密碼學確保了訊息在傳送上的安全與隱密性，量子通訊則是傳送量子態的一門技術。而在量子通訊過程中，能夠保證量子態安全且隱密地傳送的技術，我們稱之為量子密碼學。在早期70年代，歐美國家便已發覺到量子密碼學的重要性，而Steven Wiesner首先提出將量子位元編碼的方法，但他所提出的概念卻尚未用在通訊上；其他人也提出一些利用量子糾纏特性的方法。量子糾纏是量子力學中很特別的性質，它的概念是利用粒子之間某種連結的關係，使其中一個粒子的狀態改變，會立即影響其他粒子的狀態。量子糾纏這個特性應用在很多地方，像是量子隱傳、高密度編碼、秘密分享、量子密碼學、單向量子計算等。
量子隱傳不單單是傳送量子態的方法，也是量子訊息處理的最基本方法，主要使用了量子糾纏的特性和量子量測。Bennett等人首先提出一個傳送單顆任意量子態的量子隱傳，以具有糾纏性的雙光子作為量子通道，將單顆任意量子態從傳送方隱傳到接收方。而這個方法已經被一些實驗室在不同環境中以的不同的量子系統實做出來。量子態分享是能夠在一群人之間共享量子訊息的方法，倘若當中有一人想要取得完整的量子訊息，則需要其他人的協助方能取得，否則是拿不到完整的量子訊息。量子態分享最早是以三顆糾纏的GHZ state作為量子通道來傳送單顆量子，使每個人各擁有其中一顆亮子，在共同合作下即可得到完整訊息。目前，以其他量子態作為量子通道的傳送方法也陸陸續續被實做出來。
本篇論文我們使用Dicke state的多顆量子態作為量子通道，藉由它在多顆糾纏量子態裡獨具的特性，配合在不同的環境下，分別提出量子隱傳、量子態分享和一種有條件限制的量子隱傳協定。

Quantum communication is the process of transferring a quantum state from one loca-tion to another. Ensuring the security and privacy of information transmission, known as cryptography, has become a major issue of communication technology. Quantum crypto-graphy was discovered independently in the US and Europe. The American approach, pio-neered by Steven Wiesner in the early 1970s, was based on coding in non-commuting ob-servables, whereas the European approach was based on correlations due to quantum en-tanglement. Entanglement is a fascinating aspect of quantum mechanics, because non-intuitive quantum correlations can exist between two or more particles [1]. Using entan-glement, different types of quantum tasks can be performed, including teleportation [2], superdense coding [3], secret sharing [4, 5], quantum cryptography [6], and one-way quan-tum computation [7].
Teleportation is not only a transfer protocol of unknown quantum states [2, 8] but also one of the most fundamental quantum information processing protocols [9]. The essence of quantum teleportation is entanglement and measurement. Teleportation of an arbitrary sin-gle qubit through an entangled channel of an Einstein-Podolsky-Rosen (EPR) pair between the sender and receiver was first demonstrated by Bennett et al. [2]. This has been achieved experimentally using different quantum systems, with and without laboratory conditions [10-12]. Quantum state sharing can share quantum information between a group of parties, such that none of the parties can reconstruct the information without knowing the others’ measurement outcomes. This was first demonstrated for a single qubit state, using a three-particle Greenberger-Horne-Zeilinger (GHZ) state with three parties having one qubit each [4]. Experimental realization of quantum state sharing has been achieved using several states [13-15] .
A certain multipartite state, the Dicke state of n particles and m excitations [16], is a particular important class of multipartite entangled states. In this thesis, we propose proba-bilistic and deterministic schemes of teleportation, quantum state sharing and controlled quantum teleportation in different scenarios using the Dicke state.

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