**报告题目：**Giant non-linearities of quantum dots embedded in nanophotonic waveguides

**报告人：**Dr. Hanna Le Jeannic

**主持人：**黄坤 研究员

**时间：** 2020-1-10 9:30

**地点：**闵行光学大楼A408会议室

**主办单位**：精密光谱科学与技术国家重点实验室

**报告内容简介：**

Solid state emitters and in particular quantum dots have been raising considerable interest for light matter interactions towards quantum optics application. Indeed, when embedded in light-confining nanophotonic structures, they can reach ultra-efficient coupling with an incoming light field, and thus can act as suitable platforms to deterministically generate single photons or exploit single photon nonlinearities for quantum gates implementation. Long limited by decoherence processes due to phonons, charge or spin noise, more recent works shows drastic improvements of their emission making them closer to ideal two-level emitters.

In this talk we will present the first observation of near-lifetime limited transitions of quantum dots embedded in nanophotonic waveguides, as well as the consequent giant non linearities resulting from the interaction of a single photon with a single quantum dot. Applications and perspectives for complex quantum optical circuitry, opened by such an efficient light-matter platform will be discussed.

**报告人简介：**

Dr. Le Jeannic received her PhD degree from the Laboratoire Kastler Brossel in 2016, in the group of Pr. Julien Laurat. Her doctoral studies were focused on the hybrid processing of quantum information, involving the generation of discrete- and continuous- variable quantum states and hybrid entanglement. She then switched to study quantum nanophotonics at the Niels Bohr Institute in the group of Peter Lodahl in Denmark where she worked on the non-linearities provided by single quantum dots sensitive to the single photon level.

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**报告题目：**Generation of non-Gaussian quantum states of multimode light field

**报告人：**Dr. Young-Sik Ra

**主持人：**黄坤 研究员

**时间：** 2020-1-10 10:00

**地点：**闵行光学大楼A408会议室

**主办单位**：精密光谱科学与技术国家重点实验室

**报告内容简介：**

Continuous-variable quantum information encoded on the electromagnetic fields of light plays a pivotal role in quantum technologies. It enables to build a large-scale entangled quantum state for quantum computing and quantum communication based on standard optical resources: a squeezed vacuum state of light, linear optics, and homodyne detection. However, a quantum state produced by those resources always exhibits a Gaussian distribution, which is generally insufficient for quantum technologies. Subtracting a single photon from a squeezed vacuum state can introduce a non-Gaussian distribution, but the conventional method of photon subtraction works only for a single-mode quantum state, which significantly limits the range of application. Here we generate non-Gaussian quantum states of multimode light by employing a single-photon subtractor compatible with multimode light. We first prepare a multimode squeezed vacuum state and then subtract a single photon at a desired mode or at a superposition of desired modes; the resultant multimode quantum state exhibits a non-Gaussian distribution (negativity of the Wigner function in many cases) when measured at the mode(s) of photon subtraction. Furthermore, when a single photon is subtracted from a multimode entangled state, we observe that the induced non-Gaussianity is distributed to other modes via entanglement between modes. Such non-Gaussian multimode quantum states will have broad applications for universal quantum computing, entanglement distillation, and nonlocality test.

**报告人简介：**

Dr. Young-Sik Ra received his PhD degree from Pohang University of Science and Technology (POSTECH) in 2014 under the supervision of Pr. Yoon-Ho Kim. His doctoral studies were focused on the decoherence in multi-photon interference and generation of multi-photon entangled states. After one-year postdoctoral research in POSTECH, he joined in the Laboratoire Kastler Brossel of Université Pierre et Marie Curie under the program of Marie Curie Individual Fellowship. Since 2018, he has been an assistant Professor in Korea Advanced Institute of Science and Technology (KAIST) and conducted researches on Generation and measurement of nonclassical light, Quantum interference, and Quantum information processing.

**报告题目：**Photonic Qubit Memories for Quantum Networks

**报告人：**Dr. Olivier Morin

**主持人：**黄坤 研究员

**时间：**2020-1-10 10:30

**地点：**闵行光学大楼A408会议室

**主办单位**：精密光谱科学与技术国家重点实验室

**报告内容简介：**

Quantum memories are at the heart of numerous quantum information protocols. More specifically, the storage of optical qubits is highly desired for the development of quantum networks. However, the development of such a device remains very challenging, and many physical platforms are studied to endeavor to realize the best system possible.

Here we show that a single atom interacting with a high finesse optical cavity constitutes a very promising option. It can perform extended storage time as long as 100ms (with constant efficiency), a time that is compatible with global scale communication. We also demonstrated a very high control of the absorbed/emitted photon shape with the possibility to change it over 3 orders of magnitude of time duration. Eventually, we have been able to scale up our system to more than 1 qubit storage i.e. qubit multiplexing capability.

