Quantum certification and benchmarkingJ. Eisert, D. Hangleiter, N. Walk, I. Roth, D. Markham, R. Parekh, U. Chabaud, E. KashefiConcomitant with the rapid development of quantum technologies, challenging demands arise concerning the certification and characterization of devices. The promises of the field can only be achieved if stringent levels of precision of components can be reached and their functioning guaranteed. This Expert Recommendation provides a brief overview of the known characterization methods of certification, benchmarking, and tomographic recovery of quantum states and processes, as well as their applications in quantum computing, simulation, and communication. More details here. |

The stellar representation of non-Gaussian quantum statesU. Chabaud, D. Markham, F. GrosshansThis article uses the so-called stellar formalism to represent the non-Gaussian properties of single-mode quantum states by the distribution of the zeros of their Husimi Q-function in phase-space. An infinite hierarchy of single-mode states based on the number of zeros of the Husimi Q-function, the stellar hierarchy, is derived, along with an operational characterisation of the states in this hierarchy with the minimal number of single-photon additions needed to engineer them. More details here. |

Building trust for continuous variable quantum statesU. Chabaud, T. Douce, F. Grosshans, E. Kashefi, D. MarkhamThis article studies heterodyne quantum state tomography, a reliable method for continuous variable quantum state certification which directly yields the elements of the density matrix of the state considered and analytical confidence intervals, using heterodyne detection. This method neither needs mathematical reconstruction of the data, nor discrete binning of the sample space, and uses a single Gaussian measurement setting. More details here. |

A comonadic view of simulation and quantum resourcesS. Abramsky, R. Soares Barbosa, M. Karvonen, S. MansfieldThis article studies simulation and quantum resources in the setting of the sheaf-theoretic approach to contextuality and non-locality. Resources are viewed behaviourally, as empirical models. More details here. |

Semi-device-independent quantum money with coherent states
M. Bozzio, E. Diamanti, F. GrosshansThis article provides a security proof for semi-device-independent quantum money with classical verification, involving an honest bank, a dishonest client and a potentially untrusted terminal. The analysis uses semidefinite programming in the coherent state framework and aims at simultaneously optimizing over the noise and losses introduced by a dishonest party. More details here. |

Optimal quantum-programmable projective measurement with linear opticsU. Chabaud, E. Diamanti, D. Markham, E. Kashefi, A. JouxThis article presents a scheme for a universal device which can be programmed by quantum states to perform optimally a chosen projective measurement, and its implementation in linear optics. More details here. |

Tsirelson’s bound and Landauer’s principle in a single-system game
L. Henaut, L. Catani, D. E. Browne, S. Mansfield, A. PappaThis article introduces a simple single-system game inspired by the CHSH game which highlights a connection between the reversibility in fundamental operations embodied by Landauer’s principle and Tsirelson’s bound that arises from the restricted physics of a unitarily evolving single-qubit system. More details here. |

Distributing Graph States Over Arbitrary Quantum NetworksC. Meignant, D. Markham, F. GrosshansThis work studies the distribution, or routing, of entangled states over fixed, but arbitrary, physical networks. It introduces two protocols to distribute respectively Greenberger–Horne–Zeilinger (GHZ) states and arbitrary graph states over arbitrary quantum networks. The GHZ states distribution protocol takes a single step and is optimal in terms of the number of Bell pairs used; the graph state distribution protocol uses at most twice as many Bell pairs and steps than the optimal routing protocol for the worst case scenario. More details here. |

Quantum secret sharing using squeezing and almost any passive interferometerF. Arzani, G. Ferrini, F. Grosshans, D. MarkhamThis article considers the sharing of quantum secret states using continuous variable systems. Specifically it introduces an encoding procedure where the secret mode is mixed with several ancillary squeezed modes through a passive interferometer. It is shown that if the interferometer is chosen uniformly at random, the probability that it may not be used to implement a quantum secret sharing protocol is zero. More details here. |

Quantum Advantage from Sequential-Transformation ContextualityS. Mansfield, E. KashefiThis article introduces a notion of contextuality for transformations in sequential contexts, distinct from the Bell- Kochen-Specker and Spekkens notions of contextuality. Within a transformation-based model for quantum computation we show that strong sequential-transformation contextuality is necessary and sufficient for deterministic computation of nonlinear functions if classical components are restricted to mod2 linearity and matching constraints apply to any underlying ontology. More details here. |

Quantum superiority for verifying NP-complete problems with linear opticsJ . M. Arrazola, E. Diamanti, I. KerenidisThis article studies a quantum superiority procedure for verifying NP-complete problems with linear optics. It introduces a simple protocol using single photon states and a few operations. More details here. |

Verification of quantum computing: An overview of existing approaches A. Gheorghiu, T. Kapourniotis, E. KashefiThis article reviews the most significant approaches to quantum verification and compare them in terms of structure, complexity and required resources. More details here. |

Efficient quantum pseudo randomness with simple graph statesR. Mezher, J. Ghalbouni, J. Dgheim, D. MarkhamThis article shows how to produce an ϵ-approximate-t-design on n qubits by repeating a measurement based scheme an efficient number of times, on a simple graph state, with measurements at fixed angles and no feed-forward corrections. More details here. |

Experimental detection of steerability in Bell local states with two measurement settings A. Orieux, M. Kaplan, V. Venuti, T. Pramanik, I. Zaquine, E. DiamantiThis article numerically and experimentally investigate a steering inequality for generalized Werner states and successfully detect steerability in a wide range of two-photon polarization-entangled Bell local states generated by a parametric down-conversion source. . More details here. |

Continuous-Variable sampling from photon-added or photon-subtracted squeezed states U. Chabaud, T. Douce, D. Markham, P. van Look, E. Kashefi, G. FerriniThis article defines a model of quantum sampler in continuous variable and proves that it is hard to sample exactly classically unless the Polynomial Hierarchy collapses to the third level. More details here. |

The quantum Cut-and-Choose technique and quantum two-party computation E. Kashefi, L. Music, P. WalldenThis article introduces a Quantum Computation Cut-and-Choose (QC-CC) technique which is a generalisation of the classical Cut-and-Choose in order to build quantum protocols secure against quantum covert adversaries. More details here. |

Experimental investigation of practical unforgeable quantum money M. Bozzio, A. Odieux, L. Trigo Vidarte, I. Zaquine, I. Kerenidis, E. DiamantiThis article shows experimental implementation of a quantum money protocol relying on classical verification that rigorously satises the security condition for unforgeability. The system exploits polarization encoding of weak coherent states of light and operates under conditions that ensure compatibility with state-of-the-art quantum memories. More details here. |

Raman-tailored photonics crystal fiber for telecom band photon-pair generation M. Cordier, A. Orieux, R. Gabet, T. Harlé, N. Dubreuil, E. Diamanti, P. Delaye, I. ZaquineThis article reports on the experimental characterization of a novel nonlinear liquid-filled hollow-core photonic crystal fiber for the generation of photon pairs at a telecommunication wavelength through spontaneous four-wave mixing (SFWM). More details here. |

Efficient quantum communications with multiplexed coherent state fingerprintsN. Kumar, I. Kerenidis, E. DiamantiThis article provide the first example of a communication model and a distributed task, for which there exists a realistic quantum protocol which is asymptotically more efficient than any classical protocol, both in the communication and the information resources. More details here. |

Minimum quantum resources for strong non-localityS. Abramsky, R. Soares Barbosa, G. Carù, N. de Silva, K. Kishida, S. MansfieldThis article analyses the minimum quantum resources needed to realise strong non-locality. More details here. |