@article{66094,
  abstract     = {{The two-qubit controlled-not (C-NOT) gate is an essential component for gate-based quantum circuits. In fact, its operation, combined with single qubit rotations allows to realise any quantum circuit. Several strategies have been adopted in order to build quantum gates. Among them, photonics offers the dual advantage of excellent isolation from the environment and ease of manipulation at the single qubit level. Here we adopt a scalable time-multiplexed approach in order to build a fully reconfigurable architecture capable of implementing a post-selected C-NOT gate with a fidelity of (93.8 ± 1.4)%. We then show how our time-multiplexed platform can be employed to combine a C-NOT and a single qubit gate in order to generate the four Bell states.}},
  author       = {{Pegoraro, Federico and Held, Philip and Lammers, Jonas and Brecht, Benjamin and Silberhorn, Christine}},
  issn         = {{2041-1723}},
  journal      = {{Nature Communications}},
  keywords     = {{Photonic Quantum Computing, Time-multiplexing, Quantum Information}},
  number       = {{1}},
  publisher    = {{Springer Science and Business Media LLC}},
  title        = {{{Demonstration of a quantum C-NOT gate in a time-multiplexed fully reconfigurable photonic processor}}},
  doi          = {{10.1038/s41467-026-74861-9}},
  volume       = {{17}},
  year         = {{2026}},
}

@inproceedings{8161,
  abstract     = {{The polynomial-time hierarchy (PH) has proven to be a powerful tool for providing separations in computational complexity theory (modulo standard conjectures such as PH does not collapse). Here, we study whether two quantum generalizations of PH can similarly prove separations in the quantum setting. The first generalization, QCPH, uses classical proofs, and the second, QPH, uses quantum proofs. For the former, we show quantum variants of the Karp-Lipton theorem and Toda's theorem. For the latter, we place its third level, Q Sigma_3, into NEXP using the Ellipsoid Method for efficiently solving semidefinite programs. These results yield two implications for QMA(2), the variant of Quantum Merlin-Arthur (QMA) with two unentangled proofs, a complexity class whose characterization has proven difficult. First, if QCPH=QPH (i.e., alternating quantifiers are sufficiently powerful so as to make classical and quantum proofs "equivalent"), then QMA(2) is in the Counting Hierarchy (specifically, in P^{PP^{PP}}). Second, unless QMA(2)= Q Sigma_3 (i.e., alternating quantifiers do not help in the presence of "unentanglement"), QMA(2) is strictly contained in NEXP.}},
  author       = {{Gharibian, Sevag and Santha, Miklos and Sikora, Jamie and Sundaram, Aarthi and Yirka, Justin}},
  booktitle    = {{43rd International Symposium on Mathematical Foundations  of Computer Science (MFCS 2018)}},
  editor       = {{Potapov, Igor and Spirakis, Paul and Worrell, James}},
  keywords     = {{Complexity Theory, Quantum Computing, Polynomial Hierarchy, Semidefinite Programming, QMA(2), Quantum Complexity}},
  location     = {{Liverpool, UK}},
  pages        = {{58:1--58:16}},
  publisher    = {{Schloss Dagstuhl - Leibniz-Zentrum fuer Informatik}},
  title        = {{{Quantum Generalizations of the Polynomial Hierarchy with Applications to QMA(2)}}},
  doi          = {{10.4230/LIPIcs.MFCS.2018.58}},
  volume       = {{117}},
  year         = {{2018}},
}