**报告人简介：**

Dr. Olivier Morin received his PhD degree from Sorbone Université in 2013. His doctoral studies were carried out in the group of Prof. Julien Laurat and Prof. Claude Fabre at Laboratoire Kastler Brossel (LKB), Paris, France. His doctoral work was focused on optical quantum state engineering and realized the first demonstration of hybrid entanglement between continuous and discrete variables qubits. Since 2014 he works as a postdoc in the group of Prof. Gerhard Rempe at the Max-Planck Institute of Quantum Optics (MPQ), Garching, Germany.

**报告题目：**Waveguide-coupled single collective excitation of atomic arrays

**报告人：**Dr.Neil Corzo

**主持人：**黄坤 研究员

**时间：**2020-1-10 11:00

**地点：**闵行光学大楼A408会议室

**主办单位**：精密光谱科学与技术国家重点实验室

**报告内容简介：**

Reversible light-matter interfaces are crucial elements in quantum optics and quantum information networks. In particular, the coupling of nanophotonic devices and cold neutral atoms appears as a promising pathway to obtain not only better scalability and figures of merit than in free-space implementations, but also new paradigms for atom–photon interactions. To this end, dielectric waveguides offer a promising platform for such integration because they enable tight transverse confinement of the propagating light, strong photon–atom coupling in single-pass configurations and potentially long-range atom–atom interactions mediated by the guided photons. However, the preparation of non-classical quantum states in such atom–waveguide interfaces has not yet been realized.

In this talk, I will present the first experimental realization of the coupling between a single collective atomic excitation and a nanoscale waveguide. The stored collective entangled state can be efficiently read out with an external laser pulse, leading to on-demand emission of a single photon into the guided mode.

This result demonstrates a capability that is essential for the emerging field of waveguide quantum electrodynamics, with applications to quantum networking, quantum nonlinear optics and quantum many-body physics.

[1] N. V. Corzo et. al., Waveguide-coupled single collective excitation of atomic arrays. Nature 566, 359–362 (2019)

**报告人简介：**

Professor Neil Corzo received his PhD degree from CINVESTAV-México in 2012. During his PhD, he did a 4-year-long research stay at the Laser Cooling and Trapping Group at NIST (Maryland, USA). He did two postdoctoral research stays, the first one at Northwestern University (Illinois, USA), and the second one at the Laboratoire Kastler Brossel (Paris, France). For the latter, he was awarded a Marie Curie Individual Fellowship from the European Commission (2014-2016). Currently, he is a Professor CINVESTAV-México.

**报告题目：**Light-matter interface based on collective and cooperative effects

**报告人：**Dr. Alexandra Sheremet

**主持人：**黄坤 研究员

**时间：** 2020-1-10 11:30

**地点：**闵行光学大楼A408会议室

**主办单位**：精密光谱科学与技术国家重点实验室

**报告内容简介：**

Understanding and control of light-matter interactions have been central to the development of modern physics. A promising approach for study of such interactions is based on ensemble of neutral atoms. Manipulations with density and spatial organization of atoms in a system can bring fascinating results, which are interesting for quantum information applications. For example, reducing average distance between atoms up to resonant wavelength induces dipole-dipole interaction and results in cooperative effects. These effects in spatially dense atomic ensembles can modify optical properties of the system. Moreover, spatial organization of atoms in ordered arrays and optical lattices causes a manifestation of collective effects. In such systems, long-range spatial order brings dramatic consequences for the light propagation.

In this talk, I will discuss light propagation in an atomic ensemble where average distance between atoms is comparable with the resonant wavelength. I will consider the light propagation in both free space and trapped near a nanofiber surface atomic ensemble. We show theoretically and experimentally that spatially dense atomic ensembles allow obtaining effective light-matter interface and reliable light storage with essentially fewer atoms than it can be achieved in dilute gases. Furthermore, we show that the presence of an optical nanofiber modifies the character of atomic interaction and results in long-range dipole-dipole coupling between atoms not only via the free space, but also through the waveguide mode.

**报告人简介：**

Dr. Alexandra Sheremet obtained her PhD in 2013 at Department of Theoretical Physics at Saint-Petersburg Polytechnic University. During her PhD and Postdoc research she has studied light-matter interfaces in complex multi-level atomic systems in a parallel with on-going experiments of the quantum network team in the Laboratoire Kastler Brossel at Sorbonne Université (Paris, France) led by Prof. Julien Laurat. Since January 2019 she has been studying multiple light scattering in disordered and correlated atomic systems at Institut Langevin, ESPCI, Paris.