Molecular Microcavity Photon Source

光子--光的量子粒子--在量子科学和技术中发挥着重要作用。信息很容易存储在它们中。它们很容易被操纵，运输方便，而且不会受到周围环境的太大干扰。来自强衰减激光束的光子一次到达一个，但这种类型的光源在大多数量子应用中是不现实的，因为我们不知道光子何时到达。这个问题通常是通过让激光穿过晶体来解决的，晶体偶尔会随机地将一个光子一分为二。当需要一个光子时，我们等待两个光子中的一个被检测(和销毁)，然后我们就知道另一个光子已经准备好用于我们的量子应用。秘密信息的通信是该方法的一个著名应用。如果一次只需要一个或两个光子，但许多应用程序需要几个相同的光子(甚至几十个)，或者同时需要，或者需要精确的时间延迟，这种方法效果很好。不幸的是，分裂的随机性不允许这样做。我们需要一种能够在量子信息处理或复杂量子系统模拟等应用需要的时候快速可靠地传输光子的光源。光子应该是相同的，这样它们才能表现出量子干涉--即一个粒子与另一个粒子的干涉--这是量子粒子的基本特征，产生了著名的量子力学力量。这样的光源还不存在。在这里，我们建议建造一种能快速、按需产生相同光子的光源。我们的方法是将有机染料的单个分子(称为DBT)嵌入到一个耦合到光纤的小型光学谐振器中。当需要一个光子时，分子被一个明亮的光脉冲激发，之后它发出一个光子。谐振器迫使光子以特定的频率发射到耦合到光纤的特定方向，从而使光子彼此无法区分。这有时被称为珀塞尔效应，以埃德·珀塞尔的名字命名，他首先在磁共振的背景下注意到了这一点。其他研究人员试图利用珀塞尔效应来制造良好的光子源，使用各种发射器，如晶体中的量子点或色心，但由于发射器的光学性质不充分，这些发射器无法产生高产量的相同光子。我们提议的新方面是DBT分子，正如我们最近所展示的那样，对于这种应用来说，它具有近乎理想的性质。通过将这种分子结合到我们的一个腔中，我们预计基本上每次我们请求一个光子时都会产生一个光子，我们可以预计这些光子是相同的。我们还计划通过在腔内施加电场来调整分子。我们的设计将允许我们堆叠几个微型光子源，并选择是相同的光子还是调谐到不同频率的阵列。我们的DBT分子光源除了直接应用于量子信息处理之外，还为纳米光学和纳米电子学提供了一种很有前途的新元素。凭着一点想象力，我们可以看到，有一天这些分子可能会通过添加化学基团来增强，将它们变成特定分子的定制传感器，可以通过光灵敏地读出，或者直接通过有机半导体。简而言之，我们将使用腔中的DBT分子根据需要制造相同的光子，满足量子技术的迫切需求。通过努力利用这种新型的量子发射器，我们希望在纳米光学和纳米电子学的科学和技术方面取得根本性的进步。

Photons - quantum particles of light - have an important role to play in quantum science and technology. Information is easily stored in them. They are readily manipulated, conveniently transported and not much disturbed by their surroundings. The photons from a strongly attenuated laser beam arrive one at a time, but this type of source is not practical to use in most quantum applications because we do not know when the photons will come. That problem is normally addressed by passing the laser light through a crystal which occasionally, and randomly, splits a photon into two. When a photon is needed, we wait for one of the two to be detected (and destroyed), then we know that the other photon is ready for use in our quantum application. The communication of secret messages is one famous application of this approach. This works well if only one or two photons are needed at a time, but many applications require several identical photons (or even dozens of them), either simultaneously or with accurate time delays. Unfortunately, the random nature of the splitting does not allow that. We need a source that can deliver photons rapidly and reliably whenever they are needed for applications such as quantum information processing, or the simulation of complex quantum systems. The photons should be identical so that they can exhibit quantum interference - i.e. interference of one particle with another - which is the essential feature of quantum particles giving rise to the famous power of quantum mechanics. Such a source does not yet exist.Here we propose to build a source that produces identical photons, rapidly and on demand. Our method is to embed individual molecules of an organic dye (known as DBT) inside a small optical resonator, coupled to an optical fibre. When a photon is required, the molecule is excited by a bright pulse of light, after which it emits a photon. The resonator forces the photon to be emitted at a specific frequency and into the specific direction that couples to the fibre, thereby making the photons indistinguishable from each other. This is sometimes called the Purcell effect after Ed Purcell, who first noticed it in the context of magnetic resonance. Other researchers have tried to use the Purcell effect to make a good photon source, with various emitters such as quantum dots or colour centres in a crystal, but these have not been able to produce a high yield of identical photons because of the inadequate optical properties of the emitter. The novel aspect of our proposal is the DBT molecule, which has near ideal properties for this application, as we have recently shown. By incorporating this molecule into one of our cavities, we expect to produce a photon essentially every time we ask for one, and we can expect these photons to be identical. We also plan to tune the molecule by applying an electric field inside the cavity. Our design will allow us to stack up several miniature photon sources and choose whether the photons are identical or are tuned to an array of different frequencies. These can then be used to make complex quantum states of light suitable for a range of applications in quantum technology where suitable sources are currently lacking.Beyond the immediate application to quantum information processing, our DBT molecular light source provides a promising new element for nano-optics and nano-electronics more generally. With a little imagination, we can see that these molecules may one day be enhanced by the addition of chemical groups to turn them into custom sensors for specific molecules, with sensitive readout by the light, or perhaps directly through an organic semiconductor.In short, we will use DBT molecules in cavities to make identical photons on demand, satisfying an immediate need of quantum technology. By working to utilise this new type of quantum emitter, we expect to make a fundamental advance in the science and technology of nano-optics and nano-electronics.