Quantum information is a rapidly advancing area of interdisciplinary research. It may lead to real-world applications for communication and computation unavailable without the exploitation of quantum properties such as nonorthogonality or entanglement. We review the progress in quantum information based on continuous quantum variables, with emphasis on quantum optical implementations in terms of the quadrature amplitudes of the electromagnetic field.

We provide a physical prescription based on interferometry for introducing the total phase of a mixed state undergoing unitary evolution, which has been an elusive concept in the past. We define the parallel transport condition that provides a connection form for obtaining the geometric phase for mixed states. The expression for the geometric phase for mixed state reduces to well known formulas in the pure state case when a system undergoes noncyclic and unitary quantum evolution.

We show that a qubit chosen from equatorial or polar great circles on a Bloch spehere can be remotely prepared with one cbit from Alice to Bob if they share one ebit of entanglement. Also we show that any single particle measurement on an arbitrary qubit can be remotely simulated with one ebit of shared entanglement and communication of one cbit.PACS NO: 03.67.-a, 03.65.Bz email:akpati@sees.bangor.ac.ukThe state of a quantum system contains a large amount of information which cannot be accessed by an observer. How well one can extract and utilise the largely inaccessible quantum information is the subject of quantum information theory. One of the surprising discoveries in this area is the teleportation of an unknown quantum state by Bennett et al [1] from one place to another without ever physically sending the particle. A qubit, for example, can be sent from Alice to Bob provided they share an Einstein-Podolsky-Rosen (EPR) pair and Alice carries out a Bell-state measurement on the qubit and one half of the EPR pair, and sends two bits of classical information to Bob, who in turn can perform a unitary operation on his particle to get the original state. The quantum teleportation of photon has been demonstrated experimentally by Bouwmeester et al [2] and Boschi et al [3]. The continuous version of quantum teleportation has been also verified by Furusawa et al [4]. Though, a qubit contains a doubly infinity of bits of information, only two classical bits (cbits) are necessary to transmit a qubit in the teleportation process. This raises the question, whether it is really the minimum number of cbits needed to transmit a qubit. What about the rest of the infinity of this number of bits? It has been suggested that the remaining bits flow across the entanglement channel [5]. Is it that two cbits are required just to preserve the causality (the peaceful co-existence of quantum theory and relativity) or is it the "soul" of an unknown qubit (without which the qubit cannot be reconstructed, the particle is just being in a random mixture at Bob's place)?Recently several philosophical implications of quantum teleportation and its experimental verification have been brought out by Vaidman [6]. Though quantum teleportation requires a quantum channel which is an entangled pair, doubts have been raised whether teleportation is really a non-local phenomena [7]. Hardy [8]