A Large Bandwidth Room Temperature Single Photon Source

该项目致力于基于热蒸气中里德堡原子之间的强相互作用实现单光子源。申请者最近在一项原则性实验中证明了在Rb原子气体中产生反聚束光子的可能性。在这个实验中，我们已经证明，在微米大小的激发体积中，阻塞效应足以允许只有一个里德堡激发，然后这个里德堡激发可以在四波混频方案中转换为光模式。这种转换必须在强关联多体状态的寿命内发生。在我们的激发方案中，相干时间受到原子运动的限制，大约为一纳秒。这意味着需要足够强的激光脉冲才能达到GHz拉比频率。我们实验中的瓶颈之一是我们的激光系统的小重复频率(50赫兹)。在这个方案中，我们希望实现第二代基于蒸汽基的单光子源，它将更接近实际应用。首先，我们将切换到不同的四波混频方案，在该方案中，我们可以在远高于100 kHz的速率下运行激光，从而提供更好的光子统计数据。此外，部分光学元件将作为固体浸没透镜集成在蒸汽室中。为了改善原子与光的耦合，我们还将添加光学涂层来产生中低精细腔。这种涂层还将包括保护性涂层，以防止化学反应产生空洞。在材料方面，我们将研究不同的里德堡原子如何与由石英、蓝宝石等制成的近壁相互作用。使用新的激光系统，我们还将获得对实际脉冲形状的控制，精度可达50ps，这将需要扩展的数值模拟来获得最佳序列。最后，我们希望通过在一个细胞中实现两个单光子源来证明我们方法的可扩展性，并表征Hong-ou-Mandel干涉仪中发射的光子的不可区分性。该项目的一个值得注意的部分将是与以色列魏兹曼科学研究所的Ofer Firstberg博士的合作。他的团队在里德堡原子和热蒸气光谱方面拥有广泛的专业知识。由于这两个群体对带有光学涂层的蒸汽池的需求很大，我们将共同开发这种池的制造。所有这些措施都将增加光子速率以及我们来源的保真度。一种应用将是纯粹基于蒸气的量子中继器方案，其中单光子源和存储器的波长和带宽自然匹配。另一个应用在于线性量子计算或创造更复杂的光子态(更高的福克态、中午态等)。

This project is dedicated to the realization of a single photon source based on strong interactions between Rydberg atoms in a thermal vapour. The possibility to produce anti-bunched photons in a gas of Rubidium atoms has been shown very recently in a proof of principle experiment by the applicants. In this experiment we have shown that, in a micron sized excitation volume, the blockade effect is sufficient to allow for only one Rydberg excitation, which can then be transferred to a light mode in a four-wave mixing scheme. This conversion has to happen within the lifetime of the strongly correlated many body state. In our excitation scheme the coherence time is limited by the motion of the atoms to roughly one nano-second. This means that sufficient strong laser pulses are required to achieve GHz Rabi-frequencies. One of the bottlenecks in our experiment is the small repetition rate (50Hz) of our laser-system. In this proposal we want to realize a second generation of the vapour based single photon source, which will be much closer to real applications. First of all, we will switch to a different four-wave mixing scheme, where we can operate the lasers at rates well above 100kHz giving much better photon statistics. Also parts of the optics will be integrated in the vapour cells as solid immersion lenses. To improve the atom-light coupling, we will also add optical coatings to produce low to medium finesse cavities. This coatings will also include protective coatings to a void chemical reactions. On the material side we will investigate how different Rydberg atoms interact with the close by walls made of Quartz, Sapphire, etc. With the new laser system we will also obtain control over the actual pulse shapes down to the 50ps scale, which will require extended numerical simulations to obtain an optimal sequence. Finally we want to prove the scalability of our approach by realizing two single photon sources in one cell and characterize the indistinguishability of the emitted photons in a Hong-Ou-Mandel interferometer.A notable part of this project will be the cooperation with Dr. Ofer Firstenberg (Weizmann Institute of Science, Israel). His group has broad expertise on Rydberg atoms as well as on the spectroscopy on thermal vapours. As both groups have a strong need for vapour cells featuring optical coatings we will develop together the fabrication of such cells.All these measures will increase the photon rate as well the fidelity of our source. One application would be a purely vapour based quantum repeater scheme, where the wavelength and the bandwidth of the single photon source and of the storage is naturally matched. Another application lies in linear quantum computation or in the creation of more complex photon states (higher Fock states, noon-states,...).