Hari Prakash, Manoj K Mishra
Superposition of optical coherent states (SCS) Ket(plus/minus alpha), possessing opposite phases, plays an important role as qubits in quantum information processing tasks like quantum computation, teleportation, cryptography etc. and are of fundamental importance in testing quantum mechanics. Recently, ququats and qutrits defined in four and three dimensional (D) Hilbert space, respectively, have attracted much more attention as they present advantage in secure quantum communication and also in researches on the foundation of quantum mechanics. Here, we show that superposition of four non-orthogonal coherent states Ket(plus/minus alpha) and Ket(plus/minus i alpha), that are 90 degrees out of phase, can be employed for encoding one ququat defined in a 4D Hilbert space spanned by four newly defined multi-photonic states, Ket(alpha subscript j) with 4n+j numbers of photons, where, j= 0, 1, 2, 3. We propose a scheme which generates states Ket(alpha subscript j). When these states fall on a 50-50 beam splitter, the result is bipartite four-component entangled coherent state which represents equivalently an entangled ququat. Finally, we propose a linear optical scheme that gives almost perfect teleportation (minimum average fidelity greater than or equal to 0.99) of single ququat encoded in SCS using entangled ququat based on coherent states with almost perfect success rate for coherent amplitude mod(alpha) greater than or equal to 3.2. The present theoretical investigation and teleportation protocol is important in the sense that ququat allows the quantum information to be encoded and processed much more compactly and efficiently using fewer coupled quantum system.
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http://arxiv.org/abs/1209.2958
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