certify the properties of a quantum device without requiring spatial separation between its subsystems.

In addition to certifying quantum devices, temporal inequality also has implications for our understanding of quantum mechanics. This concept challenges our classical intuition about the nature of time and space, highlighting the importance of considering non-locality in quantum systems.

Conclusion

In conclusion, this article proposes a new self-testing protocol that certifies two-qubit entangled states and measurements without assuming compatibility conditions or requiring spatial separation between the subsystems. Our protocol is based on observing sequential correlations leading to the maximal violation of a temporal inequality derived from non-contextuality inequalities. Moreover, our protocol is robust to small experimental errors or noise.

This work has significant implications for the development of fault-tolerant quantum computing and the certification of quantum devices. By certifying the properties of a quantum device without requiring spatial separation between its subsystems, researchers can optimize the performance of their devices and achieve more accurate results.