The project â€œScalable Quantum Photonics with Ultra Bright Photon Sourcesâ€ (SQUAPH) was started by Dr. Carlos ANTON-SOLANAS the 1st of November 2016 in the Centre of Nanoscience and Nanotechnology (C2N-CNRS, Palaiseau, France), under the supervision of Prof. Pascale...
The project â€œScalable Quantum Photonics with Ultra Bright Photon Sourcesâ€ (SQUAPH) was started by Dr. Carlos ANTON-SOLANAS the 1st of November 2016 in the Centre of Nanoscience and Nanotechnology (C2N-CNRS, Palaiseau, France), under the supervision of Prof. Pascale SENELLART. Among some other results, this project has delivered the following main successful milestones:
(i) Advances on the path- and polarisation-encoded deterministic photon gates [1,2]
(ii) Generation of quantum light in photon-number superposition 
(iii) Demonstration of scalable multiphoton quantum protocols [papers in preparation]
The success of this project is partially based on a fruitful and well-stablished collaboration with national (Prof. Auffeves, Institut NÃ©el, Grenoble) and international actors (Prof. Sciarrino, Univ. La Sapienza, Rome, Prof. Osellame, IFN-CNR, Milan, Prof. Eisenberg, Hebrew Univ. Jerusalem, Jerusalem, Prof. White, Univ. Queensland, Brisbane).
(i) Advances on the path- and polarisation-encoded deterministic photon gates
The development of all-optical quantum networks  demands highly efficient single photon sources [5-8] and the presence of deterministic photonic gates. Linear quantum optics protocols can face severe problems to scale up optical quantum computation. An alternative to manipulate the photonic information (such as polarisation, path, or photon number), relies on the optimal nano-engineering of the light-matter interactions. The devices produced by the team of Prof. Senellart, consisting on a single QD coupled to a photonic cavity, are strong candidates for photon-gating solutions.
In the first approach, the final aim is to perform a polarisation rotation of 90 degrees of a single photon after interacting with a single charged QD (i. e., from horizontal polarisation before arriving to the device, to vertical polarisation after exiting the gate). The experiments performed during this project consisted on using a neutral QD in a cavity to study the polarisation rotation of a reflcted beam of photons resonantly exciting the device. The main result of these experiments is plotted in Fig. 1 [P1] (from Ref. 2): by changing the relative energy detuning between the QD-cavity system and the laser beam, the polarisation of the reflected beam is rotated by 20 degrees in the Poincare sphere.
â€¢ Ref.  and P. Hilaire, C. A., et al., Appl. Phys. Lett. 112, 201101 (2018) (2018).
â€¢ UK Quantum Dot Day 2017 (Edinburgh)
â€¢ PICQUE Scientific School (Nice)
â€¢ GEFES Symposium (Santiago de Compostela)
In the second approach, we have investigated the engineering of photon gates using path codification: it consists on gating photons by reflecting or transmitting them after controlled interaction with the device. In the direction of this final idea, the research carried during this project demonstrated the realisation of a single photon filter (see sketch of the idea in Fig. 1 [P2], Ref. 1).
Deliverables: Ref. 
â€¢ Single Photons Single Spins Meeting 2017 (Troyes)
â€¢ International Conference on Physics of Semiconductors 2017 (Montpellier)
â€¢ Invited Seminar: IFIMAC Institute (Madrid)
(ii) Generation of quantum light in photon-number superposition
Quantum superposition in photons, as a resource for quantum technological applications, is a very well-known phenomenon which has exploited a span of different degrees of freedom, such as polarisation, time, and energy. We have demonstrated the generation of light with quantum superposition in the photon-number basis under resonant pulsed excitation. The interest of exploiting superposition in this degree of freedom relies on the applications of these light states in different domains such as metrology (super-resolving interferometry), and computation.
(iii) Implementation of scalable multiphoton quantum protocols
Benefiting from the excellent efficiency of our single photon sources, we have proposed in [P6], and for the first time in Europe, an experimental proof-of-concept scheme for interconnecting two integrated platforms of single photon emission (using our QD-cavity devices) and reconfigurable single photon chips on glass (a three-input photon chip). The three photon interference has been experimentally implemented in the groups of Prof. Sciarrino  and Prof. Walsmley , using non-integrated sources and circuits, respectively (as opposed to our approach). A major advantage for the success of this project has been the collaboration from the groups of Profs. F. Sciarrino and R. Osellame (Italy). The deliverable of this project in preparation.
The second demonstration of scalable quantum optics has been the experimental generation of linear cluster states of single photons in an all-fibered setup in collaboration with the group of Prof. H. S. Eisenberg (Israel). Due to space limitation we will not discuss this subproject here.
â€¢ J. C. Loredo, C
This project has opened new horizons for fundamental and technological challenges on quantum photonics. The final goal of this project on the demonstration of the scalability of quantum photonics has been widely demonstrated in the results from the research of the project [P6] (and partially in project [P7]). These experiments on the three photon coalescence have been performed under higher rates on the generation and detection of three photons, having equal or even better values of single photon purity and indistinguishability, as it can be read in the Table 1. In conclusion, this positive demonstration of the efficient interconnectivity of integrated single photon sources and reconfigurable integrated photonic chips stablishes new horizons for further scaling up quantum optical technologies.
Considering the demonstrations [P6,7] of SQUAPH to build up scalable quantum optical technologies, in the next year we are envisaging to perform experiments using simultaneously up to 8 single indistinguishable photons. Simple improvements in the optical setups to efficiently collect single photons will allow us to gain a factor of 1.8. In parallel, we are working in alternative approaches to gain a factor of 2 by decoupling the mode of excitation and collection (so far, all our experiments are performed in a confocal setup, where, at least, half of the photons are lost in the mode of the excitation).
 L. De Santis, et al., Nature Nano. 12, 663 (2017)
 C. Anton, et al., Optica 4, 11, 1326 (2017)
 J. C. Loredo, C. Anton, et al., arXiv:1810.05170 [quant-ph] (2018)
 H. J. Kimble, Nature 453, 1023â€“1030 (2008)
 N. Somaschi, et al., Nature Photon. 10, 340 (2016)
 J. C. Loredo, et al., Optica 3, 433 (2016)
 X. Ding, et al., Phys. Rev. Lett. 116, 020401 (2016)
 Y.-M. He, et al., arXiv:1809.10992 [physics.optics] (2018)
 N. Spagnolo, et al., Nat. Comm. 4, 1606 (2013)
 A. J. Menssen, et al., PRL 118, 153603 (2017)