Current Projects :

Nanocrystals quantum dots in fiber based cavity


Secure quantum communications are of crucial importance for the next generation of information networks.
To become realistic with an implementation at a large scale, it is absolutely critical to be able to miniaturize the elements that will be parts of these future networks.
In optics, miniaturization of photonics devices, widely called nanophotonics, is a very active research topic. Our project lies at this crossroad between fundamental physics and technologies.
The main objective of this proposal is to investigate innovative approaches for coupling optical fibers to solid-state quantum emitters (semiconductor nanocrystals).
Two strategies have been chosen for their complementarity and their potentiality for groundbreaking experiments and disruptive innovations.

Description of the project :
We will build a 500 nm tapered optical nanofiber (TONF) to couple the light emitted by a high quality non-blinking nanocrystals directly into the guided mode of a single mode fiber.
Near field coupling via the evanescent field guarantees an ultra-high collection efficiency compared to current optical microscopy techniques.
In the second step of the project, we will etch a Bragg grating directly into the TONF to design a high finesse cavity around the single photon emitter and this setup will be the starting point of an hybrid photonics platform for cavity QED experiments in TONF.

At the same time, we will develop another approach based on fiber Fabry-Perot cavities.
Such cavities are home--made starting from a commercial optical fibers shaped using a single shot CO2 laser pulse to melt the fiber end and create a curved surface.
After high reflectivity coating deposit, the fiber can be used as one end of a high finesse stable cavity and the cavity length can be adjusted and stabilized easily with piezoelectric actuators.
These cavities are known for their high finesse and low volumes and are truly promising to achieve, by the end of this project, the still far reaching goal of demonstrating the strong coupling regime with semiconductor nanocrystals.

Exciton Polaritons Physics

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I'm now working on exciton-polaritons superfluidity and more generally on quantum Optics with semiconductors.

Previous Projects :

Gradient Echo Quantum Memory


Quantum communication protocols are based on sharing entanglement between remote locations.
Since photons are thought to be an ideal carrier of quantum states, optical loss typically limits the maximum achievable
distance over which entanglement can be shared.
Several proposals have addressed this problem by dividing the quantum channel into shorter segments that are separately
purified and connected by entanglement swapping.
These protocols rely on the availability of a quantum memory allowing for the storage and retrieval of quantum
Gradient Echo Memory (GEM) is a promising technique for achieving these goals.

Fast Light and anomalous dispersion


Many methods of generating faster-than-light pulses involve sending a pulse composed of multiple wavelengths into a non-linear gain medium. The dispersion properties of the medium (that is, the way it changes a wave’s phase velocity depending on its frequency) rearrange the pulse components so that the pulse peak is shifted forward, producing apparent superluminal velocity for the entire group of waves. Conversely, “slow light” pulses can be generated by adjusting conditions so that the peak is shifted backward.
We use four-wave mixing to send “seed” pulses of laser light into a heated cell containing the gain medium, atomic rubidium vapor, along with a separate “pump” beam at a different frequency from the seed pulses. In the medium, the seed pulse is amplified and its peak is shifted so that it becomes superluminal. At the same time, photons from the inserted beams interact with the medium to generate a second pulse, called the “conjugate” because of its mathematical relationship to the seed. Its peak too, the scientists found, can travel faster than an unaltered reference pulse would in a vacuum. Or it can be tuned to travel slower.
More details from the JQI website

Squeezed Light Generation via Four Wave Mixing in Hot Atomic Vapor


Non-classical states of light is a key resource for quantum information and communication, as well as precision
Single photon source, squeezed light, quantum correlated or entangled beams have attracted a lot of interest in
the recent years.
Multiple techniques have been investigated in several regimes from photon counting to continuous variables.
Among them, four-wave-mixing (4WM) in a hot atomic vapor is regarded as a very attractive method to produce
highly quantum correlated beams.
I have been studying 4WM both theoretically and experimentally.
Continuous wave quantum correlations for bright beams have been observed with or without amplification,
as well as squeezed vacuum and entanglement. Multispatial mode properties have also been demonstrated.

More details.

Noiseless Image Amplifier


Optical amplifiers offer the potential to significantly improve the performance of systems in a range of fields,
including optical communications, quantum information processing, continuous-variable quantum computing,
enhancement of optical resolution, and image amplification.
It is important, for practical applications, that they add as little noise as possible to the signal they amplify.

The most common type of optical amplifier is the phase insensitive amplifier (PIA), which is a linear amplifier
whose gain and noise are independent of the phase of the input signal. The output of such an amplifier necessarily
has a lower signal-to-noise ratio (SNR) than the input and the level of degradation depends on the gain.
In contrast, a phase-sensitive amplifier (PSA) is a linear amplifier whose gain and noise do depend on the phase
of the input signal. For the correct choice of the input phase, the PSA does not degrade the SNR, independent of the
gain. In this sense, the PSA behaves as a noiseless amplifier.

The quantum noise properties of both of these optical amplifiers are well understood theoretically, but there have been few
experimental implementations.
The Paul Lett group has reported a PSA that can support at least hundreds of spatial modes, making it possible to
noiselessly amplify complicated two-dimensional images for the first time. [Corzo, et al. PRL 109, 043602 (2012)]

More details.

Trapped Ions and Quantum Information

Manip-MicroPiege (30 sur 89)

Trapped, laser-cooled ions are useful tools to create new devices for the manipulation of quantum information, and demonstrate quantum operations.
During my PhD, I worked in the IPIQ group at MPQ, Paris.
This group studies ion trapping for quantum computation.
I have been involved in trapping ions in
a linear Paul trap able to confine a macroscopic cloud of ions (some tens of thousands) in a very anisotropic geometry (several millimeters by tens of microns) in order to provide an optically dense medium, which will act as a robust storage medium for quantum information carried by light. I also worked of the design of efficient numerical imaging, which helps to create new traps with original geometries, as well as understanding the collective behavior of the ions in presence of laser cooling and of various heating sources.
More details.