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Paper 1
Long-range data transmission in a fault-tolerant quantum bus architecture
Shin Ho Choe, Robert König
- Year
- 2024
- Journal
- npj Quantum Information
- DOI
- 10.1038/s41534-024-00928-4
- arXiv
- -
AbstractWe propose a fault-tolerant scheme for generating long-range entanglement at the ends of a rectangular array of qubits of length R with a square cross-section of $$m=O({\log }^{2}R)$$ m = O ( log 2 R ) qubits. It is realized by a constant-depth circuit producing a constant-fidelity Bell-pair (independent of R) for local stochastic noise of strength below an experimentally realistic threshold. The scheme can be viewed as a quantum bus in a quantum computing architecture where qubits are arranged on a rectangular 3D grid, and all operations are between neighboring qubits. Alternatively, it can be seen as a quantum repeater protocol along a line, with neighboring repeaters placed at a short distance to allow constant-fidelity nearest-neighbor operations. To show our protocol uses a number of qubits close to optimal, we show that any noise-resilient distance-R entanglement generation scheme realized by a constant-depth circuit needs at least $$m=\Omega (\log R)$$ m = Ω ( log R ) qubits per repeater.
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Quantum discord and steering in top quarks at the LHC
Yoav Afik, Juan Ramón Muñoz de Nova
- Year
- 2022
- Journal
- arXiv preprint
- DOI
- arXiv:2209.03969
- arXiv
- 2209.03969
Top quarks have been recently shown to be a promising system to study quantum information at the highest-energy scale available. The current lines of research mostly discuss topics such as entanglement, Bell nonlocality or quantum tomography. Here, we provide the full picture of quantum correlations in top quarks by studying also quantum discord and steering. We find that both phenomena are present at the LHC. In particular, quantum discord in a separable quantum state is expected to be detected with high-statistical significance. Interestingly, due to the singular nature of the measurement process, quantum discord can be measured following its original definition, and the steering ellipsoid can be experimentally reconstructed, both highly-demanding measurements in conventional setups. In contrast to entanglement, the asymmetric nature of quantum discord and steering can provide witnesses of $CP$-violating physics beyond the Standard Model.
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