Randomness-free Detection of Non-projective Measurements: Qubits & beyond
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arXiv
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| Format: | Preprint |
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2024
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| _version_ | 1866912301531004928 |
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| author | Rout, Sumit Bhattacharya, Some Sankar Horodecki, Paweł |
| author_facet | Rout, Sumit Bhattacharya, Some Sankar Horodecki, Paweł |
| contents | Non-projective measurements play a crucial role in various information-processing protocols. In this work, we propose an operational task to identify measurements that are neither projective nor classical post-processing of data obtained from projective measurements. Our setup involves space-like separated parties with access to a shared state with bounded local dimensions. Specifically, in the case of qubits, we focus on a bipartite scenario with different sets of target correlations. While some of these correlations can be obtained through non-projective measurements on a shared two-qubit state, it is impossible to generate these correlations using {\it projective simulable} measurements on bipartite qubit states, or equivalently, by using one bit of shared randomness and local post-processing. For certain target correlations, we show that detecting qubit non-projective measurements is robust under {\it arbitrary} depolarising noise, except in the limiting case. We extend this task for qutrits and demonstrate that some correlations achievable via local non-projective measurements cannot be reproduced by both parties performing the same qutrit {\it projective simulable} measurements on their pre-shared state. We provide numerical evidence for the robustness of this scheme under {\it arbitrary} depolarising noise. For a more generic consideration (bipartite and tripartite scenario), we provide numerical evidence for a projective-simulable bound on the reward function for our task. We also show a violation of this bound by using qutrit POVMs. From a foundational perspective, we extend the notion of non-projective measurements to general probabilistic theories (GPTs) and use a randomness-free test to demonstrate that a class of GPTs, called {\it square-bits or box-world} are unphysical. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2412_00213 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Randomness-free Detection of Non-projective Measurements: Qubits & beyond Rout, Sumit Bhattacharya, Some Sankar Horodecki, Paweł Quantum Physics Non-projective measurements play a crucial role in various information-processing protocols. In this work, we propose an operational task to identify measurements that are neither projective nor classical post-processing of data obtained from projective measurements. Our setup involves space-like separated parties with access to a shared state with bounded local dimensions. Specifically, in the case of qubits, we focus on a bipartite scenario with different sets of target correlations. While some of these correlations can be obtained through non-projective measurements on a shared two-qubit state, it is impossible to generate these correlations using {\it projective simulable} measurements on bipartite qubit states, or equivalently, by using one bit of shared randomness and local post-processing. For certain target correlations, we show that detecting qubit non-projective measurements is robust under {\it arbitrary} depolarising noise, except in the limiting case. We extend this task for qutrits and demonstrate that some correlations achievable via local non-projective measurements cannot be reproduced by both parties performing the same qutrit {\it projective simulable} measurements on their pre-shared state. We provide numerical evidence for the robustness of this scheme under {\it arbitrary} depolarising noise. For a more generic consideration (bipartite and tripartite scenario), we provide numerical evidence for a projective-simulable bound on the reward function for our task. We also show a violation of this bound by using qutrit POVMs. From a foundational perspective, we extend the notion of non-projective measurements to general probabilistic theories (GPTs) and use a randomness-free test to demonstrate that a class of GPTs, called {\it square-bits or box-world} are unphysical. |
| title | Randomness-free Detection of Non-projective Measurements: Qubits & beyond |
| topic | Quantum Physics |
| url | https://arxiv.org/abs/2412.00213 |