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Open Post-doctoral and PhD positions

We regularly have open positions – contact us!

We are looking for excellent candidates with a strong background on quantum technologies, quantum optics or semiconductor quantum physics to join the adventure of developing quantum technologies based on single photons – both on the quantum computing side and on the quantum communication side.

How to apply:

Candidates are requested to send the following documents by mail to Pascale Senellart (pascale.senellart-mardon@c2n.upsaclay.fr):
• Detailed CV (pdf)
• Motivation letter (pdf)

• Candidates are kindly requested to ask to at least two reference researchers to send recommendation letters directly to Pascale Senellart.

Open PhD position !

We have an open PhD position with excellent funding conditions (salary + travel + exchange programs with European research partners), provided by the Marie Curie Innovative Training Network QUDOT-TECH (www.qudot-tech.eu).

We welcome highly-motivated applicants with an excellent background in quantum physics, optics, and/or solid-state physics. Candidates must not have resided or carried out their activities – work, studies, etc – in France for more than 12 months in the 3 years immediately before starting the PhD.

Application deadline July 30th. More details here.

Dr. Lanco joins the Institut Universitaire de France

Congratulations to Dr. Loïc Lanco who was nominated as a junior member of the “Institut universitaire de France” (IUF) for five years, starting from October 1st 2019.  The Institut Universitaire de France is a service of the French Ministry of Higher Education that distinguishes each year a small number of university professors for their research excellence, as evidenced by their international recognition. The role of the IUF is to foster the development of high-level research in universities and to reinforce interdisciplinarity. Thus, it encourages the dissemination of knowledge, contributes to the increased number of women in the research sector, and promotes a policy of national scientific networking.

Read more here.

Generation of light in a photon-number quantum superposition

Physicists at C2N have demonstrated for the first time the direct generation of light in a state that is simultaneously a single photon, two photons, and no photon at all. They showed that the same kind of light emitters used for decades are also able to generate these quantum states, and expect that this holds true for any kind of atomic system.

Quantum superposition is a property of quantum physics that allows objects to exist simultaneously in different states. A famous theoretical example is the Schrödinger’s cat which is both dead and alive. Let us imagine an object trying to find the exit of a maze. In the classical realm, it will try every path, one at the time, until it finally finds the exit. In the quantum world, however, superposition allows the object to try all different paths simultaneously, therefore finding the exit much faster. For light, superposition has been shown in several of its properties. For instance, in its polarization, where the electromagnetic field of a single-photon oscillates both vertically and horizontally; or in path, taking upon all possible trajectories inside interferometers, the photonic versions of a maze. Superposition has been achieved even in time, with photons existing simultaneously at earlier and later moments.

However, creating light in a state that is simultaneously a single photon, two photons, or no photon at all, in other words a quantum superposition of “photon-numbers”, has remained elusive. Some complex experiments had already managed to obtain these superposition states a few times, but it had never been achieved on demand, which means with success at every experimental run. Moreover, it was not known whether direct emitters of these states existed. In a work published in Nature Photonics in August 2019, researchers at the Centre de Nanosciences et de Nanotechnologies – C2N (CNRS / University Paris-Saclay) and the Institut Néel (CNRS, Grenoble), have demonstrated for the first time the on-demand generation of light in a quantum superposition of photon-numbers.

The researchers studied the emission of an artificial atom, a semiconductor quantum dot inserted in an optical microcavity, a technology that has recently provided the most efficient single photon sources. By performing a coherent excitation of the quantum dot with optical pulses, they showed that the quantum coherence in the atomic state is preserved through the process of spontaneous emission and imprinted onto the emitted photonic state, generating a quantum superposition of zero, one, and two photons.

Such observations, never seen before in any atomic system, demonstrate that artificial atoms like quantum dots are now controlled to such a point that they behave as the systems described in textbooks. These new quantum states of light based on the coherent superposition of photon-number states open exciting paths for designing and implementing new schemes in quantum communication and computation.

References:
Generation of non-classical light in a photon-number superposition,
J. C. Loredo1, C. Anton1, B. Reznychenko2, P. Hilaire1, A. Harouri1, C. Millet1, H. Ollivier1, N. Somaschi3, L. De Santis1, A. Lemaître1, I. Sagnes1, L. Lanco1,4, A. Auffeves2, O. Krebs1 & P. Senellart1
Nature Photonics (2019)

DOI: https://doi.org/10.1038/s41566-019-0506-3

Optomechanical GaAs/AlAs resonators operating in the 18 GHz range

Micropillar are excellent acoustic resonators in the 18 HGz range

Optics Express 25, 24437-24447 (2017)

Recent experiments demonstrated that GaAs/AlAs based micropillar cavities are promising systems for quantum optomechanics, allowing the simultaneous three-dimensional confinement of near-infrared photons and acoustic phonons in the 18-100 GHz range. Here, we investigate through numerical simulations the optomechanical properties of this new platform. We evidence how the Poisson’s ratio and semiconductor/vacuum boundary conditions lead to very distinct features in the mechanical and optical three-dimensional confinement. We find a strong dependence of the mechanical quality factor and strain distribution on the micropillar radius, in great contrast to what is predicted and observed in the optical domain. The derived optomechanical coupling constants g0 reach ultra-large values in the 106 rad/s range.

Tunable bandwidth and nonlinearities

Tunable bandwidth and nonlinearities in an atom-photon interface with subradiant states

Phys. Rev. A 98, 013813 – (2018)

Optical nonlinearities at the single-photon level are key features to build efficient photon-photon gates and to implement quantum networks. Such optical nonlinearities can be obtained using an ideal two-level system such as a single atom coupled to an optical cavity. While efficient, such atom-photon interface however presents a fixed bandwidth, determined by the spontaneous emission time and thus the spectral width of the cavity-enhanced two-level transition, preventing an efficient transmission to bandwidth-mismatched atomic systems in a single quantum network. In the present work, we propose a tunable atom-photon interface making use of the direct dipole-dipole coupling of two slightly different atomic systems. We show that, when weakly coupled to a cavity mode and directly coupled through dipole-dipole interaction, the subradiant mode of two slightly detuned atomic systems is optically addressable and presents a widely tunable bandwidth and single-photon nonlinearity.

Tomography of the optical polarization rotation induced by a single quantum dot in a cavity

Polarization rotation induced by an artificial atom in a cavity

Optica 4, 1326-1332 (2017)

A major challenge in the development of atom–photon and photon–photon quantum gates is to provide output photons in a pure quantum state, as opposed to incoherent superpositions. Here we introduce a tomography approach to describe the optical response of a cavity quantum electrodynamics device, by analyzing the polarization density matrix of the reflected photons in the Poincaré sphere. Applying this approach to an electrically controlled quantum dot (QD)-cavity device, we show that the superposition of emitted single photons with directly reflected photons leads to a large rotation of the output polarization, by 20° both in latitude and longitude in the Poincaré sphere, with a polarization purity remaining above 84%. The QD resonance fluorescence is shown to contribute to the polarization rotation via its coherent part, while its incoherent part contributes to degrading the polarization purity. This polarization tomography technique allows discriminating between various decoherence processes, a powerful tool for solid-state quantum technologies.

© 2017 Optical Society of America