量子调控“尝鲜”方案在混合体系中实现量子逻辑操作和逻辑门

在单量子水平实现对光和物质相互作用的完美控制，不仅仅是量子光学中的一个核心问题，同时也是许多基本物理现象及其应用的研究基础。伴随着先进的光子纳米材料及其加工技术的不断革新，一场基于光学和光子学的量子信息技术革命正在蓬勃发展。

近年来，手性量子光学的快速发展得到了科技界的广泛关注，而手性的光与物质相互作用（含不对称性），顾名思义就是跟传播方向有关的光子发射器。基于这个物理现象，人们理所当然地会想到利用这种特殊的现象来实现某种特殊的调控，如非互易耦合。不仅如此，如何将这种手性器件融合到一个混合的量子体系中来实现一整套有趣的量子操作也是一个值得思考的问题。

金刚石氮-空位中心（NV）以及基于它来构建的混合量子体系已经成为当前量子信息处理研究领域的宠儿。作为一种点缺陷，NV具备很多优良的物理性质，如优秀的自旋属性、具备原子的一般特点、无需俘获或者囚禁、光学寻址方便、容易集成、室温下仍具有超长相干时间等。因此，在可见光频率范围里，人们可以很方便地将NV集成到光学微腔或者光晶格中，并在单量子水平对其进行高效地相干调控。

结合上述研究热点，湖北汽车工业学院理学院周原博士课题组在Photonics Research 2021年第3期发表的文章中（Yuan Zhou, Dong-Yan Lü, Wei-You Zeng. Chiral single-photon switch-assisted quantum logic gate with a nitrogen-vacancy center in a hybrid system[J]. Photonics Research, 2021, 9(3): 03000405）提出了一种有趣且新颖的实现量子逻辑操作和逻辑门的方案。

混合器件示意图。该混合器件包含一个手性单光子发射开关，一个NV自旋被放置在一个光学微腔中，微腔和光子开关之间用纳米光纤相连

该设计方案中，整个混和器件主要由三部分构成：一个手性的单光子脉冲开关，一个NV自旋，以及一个光学微腔。其中，对于如何实现该手性开关，研究人员提出了三种不同的技术路线，即冷原子体系实现单原子路由器、量子电体系实现路径编码光子发射以及利用表面等离子方案实现手性光子发射。

该混和器件中，NV自旋被放置于光学微腔中并且利用纳米光纤将微腔和光子开关相连。接着，在光学微腔中引入双色的微波场来驱动NV自旋的基态，同时进入微腔的手性光子信号也会以光学模式与NV自旋的激发态进行近共振耦合。

另外，研究人员还在考虑到各种实际的噪声和实验缺陷等不利因素的影响下，对整个逻辑操作进行了模拟和评估。

周原博士表示，这个有趣的研究在利用集成或者混合的光量子器件实现量子调控的领域中可以被看作是一种新鲜的尝试，并希望它能在量子信息技术的研究过程中得到更广泛的应用。

Chiral single-photon switch-assisted quantum logic gate with a nitrogen-vacancy center in a hybrid system

In the quantum optics research area, a central goal is to develop techniques for a complete control of light-matter interaction at the single-quantum level, which underlies the essential physics of many phenomena and applications. A new quantum revolution on optics and photonics is also accelerating the progress of quantum information processing (QIP), with the rapid innovation of the advanced photonic nanomaterials and processing technologies.

Recently, "chiral quantum optics" which leads to a chiral type light-matter interaction, so-called "propagation-direction-dependent" emission, has quickly attracted widespread attentions. Utilizing this kind of chiral interface, people can surely constitute an interesting quantum control of photon-emitter interaction, i.e. the nonreciprocal interaction, and furthermore fabricate a hybrid quantum system with this exciting photon-emitter setup to function some special and interesting quantum operations.

As a point defect in diamond, the nitrogen vacancy (NV) centers integrated in a hybrid quantum system have recently emerged as one of the leading candidates for QIP thanks to their excellent spin properties, such as atom-like properties, solid-state spins without any trap, optical addressable, easy scalability, and longer coherence time even at ambient conditions. In the optical-frequency domain particularly, we can conveniently fabricate the NV center with the optical cavity or optical lattice in a hybrid device, and coherently manipulate the NV center at single-quantum level with enough high efficiency.

This investigation proposed by Dr. Yuan Zhou from the quantum physics group from the School of Science, Hubei University of Automotive Technology (HUAT) in Photonics Research, Vol. 9, No. 3, 2021 (Yuan Zhou, Dong-Yan Lü, Wei-You Zeng. Chiral single-photon switch-assisted quantum logic gate with a nitrogen-vacancy center in a hybrid system[J]. Photonics Research, 2021, 9(3): 03000405) is an interesting and novel proposal for realizing a quantum logic operation and logic gate.

This hybrid system consists of a chiral switch for emitting photon pulse and an optical microcavity embedded with a single NV center, both of which are connected with an optical nanofiber

This interesting hybrid device is fabricated by a chiral photon-pulse switch, a single NV center, and an optical microcavity. For realizing this chiral photon switch, three major different practical routes are available, i.e. the "one-atom router" with cold atom scheme, "the path-encoded photon" with quantum dot system, and the "chiral photon emitter " with surface plasmon (SP) scheme.

The outputs are delivered to the optical microcavity through nanofiber in this hybrid system. A single NV center, driven by a dichromatic microwave field, is planted in the optical microcavity, which will also interact with the optical modes near-resonantly.

Besides, taking all of adverse factors into this theoretical investigation, i.e. the practical noise and experimental imperfection, this whole logic operation is evaluated numerically.

This work may be a useful attempt for implementing quantum manipulation with integrated or hybrid optical quantum devices owing to its inherent innovative and interesting nature, and may evoke wide and fruitful applications in QIP.